M20 stroker turbo - piston, cam and compression ratio choice

[14thirty]

My M20 turbo failed and I’m looking at options for the rebuild.
At minimum it needs a rebore and pistons due to ring land failure on #5 + #6, which has damaged the bores a bit.


Looking a fitting a longer throw crank, I’ve read about the M52B28 crank, 130mm rods, stock 8.8:1 pistons, 0.5mm off the block combo.
Are stock 8.8:1 oversize pistons still available anywhere? They seem to be no longer available from BMW.


If I have to go with custom pistons, am I as well using an M54B30 crank?


Want to fit a better cam, is a Schrick 288 suitable for a 2.8 or 3.0 M20 with a turbo, or are there better options?
Head is currently getting guides replaced and 3 angle seats cut, otherwise stock head. Using 885 head, HX35 (16cm split housing) on kangaroo manifold.

Are there off the shelf forged pistons that would work with the M54 crank and a 288 Schrick? Not sure if it costs more to give them a spec or use one they already have. I want the correct dome for the 885 head.

Also not sure what compression ratio to choose if I have custom pistons, I realise it has to be suitable for the cam, though I'm not sure how a turbo affects this.
Fuel is UK 98 (US 93), running 50/50 water/meth into the charge pipe.

Thanks

[hasa]

Did you do aftermath, what happened with previous setup? You don't want to rebuild engine and face same issues. Typically turbo engines die because of detonation caused by wrong ignition timing or too lean mixture, or low octane fuel.

I'd use either STD cam or some turbo grinds like Enem which has slightly larger lobe spread. Use standard compression ratio unless you run E85 fuel.

[14thirty]

I couldn't see any signs of detonation. I think the rings butted and broke the lands. Though timing won't have been great, never been on a dyno. It had the 9.7:1 pistons as well. Have some pictures here https://www.r3vlimited.com/board/for...-oil-of-m20b25

[digger]

A 2.8 is a happy medium on stock intake manifold and cam, get some aftermarket forged pistons and 135mm rods (or 24V forged rods) stock cam and 9:1 for pump fuel

It is all a waste of your time and money if you don't have a decent ECU and aren't going to tune it properly / competently. Things will just get broken you see it all the time, fancy parts will not save you. The tune is the most important part it makes or breaks the build

[zaq123]

A 2.8 is a happy medium on stock intake manifold and cam, get some aftermarket forged pistons and 135mm rods (or 24V forged rods) stock cam and 9:1 for pump fuel

It is all a waste of your time and money if you don't have a decent ECU and aren't going to tune it properly / competently. Things will just get broken you see it all the time, fancy parts will not save you. The tune is the most important part it makes or breaks the build

x100. It's amazing to see how a simple camshaft swap puts what was a proper AFR and ignition timing out of whack. I'm not even talking about large jump cam swap, 288 to 284 was enough to mess things up.

Also M20 can knock without you hearing anything I had a knock that I could pick up with a knock monitor but could not hear it at all, NA engine 10:1). I'd definely look into knock sensor/monitor for any turbo build. And as a minimum hire a remote tuner to get the car close to where your motor is happy and safe.

[14thirty]

ECU is a Megasquirt 2, I'll need to try and find somewhere to get it mapped properly once it's rebuilt. I'll look into a knock monitor.

If I don't stay with the stock cam, can I use an NA profile? I see turbo builds sometimes go with an NA profile, others use a turbo profile. There's conflicting information about whether a turbo profile is best, or just building the best NA engine you can, then adding boost.