Choosing final drive ratio

[HKS]

Hi guys, need your opinion for choosing final drive ratio.
Vehicle's weight would be about 2100 lbs, engine 155kw/305Nm (M30 engine).
Will use 24,5 x 8 x 15 drag tires and LSD.
Redline could be maybe about 5500rpm ?

Any ideas?

[HKS]

Updated first post with tire height and redline.
Will try to get the transmission ratios as soon as possible.

[MrBlonde]

Tell us your expected best trap speed

[HKS]

Made a little research and at the moment I think the ratios are :

3.83
2.20
1.40
1.00
0.81

Engine and gearbox are from E34 as far as I know about.


here is a link to the site i would use to help you www.f-body.org/gears/ (http://www.f-body.org/gears/)
is the m30 being used in the e36 chassis and we still need the ratios for the transmission you intend on using in order to better assist you.
if my memory serves me correctly the ratios in a zf for e36 is
4.23
2.53
1.67
1.23
1

[HKS]

Just for information, took my car to the airfield for the first time and did some runs with G-tech.

Best result so far 14,06 @ 164,47.
Diff is 3,91 viscous. Slick size 24,5 x 8 x 15. Started at 6000rpm with clutch drop. Looked like no problem with friction (not enough power :)). I finish with 4th gear.

[MrBlonde]

+ From your tranny ratios you're running a Getrag 260. With 1:1 in 4th gear you should aim to cross the stripe at redline in 4th gear.

+ Your redline sounds like it would be 6,000 RPM for drag racing purposes (you said you launch at 6,000 RPM).

+ Your slick height is 24.5".

+ Your best trap speed guess is 103 MPH (~ 164.5 KPH). Let's give you the benefit of the doubt and say you can run 106 MPH on a special night.


So with 391 diff:
1st 29 mph
2nd 51 mph
3rd 80 mph
4th 112 mph
5th 138 mph

With 410 diff:

1st 28 mph
2nd 49 mph
3rd 76 mph
4th 107 mph
5th 132 mph

With 427 diff:

1st 27 mph
2nd 47 mph
3rd 73 mph
4th 103 mph
5th 127 mph

You should run a 410 diff. It gives you some headroom over a 427 (if your estimate of best trap speed is good) and still gives you some room if you get a bit more power. you'll cross the line right up the rev range in 4th gear which is perfecto.

[HKS]

Thanks. I probably get LSD diff sometime in this summer. Current viscous feels a little..not tight enough. So I will get 4,10. But it may take some time considering finance.

What I can do is to lose some weight. This time I had my spare in the trunk and also back seats in. Will get rid of them for next time(can't just throw them away, there will be a problem with the police :rolleyes).