M42 turbo build notes/questions

[tjclemens2]

Hey yall,

I am M42 swapping my 2002 but I have some questions and I feel the e30 forums would be best for the help. Pretty much I want to build a reliable turbo build with a goal of 220-250 CHP. I’m going to run a gt28 turbo at 10-12 psi. I just got an m42 given to me for free and that’s what I’m going to use to build it up. I’m planning on replacing everything for the most part but here is a list of what I’m planning on doing to it and I want to hear you feedback on how it looks and if there are any changes you would make. Also at the bottom I have a few questions.


M42 Plans




Bottom End

Stock Crank

Block Bored to 85MM

ARP Head stud Kit

Cometic MLS 85mm Head gasket 0.060”

ACL Main and Conrod bearings STD

Timing cover conversion from M44 w/o sprocket

JE forged pistons 85MM

Carillo forged Conrod




Top end

Stage 2 Port Kit from VAC motorsport

VAC high performance valves STD

Schrick Performace 256/256 Camshafts




ECU

Haltech Elite 550 or 1500

Elite 550 or 1500 universal harness




Fuel

Bosch Ev14 550cc injectors

Walbro GSS340 225LPH in tank pump




Parts from E30

Getrag 240 or 242/5

Driveshaft

Shift linkage




Questions:

Is 85mm bore OK? Worried about block strength




Should I go +1mm on valves or are stock ok?




Haltech 550 or 1500?




Are Schrick Cam degrees good? Or should I go more aggressive?




Getrag 240 or 242/5?





Which dif should I run?

thanks,
Travis

[varg]

Why so much expense for so little power? Things like

• forged pistons
• forged rods
• worrying about block strength

Are just not necessary at 250bhp, or 250whp. That's a pretty mild goal and you can manage it with a stock engine, T3 sized turbo and around 1atm of boost. Further, a thick MLS head gasket is not necessary with aftermarket pistons. You can choose a stock thickness and set the compression ratio with the pistons. Personally I don't even think MLS is necessary with such a low power build and it may be a liability because they are prone to leaking without perfect prep, I know a guy who DDd a turbo M42 car with a stock gasket and studs for years, I put a .120" MLS on mine and it was too much, the compression was too low and I lost low end to that. Gearing is preference based, use a gearing calculator like https://e30goodies.com/gearing-calculator/ and figure out what sounds good to you. Some guys run low ratios because they want to make the highway miles easy, some guys don't care if they're turning 4,000rpm at 80mph.

[ccsdo5]

I agree with Varg here. a built engine is not really needed for your power goals. Personally I think a lot of what you posted isn't really needed for a goal of 200-250CHP heck not even needed for a M42 that makes 250whp. I would do the following:

- stock bottom end but gap the piston rings a little bigger
- new main and rod bearing ACL is fine
- ARP head studs with stock HG
- the 256/256 can be used just a stock refreshed head and help with the car falling off up top.
- gtx2867r or g25-550 sized turbo be perfect for response and power goals.
- whatever ecu you want
- walboro 255lph pump is fine
- I'd so some 660# siemens injectors

Since you need to swap it anyway I would opt to do a e36 getrag 245 the e30 m42 getrag 240 is very weak.

My drift car is probably making around 300whp with a stock bottom end and has been for a few years now. It's basically the same of what I posted above. I don't think there is a reason to run a MLS head gasket for that power.

[tjclemens2]

Why so much expense for so little power? Things like

• forged pistons
• forged rods
• worrying about block strength

Are just not necessary at 250bhp, or 250whp. That's a pretty mild goal and you can manage it with a stock engine, T3 sized turbo and around 1atm of boost. Further, a thick MLS head gasket is not necessary with aftermarket pistons. You can choose a stock thickness and set the compression ratio with the pistons. Personally I don't even think MLS is necessary with such a low power build and it may be a liability because they are prone to leaking without perfect prep, I know a guy who DDd a turbo M42 car with a stock gasket and studs for years, I put a .120" MLS on mine and it was too much, the compression was too low and I lost low end to that. Gearing is preference based, use a gearing calculator like https://e30goodies.com/gearing-calculator/ and figure out what sounds good to you. Some guys run low ratios because they want to make the highway miles easy, some guys don't care if they're turning 4,000rpm at 80mph.

hey Varg, sorry I messed up, I posted this last and didn’t read through it. I meant to say 350 CHP. Hopefully that increase explains the reasoning for forged internals. Let me know if that is still overkill though. I’m planning on running 8:5:1 compression. What thickness gasket should I run? Or is stock still ok for that hp goal

[tjclemens2]

I agree with Varg here. a built engine is not really needed for your power goals. Personally I think a lot of what you posted isn't really needed for a goal of 200-250CHP heck not even needed for a M42 that makes 250whp. I would do the following:

- stock bottom end but gap the piston rings a little bigger
- new main and rod bearing ACL is fine
- ARP head studs with stock HG
- the 256/256 can be used just a stock refreshed head and help with the car falling off up top.
- gtx2867r or g25-550 sized turbo be perfect for response and power goals.
- whatever ecu you want
- walboro 255lph pump is fine
- I'd so some 660# siemens injectors

Since you need to swap it anyway I would opt to do a e36 getrag 245 the e30 m42 getrag 240 is very weak.

My drift car is probably making around 300whp with a stock bottom end and has been for a few years now. It's basically the same of what I posted above. I don't think there is a reason to run a MLS head gasket for that power.

hey I appreciate the response, especially about the transmission. Little typo. Meant to say 320-350 chp not 220-250. Sorry. Let me know how this changes your views. Thanks

[Dj Buttchug]

OP can make 400 hp on the list provided above however it will not happen on 12 psi... For example my engine makes 340ish WHP at 19-20psi. Good luck with the build OP. If I could interstellar time travel back in time 10 years I would say to myself one thing






K swap it.




And id be alot better off. To each his own. M42 is still a great engine. Also on the subject of transmissions, put a zf behind it. I have no idea how my G240 has made it this long under boost.

[TobyB]

350 bhp in a 2002? erp.

You'd best get the ZF 320 5 speed or the 370 6- speed from the E46 for that,
and maybe a mid- case diff, some seriously custom axles,
trailing arms from a...

Oh. well, hell, there's your problem:
You want an E46, not a 2002.

Nothing in the 2002 is going to hold up to 300 ft/lbs, from the rear hubs to the front radius arms...

t

[e30davie]

Spent a bit more on the electronics. Something that has an onboard wideband controller and drive by wire compatibility. really simplifies the wiring and plumbing. and you can do so many cool things once you have dbw (traction control and cruise control for example)

[varg]

hey Varg, sorry I messed up, I posted this last and didn’t read through it. I meant to say 350 CHP. Hopefully that increase explains the reasoning for forged internals. Let me know if that is still overkill though. I’m planning on running 8:5:1 compression. What thickness gasket should I run? Or is stock still ok for that hp goal

Depends on the tune, there's definitely less safety margin there but I don't think it would warrant an all forged build. I'm guessing it's a pure street car because there's no way that much power will be usable in a 2002 on track. 8.5:1 compression is pretty low, I'd try to go for 9:1 or so for better response. FWIW, to make 350hp with even a big T28 like a GT2871R you'll probably be running nearly 20psi, small turbine doesn't help flow.