MX5 NB Track Project

Please update when you can. We are building an exocet with VVT, 6 speed and a 4.1 LSD. Maybe you can make a cold airbox out of fiberglass to go over the filters?
Slightly disappointing but not totally unexpected. Accidentally left the exhaust bung in so not sure what that was worth, and was having some weird fuel issue on the way there at very slight throttle, so perhaps something going on. AFRs on the dyno spot on though so the remote tuning did it's thing. Pulls nicely all the way to redline as well.

Thought I'd do a compression test when I got home just to check things over and was bang on 175psi for all four so nothing too bad, but equally not amazing there. Tossing up whether to redo the block when I finish building the new head now just to make the most of things while the engine is in bits.

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Cool project. If you can live without the ITB's I suspect you'll see much better results on the dyno with the standard intake system. Not what you want to hear probably but ITB's are nearly always a PITA.
 
I take it that is at the wheels?
Had assumed at the engine but not sure now?!

Not sure about ITBs being a pita. Mine have been pretty painless so far once installed. Just need decent tuning from what I can tell. Idles perfectly, starts easily etc. the only minor downside is cruise/transient throttle is a bit choppy but it’s not a daily driver so no issue. Definitely wouldn’t have had as much at the top end with the standard intake either, was so flat before it was changed.

In any case the rebuilt head should make more use of the itbs. Just debating whether to get a new block to bore out to 85mm or so.
 
Pretty sure Surrey RR quote flywheel HP, so all the effort and it makes less power than standard, is what I meant by a PITA.
 
Dyno spurred me on to finally get the head I’m building together. Machining is all done and ready for the cams. Just installed the new titanium Valve springs and retainers. Left the two front valves with machine springs so I can test for piston to valve clearance. Just waiting for some new lash caps for the shim under bucket lifters I have ready to go but annoyingly there’s a longish lead time. Once I have them I’ll be ready to go.

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Pretty sure Surrey RR quote flywheel HP, so all the effort and it makes less power than standard, is what I meant by a PITA.
Don’t disagree to that end, but it’s quicker now than it was standard so would have likely been less than that in any case. Not that I’m chasing numbers anyway, but new head should free things up and new bottom end still a possibility depending on how things look with the head off.

Also looking at the map I’m not sure if it’s as good as it could be either quite a flat spot at 5700 which aligns with timing and fuelling changes so will have that looked at too
 
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Finally got the new head on the car. Got fed up of waiting for the new shims for the shim under bucket conversion, so used the standard set for now, will just mean I can't yet go over the stock rev limit which shouldn't be too much of an issue yet.

Took a bit of time to get everything switched over, and adjusted well but think I’m there. Ended up using an endoscope camera to check I had plenty of valve clearance, especially when the intake cam is on full advance, as the valve is cracking open whilst the piston is still on the way up the cylinder but looked fine. Potential to skim the head further in the future to increase compression as well, but not sure by how much yet.

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Was very nervous on first start up given what was at stake. Made sure everything was spinning freely then turned over without spark to make sure I had oil pressure. Then gave it a push and it started up straight away, not even any lumpy idle which I was kind of hoping for lol.

Anyway, now been out and mapped a few times and it's pulling a lot harder. Redline is still at 7400 for now, so more to come, but feels quite a bit quicker at top end, suddenly comes on strong after vvt at 5k revs or so and sounds a lot more intense than it did.

Still keeping the exhaust bung in for now so potentially losing some horsepower there too.

Next job is to get a better exhaust manifold, and do some port matching work to the jenvey inlet manifold as I think there is a bit of a step to the head which won't be helping things.
 
Nice thread!
I own a 1992 MK1 1.6 turbo at an estimated 220hp/190lbft and plan to get an mk2 engine (likely the 99-00) at some point.
Great car with fairly priced parts :D.
 
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Yeah sounds a lot more aggressive now than it did previously. I think there’s more to come, would like to arrange a dyno day to properly test things as it’s just being road tuned at the moment. I think there’s maybe some vvt changes for the low end that could help and the possibility to tweak exhaust cam timing and ignition timing to help top end as well.

It’s also burning a bit of oil so not sure if that’s piston rings or valve stems. If it’s the former then I may look at building a new bottom end. Last time I just put the rods and bearings in, leaving everything else as was.
 
Quite a bit happened since I last updated this thread. Did another track day at brands indy which was great fun, and a lot more engaging since the updated suspension and wheels. Less track orientated tyres made things quite a bit more interesting. Though there were a few things that stood out. Day started wet and got drier so interesting to have both, but the diff wasn't working properly and didn't seem to be locking reliably or even at all in some cases. Otherwise cooling was ok, but possibly a bit hot on oil.

Following this I noticed the engine started burning a bit of oil which given I'd relatively recently rebuilt the head I decided was likely to have been down to piston rings which I'd previously not changed despite changing out the rods etc. Probably a bit of a missed opportunity, but decided it was a good time to rethink the bottom end anyway especially as not long after i'd noticed a small amount of metal in the head. I pulled the filter off and saw some further small flakes. Enough to decide to investigate further and pull the motor. After doing so the thrust bearing had absolutely had it and was machining the crank down to the point where had I left it it would have likely not lasted very long at all. The bottom end was scrap so decided to double down and go fully forged on a new bottom end, upping the displacement slightly with a set of 85mm Wossner 12:1 pistons.

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Whilst the engine was out I decided to take a look at the front chassis rails as they were pretty clearly done for. I'd thought they were ok when I bought the car, but on closer inspection with the engine out it was apparent someone had patched over them to hide the rust rather than replacing them, so that was the next task. While front subframe was off I managed to pick up a galvanised one for little money so decided to replace that as well as refreshing the engine bay which was a bit of a half job and then all suspension arms and polybushing.

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That led to doing the same on the rear subframe and adding new anti roll bars all round.

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While the diff was out I'd sourced a 4.7 crown wheel and pinion from a Kia sportage along with a new MSport locking unit to replace the Blackline which I sold as a whole. The 4.7 will mate with the 5 speed and should meaninggully imrpove acceleration, obviously cutting down on top speed. No photos of this at the moment as it's off being built up by a local classic car gearbox rebuilder.

So all in essentially refreshed the entire running gear, brakes aside. I also added a new GCFab roll bar, as running on track without one always felt pretty sketchy which allowed me to move to full harness for the tillet seat.

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Engine was in build for a long time as I had issues with getting subs working properly along with the right shims, eventually sourced a good set from a chap in australia and altered to MazdaSpeed Subs; so will have to see how those work. I ended up having to grind away a bit of material on the pistons in order for the valves to clear at max vvt angle, but may choose to limit how much or if at all I use VVT as I'm a bit nervous as to how well it works in this instance, especially at higher RPMs.

At the moment the engine is still sat on the stand but pretty much ready to go back in altogether with the new diff. Then once all run in will be back to tuning and dyno again. Should be quite a different car with all the new refresh work, new parts, more power (fingers crossed) and diff ratio change.
 
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Nice thread! Your car looks in decent nick.
I need to get the door and wing onto the mk1 turbo I crashed into a ditch in Nov :D.
I am on the original 1992 engine. I was about to buy a mk2 engine pre-crash! Would be great to do one up on the stand whilst the car remains functional.
 
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Post running in, need to get it booked in for some proper mapping but seems to go ok for now. Need to do something with the speedo as I've had the diff rebuilt with a new LSD and a 4.7 crown wheel so the speed looks a bit spicy but is quite a way out now. Excuse the awful video on my private runway.
 
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