Change the rear end Ratio

[Nantucket427]

I have 3.73 gears in my SPF and that coupled with a big block makes first and second gear useless. I want to change it to 3.50 or 3.25. I understand I may not be able to do it myself. Who would do something like that? Anybody in Mass or New Hamshire?

[turnpike boy]

Since that rear is a Ford 8.8 IRS, any drag race shop you can find can do that for you. They will likely be a bit more used to seeing the straight axle 8.8, but the guts are the same. Of course, Ford dealers can do it but then you want some $$ left over for heat or food, so avoid these guys.

[mickmate]

Why don't we do it John?

[ken swart]

I have spf 2489, dana rear end, I think. What is the ratio?
Thanks

[Got the Bug]

Originally Posted by ken swart

I have spf 2489, dana rear end, I think. What is the ratio?
Thanks

The later cars have a 3:45:1 rear end.

[ken swart]

Thanks Doug

[Got the Bug]

Originally Posted by ken swart

Thanks Doug

Sure. I'm still not sure when the moved from the 3.73, but I think it was about 4 or 5 years ago.

[PANAVIA]

Doug-

This probably coincides with the shift from the FORD 8.8" third member /pumpkin to the DANA Holden - GTO units if I put my logistics hat on ...

Steve

[Randy Rosenberg]

Steve's right...

[Tony Aprile]

Nantucket...Im here on Long Island, and although I swapped out the 3.73's at Classic Concepts ( the local Superformance Installer) there were plenty of speed shops to handle the swap. Look for shops that build roadrace/dragrace cars or even shops that work on late model muscle cars like mustangs and such as there constantly changing gear ratios on street cars.

Do you know which Tremec transmission you have ????

Im guessing since your SPF car # is in the 1300's like mine it originally had a Tremec TKO with a 3.27 first gear,....was in the same boat, big block with 3.73's rear gears and a 3.27 first gear in the trans. First gear was totally useless and annoying to drive in traffic. The dana rear came out around car # 2000...so like mine you should have the ford 8.8 rear.

You might want to try the Second Strike gearing calculator first to see the difference in ratios to actual speed. I say this because...if you have the trans with the 3.27 first gear....changing the rear end ratio from 3.73 to lets say a Ford motorsport 3.55 or 3.27 will not drastically change the annoying driveability of a useless first gear.

http://www.secondstrike.com/Technical/GearCalc.asp

I know that first hand as I also changed transmissions to a TKO 600 with a 2.87 first gear....that and the 3.27's in the rear made it a pleasure to drive.

[PANAVIA]

Of course you probably have enough torque where 3.08s would light up nicely. and you could get some of your cruising mileage back. -- !!! since it is a ford 8.8 you might be able to find a set of good 3.08s for dirt cheap.

Steve