Novice: Brass shifter bushes

A short blog on these as many people don’t seem to know the facts, as the supplier of these to MX5parts I do 🙂

The problem we are fixing arose because the original 6 speed plastic bush doesn’t fit very well. It never did, right from new. It doesn’t wear out, it just never fitted properly. The NC1 ‘box has a different size bush to the NC2/3 type, if you look carefully at the picture you can see the difference.

Originally I got a fellow enthusiast (thanks Archie) to check out the 5 speed bush to see if the same applied, I sent some precise measuring equipment and he advised it fits perfectly. Since then I checked a few more and can confirm it doesn’t wear and does fit fine.

So to sum up; buy a bush for a 6 speed to make those changes more precise, don’t waste your money on a 5 speed one. Buy from MX5parts to be assured absolute precision and quality, buy elsewhere for questionable quality – you won’t know the difference as you can’t measure it. I only know it can be made worse, not better, as the ones we sell are a perfect fit.

Where does it go? It goes here:

The gearshift bush (4) clips onto the lever ball (6) and sits into the hole in 5.

Tips for fitting: There are plenty of online guides, Youtube etc. One thing I would add is put the new bush on your finger and drop or push it into the hole in the turret. As it’s a very precise fit you may need to rock it around a bit before it slides in. Then put the lever ball into it. Don’t drop it into the turret elsewhere! You’ll spend ages with a piece of bent wire trying to find it. Don’t ask me how I know this.

There is also mucho confusion about turret oil. It is separate from the main gearbox. It needs nothing more than the same oil you put into the gearbox. I would just put enough in to cover the moving parts you can see, no more. There is no reason to put special magic fairy tears £50/litre oil in there. All that lives in there is a few levers and joints, nothing high tech or rotating.

Amateur/General interest: Hitler does Blyton, July 2020; General trackday banter, reminiscing and wittering.

This is just a gentle natter on trackdays and track cars in general, how Hitler performed on his maiden voyage and of course the MX5 NC.

Back in 2019 a few of us met up for an evening session at Donington, I love Donington and always have, it’s a fantastic place, it used to be Britain F1 GP venue at one time and is steeped in history. It also faced closure and was indeed closed for some time in recent years, but is now back as it should be.

It has everything you want from a track, a long straight, high speed S bends, hairpins, chicane, double apex corner uphill section, downhill section, loads of run-off, pit garages (i’m not sure if they are free now like they used to be). Craner is the bit people usually talk about as it’s a proper heart in mouth, grit your teeth, foot to the boards and hang on for dear life kind of section! It’s a downhill stretched out S and IIRC is a bit off camber too which means when you’re flat out you can feel the back going a little light and squirming as it nears the limits. If you’ve never driven at Donny it must go on your bucket list.

Sadly as it was the day before a Caterham race many of them had booked on to test their cars and skills to the limits along with us. So we had hardened racers on the track with novices; bad idea. It was like holding an F1 race on the same track as a saloon car race.

You had people overtaking wherever they wanted as if in a race, on the left, the right, mid bend, you name it. As if that wasn’t bad enough one of them stuck it in the gravel every few laps closing the track down time and time again. The session ended earlier than advertised and unsurprisingly on an already red flagged and closed track. We’d done something like 40 miles and used less than 1/4 of a tank! We had travelled for two hours to get there, one of my mates James had done about 4hrs I think from the deep South for that amount of driving. It was a complete and utter waste of time and money.

I don’t know whether TD organisers have lists of who is going and in what anymore, MOT certainly don’t. It was a great idea as obviously you could see in advance what kind of day it was going to be, maybe see cars and people who you’d like to go up against and have a chat with.

I felt saddened and embarrassed for my friends, also cross that i’d put so much time into getting the car ready for this. I complained to the organisers who took the time to explain their position in detail and was offered a ‘freebie’ at Blyton in Spring. This was then cancelled due to the CV19 outbreak, then as things calmed down a bit another one was allowed to take place in June.

Project Hitler 2.3 was nearing completion so it was a good time for a shake down and see what the Winters work had brought about. CV19 has set us back something like 6 months, not only because of the complete closure of many businesses, but also the supply chain being interrupted and now a huge backlog of things has backed up to be cleared. It’s been difficult to get dyno time, my local friend who helps with mapping on the road went abroad and got stranded, then decided not to come back for a while anyhow! All in all it’s been a difficult time for many people.

Jawohl, mein Führer, I will hunt you down and whip your butt mofo!

I already have a ‘winning formula’ to work from as far as suspension and set up is concerned so knew that would be ok, but it was on different tyres, wheels, brakes and of course a new 2.3 engine. The engine hasn’t been fully dialled in yet nor is mapping complete, but it was good enough and safe to drive it.

I’d built a big bore exhaust and put a Cobra Race back box on, whilst it sounded fantastic with lots of burble, pops and crackles, it was also very loud, the driveby at Blyton is 95Db at 20m. I’d bought a quite professional Db meter, (all the way from China for a tenner! ) and we tested Hitler at 105 at max rpm. One thing you can’t really do is change an exhaust system at the track side and given it had two tail pipes, two push in ’emergency’ Supertrapp style things were far too much money. There was no room underneath for anymore silencers, Cobra had no road silencers in stock for weeks and I was running out of time and ideas. In the end I was forced to put a standard (apart from a de-cat) system on so it lost a few bhp and sounded like an angry wasp in a tin, pausing to fart every now and again. Nevermind, it would have to do, I couldn’t risk being sent home. I’ll work on a solution to this, probably just a Cobra road back-box will do the job coupled up to the big bore mid section.

I’d obtained some 17 x 8 Enkeis with a good offset, painted them the usual trademark satin black and shod them with some NS2Rs. When they weren’t quite up to temp it was quite easy to powerslide out of the chicane with the torque of the 2.3, once warmed up you could throw the thing about however you wanted as per usual. To me this is what a properly set up MX5 is all about, you can head off to the track with your mates or your family and put anyone (within TD rules) in there. Your mates, the kids, your granny, wife, whatever. Send them out and they’ll be able to drive it to their maximum ability. You can push the thing as hard as you want and it doesn’t bite like some cars do. There is so much communication from it it’s amazing and I’ve tried really hard to keep it neutral, overcook it on a bend and it’ll just four wheel drift.

I wouldn’t have said there was much in the way of serious MX5 competition for Hitler out there that day, just some mildly modded road and race cars so it was easy to reel them in and dispose of with ease. It certainly wasn’t down to my skills as i’m no driving God, so with the right person behind the wheel it would be quite a weapon.

It’s got SRF fluid in and a big brake kit on which had some Mintex pads already included, also larger dimpled and grooved Mtec discs, vented all round. I looked up the part numbers for the pads and they didn’t look to be anything special (definitely not the 1171). They felt a bit wooden on the roads when cold, needing a bit of heat in them before they worked. I figured i’d give them a go as they were, but took some Stoptech fronts with me just in case.

They clearly hadn’t had any hard use or bedding in procedure done as the nature of them changed with the hard use I was giving them. At first they smelled as hard used pads generally do (at least, I think they were mine I could smell!), then developed a really loud squeal as some track pads often do. I wondered at first if they were going to give up on me, but despite the smell and noise performed well. This is the thing about using a bigger disc and pad, you can get away with using a softer pad. On the other track car the discs and pads are so big it uses nothing but road grade, yet you can stand on the brakes time after time from 100+ and it doesn’t struggle in the slightest, the discs don’t warp, go blue or whatever and you get good feel and bite from cold.

Whilst PJ is built on a cheap base it’s undoubtedly quick, also it’s still sensible and easy to drive on track being an NA engine. I do have a history of going insanely quick in stupidly cheap, but chronically powerful cars. I have a liking for street sleepers. There is something very satisfying about blowing away an expensive car in something which looks like a piece of shit. The thing is (and it’s mentioned in another blog) if you end up in a wall then you haven’t lost much, if it’s not a HUGE accident then your go-faster goodies (and your good self) may survive and be bolted back onto another car.

This is Project sausage, it was the most powerful 16v turbo Fiat Coupe the UK has ever had:

Project Sausage at Blyton, a bit like locking a Doberman in a toilet.

I was back then developing parts for integrales and the Coupe 16vt shared the same engine. integrales are expensive, Coupes are cheap as chips so one was found locally for about £400. If any engine bits were created which weren’t quite up to scratch or needed testing then they were bolted onto Project sausage. Sausages are known as the butchers friend, made up from floor sweepings, but still a fine piece of food when you’re in a rush.

PS put out just over 500bhp on an honest dyno, it was FWD, had a very basic cast iron swing arm suspension, coilovers, big brakes and thicker ARBs to cure its tendency to understeer. It was properly evil. You had to commit to a corner and keep your clog buried in the carpet, back off midway and you’d find yourself pointing the wrong way in a split second. Lift-off-oversteer in large quantities.

It was a good straight liner once on the move, but would spin the wheels in first and second if you had a heavy foot until it was hooked up to third. It had so much power going through the front wheels it was like watching a little old lady being pulled up the road by a Rottweiler, it would weave from side to side as you hung onto the steering wheel whilst the scenery flashed past at comical speeds. It totally slayed many expensive motors, mainly on the motorway, BMW M3s were just breakfast for Project Sausage.

I remember driving along a local bypass one night on my way home, some guy in an Astra VXR was all over my tail wanting some, aggressive driving, weaving all over, pulling up to my rear bumper etc. I knew what he’d do and I also knew there was a long clear straight coming up where he’d do it. So I shifted down a gear and held it at 3k whilst looking all innocent. Right on cue he dropped a cog and made his move.

So did I 🙂 The loud pedal got pushed into the mucky old carpet and he got as far as drawing alongside before the GT30 got into it’s stride. That was it, he appeared to go backwards at a rapid rate. Bye bye matey boy and I just hung onto the wheel whilst PS did it’s party trick. 3 seconds later I changed up and cruised along grinning at the spec floundering in my rear view mirror about 1/4 of a mile away. Some kid learned a valuable lesson that night that things aren’t always what they seem 😉

Anyhow I digress, we aren’t really here to talk about rusty old Fiats. Just rusty old Mazdas. So all in all Hitler 2.3 proved to be all we needed; fast, great handling and reliable, the extended redline up to 8k is a big help in the corners along with a powerband starting at 4k.

Whilst Blyton is cheap and great for the beginner or testing it gets a bit boring for me after a while. The heavens then opened at about 2 and quite a few people had gone home for a variety of reasons so we packed and left too. Job done.

It’s a shame there aren’t many (if any) photographers at trackdays anymore, even if you’ve got friends with cameras you can’t get to any good vantage points to get the best shots (check out the wire fencing on the pic right at the top there), especially at Blyton.

Next I will tweak the cam timing as I think there is a little more to come from this combination, then we’ll finish off the mapping, write an article outlining what’s all about, then it’s for sale.

Considering a track car, road car or both?

This is a blog of my personal opinion based on my experience as to whether you should join the 5% elite and have a 100% track focused car or do the usual thing and drive a compromise car. As i’m of a certain age I’ve owned and driven them all from being a teenager to where I am now. It seems quite obvious to me, yet not a lot of people seem to get it, or think it doesn’t apply to them, or indeed just don’t have the space or plain can’t afford it. Nothing wrong with the last reason there of course.

The article is mainly based upon N/A cars, not so much ones with forced induction, the differences on those have already been discussed in another blog, although a lot of what is written does apply to both. There are three basic types of car discussed here with their abbreviations: Road car (RC), track car (TC) and the combined road & track car (R&T car)

In a Ratneresque (you might have to look that one up, lol Google ‘Gerald Ratner’) I’m going to say I have a dislike of combined road and track cars! I’m sorry all you 95 percenters and I know it’s largely down to money, but I just do.

It’s largely to do with age and money of course, maybe your job too, but I’m lucky that I qualify for a track car, I have what is needed and I understand that others don’t have what I have, here is what you’ll need:

  • A suitable vehicle to tow your track car with and appropriate driving licence privileges. (I have a van for work purposes)
  • A trailer and somewhere to keep it. (I have a spare bit of land)
  • A garage to keep your track car in. (I’m lucky enough to have one)

The advantages of a standard or mildy modded road car is that they are comfortable, reliable, cost effective and good on fuel.

At the moment I can only think of one advantage to owning a combined R&T car and that is you can legally road test it or take it to the dyno, maybe for the occasional Saturday morning blat around your favourite roads, do some illegal and dangerous speeds, maybe have an accident if that’s your thing.

The advantages of a track only car:

  • It won’t cost you any money whilst its stood, no MOT, no Tax or even insurance (the last one is debatable, but I don’t bother).
  • If it’s kept in a dry garage it won’t have ongoing rust issues, you can buy an old car, fix any problem areas and it won’t reoccur or get worse. Not only the bodywork & chassis, but a car stored outside for long lengths of time, particularly in Winter will suffer from the brakes corroding and potentially seizing and corrosion to any other metal parts.
  • If you’re working on it you won’t need to rush the job so the car can get you to work on Monday morning!
  • My track car has no cloth roof, just a removable (lift off) hard top, this would be a pain in Summer as a daily drive.
  • You don’t have to worry about having a working and legal car to get home in. Many track cars break down at the track, they also wear their tyres down rapidly, often to the cords.

Disadvantages of using a track car as a daily drive:

  • Whilst it will be fun for the first half hour it’ll soon wear off! Track cars are tiresome to drive on the road, the older you are, the worse it gets. Stiff and noisy suspension (bushes and dampers), firm noisy tyres, noisy exhaust, bucket seats, harnesses are all a major PITA when off track.
  • Dangerous to drive: Brake pads which don’t work too well when they are cold, semi slick tyres, track based geometry, safety features which no longer work (ABS, air bags, seatbelt pre-tensioners, stripped out interiors, cages etc)
  • You’ll need a cat to pass a legal MOT, track cars don’t require cats.
  • It’ll scrape, bang and damage itself over every speed hump and pothole. The underside will get damaged, wheels crack and buckle, front splitters ripped off in standing water or speedhumps, certain air intakes will drag in deeper standing water and destroy the engine.
  • Engines built for track use are generally not happy on the road, the pistons are loose in the bores when cold so will rattle, they have little low end torque and need to be fully up to temp to give their best and burn off any moisture or fuel present in the oil. They can idle quite high because of the lumpy cams.

To sum up and put it quite bluntly a well sorted and driven track focused car will perform well on track and you’ll be going quicker than many of them out there. Likewise a properly sorted road car will perform well on the road to get you there safely and in a dignified manner.

Neither one of the above will do each others job as well, a compromise R&T car will also do neither of these properly, you’ll be overtaken on track, on the road and by and large be nothing but irritating and disappointing whilst attempting either.

Suspension arms, Subframes, geometry and bushes.

This article is for the hardcore enthusiast, if you’re Mr or Mrs 2006 100k miles ‘I’m not spending that much on a £xxxx car!’ you’re probably best off not knowing what is written below.

If you’re looking for suspension settings this isn’t really the place either, they are a very individual and personal thing so I apply whatever is needed to the car after a chat with the client and their proposed use. What different settings do and what to use is easily found on the internet already. This article aims to show you some things maybe you never knew about your NC because they are hidden right under there where I tend to work, we’ll discuss the pitfalls, what to watch out for, why not to bother and the actual mechanics of it.

One of the main attributes of an MX5 is the handling and they did of course handle superbly when they left the factory many years ago. If this is why you bought one you need to know that if it’s your typical ’06 with 100k on the clock it won’t be handling very well now at all due to much of it being worn out. Sorry to be the bearer of bad news.

The Haynes manual states to jack the car up using the diff which rests on two of these. Good workshop practice? Not really. This is also one of the worst ones to get out too.
“Well it had a valid MOT and it handled really well” Hmmm, ok, compared to what, a three legged bar stool? Slackasabagoknackers as we say round these parts.

Anti-roll bar links are known for wearing out and causing a knock or rattle over the bumps, this is also an MOT failure. They are relatively easy and cheap to replace, just be warned you will quite likely have to resort to cutting them off with a grinder as they just spin round internally when the nut is turned. It is worthwhile putting an allen key in the cleaned out end there and trying it with a spanner first, you never know, miracles do happen sometimes.

The rear bush moves to control castor, front one camber and (age and use dependent) the through bolt is quite often seized in there as you can see.

The bolt head pictured there in a handy recess to hold the water.

What happens is water (sometimes salty of course) sits on the top of the subframe and runs down into the joint where it sits there doing it’s stuff. On a similar note it also gets into the subrames themselves and their mountings, it’s quite common to drop one down and get showered with rusty water or have it running down your arm. The subrame mounting nuts and bolts themselves (exposed as they are) are actually one of the easiest fixings to get off.

Like the front, the through-bolts at the rear are often seized solid to the arm bushes, after bashing them and heating them it’s time to just cut them out.

Thinking of having a go?

You’ll need to be a top level DIYer with access to some decent tools, a good vice and/or press, angry grinder, drills, heat, small chisels and a fair amount of time. The bushes themselves are bonded to the arms so require a combination of drilling, chiselling or even burning out so plan ahead if your car is a daily and get the swear box out, it really is a pig of a job if you’ve never done them before.

I sell and recommend Powerflex for the job, yes they are expensive, but they will tell you how stiff their bushes are, this is known as the ‘Shore rating’. You’ll need the black ones for the suspension. If you’re thinking of using any other brand make note how they don’t give you this important number on the screen so ask for it. What you will find is that some aftermarket bushes are actually more flexible or no better than the ones you are removing, this is because they use a lot of Polyurethane and less metal content than the originals, metal is very stiff right? Of course it is 🙂 Powerflex also use stainless steel for the crush tubes, so seizure is a thing of the past and they are guaranteed for life. We can discuss discounts if you want to purchase a reasonable amount at one time.

Setting the geometry

So many people bang on about their Hunter alignment these days as if the car drove much better because it’s been done by a Hunter and a laser.

How well your car is set up is solely down to the guy doing it not the equipment! That’s a sure fact.

The Hunter is a fantastic piece of kit and the main advantage is its adaptability and speed, the disadvantage is it’s obscene purchase price. An idiot can then mess things up faster and easier if you let him.

WTF, it’s nothing but a piece of string!
Some of the basic tools needed.
Perfect to the millimetre, Mazdas tolerance is to within 4.4.

If you’re simply setting the toe angles to average road settings then generally you don’t have to pull the seized bolts from the bushes. What you will find is because it only needs a little tweak to get it right the now worn rubber bush will twist within itself to allow a setting. I know it’s not 100% correct, but inevitably it is what happens and is just about good enough to keep an old snotter on the road for a bit.

Sand blasted and ready for specialised paint to be applied, the hollow sections are then wax injected. I don’t recommend powder coating, but will maybe discuss this at a later date.
After blasting these were also left to soak in a chemical rust eating solution which we sell before painting.
Don’t forget to paint them a really lurid colour because racecar innit.

Obviously when you’re reassembling everything will be blathered in grease won’t it? Of course it will, shame Mazda never did, but that’s life. If you have a later car and/or one which you intend to hang onto for a while it can be worth your while to pull all these bolts out now, grease them and put them back in, make sure you mark off the alignment on the discs and frame before you attempt anything with a paint mark, dot punch, chisel etc.

So ends another blog, hope you enjoyed or learned something from it, you can leave a comment or questions over there somewhere 🙂


An often talked about subject in the NC community, especially in Autumn/Winter.

They tend to last roughly about 40k miles, that’s very, very roughly as there is no exact point where they fail, the rubber seals distort, go hard or shrink and begin to pass a bit of water when they shouldn’t and gradually get worse over time.

I think most people realise that the ‘stat is an important part of the engine, it ensures it gets up to temperature quickly and that is stays at that ideal (minimum) temp too. Don’t ever think a cool engine is a happy engine, it is certainly not – but then neither is an overheated one either. Engines are happy at around 85 to 95’c. This where the oil viscosity is at its best and economy is good due to ideal fuel burn characteristics. Engine oil contains contaminants such as moisture, fuel and other byproducts, when the oil gets hot they evaporate off and are sucked out. This is one of the reasons why cars which are only used for short journeys need their oil changing more regularly.

Deciding whether your car’s ‘stat is faulty is relatively simple, even though the temperature gauge (as previously discussed) isn’t very accurate and in warmer weather we don’t use the heater so it often only gets diagnosed in Autumn and Winter.

Using an OBD reader which measures the real temperature will help, but also take a look at your gauge before you start the engine for the first time that day, the needle should move from there within 3 (Summer) to 5 (Winter) minutes of driving it. When the engine has been running for at least 10 mins the heater should be blowing warm, after 20 mins fully hot, if you’re driving down the motorway on a cold day with the heater on and it starts to blow a bit cooler than it was then that’s a sure sign it’s failing. Don’t perform any tests with it idling.

Changing it is fiddly, but easy enough with the correct tools. There were two types, long hose fitting (later models) and short hose fitting (early models), it doesn’t matter which you buy, they both fit as the rubber hoses move to take up the difference. We sell high quality Mahle brand for £20.

I’m not spending that on a £2500 car!

Is the wrong answer 🙂

In defence of the cheap MX-5 as a base for a track car…..

I suppose this also could be about thinking you can buy and run a cheap MX5 and not spending anything on it.

Many people think it’s better to spend £6k on a £10k car, rather than £6k on a £2k car. So our two examples for this article are at two extremes – the modified £8k ’06 and the equally modified £16k 2012 car.

We hear and read “I’m not spending that on it! it’s only worth £xxx” all the time, I guess that’s one way of looking at it, here is another.

Whilst there are very good reasons to start with the best and latest example you can find, If you’re building a track car there is also a strong case to start with something cheap – as long as the rust hasn’t taken it’s toll on the external upper bodywork or gone too far underneath.

With any serious track car, you’re going to throw out so much stuff that (snobbery aside) it often doesn’t really matter what you started out with. They’re both going to need the engine, the suspension bushes, original coilovers, wheels, air-con and various other bits throwing out and replacing.

“Aha!” Says £16k man, “but my car has the later stronger engine!” It is a very good point too, lets look at that in detail. The pistons are essentially the same strength (and CR), the rods are ‘proper’ traditionally forged steel, the crank is steel as opposed to the earlier cast iron one and it has improved valve springs fitted which will cope better at high rpm. Ultimately it is the better engine up to a point. Did anyone ever say ‘Hey I broke my cast iron NC crank?’ No, they never did, also as cast iron is less dense than forged steel it’s actually 1.4 kg lighter too. That is a big saving in a place like that.

The valve springs and rods were also a worthwhile mod and we sell the springs for a few quid, if you’re putting big high lift cams in you’ll need different extra higher lift springs anyhow. If you’re ditching the engine for a bigger one, none of this matters.

There are a few reasons why the later models got a forged crank:

1. The main and the most interesting one is that an engine with a steel crank is slightly smoother and quieter – it has less NVH (Noise, vibration & harshness). Whether noticeable or not to your average driver I don’t know, but it is there and engine designers do site it as a reason.

2. Every new model has to be better than the last to get people to buy it. Selling cars is about making money, end of story. If Mazda bought in a job lot of different spec engine parts which added £200 to the cost of the car, they could charge the customer another £2k for them.

3. As the model got older, racing series were springing up to accommodate the NC, racers want racer parts…..

As discussed previously if there is rust showing on the upper bodywork then just walk away. The favourite starting spot underneath is the rear of the cill where it meets the wheel arch and this is easily remedied. If you buy a late model (previously stored outside) NC then you’ll still have to do some kind of remedial work underneath to prevent it getting worse as it’ll have surface rust all over it.

So we take our two equally modified cars to the trackday or even a road trip; the £8k ’06 and the £16k 2012. Who will be going the quickest? Well theoretically they’ll be both the same as they’ve both had the same mods done to them.

However in practice maybe the older car will be going faster, the reason for this is the £8k guy has less to lose so is pushing the limits further. His car is also lighter due to the rust, no I can’t write that. The £8k guy also has more money to spend on further modifications so a couple of grand more and he’ll be going even quicker, still for less money. He’ll also have a warm glow all over and be sniggering like Muttley as he keeps up with, or beats £16k guy with his £8k car.

If you do have an accident which is repairable then NC1 parts are much cheaper and plentiful than NC2 and 3. These later models are only ever scrapped if they’ve been in an accident meaning lots of damaged panels, early cars are sold off cheap or broken up due to engine failures or corrosion.

It’s not all about where you start, it’s more about where you end up. All our track and test cars are based on the cheapest, but solid cars I can find. As long as i’m fast and safe I don’t care what the snobs say, as long as I can snigger like Muttley when i’m overtaking you 🙂

Technical: Duratec ports

If you own an MX5 derived 2.0 engine and aren’t interested in all this technical gubbins then you just need to know you’ve got the one with good flowing ports; they never put a bad head on a 2ltr NC engine. If you’re reading this as a non MX5 owner or are doing an engine swap and need to know more about heads then make yourself a brew and read on, I try to make it easy to understand for the average Petrolhead, but it’s difficult for me to judge the possible gulf between my knowledge and yours so bear with me. Similarly if you want to know whether to get your head ported or not then we’ll get to that later too.

Studying where the air goes inside a flowing port. The smoke leaves a residue behind so you can actually see afterwards where the flow is concentrated.
I usually do this last thing before going home, it fills half the workshop with smoke!

As far as the N/A (naturally aspirated) engines are concerned all the exhaust ports, exhaust and inlet valves are the same, however there are 3 different shapes of inlet port. It’s been debated for many years, but no-one has ever gone publicly into too much depth about it. Whenever I encounter a new head that i’m going to be doing a few of I study it in quite some detail and spend many hours with it on the flowbench getting to know what works and what doesn’t. A flowbench is just one of many tools which help an engine builder create a picture of the engine because once you’ve understood it, then you can start to modify it. The bench does more than just give you a CFM figure, with the right additional equipment you can also check velocity, flow bias, disruption etc. Velocity yeah, how many people consider how important that is whilst waving their cock around with their big CFM figures as if that’s all that matters?

Real porting is about changing the shape of the ports, it isn’t about smoothing and polishing the walls. For various reasons the engine does not want smooth polished ports, it needs a rough finish. Think about it, the engine manufacturer sets up a mould to cast thousands and thousands of heads from. If they wanted a smooth port finish they would have made it smooth, but they didn’t. Anyone who polishes an inlet port is clown.

I’ve been doing head flow development and porting heads for many years now, so much so I’ve got nerve damage in my fingers from holding a grinder for so long. The first time I saw a Duratec head I thought yeah, they REALLY knew what they were doing here, it’s an automotive work of art. All the features we’ve been creating as much as possible to old heads over the decades are there already. Perfect short side radius? Check. Well formed splitter? Yep. Min CSA ratio matches valve throat? Of course. Strengtheners in the bowl to prevent cracking on an overheated head, D shape over the SSR, 3 angle seats, lightweight valves with thin stems, a hump in the middle of the SSR to divide the flow around the valve stem, well formed bosses cast around the valve guide; the list goes on. Someone with a CNC mill or a hand held grinder will go in and plough all these features out in the wink of an eye. The valves will flap around in the shortened worn guides that they couldn’t be bothered to replace, never seat properly and wear prematurely, but because they smoothed everything out, got 20 likes on FB and told you they’ve put a 3 angle seat on you’ll think they’re great.

Here’s a thing; if I took a grinder (only) to a port, re-shaped it here and there and bolted it onto an engine we’d see a power increase. If your average customer saw it they’d say ‘wtf is that i’m paying for? It looks like a dog has chewed it’. The customer thinks he knows what the engine wants; lovely smooth polished ports. The engine on the other hand doesn’t give a toss what it looks like, it just wants airflow and properly homogenised fuel/air. So we finish the ports off to satisfy the customer and charge them accordingly, they post pics on FB and get 30 likes, job done.

Port molds are one of the tools I use to get an idea of what i’m looking at, If you don’t spot relevant features simply by looking into a port, you’ll see them on a mold. Here are the various parts of a port labelled, but I generally refer to the ‘short turn radius’ as the short side radius (SSR) and the area opposite it below the valve seat (shown here as long or back wall) the bowl.

What isn’t marked on there is an important feature called the minimum cross sectional area or Min CSA. Also known as the choke point this is one of the main governing parts of the port, the other being (aside from valve lift) the valve throat, remember this, it’s very important.

The Non VVT 1S7G and 3S7G head found on low powered Duratecs such as the Focus, all 1.8 engines and some Mazda 6 are to be avoided if a good port shape with equally good flow is desired, it cannot be improved upon to the same shape as the 3S4G (2.3) 6M8G (2.0) & L5 (2.5) which are found on the VVT engines. The ports have been given the label ‘High port’ and ‘low port’ years ago and we’ll stick with that, no point in trying to change things now and it’s difficult to describe them in a handy to use term as you will see below. The reason it doesn’t flow as well is quite apparent when you look at these molds. Low port is on the left, high port on the right.

This picture is a touch deceiving as the port on the left looks shorter and of lower angle, but in reality it isn’t. If you look at the line where the valve seat ends you’ll see it’s canted over a bit.

As you can see the low port has no SSR or bowl. These two features are solely responsible for its lack of flow as they are very important parts of a port and help turn the air. I haven’t spent much time on it as it’s a non starter as far as power is concerned, but it looks like a tumble port which is good for economy and low rpm performance.

When designing or porting a head there are a lot of criteria to be met and the unwary can really mess things up with a grinder, but one thing stands out over all the rest and it is the fact we are trying to get the air to turn a corner losing as little mass flow and velocity as possible. You can liken this to a car taking a corner at speed, if you try to perform a sharp 90 degree left at high speed you won’t make it and the car will simply skid straight on. If the angle of the corner is lessened, lets say to a large radius or two 45 degrees then you stand a better chance of making it round at the same speed. Air flow behaves in much the same way – the greater the radius, the more chance it has of hanging on and getting round without undue turbulence which slows it down.

Taking the above into account there is something else to be wary of. That is people who think they can flow test at 10″ of test pressure and scale it up accurately to 28″ or more. Air is heavier than you think, if it makes it round the SSR at 10″ it may not at higher test pressures when it’s flowing faster. This is quite easy for me to prove, I can test at 10″ and scale it up, or ‘correct it’ to 28″ (multiply by 1.670), record that figure. Then switch some more motors on (I have a 6 motor bench) and actually test at a real 28″. Do the new test figures equal the calculated figures? No sir they do not. Do major car manufacturers test at 10 or 28″? Nope. The higher the test pressure, the closer to real life you will be and the more accurate your figures will be too.

So what of the 2.5 head?

2.5 port on the left with wider entry (only).

Often touted around as the one to have and has massive flow you’ll be surprised to learn it actually isn’t all that and many people were duped into buying one. The port entry is larger, but it soon reduces down to the same SSR and Min CSA. It does give the ready made advantage of taking large diameter throttle bodies for high power/RPM use though, but then a 2.0 or 2.3 can be enlarged in the same way.

It’s all about what power level you are at, as pointed out earlier the controlling parts of a port are the valve (throat) and lift, the Min CSA and the SSR so whilst they stay the same so will the flow – and it does. The reason it has a wider entry is to match the bigger diameter runners of course, these are used to slow down the velocity and weaken the intake pulses flattening the torque curve and making the engine less peaky. Exactly what you want in a van or heavy four door saloon of course which is why Mazda did it, it’s behaviour is very much like a diesel engine. Is this a bad thing? No, it’s just a different thing, you or I have to decide what kind of personality we want the engine to have and specify it accordingly – or just dump it in as is, no problem with doing that. 30ft/lbs more of torque and good economy? Yeah i’ll take some of that.

CNC porting

Having a CNC ported head does not mean the end result is any better whatsoever. A head had to be ported and developed by hand in the first place for the CNC machine to copy it. Porting is hard work end of story. If you can get a machine to do it for you then it’s going to save you time and also wear and tear on the human body. You can mess a head up repeatedly without having to leave your office with a CNC machine! Many do, lazy programming and the need for that all important CFM figure (sic) can remove many of the important port features without giving it a second thought. Copying a well modified head though with a CNC machine and yeah, now we’re talking.

So should you get your head ported?

It really depends on what power output you are looking for. Other engines from earlier eras had ports which didn’t have a fantastic shape to them so could be modified if you knew what you were doing. The modern car market is very competitive, you absolutely can not afford to leave power and economy on the table by putting a poor engine (with bad ports) in a car. The ports on Duratecs can be lightly modified to flow a little bit more whilst retaining the same valve sizes, but not a lot. You’re wasting your time and money trying to get it to flow much more whilst retaining the same valve size as Mazda got the ratios right from the start. Increase the port size and the next restriction is the valve throat, so next on the list is bigger valves, then you can port the heads a bit more aggressively.

If modified appropriately the 2.5, 2.3 and 2.0 heads flow enough for 300bhp and more without forced induction. As a rough rule I would say (N/A) that up to around 200bhp you’ll be ok on standard ports. 220 – 240 lightly modded ports, 250 onwards you’ll need bigger valves with associated porting. As you can see there is no cut off point, it’s just a gradual reduction the further you go and of course it’s highly dependent on other mods.

As far as forced induction is concerned then 500bhp is easily achievable without getting the grinder out, pushing it further than that and i’d be looking at bigger valves with some porting.

Novice: Engine swaps Part 1, decisions, decisions…

This article discusses what to look out for if you are considering an engine swap for something a bit bigger.

Give me a large sum of money and i’ll get you a large power output. How many people in the UK NC world have that kind of money and ambition?

Probably about 3 🙂

So what about a reasonable amount of money and a reasonable power output? A strong reliable base which you could develop even further if you wanted? Maybe….

If you’ve read about 2.5 engine swaps on US based FB pages or forums then i’m sorry, but you need to quell your excitement and forget most of what you read, things are very different here in the UK and indeed, the whole of Europe. Over in the US a heck of a lot of cars and vans were fitted with 2.5 engines over a lot of years. In comparison we didn’t get many over here at all. Also what you’ll find is the average American will drive a new car out of a showroom and into a wall therefore writing it off. These facts mean there is an abundance of cheap low mileage engines over there.

Import one over here? After freight and tax you’re looking at about £1k and if it’s faulty then no chance of refund or return.

Generally all you can find over here are new crate engines or old high mileage ones.

To sum up so far, the NC came with a 2ltr*, as said 2.5 swaps are popular in the US because it’s readily available there, but here in the UK less so. We do have a 2.3 too and it’s often overlooked, not at DuratecNC it isn’t 🙂

Unmodified power figures for comparison:

 2.0: 158 Bhp  138 ft/lbs torque
2.3: 163 Bhp  153 ft/lbs torque
2.5: 170 Bhp  172 ft/lbs torque

As you can see the biggest gains are in the torque department, this is what Mazda wanted as the engines were going in heavy four door cars and is why they stroked them. What we need to do is take that engine, make it rev further safely and produce more power and torque.

*You may notice I never mentioned the 1.8. This is an engine performance company Blog so for all intents and purposes i’m expecting no-one to be really interested in this engine unless you have to meet a racing regulation of 1.8 litres or less. We can certainly replace a 1.8 NC with a more powerful engine, but remember you’ll maybe want an LSD as it never came with one and the ECU and engine have no VVT.

So 2.0, 2.3 or 2.5? (or even a 2.4, but that’s another story). Obviously you’ll make more power with each step up, but there are pros and cons for each.

Take a 2.0 for its revvy nature and maybe you need to meet class rules of 2.0 and less, it will rev further safer than all the others and give a decent BHP figure, but lack in torque.

For maximum potential and cost take the 2.5, less potential and less cost then start with a 2.3. You need to decide whether that extra money is worth it and if you’re putting in a brand new 2.5 new engine, a used 2.3 one, if you’re going to rebuild it for strength and power or not. Obviously if you’re just going to put in a stock motor with no mods then perhaps a new 2.5 is the way to go. If you’re going the whole hog with replacing components then the 2.3 with its lower initial purchase cost starts to look more favourable. What I mean is if you’re going to start throwing out the pistons, rods, cams etc to replace with more performance orientated components then there is less point in throwing new ones away which you may have just bought as part of a whole engine.

Would you put an untouched high mileage engine in? Well you might, but I certainly wouldn’t. We don’t get to spend any time with the cars the engines came from to fully evaluate the engines before they are fitted. You could end up fitting an oil burner and that would be a very expensive mistake.

All the engines we fit have been stripped down to the core, checked and rebuilt with many new parts to whatever spec you require. To rebuild it as standard is not a problem, but obviously adds cost and takes away any risk.

Many external parts will need to be swapped over to make the new one work so an original engine in one piece will be needed.

2.5 and 2.0 packages are also available, please contact us for details.

Novice and intermediate: Turbo or high powered naturally aspirated NC?

The answer is simply this; for maximum and effortless performance on the road turbo it, on track N/A is the way to go.

That is the general rule as I see it, it’s black and white, but there is some grey in between and of course rules are there to be broken. Let’s break that blanket statement down.

I haven’t included supercharging in this article as basically I have very little experience with them, but some, if not all of the downfalls could be similar to turbocharging apart from fuel economy, a SC engine will be worse than a turbo and obviously an NA too in every day driving from an economy point of view, they drink fuel at a seriously rapid rate. It’s belt driven, so the engine has to be turning this thing over all the time, it takes energy (from fuel) to do this. If you’ve never tried to turn over a Supercharger over by hand you’ll be quite shocked when you do. From a packaging point of view the supercharger lends itself quite well and at least here in the UK you don’t tend to hear many bad experiences of SC packages.

Before we go too far let me tell you this; I’m not some old geezer who thinks N/A rules because it’s all i’ve ever known. Absolutely not, I was brought up on a diet of turbo engines, they’re like an old friend and i’ve built many from 300 to 600+ bhp so I know them inside out, I still own some too. You can’t beat that feeling as the turbo spools.

A turbo NC on the road is a great thing, that huge gob of mid range torque when you need it is not just useful, it’s addictive. On a decent stretch of road, drop a cog and boot it, take one, two or three slower cars in one shot with ease. Yet when you’re cruising down the motorway off-boost it’s reasonably economical and will pass an MOT emissions test, best of both worlds? Yes pretty much so, it’s like having two different engine modes.

Many turbo cars come undone when on track though, the reasons are:

The heat created is constant and cumulative, not occasional like it is on the road. When you’re pushing hard there everything gets heated up, but then gets chance to cool off, there simply is no chance whatsoever of holding a turbo car at full throttle everywhere unless at the track. The more power you put through an unmodified engine the more reliability issues you will have.

The intercooler blocks some or all of the flow to the radiator so the engine can’t cool down enough (as does the aircon rad if fitted), there is either no, or a very small oil cooler (as standard), the intercooler itself is often too small to enable it to fit into the nose of the car. The NC1 actually had two intakes at the front (upper and lower) whilst the late models only had one so have much less cooling area available. The intercooler on these models actually blocks the airflow to the rad completely.

The turbo is mounted high up which introduces heat into the engine bay and spoils the handling of the car due to a high centre of gravity, along with the substantial weight of the entire turbo kit*. Could you mount it lower? Well the steering column is in the way of a decent internally wastegated turbo and the manifold runners made from welded stainless steel are likely to distort and eventually crack. This is why left hand drive cars lend themselves to turbo conversions a little better.

I’ve seen a few turbo conversions and once you scratch beneath the glossy surface you’d be surprised how shoddy some are, if you buy one with a view to taking it on track you need to look at it as a probable project and be prepared to repair and improve the worst bits. The result of this will be that it starts to change from a road car to a track car.

*Weight, how much extra weight? When Jota were asked to prepare two cars for racing they produced an N/A at 850kg and a turbo at 1000kg. An extra 150kg (23.6 stones) in the front of a car is a heck of a lot. Not only do you have the weight of the turbo kit, but often also a heavier thicker radiator filled with more water. What was the original design criteria for the MX5? It had to be light and handle well with a 50/50 weight distribution, stick all that weight up front and it won’t that’s for sure. You won’t be going through the bends as quick, will need bigger brakes to stop and use more fuel, wear the tyres and brake pads out quicker.

The gearbox will only cope with a certain amount of torque before it starts to give major issues, (the later they are, the stronger they got however) although it has to be said that on the usual (N/A engines running turbo) low power outputs of our UK mainstream ones with an average 7″ wide wheel they seem to be coping ok, gearbox strength will only be an issue with really high outputs, aggressive and track use.

Thinking of buying a force fed car for track use? Ask the creator if they’ll warranty it for that, if they don’t, well…..

You can of course create your own turbo track car, but finding a way around all those issues is a big job taking a lot of dedication, time, money and patience so really you have to decide if it’s worth it. Personally I didn’t, life is too short and the older you get, the more you realise it, but hats off to those who do eventually make it work.

So a high powered N/A car for the road? Well the more power it gets, the worse the road manners get. Turbos are all about mid-range torque, N/As need to be revved out to make the best of them. It’s ok if you want to drive to the shops with your mum at between 3 and 8500rpm and sit outside with it ticking over at 1500, bellowing out 105Db via the performance exhaust, but um well, not really. You’ll lose some power at the bottom end and gain mid-range and at the top end of the rev range. The VVT will help here, also we can fit a bigger CC engine such as a long stroke 2.3 or 2.5 which will also help offset the loss of low down power. The stock 2 litre is what we call ‘over square’, whereby the bore diameter is less than the stroke. This means it’s lacking in torque compared to the others, but able to make good power at higher rpm than they will go to.

On track you will want something with a wide power band that will pull hard from mid range to the redline, something light, uncomplicated and reliable.

An N/A car is a lot easier to drive fast on the track than a turbo, especially for an amateur. The reason is down to the power delivery as it’s much more linear and controllable. When the turbo spools and a whole lot of torque goes to the rear wheels mid bend it will cause the car to go sideways very quickly. Admittedly this can be just as fun to some people as it is frightening to others!

This is where Duratec NC comes into it. Here we have a range of N/A options, you can have a mildly or heavily modded 2, 2.3 or 2.5 engine depending on what your requirements are. You just have to realise you can’t have everything, you either have a car which copes on track and road to a certain degree of success or one which does either of them exceptionally well. That’s the choice you have to make at the start of a project and stick with it.

Technical: The 2.5 Duratec I4

There is no shortage of myths and rubbish written about the 2.5 litre 4 cylinder Duratec, here are some facts.

Whenever something goes wrong with an NC engine someone always says ‘fit a 2.5’ even in the UK where they are rare and expensive compared to the US, where they have read about how cheap they are.

There is no doubt it is The Daddy. The widest bore* and the most CC takes care of that. In standard form (with its original large bore inlet manifold) it’s got a very flat torque curve, some would say dull, lazy and even diesel like in its delivery, yet in a light car like an MX-5 it’s not a bad move and certainly a relaxing drive whilst being quick when it wants to be. You have to remember it’s come from a van and heavy large family car so won’t struggle to power a much lighter car along briskly and with ease.

Look at the torque spread there, it’s almost flat from 2500 to 5000. For the record a standard 2.0 VVT makes 190 Nm @ 6700 rpm.

*You may wonder why I noted the bore size, well the 2.3 has the same bore as a 2.0, but longer stroke making it a more ‘torquey’ engine of the two, but with less of a revvy nature although It can be massively improved with the right mods. The 2.0 is known as an over square engine whereby the bore diameter measures more than the stroke so will rev safely to a greater RPM. A good example of an oversquare engine which really does rev well is of course any F1 engine from the last 20yrs or so. Thinking of overboring a 2.3 block to make a 2.5? Or even massively over boring a 2.5? Forget it, the bore walls aren’t thick enough for that or re-sleeving either and boring a 2.5 to more than Mazdas recommended will lead to a weak engine and the problem of where to get a head gasket from. Be very wary of anyone who claims to be doing this.

The 2.5 engine does not have:

Bigger valves

A higher flowing head

A forged crank

Ductile steel liners

It has:

Cast iron liners and crank

+10bhp and at 700 less rpm

+30ftlbs of torque at 1000 less rpm

The Mazda version has forged steel rods, the Ford one doesn’t.

Balance shafts

Both the 2.3 and 2.5 have a balance shaft assembly hanging underneath, it’s usually removed when fitting the engine in another car due to its size, weight and it saps some of the power from the engine to drive it. These are fitted to counteract second order forces and vibrations which naturally occur in an I4 engine. The bigger the engine gets, the greater the vibration. Removing them won’t damage anything, re-balancing the engine will not get rid of the vibration, nor will a crank damper.

“The ports are bigger and flow much more” is often bandied about on the internet. ‘Bigger’ is a very general term when it comes to ports, you need to be more specific. We look at that in more detail in another blog, but I can tell you that only the inlet port entry is larger on a 2.5, the rest is just the same as the 2.0 and 2.3 VVT heads and that includes the governing parts of a port (the choke points) which are the valve throats and the ‘Min CSA’ which is the minimum cross sectional area of the port.

In my opinion, the best way to get the most out of a 2.5 for the road/occasional track on a reasonable budget would be a set of higher CR pistons, cams and a remap on 99 Ron fuel. 200+bhp and a shed load of torque won’t be a problem with those applied to it.