M42club.com - Home of the BMW E30/E36 318i/iS

DISCUSSION => Swaps, Turbos, Buildups => Topic started by: Windsma on September 11, 2009, 12:06:39 AM

Title: Which Gear ratio for a turbo build?
Post by: Windsma on September 11, 2009, 12:06:39 AM

10psi max.
5spd
M42
e36

I have an open diff now and found a LSD 4.44 local for a good price.
I will later turbo the m42 so i want to get the right thing.

?

Title: Which Gear ratio for a turbo build?
Post by: Danny707 on September 11, 2009, 01:38:23 AM

3.73

Title: Which Gear ratio for a turbo build?
Post by: Boyracer on September 11, 2009, 01:39:08 AM

LSD is always goooooooooooooooooood but...

Short ratio diffs are somewhat weaker than long ones because design and number of the gear tooths. Short ratio like 4.44 would be very nice in very high revving NA engine which produces little torque. Turbo engine produces far more torque and it does not rev that high so the diff should have longer ratio and it should withstand more torque.

You can swap the gear ratio of LSD diff but it is not easy job... I have 3.67 and 4.1 ratios waiting.

Title: Which Gear ratio for a turbo build?
Post by: fabe on September 11, 2009, 05:03:31 AM

If i'm not mistaken, stock E36 318is manual should be running 3.45.. With more torque and power from a turbo, u might wanna consider 3.15 or lower...

Title: Which Gear ratio for a turbo build?
Post by: AcSchnitzer318is on September 11, 2009, 10:18:34 AM

In the e30 I want 3.73LSD as Danny said.  The 4.10's are ok, but pull would be much improved with longer gearing.

Title: Which Gear ratio for a turbo build?
Post by: 1991 E30 M42 on September 11, 2009, 11:26:55 AM

lower gear= higher engine load= faster spool

Title: Which Gear ratio for a turbo build?
Post by: deekay on September 11, 2009, 11:47:06 AM

did e36s in europe come with a 1:1 5th gear? if so you are absolutely not going to want that 4.44 diff... that would be too short no matter what your engine configuration was.

Title: Which Gear ratio for a turbo build?
Post by: tjts1 on September 11, 2009, 12:19:40 PM

All E36 everywhere had a 1:1 5th gear. A 4.44 diff is going to suck no matter what you do to the car.

Title: Which Gear ratio for a turbo build?
Post by: Boyracer on September 11, 2009, 01:32:13 PM

Hey, 4.44 is just about right for twisty racetrack without long straights when your engine can rev to 8500 rpm all the time :)

Title: Which Gear ratio for a turbo build?
Post by: Windsma on September 11, 2009, 02:40:53 PM

4.44 LSD  $200 & 2 hrs round trip..... what would you do?

I have no idea when it will get the turbo, just wanted to get the right thing first.
It might be worth it.

Title: Which Gear ratio for a turbo build?
Post by: Awgy on September 11, 2009, 06:56:15 PM

I grabbed a 3.73 lsd for my e30 cause the 4.10 lsd with the turbo is just to short. I actually like driving on the highway now.

What diff do you have now?

Title: Which Gear ratio for a turbo build?
Post by: tjts1 on September 11, 2009, 07:22:00 PM

Quote from: Windsma;78306

4.44 LSD  $200 & 2 hrs round trip..... what would you do?

I have no idea when it will get the turbo, just wanted to get the right thing first.
It might be worth it.

With a 4.44 diff in the E36 the engine will be spinning about 50% too fast for any sort of sane highest drivng. Imagine driving around town in 5th gear at 25mph. 3rd gear starts will become routine. How about 60mph in 5th gear at 4000rpm. That diff is useless at any price.

Title: Which Gear ratio for a turbo build?
Post by: Windsma on September 11, 2009, 07:46:19 PM

Quote from: tjts1;78316

That diff is useless at any price.

/thread

;) thanks.

now 1st gear only lasts 4 seconds. I dont want to know what it would be like w/ the 4.44