6 vs 4 cylinders!

Mon Apr 06, 2015 8:53 am

Right im already aware that this will spark a debate, and that most of the cars on here are running 6cylinder engines of some variety.

I am rebuilding a rally car into another bodyshell as my last one was written off a couple of years back.
I currently run an M42 engine that is standard apart from re-profiled cams, e36 direct top gearbox and a 4.445/1 lsd.
The car was originally a 325i but i removed that in favour of the m42 due to the class of events i was aiming at.
I have now compiled a lot of the parts to build a 2.1 m42, however i am starting to wonder if the cost of buying custom camshafts for this build and the machining costs will be worth it to get maybe a 200hp M42?
The regs have now changed slightly regarding historic stage rallying allowing cars up to 1988 to run, however if im correct M42s were not introduced until 1989/90.
My thoughts are now to go back to a M20b25 engine although i feel they do spoil the nimble handling compared to having the little 4 pot engine!??

Your thoughts please.

Mon May 25, 2015 5:22 pm

I've run both M20 and S14 in mine... I'm not sure I hold with the idea that the 4 pot cars are more nimble - you can make the 6 cylinder cars as nervous as you like with lots of negative camber and toe out...

I went 4 cylinder because an engine came up at the right money, plus I've always been a fan of the S14 lump. I think a well sorted 6 cylinder and a decent geometry set up is really really good. S50s are a bit heavy but really get the job done, M52s are a nice way to get more modern hardware in and produce decent power and M20s just run and run even if they do leak and leak.. Don't have much experience of M42s honestly so I'll let someone else comment on those!

The key bit is getting the geometry right - or me that makes ALL the difference.. Mine with the M20 in with decent negative camber and coilovers was sweeeeeeeet....

Mon May 25, 2015 5:30 pm

If your choice of M42 or M20 is limited by a cut off date of 1988, you'll be stuck with the M20 as the M42 was 1990/91.

Mon May 25, 2015 10:03 pm

Good point Jim....!

Tue Jun 02, 2015 11:00 pm

Cheers lads, I have now gone with the m20 2.5 engine. I'm going to keep my eyes peeled for a decent s14 along the way. I do agree that the m20 generally seems like a good power plant based on the years of production it was used for.
Think I'm going to have to put my m42 engine in a spare 2 door she'll I have!