m20 or m42?

[nando]

it's true; an M42 might be 10% more efficient, but the M20 is ~40% larger. you can make the same amount of power, it will just cost more, and require *more* boost.

[MikeDE]

DO the m42. More HP per PSI (in essence, i understand PSI =/= HP in many cases) if you know what you are doing.

Have to disagree, Boost likes displacement. Picture an M42 with a JRSC running 6-8 psi. Whadda ya gain, like 50hp max. Now picture a C5/6 Vette with a 5.7 running 8psi, what does he gain?? Probably 2x that. Granted these are two different animals, but the displacement takes the boost further.

[Dj Buttchug]

listen betch stop being a pussaay and turbo a m42

[slammin.e28]

Just say fuck M20, fuck M42. Get an M30, boost it, and roll on with life.

[amcp]

M42 can be built for boost but make sure you're Johny on the spot in regarding to maintenance. Tiiming chain tensioners go out... new valves and pistons.

[nando]

I'd say M20; every aspect of boosting an M20 is going to be simpler/cheaper and a 300whp turbo M20 is going to be far more tractable and less stressed than a similar M42 build.

I do like the idea of a turbo M42, but the extra expense doesn't add up for me.

[iamsam]

I hear the M20 loves boost, but I know that M42 turbos are much much more badass.

[e30Rooster]

IIRC the m42 has a timing chain, and its comes from the factory with foraged internals.
I'm not sure where I read it but, why don't you just practice tuning, and installing a turbo on the m42 and see what it can do. get a new head gasket and some good head studs and go to town.

Worst case the m42 takes a shit, then you have an m20 and some experience so you have a good idea of what your doing, and you will know what you want and how to do it.

[Pantless Spency]

just get a boosted m42 or an m20.

anddddd sr engines< rb engines :)

[BMC227]

M42 is gay, go M20 because parts are much cheaper.

[acolella76]

you dont know what your talking about. clearly you have not ridden in a stroked m20

Oh, not only have I ridden in a car with a stroked m20, i own one!

there is a 50hp difference right from the beginning before you would even turbo the motor. of course you will get more power out of a 2.7l displacement. the sound of the M20 alone is reason enough to swap to it!

What I meant was the difference in hp between boosted 2.7i and boosted m20b25 is not going to be that much to justify spending the extra money on a new bottom end.

[AndrewBird]

I'd say the M20 purely on the fact that you can build it while still driving the car. Spread the spending out so it isn't such a big dent to the checkbook, then just drop it in on a weekend when it is ready.

[blueapplesoda]

DO the m42. More HP per PSI (in essence, i understand PSI =/= HP in many cases) if you know what you are doing. DOHC flows better than SOHC.

I love the simplicity of turbo m20s, but m42 are fantastic alternatives if you know how to build/tune your engine for boost.

[Dozyproductions]

ok so i have a 91 318is with the 1.8l 4cyl m42 motor in it, i also have a m20b25 motor and trans that i bought. my goals for the car are around 300hp when its all said and done. this said i have read both m20's and m42's can achieve this hp range (if i was turboing a m20 i would do a Frankenstein with build with 2.7 lower and 'i' head). so with that in mind that I have both engine options, its really just which one should i invest the money into?

considering:
-money needed to achieve desired result
-power to weight ratio
-reliability (as it will be on the street with occasional canyon running and track days)
-etc.

any opinions would greatly help!

dude, do you know camacho? I'm the one that got him in his e30 that he drives :D

[gearheadE30]

More displacement will almost always be easier to make more power from. You'd have to seriously build the M42 to get in that range. That said, I'm a proponent of the M42 and have a turbo one myself.