What are your RPMs . . . ?

[saace7]

After my recent purchase I was curious if my car was actually geared like the PO advertised. Was told the rear diff. was changed out with 3.38. When I am cruising in 6th gear (MT) at 65mph I am exactly at 2500 rpms. For those with regular 3.07 gearing. What are your RPMs at when cruising 65mph. Curious to know if I have the stock 3.07 gears or 3.38 because if so Im pretty sure my RPMs should run higher in 6th gear. Also I have stock wheels.

[3ZHPGUY]

If you go a little faster you can compare it with this.

http://i591.photobucket.com/albums/ss351/3zhpguy/ZHP/IMG_0931-Edit.gif (http://s591.photobucket.com/user/3zhpguy/media/ZHP/IMG_0931-Edit.gif.html)

[derbo]

for reference my 70mph is 2700rpm with the M3 3.62 LSD.

http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm

according to this calculator

3.07 @ 65mph = 22xxRPM
3.38 @ 65mph = 25xxRPM
3.62 @ 65mph = 27xxRPM

[saace7]

Just from looking at that picture I am almost certain mine must be geared. If I remember correctly when I am at 80mph I am hovering over 3k by maybe a few hundred rpms. Not 100% sure though.

[3ZHPGUY]

Can't remember the grade of the road when I took that picture so, there may be some variation.

[saace7]

for reference my 70mph is 2700rpm with the M3 3.62 LSD.

http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm

according to this calculator

3.07 @ 65mph = 22xxRPM
3.38 @ 65mph = 25xxRPM
3.62 @ 65mph = 27xxRPM

looks like you have nailed this one on the head. Thx for the info!

Now I need to figure out.. If the original owner was willing to swap the diff., maybe he had an LSD installed and don't even know it yet. . . lol

[derbo]

looks like you have nailed this one on the head. Thx for the info!

Now I need to figure out.. If the original owner was willing to swap the diff., maybe he had an LSD installed and don't even know it yet. . . lol

Jack up the car and put it in gear. See if both wheels turn the same direction. :)

[saace7]

spinning freely, I assume with motor off. I spin wheel with my hand? If its an open diff. One wheel will spin in the opposite direction? Or stay stationary?

[BavarianZHP]

Jack the rear up. You can spin one wheel by hand while in neutral:

1) If the opposite wheel remains stationary - open diff
2) If the opposite wheel spins with (same direction) the wheel you are spinning - LSD

[saace7]

Great, thanks for the info! I will try this as soon as possible.

[webster]

You should definitely be able to feel an LSD by actually driving. Just kick the rear out a little, if you get inner wheel spin, no LSD.

[saace7]

You should definitely be able to feel an LSD by actually driving. Just kick the rear out a little, if you get inner wheel spin, no LSD.

Well as I have just recently purchased the car I have been babying the hell out of it until I finish refreshing everything. I am about half way done. Need to tackle the suspension next because the shocks and struts and definitely blown. Need to change out some bushing too. But the one and only time I did get to experience a little something was one day while on the way back home it was raining and at a back road intersection I did a little burn out through first gear and it totally felt like both wheels were spinning. This was about a week or so ago and what initially struck my curiosity about my differential. Next time I get it jacked up in the air I'm going to spin the wheels to test.

[derbo]

Jack the rear up. You can spin one wheel by hand while in neutral:

1) If the opposite wheel remains stationary - open diff
2) If the opposite wheel spins with (same direction) the wheel you are spinning - LSD

Thanks for clearing up what I meant lol.

[BavarianZHP]

You should definitely be able to feel an LSD by actually driving. Just kick the rear out a little, if you get inner wheel spin, no LSD.

I agree. You don't have to press the car hard either. Just park the car with one wheel in some grass (something slippery: mud, wet grass, gravel etc...) and the other in pavement. Punch it a little and see if the slippery wheel spins or not. Depending on where you are, this may even be easier than jacking it up.

[terraphantm]

Jack the rear up. You can spin one wheel by hand while in neutral:

1) If the opposite wheel remains stationary - open diff
2) If the opposite wheel spins with (same direction) the wheel you are spinning - LSD

In my experience, if the diff is open, the opposite wheel will spin in the opposite direction

[BimmerWill]

In my experience, if the diff is open, the opposite wheel will spin in the opposite direction

+1

Sent from my DROID RAZR using Tapatalk 2

[saace7]

I lifted the car today. Spun a wheel and nothing happened to the other. Got on the other side. Spun the wheel and the other did nothing again. I'm almost certain this shows an OPEN diff. I think if it is an LSD the opposite wheel should of spun in the opposite direction.

[derbo]

If you had an LSD, both wheels will move in the same direction when you move one wheel.

But it sounds like you have an open.

[Avetiso]

It's possible that by spinning with your hands, there's not enough force to turn the opposite wheel. Do it in first gear and it should spin opposite.