Forged engine build – stripdown

A few weeks ago I went to Skuzzle motorsport so that the Westfield could be put back on the rolling road to check all was functioning correctly still. I felt it had run rich ever since updating the MegaSquirt firmware to work with RaceTechnology gear and indeed it was. It was also down 30bhp at the wheels. Nick was able to add more boost and ignition advance to compensate but we didn’t go too far and I left with 210 at the wheels. It was 229 last year. The logical explanation for that is the rods are bent – adding boost and advance is something you’d be able to do if you lowered compression. I’m not 100% convinced as I’m of the opinion that the rods aren’t going to bend a little bit and then be nice and stop, but I’m not dismissive of the idea either.

I’d had a plan to build a forged bottom end and go for more power, and this just kick started it really. I was going to do it over the summer so it’s not that early. I picked up another mk2.5 engine; going for mk2.5 because I wanted the main bearing support plate. The alternative was to get an early mk1 1.8 block with the oil feed under the exhaust manifold which would have tidied up the pipe work but I felt the main bearing support plate was more beneficial.


Mk2.5 engine

I stripped it down, throwing most parts in the bin as I already had a lot of spares from the last engine. With the head off, I was able to inspect the bores which were the important part. They weren’t in as good a condition as the previous engine but still fine


Vertical marking on bores

All four cylinders showed this marking to some degree with cylinder 1 (pictured) being the worst. It’s nothing too sinister as it can’t be felt with the fingernails. It’s marking rather than scoring so should go when it’s honed.

Cracking on, I removed the sump and began removing the crank and pistons.


All looked fine here, and likewise with the crank removed.



I’ll be removing the oil squirters tonight, cleaning it up a bit then dropping it off tomorrow for cleaning and checking… along with getting a second opinion on those cylinder marks. Just in case!

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Action Clutch (Stage 3) – Review

Now that the clutch has done one reasonable journey, one commute to work and one track day I felt it was time to write it up. Ok, so that’s not enough time to comment on the reliability of it but if that proves problematic I’ll come back and update this page.

Initial impressions of quality were good, though I must admit I wouldn’t know too much what I’m looking for here. Suffice to say, it didn’t look hand made so a credit to the guy who put it together! The paint on the clutch cover was applied well if no overspray, though I did scratch it quite impressively when trying to refit the engine in the tight confines of the Westfield engine bay! Never mind… can’t see it…


It also came with a sticker which is perhaps a little too big for the Westfield. Being white, also not all that visible. I might have to affix it somewhere though as I’m pretty sure stickers=power.

Pedal Feel

This was my biggest concern, and the reason I went for a 6 puck clutch rather than uprated full disc. With the smaller contact area, a less meaty pressure plate would be required. As expected, clutch effort is increased but not massively so. With the smaller master cylinder of the Westfield the clutch effort is already increased but I don’t think this has made it significantly worse.

Low speed slip

One of the biggest complaints about 4-6 puck clutches is how unforgiving they are when trying to slip them, leading to stalling or juddering. Firstly, pulling away is easy. You have to be a little more committed than before but not as bad as some would say. Certainly can still pull away at normal speeds and don’t have to do full on racing starts everywhere! Reversing however where you’re typically slipping the clutch whilst manoeuvring does induce a fair amount of judder. Maybe I’ve not learned to drive around it yet, or it will go away over time, or it’s just going to be like that. One to consider if you spend a lot of time manoeuvring.


There was no way I’d have been able to launch the car with the OEM clutch. The torque and quick gear changes would have seen it melt I’m sure. However, with this clutch, it’s not a problem. The bite point is higher up than the standard clutch so there’s not a lot of room to play with, but that hasn’t been a problem when pulling away normally so definitely wasn’t a problem when pulling away at speed.

If only the tires offered as much grip!


I think there’s two approaches to this. If you’re in a Mazda engine Westfield, go for the 6 puck clutch. If you’re in an MX5, odds are its a daily driver too in which case a stronger pressure plate and full disc is perhaps preferable to a 6 puck. Whichever, Action Clutch seems to be a credible alternative to Competition Clutch. I ordered mine from H-Tune. They’re very Honda orientated but do Mazda tuning parts hidden in there. A good bunch of guys to deal with too…


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Action Clutch (Stage 3), Part 2

After messing around with the clutch and seeing how it looked (because it was red and pretty), I got back to the proper tasks and set about removing the flywheel to inspect the rear oil seal. To aid this (more to aid the refitting actually as an impact wrench will remove the flywheel bolts fine) I bought a JAS crank locking tool from autolink.


Crank Locking Tool

Very simple to use this – four bolts connect to where the crank pulley would be, then one of the oil pump to lock it. No more messing around trying to hold the flywheel whilst torquing it up!

With the flywheel subsequently removed I could see what was going on with the rear oil seal.

OLYMPUS DIGITAL CAMERANothing too alarming, but definitely not clean! On closer inspection it seemed to be the sealant at fault rather than the seal itself. I removed the seal housing, replaced the seal with a genuine item and cleaned off the sealant/re-applied. I then refitting the housing, which is surprisingly difficult with the sump in situ! Got it in the end but I wouldn’t recommend doing it that way to anyone.

I torqued the flywheel, then the clutch. I had real problems refitting the engine, but then I always do. The problem I have is I’m always too quick to remove the engine and re-centre the clutch when it won’t go together when it’s usually just the angle of the engine and box. In the end, I removed the engine for what felt like the millionth time and refitted it without adjusting the clutch position. It took a few tiny adjustments on the balancing bar to get the engine and gear box to go together but got there in the end.

It’s after this that I paid the price for being clever and leaving the inlet manifold on. It just makes access to the starter motor, engine mount, oil filter and so forth that much harder. I reckon I spent an extra 2 hours fiddling around to save 30 mins of refitting the inlet manifold. Lesson learned on that front.


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Action Clutch (Stage 3)

As mentioned previously, on the last track day I was having issues with the standard (possibly pattern part I think) clutch slipping on the quicker gear changes. It was fine otherwise. However, it was dealing with double the power it was intended for and so was only a matter of time before it gave up. I spent some time researching what would be best, and ended up deciding on a Competition Clutch, Stage 4. This would be a 6 puck paddle clutch, so not great in traffic but pretty well suited for track work.

The company I ordered the clutch from suggested I instead change for a clutch by Action Clutch. They said they saw many failures from Competition Clutch but are yet to see a single one from Action clutch. They’re a Honda orientated company ( and a quick internet search suggested they were right – I found numerous instances of failures with the Competition Clutch. But, these seemed limited to Hondas and Mitsubishis. I didn’t find a single problem with a Mazda one.

Either way, I took their advice and opted for a clutch by Action Clutch. This company has been around since the days of the hot rods and whilst the ownership has changed hands (from original owner to apprentice), they’re still hand made in Los Angeles. Being hand made, I was fully expecting it to turn up with blood on it.

After just over a week, the clutch arrived directly from the states.

I think the shiny redness is good for at least 10bhp.

So, this weekend I set about removing the engine. I made life a bit hard for myself as I wanted to remove it as complete as possible, just to see how little could be removed. This is fine, but removing the inlet manifold really would have made getting at some of the bolts a lot easier. I miss those throttle bodies! In the end, the engine was removed complete with manifolds, turbo, downpipe and oil cooler. I removed the standard clutch and was greeted with this:

That’s not too bad. A bit more wear than you’d expect for about 2,000 miles but it wasn’t showing signs of completely letting go any time soon. I think that if you were just road driving then it would have lasted fine. Being impatient, I quickly offered the new clutch up to the engine:

Yep, seems to fit! It’s not torqued up though, I need to remove it and the flywheel to replace the rear crank oil seal. This was done when I rebuilt the engine last year but I was never completely happy with it and it does show signs that it has been weeping a bit. Better safe than sorry on that front and given removing the engine is not as easy as I remembered, should really do it now.

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End of year review

Ok, it’s not quite the end of the year but I’ve just declared the Westfield SORN so it might as well be. Not necessarily the fault of the Westfield mind – I’ve just got some jobs to do on the Land Rover and that parks in front of the garage so may as well SORN them both.  For the non-UK readers, SORN is where you declare the car off the road and so can stop paying tax for it.

So what a year its been! I’ve definitely spent more time tinkering with it than I have driving it, completing two pretty major engine projects. They’re both at odds with each other really, but given the choice I’d still do them both again. I learned a fair amount and its quite pleasing to knock something up in the garage then see how it performs on the road and track.

The engine build and throttle bodies was a real confidence boost for me. I was advised that it would be a bit pointless and cams/headwork was the way to go, but I couldn’t see how the throttle bodies wouldn’t add any power so just had to give it a go myself. I wasn’t brave enough to sink a couple of thousand pounds into a Jenvey kit so the idea of essentially prototyping it first with a set of motorbike throttle bodies really appealed. In the end, netting ~165bhp when the cam/headwork kit didn’t achieve that was a real bonus. I still wonder how much of that was due to the throttle bodies and how much due to the Mk2.5/Mk2 combination plus maybe a bit of luck in having a decent engine.

And of course, the noise…

Ok yes, I should have kept the throttle bodies on for longer. It would have been interesting to see how the engine responded to a set of uprated cams and a higher rev limit. Granted neither of those modifications would have been useful for the turbo conversion, but interesting all the same. As it is, all I miss is the noise… and another aspect that I’ll come on to later.

I kept the turbo project pretty quiet (which is exactly how it turned out). I knew it could be done. Firstly, people have been turbocharging MX5/Miatas for donkeys years. Secondly, both Flyin Miata and a Belgian guy called Frank have managed to fit the Mazdaspeed kit to Westfields. Both LHD too which is probably more challenging. I’d keep coming back to the turbo idea whilst forming my tuning plans but would always dismiss it as I could never find a Mazdaspeed turbo manifold, and all the aftermarket ones looked like they’d never fit. In the end, an innocent question to a well known supplier of turbo manifolds for the MX5/Miatas quickly spiralled from wondering if he could make a copy of the manifold to having a manifold and downpipe kit land on my door mat. I still can’t believe that some measurements taken with a tape measure and photoshopped onto an image of my engine bay can result in a kit being made the other side of Europe that would fit without modification.

It wasn’t even close to not fitting. To top it all off, not only did the project go surprisingly well, it exceeded all expectations when it came to power and delivery.

MX5 1.8 TD04 Power Chart

At the wheels. For what I’ve done, that’s a strong figure. Perhaps it is a case of a strong engine helping on the power front. The way it drives is baffling at times. It seems you can put your foot down in any gear at any rpm and it will just build speed relentlessly. This is great, but also perhaps a bit of a curse. I was reminded whilst watching the throttle body sound comparison video posted above. On those videos I’m braking well past the brake board. I did Hullavington again in October, and I was braking at the brake board. Ok, I’m arriving at places with significantly more speed, but my confidence on the brakes just isn’t there any more. For a while I wasn’t even confident around the corners, like I was scared of what I’d built. Perhaps I just need to adjust, or maybe I truly have created a monster? Needs analysing…

Comparison with throttle bodies

So, that’s an overlay of speed comparing the fastest lap on the throttle bodies to the fastest lap on the turbo. For what it’s worth, the turbo lap was a few tenths quicker – the straight line speed making up for not being as quick through the corners. In the chart above, the red line is the turbo and the blue is throttle bodies.

Immediately you can see the gear change come in earlier. Rev limit hasn’t been changed, so that’s a conscious decision for whatever reason. Probably arriving at the rev limit quicker. You can also see how much quicker it builds speed, changing into 5th which I never had to before. I end up braking around 60m earlier but otherwise decelerate to the same speed where I was braking before. I corner slower, but that corner was tighter than last time I’m sure! The next section is telling – this time with the turbo I would practically coast around a few corners, where as before I was accelerating right up to them. You can see a short shift in the red line. A confidence lift coming out of that section but soon overcome the speed difference compared to April. Brake earlier and softer initially, but after that it’s largely the same just with additional straight line speed.

I didn’t make a post about Hullavington for two reason. The first and foremost is because my GoPro broke the night before and that really annoyed me. Expensive bits of kit to break in just 2 years. The second is that I didn’t enjoy it that much. I enjoyed it, but not massively. The main reason for this it I kept popping off a boost hose, usually on the outlap or second lap. I’ve fixed it now of course, but with limited tools (and being next to a hot turbo) I couldn’t make a lasting fix in the paddock area. I also discovered that the clutch was unappreciative of my new found power and would slip with the faster gear changes. Change gear at a ‘road speed’ and it was fine, but hammer it home and it wouldn’t play ball. Uprated clutch required this winter, and perhaps a lighter flywheel whilst I’m at it. The gearbox also leaked oil, perhaps a sign of it getting too hot but it wasn’t that warm a day and was impeccable during the summer track day.

So, in all a very productive year and I can’t wait to get back out on track and try and get on top of the car again. Just a few sensible maintenance type projects for this winter. Clutch and flywheel, check the brake wear and may need a new set of track tyres. For non-maintenance stuff, I’m tempted to increase the diameter of the exhaust to make it 2.75″ from turbo back. It currently reduces to 2″. I’m hoping that will help with some extra noise.


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