I found the place to ask questions...

[Stevin]

Ok, so here it is.

I'm planning on building a track e30...

Now I know I will prob get a biased opinion towards the M42 on this forum, but I should ask here anyways.

I have to idea's for a motor, and once I've decieded what I'm going to use, I can carry on with the suspension, as I need to decied what spring rates and such to use.

2 choices...

M42

Stroker, with (M47 crank, and  86.5mm forged pistons 12.1 CR) , ITB's, Solid Lifter Setup, wild cams to take advantage of the High CR, and high Rev limit.

or

M20

I've already got a M20 2.9lt stroker.

288deg shrick, cam... pretty much everything is modded. Although, if I choose this motor, I will more than likely add ITB's , or maybe a custom plenium, with a BIG TB... and another head, with much bigger valves (was lookin at a E39 540i TB the other day, I figure I could get it to work on a custom Plenium)

Now here it is... What do u think will make the better track motor ? I think with the bigger valves and and ITB's or BIG TB, I could get the power up another 10kw, and go stand alone, with a MAP sensor... I think this will help the already impressive throttle response that I have from using an Ally Flywheel.

With the M42, I would think that it's going to make all it's power right up at the top of it's rev range, and not make nearly as much torque as the M20, which makes it's power lower down, and has more torque available lower down.

Also, reliability comes into play, I know the M20 will rev to 7000rpm all day long, and will have great engine life, so long as it's not really revved past 7200rpm on the stock rockers. (plus there is no point revving that high when the power is dropping off way before then)

With the built M42... I'm wondering what power it will make ? torque ? ... and I honestly dont think it will be as reliable as the M20, due to it being a much wilder engine, and having to operate at higher RPM's to make the power, then  I would also gather than the M20 is cheaper to maintain.

What are your guys opinions on this subject ?

[RED IS 91]

and I honestly dont think it will be as reliable as the M20, due to it being a much wilder engine, and having to operate at higher RPM's to make the power, then I would also gather than the M20 is cheaper to maintain.

Sounds like you've already made your decision .
good luck

[AL GReeNeRy]

i say it depends on what kind of track car its going to be.  if its a auto-x or any other kind of racing car, go with the m42 stroker...   if its a straight line car, i would say go with the m20.. but if you were to go with the m20, i would say just sell the stroked out engine or part it out and get a m50 or s50 and start from there.. you would have an unlimited amount of options for the m/s50 engine

[2002maniac]

If I were building a track car for fun only, I would use an aluminum block
M52B28 with M3 cams and bolt-ons.

It would be lighter than the M20 and more powerful/reliable than either of the motors you listed.

[D. Clay]

What kind of tracks are you going to be racing on? Are there rules for different classes - i.e. will the M20 and M42 be in the same class.

[Stevin]

It's not for any class racing... Here in SA, we dont really have any club events where e30's compete competively.

I'm not lookin at using the M50/S50 motors, just for the fact I dont feel comfortable doing that swap myself. I want to do the work all myself.... thats half the fun.

I just dont want to break the bank with a M42 ... to only get around 250hp, that will be pretty relaible.

Where as with the M20, I can get that very easily... and FROM WHERE I'M SITTING it looks like it will be more reliable.

The car is being built for my enjoyment... Also, I think with the M20 there will be a better torque curve from lower down, with more torque to boot.

I'm still really thinking about this... ATM I'm leaving towards the M20 again, but I've changed my mind a few times... so I'm getting all the info I can.

[kowalski]

the m20 is going to be more powerful, no 2 ways about it. no replacement for displacement. the m42 is a lighter motor then the m20 so your car is going to be more tossable, personally i would rather sacrifice 30-40ish hp for a car i can toss around more, and something you don't see every day (i.e. built m42 vs. built m20) the m42 is a reliable motor and you wont have to be adjusting valves like the m20. it can definitely handle revs, mine's got 300,000 km's on the bottom end, burns no oil, and i take her to 7,100 daily.

What i'm going to go ahead and say is, you have a built m20, you evidently have experience with m20's, so stay with what you know/have already sunk a bunch of cash into. If your budget isn't much of an issue go m42 for something new and different and fun. if you want more power with it you can always go a turbo route instead of a high compression na. since your going stand alone it wouldn't be much of an issue to do this, other then piping in the turbo.

[Stevin]

Thanks man... I think I am going to stick with the M20...

I figure I can make the car handle just aswell as the M42 powered ones... as I'm going with coilovers... etc.

Although the Idea of a 2.0lt M20 ... spinning to 8500rpm running massive cams, and ITB's still sounds incredibly good... haha.

Guess, I will eventually build one up... maybe when I get bored, or pop a motor...

[scottiesharpe]

1.8  4 banger   vs.    2.9 6 cyl   ??

Both fairly close in weight and both normally aspirated. I don't think there is much of a decisioin to be made.

[Stevin]

Will be a 2.0lt

With pretty much similar mods.

but as my one mate said, I alreayd have the knowledge and the M20... so why not start with that, and maybe at a later stage swap in a built M42...