ZFQ final drive ratio, which ratio is most useful/popular?

[Malcolm]

As is well known there are two final drive ratios as options when ordering a ZFQ gearbox, 3.5:1 and 3.75:1. I would be inetrested to know what the preferred choice for a typical GT40 replica uses. My engine revs to 6500 and has just under 400 bhp. Whilst I will put the car on track I will also drive down the motorway more sedately. At 70 mph the taller drive ratio is circa 2200 rpm and the lower ratio 2500 rpm. Neither get me to 60 in first gear although 3.5:1 is close at 57mph. Both top speeds are more than my engine will pull and there is nowhere in the UK where I will be able to go for it anyway.

If you have a ZFQ please could you post your final drive ratios here? It would also be useful to know if you use an external slave cylinder or internal hydraulic bearing, and if you have the oil pump drive option fitted for an oil cooler! Thanks

 

[bryanf]

This may be useful: Comparison of 3.50 and 3.75 final drive ZFQ speeds in gears, shifting at 6250 rpm.

Bryan's RCR40

Today I placed my order for an RCR40 MkI LHD with double nostril. Some of the parts I plan to use include: Craft 347 Ford small-block RBT-5 DS-25/2 gearbox (1st: 2.23; 2nd: 1.47; 3rd: 1.04; 4th: 0.846; 5th: 0.705; Diff: 4.22) Quaife E62G1121 bellhousing McLeod flywheel and clutch External...

www.gt40s.com

 

[Glenn M]

You won't need an oil cooler IMHO Malc.

 

[Malcolm]

Thanks for the feedback, much appreciated.

Looking at the gear ratios in your build Bryan, the speeds with the ratios in your box are quite close to the speeds with a ZFQ with the 3.75 diff. Only 5th gear is significantly different but how often do we expect to go over 170 mph?

Thanks Glen. From the Southern GT and AK 40 cars that I have seen to date very few use the oil cooler option. Happy to save a few £££! How is the sale of your car going? Best spec Southern GT I ever saw, and proven in competition!

 

[Warren]

Don’t track a ZFQ, they break so keep it for the road only.

 

[Randy Folsom]

I used Dragtimes.com to make a table showing the RPM vs speed with Avon tires and 3.75 final drive. The result is just about the same as a late model Corvette.

Post in thread 'Randy's RCR40 MKI'
https://www.gt40s.com/threads/randys-rcr40-mki.57066/post-587456

 

[Glenn M]

Don’t track a ZFQ, they break so keep it for the road only.

Damn! Lucky I didn't see this expert warning 16 years ago, I might not have had all those years of trouble free track fun enjoying myself!

 

[Malcolm]

16 years ago? Dang, we are getting old!

Warren, is that from personal experience? Personally I have not heard of that concern adn considering Quaife are race gearbox manufacturers in the main, it would be a bad look for them if so.

If you have a ZFQ, can you advise what final drive ratio you have please? I know all the speeds, that is easy to calculate.

 

[Warren]

Yes my experience is unfortunately the ZFQ is not up to it for track stuff, it’s well known that ZFQ are not basically strong enough. I’ve had mine rebuilt several times and actually broke in half not long before it was rebuilt yet again. Keep it for the road.

 

[Andy Sheldon]

At the end of the day they are not ZF gearboxes

Most of the internals are off the shelf bits