Best diff ratio for turbo cars

[///schwartzman]

Just left Chris' seeing the car makes me miss driving it. I got your tappet gonna see if Rick Kemph has one to match.

[e30polak]

Agreed, I like the 3.46 ratio for a US spec 265 trans. I think the road manners would be similar to a 4.10 under boost, with higher shift points.

Yea, Castro's m3 with the 3.46 is awesome in NA form, with only about 190whp! would love to see how crazy your will feel with 2x the power! :blues:

[///schwartzman]

Agreed, I like the 3.46 ratio for a US spec 265 trans. I think the road manners would be similar to a 4.10 under boost, with higher shift points.

[e30polak]

Factory gears are way too short to really take advantage of time in boost. A lower numbered gear like a 3.46 or a 3.25 would help spool time and allow for more time in boost in each gear.

[Ted B]

The 'ideal' diff ratio really depends upon factors such as vehicle mass, traction, transmission gearing, engine displacement and off-boost torque, and turbo size.

Smaller displacement engines, larger turbos, greater mass, and better traction tend to favor higher numerical diff ratios.

Larger displacement engines, smaller turbos, less mass, and limited traction are better off with lower numerical diff ratios.

In any case, it's definitely worthwhile to work out the speeds and shiftpoints vs. gearing before making a decision.

[Anders]

I have a Tremec TKO dogbox that I run with the 4.10 diff on my S14 turbo. Speed in gears are:

45
68
100
128
156

THis is almost equal to running the Euro CR box with a 3.25 diff, but 3rd and 4th are much nicer on the TKO. I find it ideal on the street. On the track, you'd surely want a taller 1st gear.

[GGray]

2.79 eta cars
3.25 E28 535s
3.46 E24 635
3.73 E30 325
3.91 E28 M5/Auto E30
4.10 M3/Auto E30

I think thats it. These are US spec cars. Bolt in as in swap output and driveshaft flanges and diff bolts right in...

[OZM3]

What diff ratio's are available that bolt stright in?

[GGray]

I have a 3.73 in my 535 turbo and its still too short geared 1/2 are pretty much useless... 3/4/5 go like hell though.

I think a 3.46 would be better or even a 3.25 for higher HP cars.

In the E36M3 turbos highHP guys go from a 3.15/3.23(depending on year) to a 2.79 or a 2.97 they freaking haul balls with the longer gearing...

[Mortimer]

I have 2.93:1 with CR gearbox.
Gears 7500rpm, 215/45-17": 80-124-168-236-297km/h. Fifth gear 2000rpm = 80km/h.

[BingM3]

2.93-3.25 ratios

[OZM3]

Yes but keeping in with how I like to do things, try before I buy. So I may as well use it and if itsnt working then look lower. The E34 M5 rear end someways off at this stage.

[Ted B]

Just keep in mind that 4.10 to 3.91 is only about 5%, which is a minimal difference and may not be worth the effort. I located and rebuilt a diff from a 325 with a 3.7 ratio, which gives about an 11% difference, and I'm thinking that I could have gone even a step lower.

[OZM3]

US H Pattern.

[Ted B]

Which gearbox does your car have?