M42 turbo or Sr20det

[DaveMcleod88]

Had my m42 on the dyno last night and it made 131 whp around 150bhp at the flywheel and that was running a bit lean, I was testing the engine go see if its a good one or not to ask top coin when I sell it so I have proof of its performance along with compression tests ect to replace it with a Sr20det.

But now thinking why go through all the effort of changing the engine when I can just turbo the M42 what are you're thoughts on this, seem some hihighower figures from m42's but some say there too high compression, discuss

[HairyScreech]

The comp is fairly high on the M42.

However that is simply a set of pistons away from anything you want.
With the 84mm bore of the M42 there is plenty of scope for using a set of pistons from one of the 6 cylinder cars to drop this down.

SR20s are good engines but personally I feel a turbo M42/44 is a more durable package. It's just a bit more hassle on the electronics front.

There's quite a few supercharged M4x engines on here.

edit - bearing in mind 250hp or more from an sr20 needs a turbo and manifold swap, a set of injectors and remapping your half way to a turbo M42.

[DaveMcleod88]

I'd be more than happy with 250-300hp its finding a manifold and read up on a turbo to use to run safe and not pushing itself at 250-300, so that's T28 out the way I'll scoop 200sx forums for a good T28 upgrade when they go above 300hp

[jmc330i]

M42 has a 10:1 compression iirc. Its high for an FI engine but from memory around 8psi is doable, as long as it's tuned/mapped properly. From what I've read, 190-200bhp is about the reliable max from a stock M42. You won't be getting 250+bhp without dropping the compression ratio.

With the 84mm bore of the M42 there is plenty of scope for using a set of pistons from one of the 6 cylinder cars to drop this down.

Any idea which pistons? The wiki suggests the opposite

Don't be tempted by a thicker head gasket to lower the compresson as apparently this can cause issues with the profile gasket - I've read some proper bodge job fixes for this including silicon bathroom sealer


As above, I'd personally go for an M42/44 turbo. At least that way you've only got the turbo build to worry about and not an engine swap as well!

[DaveMcleod88]

I've a couple friends local who have sr's in there 30 who can make mounts assist wiring for me, but seing as this engine is pretty healthy thought may as well or just sell the it isn't 150at fly good for the m42

[jmc330i]

isn't 150at fly good for the m42

Yes, that sounds like a healthy M42
I meant for a turbo M42 using a stock engine (at 10:1 CR). More boost and the M42 is likely to pop. I have heard of people running 10psi on a standard M42, but no idea for how long

Try some of the US forums. There's a lot of boosted M42s over there.

[DaveMcleod88]

I found a post yesterday with a guy running stock internals but arp head studs injectors a mls head gasket (can't recall thickness but wasn't massive) running 350whp videos of him nailing 36 2jz and a tunnel run I'll try find it

[DaveMcleod88]

Here's the fella http://forums.bimmerforums.com/forum/sh ... -Internals

[jmc330i]

Stock internals are forged so should and apparently do cope with 300+bhp. But the compression needs to be dropped to around 8.5:1 for that sort of power. I don't know how thick the head gasket would need to be to drop it that far (don't forget the profile gasket) but I do know most (who are serious and want a reliable engine) use aftermarket forged pistons to drop compression to 8.5:1.

350whp - that's 390+bhp at the crank???

[jmc330i]

Here's the fella http://forums.bimmerforums.com/forum/sh ... -Internals

Fair play
If those figures are accurate, I definitely wouldn't bother with an SR conversion.