Anyone Know Gear Ratio?

[uBoat Commander]

Anyone know, or know where I can find, the actual gear ratio for a 928 differential? (Ring & Pinion)

Bonus Question - anyone manufacture custom ratio differentials / ring/pinion?

[153bigblock]

928 Specialists (928 SPECIALISTS ONLINE STORE - 30,000+ 928 Parts - 928 SUPERCHARGER KITS!) has a transaxle spec sheet for the 928, for all models in their tips/links section.

[Danglerb]

Pinion on a manual transmission is part of shaft the gears are on in the main section, nobody makes replacements. Some limited swapping is possible with automatics, but typically people buy the transmission with the ration they want.

Ratio of the diff and each gear varies between model years. 5th gear is 1:1, 2:20 is common for diff in later years, nothing higher than about 2.70. Most of the guys with boosted or higher HP motors opt for the 2.20, otherwise you just spin the tires in 1st and 2nd.

[uBoat Commander]

Originally Posted by 153bigblock

928 Specialists (928 SPECIALISTS ONLINE STORE - 30,000+ 928 Parts - 928 SUPERCHARGER KITS!) has a transaxle spec sheet for the 928, for all models in their tips/links section.

Thanks - it is here -

https://www.928gt.com/t-928trans.aspx

2.2:1 looking to be the lowest. Anyone know of the ability to make it 2:1 OR LESS?

[Danglerb]

Originally Posted by uBoat Commander

Thanks - it is here -

https://www.928gt.com/t-928trans.aspx

2.2:1 looking to be the lowest. Anyone know of the ability to make it 2:1 OR LESS?

Lots and lots of money. Cheapest is for automatics where the pinion gear isn't part of the shaft in the transmission like it is for the 5 spds, but still thousands and minimum quantities.

Why would you want a lower ratio, MPG?

[uBoat Commander]

Originally Posted by Danglerb

Lots and lots of money. Cheapest is for automatics where the pinion gear isn't part of the shaft in the transmission like it is for the 5 spds, but still thousands and minimum quantities.

Why would you want a lower ratio, MPG?

Matching power & speed curves

[Danglerb]

Some of the stroker/boosted guys prefer the 2.20 because traction is such an issue in the lower gears, the high speed guys look for more like 2.54 to break 200 mph.

I don't recall the details, but you can mix and match some option for 2nd or 3rd gear to tighten up the ratio's on track cars.

You can also get about an 8% effective reduction from 2.20 by running as tall of a tire as possible. Drag racers do the opposite, shortest tire for highest ratio.

[SeanR]

Originally Posted by Danglerb

Some of the stroker/boosted guys prefer the 2.20 because traction is such an issue in the lower gears, the high speed guys look for more like 2.54 to break 200 mph.

I don't recall the details, but you can mix and match some option for 2nd or 3rd gear to tighten up the ratio's on track cars.

You can also get about an 8% effective reduction from 2.20 by running as tall of a tire as possible. Drag racers do the opposite, shortest tire for highest ratio.

I had to toss this around a few times as I have both the 2.54 and a 2.20 box sitting here. So far I've kept the 2.20 in the car due more to the highway speed RPM/Mileage thoughts. I know if I'm cruising at 70mph the RPM's are below 2k, with the 254 box they are up close to 2500. (auto trans)

You are right though, the lower gears are useless when SC/Turbo'd on either box.