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Old 04-30-2006, 06:55 PM   #1
Mitch555
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What Is A Good Diff To Use For A 325 + Turbo @ 8PSI?

Hey guys.

I do mostly city driving and don't drive on the highway much, but I also don't want to be high rpm on the highway but still want to have really good speed/pickup on the street... My question to you guys is... Would a 3.15LSD diff do this job for me? Or is it too long? What bout a 3.23LSD? Would anything shorter be of any good use in this setup? Like a 3.38LSD or even a 3.45LSD?
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Old 04-30-2006, 07:05 PM   #2
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I dunno where youre gonna find a 3.45 LSD, and it will be too short for turbo 325. It's the one I have BTW. Because I just could not go with anything shorter. Well there is the 4.44 LSD that came with the 318i auto, that one would be brutal in any e36 other than that one ..

If you want acceleration your best bet would be 3.38 if you can find it.
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Old 04-30-2006, 09:12 PM   #3
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Like I said 3.38 or 3.46 at most.

We already talked that it will somewhat similar to E46 M3. E46 M3 has 3.62 final drive. I know it has an extra gear, but first five are pretty much the same.
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Old 04-30-2006, 09:21 PM   #4
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I would say lower; more like 3:25 or 3:15
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Old 04-30-2006, 10:32 PM   #5
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I have a 3.38LSD in my car and it's cool, but at the same time I run out of 2nd gear in a big hurry when I go sideways around a corner. Since mine is quite mildly modded, I need the power in the RPM's to get it to swing out in the first place and then I quickly run out of gear. And I'm thinking of turbocharging my car in the future and I know I would prefer a 3.15LSD. Unless you have the power to break loose in 3rd gear I guess, then a 3.38 might be ideal(But that's just me). All in what you want with the car I suppose. My car rev's around 3200RPM I think when doing 120km/h and 4000RPM at 140km/h. And it's a '98 323is.
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Old 04-30-2006, 11:10 PM   #6
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I'd say 3.15 or 3.23LSD at the highest. I have a 3.38 as well, I can't imagine going any shorter. Plus you might have a better 1/4 mile time with a taller diff if that's one of your concerns. I have to shift into 4th before the end of the track, which definately slows me down.
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Old 04-30-2006, 11:15 PM   #7
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Quote:
Originally Posted by thinair
I'd say 3.15 or 3.23LSD at the highest. I have a 3.38 as well, I can't imagine going any shorter. Plus you might have a better 1/4 mile time with a taller diff if that's one of your concerns. I have to shift into 4th before the end of the track, which definately slows me down.
He'll have to shift to 4th anyway with a quicker car.
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Old 04-30-2006, 11:19 PM   #8
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Nelsons got the hang of things, i think a shorter one would work better with a turbo application. 3.15 seems like a cood number. The guys on BF.com that turbo they're M's end up grabbin 2.92's cause the gears become too short for the power they're pushing, nothing but tire spin!
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Old 04-30-2006, 11:21 PM   #9
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Quote:
Originally Posted by Soldo
Nelsons got the hang of things, i think a shorter one would work better with a turbo application. 3.15 seems like a cood number. The guys on BF.com that turbo they're M's end up grabbin 2.92's cause the gears become too short for the power they're pushing, nothing but tire spin!
The ones that use 2.91's are not using ~6psi'ed 325 car either.
Of course if its a 500rwhp car 3.38 is useless.
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Old 04-30-2006, 11:22 PM   #10
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With a 3.15 for example if your trap is lower then 96mph you wouldn't need to shift into 4th. A taller diff will also keep you boosting in every gear longer.
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Old 04-30-2006, 11:25 PM   #11
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Quote:
Originally Posted by thinair
With a 3.15 for example if your trap is lower then 96mph you wouldn't need to shift into 4th. A taller diff will also keep you boosting in every gear longer.
But you know its going to be higher.
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Old 04-30-2006, 11:36 PM   #12
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Hey nelson, vlad.. lets say I put in eurosport cam kit + pulleys (240-250RWHP) on my car s52 with 3.23:1 final drive.. Should that be ok or do I need to change that to 3.15:1 like what they put into the s54 M Coupes? Looks like even the euro 84 m3's have a 3.15:1 final drive with 286hp..

Lastly, should I be looking into putting in forged piston now?
There's a few
JE Forged Pistons http://www.racetep.com/JE.html and
Wiseco S52 Piston Kit, E36 M3, 3.2L, 13:1 CR

s54 M Coupe = 11.5:1
s52/s50 M Coupe = 11.3:1

What would a higher 13:1 compression do?

Thanks
Jeff
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Old 04-30-2006, 11:39 PM   #13
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Quote:
Originally Posted by crusher
Hey nelson, vlad.. lets say I put in eurosport cam kit + pulleys (240-250RWHP) on my car s52 with 3.23:1 final drive.. Should that be ok or do I need to change that to 3.15:1 like what they put into the s54 M Coupes? Looks like even the euro 84 m3's have a 3.15:1 final drive with 286hp..

Lastly, should I be looking into putting in forged piston now?
There's a few
JE Forged Pistons http://www.racetep.com/JE.html and
Wiseco S52 Piston Kit, E36 M3, 3.2L, 13:1 CR

s54 M Coupe = 11.5:1
s52/s50 M Coupe = 11.3:1

What would a higher 13:1 compression do?

Thanks
Jeff
You will be fine.
94 M3 uses 3.15, that's correct, but 94 M3 GT uses 3..23 and 321hp M3 uses 3.23
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Old 04-30-2006, 11:49 PM   #14
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Quote:
Originally Posted by SickFinga
You will be fine.
94 M3 uses 3.15, that's correct, but 94 M3 GT uses 3..23 and 321hp M3 uses 3.23
Thanks, I figure it should be fine although can't believe the put in 3.23 on the 94 M3 GT..
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Old 04-30-2006, 11:51 PM   #15
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Jeff, a 13:1 compression ratio on a street car is probably a little much, I don't think you can run pump gas with something that high.
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