Diff ratios how and where

[vpr]

Need to get the ratios upped or lowered or whatever it needs.It revs its nuts off at 70 and really only needs 2nd and 4th.

It's a 66 big block vet.

Does anyone know who might beable to undertake this job?

[roscobbc]

Sounds like you need a 3.08 diff. My '68 427 with 235/60/15's tyres and manual runs 70 mph @ 2650 rpm approx. You can try Andy at T & A Autos at Wickford 01268-590891. They have been doing Vettes for 30 years or so!

[anonymous-user]

The alternative is to increase rear wheel/tyre diameter a little. Can look good and saves dismantling the car. Need to remember speedometer under-reading though!

[roscobbc]

5 USA said:

The alternative is to increase rear wheel/tyre diameter a little. Can look good and saves dismantling the car. Need to remember speedometer under-reading though!

Exactly what I have done (gone from 235/60/15 @ 26.10" tyre diameter to 285/40/18 @ 27.2" tyre diameter)This was as close as I could get to original stock tyre diameter. It has reduced GPS calculated 70 mph revs by about 100 rpm. Doesn't sound much but makes a difference.
Even with 3.08 rear end and the factory 'soft' L36 engine option with close ratio 4 speed it is still possible to select 3 rd instead of 1 st when pulling away (and actually pull away!)

[vpr]

tyre rolling radius is at the max....not much clearance on these and the rear is sitting up higher than the front anyhow.

it's going to have to be a final ratio change I'm afraid

[roscobbc]

vpr said:

tyre rolling radius is at the max....not much clearance on these and the rear is sitting up higher than the front anyhow.

it's going to have to be a final ratio change I'm afraid

There is another option. Replace gearbox with Richmond or Tremec 5 or 6 speed. Some of these have o/d ratios. In fact the 6 speed as used on late model Vettes has a .60 o/d ratio I think. That will do the job. As to whether it will fit, and if you want to spend that sort on money - well thats another matter!