My e30 318is s52 swap thread

[e30serg]

You guys are not understanding what I'm saying. The torque# that I wrote in is AT THE WHEELS.

Ever heard for the term "Torque multiplier"? aka transmission, aka final drive?

The gear ratios in transmissions and final drives DO multiply the torque that is put out by the engine. That is why putting a lower ratio (numerically higher) final drive makes your car take-off faster. This is the increased in torque that is making your car accelerate faster.

The downside of low gears is a higher RPM at the same road speed.

I know that the torque an engine puts out cannot be increased by changing the gears. However, the torque AT THE WHEELS CAN be increased by changing the gear ratios.

Btw, LOW gears are numerically higher, and HIGH gears are numerically lower.

4.10 = super low
3.73 = low
3.46 = higher than 3.73
3.25 = higher than 3.46

The higher RPM I mentioned is when comparing the RPM of the engine with the car going a given speed and using the 2 different ratios. Using the 3.46 diff will increase the RPM of the engine at a given speed.

Read for a bit and get back to me:

http://www.car-videos.net/articles/horsepower_torque.asp

http://www.blueink.com/CLASS/physcom1/gear.htm

[e30polak]

O okay. I really just want to reach 3k quicker, especially since I'm getting some Sunbelts for it...:twisted:

[318isbmw]

I know it doesn't create more torque from the engine, but by shortening the gears, i know that I will get into higher rpms quicker. That means I will achieve my peak torque earlier. ;)

I don't track the car, don't really plan to ever track it extensively, and would rather have it shoot out of the hole a little quicker for street driving. I don't ever drive over 85, normally I cruise between 70-75, so running a little higher rpms on the freeway wouldn't bother me too much.

I simply wanted to know if a 3.46 would be decently shorter then a 3.25?

Yeah it'll be shorter. My response was directed to the e30serg who was saying that you would get higher rpm and more torque with shorter gears.

[e30polak]

I know it doesn't create more torque from the engine, but by shortening the gears, i know that I will get into higher rpms quicker. That means I will achieve my peak torque earlier. ;)

I don't track the car, don't really plan to ever track it extensively, and would rather have it shoot out of the hole a little quicker for street driving. I don't ever drive over 85, normally I cruise between 70-75, so running a little higher rpms on the freeway wouldn't bother me too much.

I simply wanted to know if a 3.46 would be decently shorter then a 3.25?

[318isbmw]

e30polak-with a stock s52:

225 ft-lbs * 3.25 ratio = 731.25 ft-lbs
225 ft-lbs * 3.46 ratio = 778.5 ft-lbs

47 ft-lbs more in 5th gear

Also, your RPM's are going to be (3.46/3.25)=1.06, so 6% higher.

Can you live with that?

um....

Like corvallis said, gear ratios don't change torque, they only change the ratio at which the torque gets to the wheels. A taller ratio like 3.46 means that the user is closer to a 1:1 ratio in the rear end, and thus for one rotation of the driveshaft is less of a rotation in the tires. The torque is all the same, that's all within the motors, and the rpm's are all the same, that's within the ecu that determines the redline.

[CorvallisBMW]

ummmmm... gear ratios don't multiply your engine torque. You cannot get more torque by lowering gear ratios.

[e30serg]

e30polak-with a stock s52:

225 ft-lbs * 3.25 ratio = 731.25 ft-lbs
225 ft-lbs * 3.46 ratio = 778.5 ft-lbs

47 ft-lbs more in 5th gear

Also, your RPM's are going to be (3.46/3.25)=1.06, so 6% higher.

Can you live with that?

[e30polak]

3.23 came in the M coupe, 3.25 came in the e28.

[BigD]

3.25s came in some e28s.

Yeah, super eta 528s I think or possibly 535is (but I think those came with 3.73...). Anyway, just go on ebay and search for bmw 3.25

[matt]

3.25s came in some e28s.

[windsor318is]

No 3.25. I think it's the ideal diff. I had a 3.73 in there before but I found that too tall even for the Getrag. I think there's a dude on max selling a 3.46, you can try that for more punch. My buddy who is an autox fiend with his 328 says his 3.38 diff is a bit tall - good acceleration but he can't hit 100 in 2nd. The 3.25 is perfect, 150mph top speed, 62mph in 2nd gear (esp with my oversize tires)

Play with the numbers here:

http://www.unixnerd.demon.co.uk/revs.html

For reference your gear ratios are: 4.20, 2.49, 1.66, 1.24, 1.00 and with Matt's chip your rev limiter is probably 7k.

what does the 3.25 come in?ive been searching for z3 diffs but cant find one anywhere, fugure it would be alot newer than an e30 one.

[e30polak]

4.10 with an e36 ZF is simply retarded. I have a 3.25 right now, but wouldn't mind shortening the gears a little. Do you guys think a 3.46 would make a decent difference torque wise, or am I just wasting my time?

[matt]

3.25 is the best all around gear ratio for an e30 with an e36 trans, I think.

I don't have the chip archive at home, but I would say 85% of our chips have 7k rev limits.

[BigD]

lol! dude, after driving it down the street, definelty a waste of time, i can shift 2nd to 5th no problem, its waaaay to short, it does 90km at 3000rpm!! it actually slowed the car down huge, with all the shifts i need. what you running bigD? 3.73? i think im going to take the 2.93 apart and see what the issue is, maybe i can save it, ill prolly get the same gearing if its fucked.

No 3.25. I think it's the ideal diff. I had a 3.73 in there before but I found that too tall even for the Getrag. I think there's a dude on max selling a 3.46, you can try that for more punch. My buddy who is an autox fiend with his 328 says his 3.38 diff is a bit tall - good acceleration but he can't hit 100 in 2nd. The 3.25 is perfect, 150mph top speed, 62mph in 2nd gear (esp with my oversize tires)

Play with the numbers here:

http://www.unixnerd.demon.co.uk/revs.html

For reference your gear ratios are: 4.20, 2.49, 1.66, 1.24, 1.00 and with Matt's chip your rev limiter is probably 7k.

[318isbmw]

Ah, a zf, didn't realize you threw a zf in there. Gotcha now. yeah a 4.10 would be short...