ZF R&P and gear sets

[Brian Westmoreland]

Researching an upcoming change to the original ZF box in my RML GT. This car is one of 5, and the box came from units that RML ended up with after Safir stopped making GT. So late 80's, early 90's. Currently car is set up in full race mode, has a 3.77 r&p, gears 1 to 5, 2.58, 1.52, 1.04, .846, .740. The seller, a friend and fellow vintage racer said his wrench in England recommended a change to a R&P of 4.22, and gears, 1 to 5 of 2.23, 1.47, 1.04, .846, .705. His calcs say even if I just do the R&P swap that the car will be much more 'roadworthy' . He said 75 mph at 6k rpm. RIght now I'm doing leg work, mainly to find solid resources to get what I need? I've got a great wrench to get the work done, but just seeing what the GT universe says. Car has a SBF, classic Gapp & Roush built, with all the cool tricks, including the Cross Boss intake and Ford Autolite inline carb set up, about 475hp. Sorry, that last part is just fun to say. Looking forward to comments, helpful advice.

 

[Bob Putnam]

When in doubt, do a spreadsheet...

 

[Lee Patterson]

Search of the forum when I asked the same question. I stayed with the Pantera gearing (4.22) based on feedback from several owners. The SAFIR cars as well as Mk iii used 4.22 as well.

P

Post in thread 'SPF ZF Gearing'

Jul 16, 2024

Several people building cars now would love an update on ZF gearing from those with real world driving experience. Input on 5th gear and final drive ratios appreciated.

Would particularly like feedback on street ratios. I already own a Pantera with a .705 5th gear and 4.22 final. Is a .642 5th gear with the 4.22 better and also, what about a 3.77 final drive. Again, street car, not track. Want drivability. Pantera in 5th RPMs are too high.

thanks

• pattersonlee

 

[Rick Muck- Mark IV]

Be aware that SAFIR used the "BMW M1" ZF configuration and the input shaft extends father out than the Pantera/GT40 shaft. Be sure to measure the crank pilot hole depth and the pilot shaft. Ask me how I know!

 

[Rod Dittmar]

I have a ZF with a 4.22 diff ratio in my SBF RCR40. 2.23 First, 1.47 Second, 1.04 Third, and .846 Fourth. I recently had Ron McCall switch the .705 Fifth ratio to the .621. Highway speeds in fifth are much more pleasant now with 70MPH @ 2300RPM and 90 sees about 3K.
Rod

 

[Rod S]

Mine has long legs with the 3.22 RP. 2.58 1.61 1.41 .846 .655 once it's moving its great. The Pantera is quicker off the line tho with 4.22 RP.

 

[LButfoy]

Researching an upcoming change to the original ZF box in my RML GT. This car is one of 5, and the box came from units that RML ended up with after Safir stopped making GT. So late 80's, early 90's. Currently car is set up in full race mode, has a 3.77 r&p, gears 1 to 5, 2.58, 1.52, 1.04, .846, .740. The seller, a friend and fellow vintage racer said his wrench in England recommended a change to a R&P of 4.22, and gears, 1 to 5 of 2.23, 1.47, 1.04, .846, .705. His calcs say even if I just do the R&P swap that the car will be much more 'roadworthy' . He said 75 mph at 6k rpm. RIght now I'm doing leg work, mainly to find solid resources to get what I need? I've got a great wrench to get the work done, but just seeing what the GT universe says. Car has a SBF, classic Gapp & Roush built, with all the cool tricks, including the Cross Boss intake and Ford Autolite inline carb set up, about 475hp. Sorry, that last part is just fun to say. Looking forward to comments, helpful advice.

RBT Transmissions we have all ratios in stock 714-630-2450 our new web page will be up in a few days www.rbttransmissions.com

 

[Randy V]

It’s been a while Lloyd…. I hope you’re doing well.