My e30 318is s52 swap thread

[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.

[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]

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]

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

[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

[318isbmw]

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

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

Pretty sure we're misunderstanding eachother. You never did mention you were meaning at the wheels the torque was changing, merely said the torque is changing. Big difference there... As I said earlier, the gears merely change how it gets to the ground.

[318isbmw]

Also, torque multiplier was a new term, so I did a few searches, all I got was a torque multiplier wrench... Its a series of torque wrenches used to of course, increase torque.
Torque Multiplier
Torque Multiplier Info

[e30serg]

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.

This is wrong, plain and simple. a 3.46 compared to a 3.25 is LOWER and I'm not sure what you mean by "closer to 1:1 ratio". This means nothing to me. Your wheels will only see the same amount of torque your engine is putting out (1:1) if your transmission ratio is at 1:1 (5th gear in a ZF) and your diff ratio is also 1:1 (never).

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.

This is true. The torque the motor makes stays constant and the ecu determines the redline. I didn't mean to say that changing the final drive gear ratio would somehow increase the redline. It only increases the RPM of the engine at a given speed. For example:

at 80mph with the 3.25 ratio, lets say he spins at 3500 RPM
at 80mph with the 3.46 ratio, he would spin 6% faster, 3710 RPM

Did you bother to read the articles?

[e30serg]

Yep-I guess "torque multiplier" is not a very popular term. Just trying to inform people man. Not trying to be a dick. I hate to see misinformation being thrown around.

Btw, those are pretty cool tools!

[windsor318is]

so basically...........get a 2.93lsd lol

[e30serg]

No no no! a 2.93lsd would make you a dog off the line. If you want to take off fast, get a 4.10! or a 3.73.
Hell, get a few different ratios, try them out, sell the rest.

[318isbmw]

This is wrong, plain and simple. a 3.46 compared to a 3.25 is LOWER and I'm not sure what you mean by "closer to 1:1 ratio". This means nothing to me. Your wheels will only see the same amount of torque your engine is putting out (1:1) if your transmission ratio is at 1:1 (5th gear in a ZF) and your diff ratio is also 1:1 (never).

Sorry I said higher rather than lower, I apologize.

Next time your working under your car, spin the driveshaft and count how many spins it has to one revolution of the tire. If you change to a more agressive(lower) gear it will be less revolutions of the driveshaft to one revolution of the tire(edit: I believe, its been ages since I used that test for gearing in hotrods). I said it was closer to 1:1 with a 3:46 than it was w/ a 3:23 with what I just said about the spins of the driveshaft in terms of the tire revolutions.
BTW, you can't do this test with it in gear, unless you do it with it in gear and running, which would be plain stupid, so therefore your little argument about gearing in the transmission just doesn't make sense with what I was saying.

Also, the reason we're talking about this is because he has a 4.10 and its too agressive with his 1:1 5th gear, so really, the 3:25 he was talking about wanting to use, is the correct gearing and we're arguing for no reason...

[e30serg]

Sorry I said higher rather than lower, I apologize.

No worries.

Next time your working under your car, spin the driveshaft and count how many spins it has to one revolution of the tire. If you change to a more agressive(lower) gear it will be less revolutions of the driveshaft to one revolution of the tire(edit: I believe, its been ages since I used that test for gearing in hotrods). I said it was closer to 1:1 with a 3:46 than it was w/ a 3:23 with what I just said about the spins of the driveshaft in terms of the tire revolutions.

Actually, with a more aggressive, lower gear, the driveshaft would turn MORE times per 1 revolution of tire. 3.25 means that the driveshaft would turn 3.25 times for 1 revolution of tire. 3.46 means that the DS would turn 3.46 revs for 1 rev of tire.

BTW, you can't do this test with it in gear, unless you do it with it in gear and running, which would be plain stupid, so therefore your little argument about gearing in the transmission just doesn't make sense with what I was saying.

OK.

Also, the reason we're talking about this is because he has a 4.10 and its too agressive with his 1:1 5th gear, so really, the 3:25 he was talking about wanting to use, is the correct gearing and we're arguing for no reason...

We're talking about e30polak right? He has a 3.25 and was wondering about using a 3.46 to gain some acceleration. He would gain some, but if he didn't really car about high rpm's he should use a 3.73.

[318isbmw]

Actually, with a more aggressive, lower gear, the driveshaft would turn MORE times per 1 revolution of tire. 3.25 means that the driveshaft would turn 3.25 times for 1 revolution of tire. 3.46 means that the DS would turn 3.46 revs for 1 rev of tire.

We're talking about e30polak right? He has a 3.25 and was wondering about using a 3.46 to gain some acceleration. He would gain some, but if he didn't really car about high rpm's he should use a 3.73.

Yes your right, I spaced on the 3.25 vs 3.46.

e30polak was randomly throwing a question into this thread which we were talking about the gearing of a zf who just finished his swap and noticed the 4.10 is way too low and we were discussing 3.25 putting into because he has no overdrive gears and therefore a 1:1 5th gear.

[e30serg]

Oh crap-sorry for the off-topic! Yeah, sounds like a 4.10 would be too low. I'm going with a 3.25lsd myself. They're found on e28 535is'. Swap the cover and output flanges and you're good to go.
Keep the old output flanges if you want to use the bigger half-shafts out of a z3 (I think?)