Turbo M20 guys, what gear ratio's are you running?

[z31maniac]

I was thinking a 3.25/2.93?

I'm wondering if the 2.93 might be a bit too low.

Thoughts?

[Andy348]

Quick search on e30tech:

http://www.e30tech.com/forum/showthread.php?t=54356&highlight=diff+ratio

http://www.e30tech.com/forum/showthread.php?t=44309&highlight=diff+ratio

[nando]

depending on what you want to do - I'd try the 3.73 first.

[JTapper]

I have a 3.73. It's too short.

[z31maniac]

depending on what you want to do - I'd try the 3.73 first.

Autotragic 'vert, so 4.10.

And I know that will be too short. I'm leaning toward the 3.25.

[der affe]

a 2.93 will be easier to come by as it is orginally from an e 30.

IIRC the 3.25 is from an e28 with a different cover and flanges.

i know of a few 2.93 lsd rear ends at a local pnp. one is from a low milage auto eta. if you are genuinely interested.

[nando]

people have this wierd idea that they'd rather be "boosting". I'd rather be accelerating, boost is just a pressure delta. :)

4.10 is definitely too short though, lol. not unless you want to build an 8500rpm screamer :D

[ejnight]

3.73 but mine is a 10psi car with 29lb injectors. Does just fine.

[z31maniac]

people have this wierd idea that they'd rather be "boosting". I'd rather be accelerating, boost is just a pressure delta. :)

4.10 is definitely too short though, lol. not unless you want to build an 8500rpm screamer :D

I'm just thinking even a 3.73 might end up being a hair short based on the power goals.

After reading up on dynamic compression vs RPM when it comes to the load the engine sees. I'd rather push more boost at a lower RPM, then run less boost at a higher RPM.

[bimma360]

DO NOT do a 2.93... I have freakin grown to utterly hate mine. Having said that, I'm tossing a 3.73 back in. I am guessing a 3.4x Would be ideal, but I really wouldnt know. I'm with Nando, I rather be accelerating.

[z31maniac]

I'm just thinking a 3.73 with 450-500hp/tq at the crank, that even a 3.73 is going to make for short gearing.

[nando]

Not if you can turn it past 7k :)

[325ix]

Not if you can turn it past 7k :)

And that would definitely be fun! What does an m20 need to turn that high? I'm guessing rockers, valve springs and a cam on top and at least arp studs on bottom. Or is it good to go that high stock in good condition?

[reelizmpro]

3.25 feels perfect to me.

[nando]

And that would definitely be fun! What does an m20 need to turn that high? I'm guessing rockers, valve springs and a cam on top and at least arp studs on bottom. Or is it good to go that high stock in good condition?

New OE BMW parts and an appropriate cam will do 7200+ all day long.

Springs are more dependent on the cam choice, so obviously an agressive cam will need stiffer springs.