ZF Transaxle -- Final Drive Ratio

Hi all,

First time posting here, so apologies if this has been addressed elsewhere on the forum. We are just beginning a new RCR GT40 Mk I build and can't seem to get clear information on the transaxle selection.

We have ordered a ZF transaxle with 4.22 final drive ratio but I am now beginning to think this may not be optimal for our intended use. The car will likely never see a track but rather be driven around town (speed limit is about 30 on most roads around here!!) and on the highway. Obviously we want it to be quick off the line but, equally we don't want to find ourselves at 75MPH on the freeway with annoyingly high rpm in 5th gear and wishing we had an overdrive!

The engine will be a 363 (302 Dart Block) with 4 double-barrel Webers, producing 500HP/450 ft-lbs torque from Craft Performance Engines.

Welcoming any and all suggestions on the best transaxle setup for this motor for our intended purposes.

Thanks!
 
Depends what your 5th gear ratio is as it is an overdrive ratio that you must multiply your 4.22 R&P ratio to get the actual final ratio. Dont forget to factor in the tire size, dia as well.
 

Kirby Schrader

They're mostly silver
Lifetime Supporter
Supporter
Hi all,

First time posting here, so apologies if this has been addressed elsewhere on the forum. We are just beginning a new RCR GT40 Mk I build and can't seem to get clear information on the transaxle selection.

We have ordered a ZF transaxle with 4.22 final drive ratio but I am now beginning to think this may not be optimal for our intended use. The car will likely never see a track but rather be driven around town (speed limit is about 30 on most roads around here!!) and on the highway. Obviously we want it to be quick off the line but, equally we don't want to find ourselves at 75MPH on the freeway with annoyingly high rpm in 5th gear and wishing we had an overdrive!

The engine will be a 363 (302 Dart Block) with 4 double-barrel Webers, producing 500HP/450 ft-lbs torque from Craft Performance Engines.

Welcoming any and all suggestions on the best transaxle setup for this motor for our intended purposes.

Thanks!
I use a 4:22 in all my ZF cars.
When I was getting things together for my GT40, lots of people said it wouldn't be an optimal solution, but as Jac says.... What is 5th?

I have a .655 in my street Pantera and a .642 in my GT40.
I really like them both. 5th is too close to 4th in the stock Pantera configuration of .705.
But that's just my opinion.
And yes, tire diameter plays a big role.

FWIW,
Kirby
 
Remember that in the ZF both 4th and 5th are overdrive, normally .84 and .705. So “4.22” gearbox final drove doesn’t really behave like a traditional car with such a low (numerically high) rear end ratio.

With 15-inch wheels and 295/50 tires, you will turn about 3000 rpm at 70 mph. That’s fine in most parts of California. In more wide-open states, a taller .655 or .642 5th gear makes more sense for highway cruising.

Some people will fit a 3.77 ring and pinion, which works okay too (with stock gears). Fitting both 3.77 and a higher 5th gear is a big mistake though.

If you don’t already have the gearbox in-hand, I would keep the 4.22 and specify a taller 5th gear. You will live happily ever after.
 
Thanks for the great advice! Looks like we are sticking with 4.22 ring and pinion with "standard" ZF ratios for 1-5.

Sound like we can't go wrong with that setup.
 

Chris Kouba

Supporter
...The car will likely never see a track but rather be driven around town (speed limit is about 30 on most roads around here!!) and on the highway...

Welcome to the circus. With the sort of mill you're building in a car like these, you'll feel like you're bringing a race horse to a carousel.

I am pretty sure I have a 4.22, and it's just about perfect. 3k RPM's gets me 75 MPH with 295/50-15 BFG POS T/A's. You'll be just fine.

Chris
 
Top