3.73's or 4.10's ? on a 89 vert?

[E30Jigzaw]

Not the LSD itself, the higher revs will be louder. For example, at 65mph with the 4.10 you may be at 3,200 vs 2,900 with a 3.73. I'd focus on the swap and leave the 3.73 alone until you drive around and decide if you prefer a little more zip and more shifting and noise or like it the way it is. Diffs can be a serious pain to swap.

im taking off all my suspension and getting everything powder coated so Diff is coming off either way ;)

[325ix]

Not the LSD itself, the higher revs will be louder. For example, at 65mph with the 4.10 you may be at 3,200 vs 2,900 with a 3.73. I'd focus on the swap and leave the 3.73 alone until you drive around and decide if you prefer a little more zip and more shifting and noise or like it the way it is. Diffs can be a serious pain to swap.

I feel like that is a ridiculous reason not to swap diffs. If you have a decent exhaust it wont make that big of a difference. I had a 3.91 in my ix which was for all intents and purposes no louder than the 3.73s in my roommates car.

[E30Jigzaw]

I feel like that is a ridiculous reason not to swap diffs. If you have a decent exhaust it wont make that big of a difference. I had a 3.91 in my ix which was for all intents and purposes no louder than the 3.73s in my roommates car.

i am ruinning stock exhaust i don't like my car's loud .. plus its a vert just somethging to cruise with

[87cabrio89is]

FACT: if your vert came from the factory with a 5-speed it WOULD have come with a 3.73 unless custom ordered. If it came with an auto tranny, it MAY have come with the 4.10 depending upon MY. As stated already by some, you'll shift sooner with the 4.10 and a 5-speed, you will run higher RPMs at highway speeds (therefore, more noise and wear on the engine) and may not be able to go as fast, which is irrelevant since you'll still be able to go faster than US laws permit!

[fporro]

I'm running a 4:10 lsd on my 87 325iC.

Shorter first gear and 3000 rpms at 60mph's but not much louder than 3:73 it came with.

[fronton]

I feel like that is a ridiculous reason not to swap diffs. If you have a decent exhaust it wont make that big of a difference. I had a 3.91 in my ix which was for all intents and purposes no louder than the 3.73s in my roommates car.

3.73 to 4.10 is not the same as 3.73 to 3.91. I can say from person experience with my actual car that swapping from 4.10 to 3.73 being the only variable, the noise level was noticeably reduced for any sustained driving RPMs.

It is unlikely that your roomate's car and your car are identical in every way except for diffs, and if they were, that is only half the change in ratios OP is asking about.

Also, unless you are also changing exhausts with diffs, it is irrelevant how 'decent' of an exhaust you are starting with. It will be the same change in volume percentage-wise.

[jeffnhiscars]

Let me complicate this even more. My 89 cabrio has a 4.10 and the 87 Cabrio has a 3.73 (both autos) and the 87 feels much zippier. Could be cause it has 98 k and a fresh head (including guides) so it doesnt mind working a bit harder but there is no comparison to my mind

[E30Jigzaw]

Let me complicate this even more. My 89 cabrio has a 4.10 and the 87 Cabrio has a 3.73 (both autos) and the 87 feels much zippier. Could be cause it has 98 k and a fresh head (including guides) so it doesnt mind working a bit harder but there is no comparison to my mind

so the 4.10's will feel more tourquee? than the 3.73's ??

[jeffnhiscars]

so the 4.10's will feel more tourquee? than the 3.73's ??

Conventional theory is that the higher gearing provides better acceleration and less top end which is why the M3 has a 4.10. The math supports this since but my experience leads me to a different point of view. I say it also depends on the balance between your gears and the torque band of your engine. Set aside for the moment that the lower ratio will give you better fuel economy due to lower rpm (and noise) at highway speeds.

Clearly it takes more hp to turn a 3.73 than a 4.10 at any given rpm (why you even have gears in the 1st place) but as long as the engine is in its sweet spot it should rev just as easily but the 3.73 will move the car further per rpm. My 84 318i has a 3.46 and I think any higher would have me going through the gears ways too fast. This is in part due to the 8lb flywheel which lets it spin more easily due to the lower rotating mass which ties in to the subject. Since the engine spins freer it handles the lower ratio more easily as if it had more HP despite the fact that it doesn't but I go further per rev than if I had say a 3.64....so its quicker from where I sit. Make sense ?

Since the engine in my 89 w the 4.10 is not quite as fresh as the 87 (3.73) it appreciates the higher ratio as it doesnt have to work as hard. Since the 87 is up to the task it revs just as quickly but the goes goes further per rev which (again from where I sit) makes the car feel quicker.

Keep in mind these are both auto trans cars. With a 5spd (like in my 318i) where you can micro manage the sweet spot the potential to take advantage of a lower ratio is even greater.

Now I know there will be a ton of disagreement with me and I do know the science, but I've had my coupe for 14 years and there are days when I think about an even lower ratio to get the highway revs down and to give me more time in each gear and there is no denying that the 3.73 Cabrio has more snap than the 4.10...so there you have it :)

[fronton]

Conventional theory is that the higher gearing provides better acceleration and less top end which is why the M3 has a 4.10. The math supports this since but my experience leads me to a different point of view. I say it also depends on the balance between your gears and the torque band of your engine. Set aside for the moment that the lower ratio will give you better fuel economy due to lower rpm (and noise) at highway speeds.

Clearly it takes more hp to turn a 3.73 than a 4.10 at any given rpm (why you even have gears in the 1st place) but as long as the engine is in its sweet spot it should rev just as easily but the 3.73 will move the car further per rpm. My 84 318i has a 3.46 and I think any higher would have me going through the gears ways too fast. This is in part due to the 8lb flywheel which lets it spin more easily due to the lower rotating mass which ties in to the subject. Since the engine spins freer it handles the lower ratio more easily as if it had more HP despite the fact that it doesn't but I go further per rev than if I had say a 3.64....so its quicker from where I sit. Make sense ?

Since the engine in my 89 w the 4.10 is not quite as fresh as the 87 (3.73) it appreciates the higher ratio as it doesnt have to work as hard. Since the 87 is up to the task it revs just as quickly but the goes goes further per rev which (again from where I sit) makes the car feel quicker.

Keep in mind these are both auto trans cars. With a 5spd (like in my 318i) where you can micro manage the sweet spot the potential to take advantage of a lower ratio is even greater.

Now I know there will be a ton of disagreement with me and I do know the science, but I've had my coupe for 14 years and there are days when I think about an even lower ratio to get the highway revs down and to give me more time in each gear and there is no denying that the 3.73 Cabrio has more snap than the 4.10...so there you have it :)

Scary.

The only way a lower gear ratio will be "faster" is for specific testings that are manipulated to decrease gear changes for static speed or distance. For example, in my car with a 4.10 it required getting into third gear to hit 60mph. Since it costs me at least 0.75 sec to shift, a 0-60 of 7 sec included 1.5 seconds lost to shifting. So I switched to 3.73 which now allows up to 65mph in second rather than just 59mph with the 4.10 and I save 0.75 seconds off my 0-60. So the result with a lower ratio can be effectually 'quicker' by saving you shifts. You are actually accelerating slower but that loss is overcome by less shifting. If you measure 1-100mph however it would be better to keep 4.10 because despite the extra gear change loss of .75 sec, the quicker acceleration has enough time to make that back up over say 14 seconds vs 7 sec.

Keep in mind that your transmission ratios and tire diameter play into acceleration as well but obviously are irrelevant if the diff is the only variable you are changing.

[VANOS714]

4.10 You homo!

[E30Jigzaw]

4.10 You homo!

Vanos.. i went with the 3.73's lol and my boss trasshed my 4.10's
:(