Gearbox ratios.

Rick,

You may want to re-direct your question to the ZF specific category below. You also can search there for similar past questions.

I'm considering the same issue as you are, and have found no low cost solution. I'd like to be at or below 5K RPM at 150 MPH, and it looks like gears in the low 3s (I think there are 3.40s?) are out there. But this looks like a $3K solution. The alternative is to change both the ring & pinion, and 5th gear.

The choice of approach probably depends on your goal for your car. The 3.40s probably don't launch like a dragster, but if you aren't worried about coming off the line hard, that may not be an issue.

I also plan to go to EFI, and I think that the low RPM efficiency an EFI system can add to a mediumly hot engine should make it easier to live with a higher 1st gear. I'd image that an 850 Holley with a big cam, doesn't work to well with 3.40s.

Ken

I think Lloyd list ratios on his site . .

rbt.com or something - PI has a direct link.

pantera place website has a downloadable excel sheet that allows you to change tire sizes and gear ratios to find rpms.

have fun,

David

Thanks guys. I have been in touch with Lloyd Butfoy and he has given us options on cogs and prices.

Lloyd probably mentioned this, but for GT5-S cars, there may be a few that got the so-called BMW M-1 version of the ZF (dunno the designator number). These gears and ratios do NOT interchange with our 5DS-25/2 ZF gearbox, as the case is different, the mainshaft diameters are changed and bearing sizes vary. My understanding is, all the gears and internals can be swapped en masse from early to late cases, but one cannot mix-and-match a 5th gear from a new box with 3rd gear from an old box etc. I'm also not sure if early & late rings and/or pinions are interchangeable between the two different ZFs

As a matter of general interest when calculating correct road speeds. The Yoko 345 x 35 x 15 diameter is 23.75 inches when fitted to original campy wheels, which gives a road speed of 71 mph at 3000 rpm with a 4.22:1 ZF final drive. Too many revs for comfortable freeway cruising. Top speed of around 140. Unacceptable. Thats why I am considering changing the final drive to a 3.77 or even a 3.4 (which I believe can be sourced). Any further input from anyone who has done cog/final drive changes is most welcome.

RICK LAST MONTH RBT INSTALLED 655 5TH GEAR SET IN MY GT5S WITH 17 INCH WHEELS. THIS PROVIDES AN INDICATED 80 MPH CRUISE AT 3000 RPM INTEAD OF 3800.IT IS ALSO MUCH QUIETER NO WHINE AND ADDED MPG. LLOYD DOES A GREAT JOB

Re changing ratios: I just finished putting 350 miles on a Pantera with 3.77 R&P ratio and a.655 5th gear. This car has a very high-torque 351-C engine (490 ft-lbs of torque & 445 horses at the flywheel). The car drove as-stock in traffic and had plenty of go in 5th as well. Had I not known of the regear, I would have thought it was stock. Top end is "only" 190mph. This contrasts with the same car running a stock 5th gear and a 3.20 R&P ratio; top end of maybe 215 mph. In this config with the same engine, driving was difficult. 1st gear was about like starting in 2nd in a std Pantera. The car used up three Centerforce 10-1/2 inch Mustang clutches in five road events (covers overheated the springs from slipping at the start & also warped the clutch faces). NOT recommended. Incidently Rick, the photo of your car shows it probably has the later M-1 transaxle (pg 23 of the latest P.I.) So be sure to mention this to Lloyd Butfoy if you decide to re-gear it. The R&P probably fits but not the .655 or .645 5th gears.

What about the 6 speed?? I think the idea is to have the lower 1st gear AND the "Taller" 6th; the best of both worlds! But at $15,995.95 Will loydd Butfoys' Panther be the only machine to have one? If I can find 2 serious buyers for my TWO (Dash 2, 5 speeds (one has never been installed, and comes with it's own bellhousing; the other one resides in my '74L, and shifts brand-new, smooth and perfect). If these two serious buyers would pay me what they are fairly worth; I would go for the 6 speed! Regards, Marlin. (forgot the .95 cents)

[This message has been edited by MARLIN JACK (edited 09-20-2002).]

Marlin, the 6 speed is probably a fantastic piece of engineering but I want to keep the GT5S as stock as possible.

Mr De Ryke, thanks for spotting the M1 box Jack. Also for telling us of your experiences with the 3.2 R+P. I'll probably go for a 3.77 if Lloyd has the parts.