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View Full Version : HP Loss with a 9" Ford Rear

Tom.A
03-03-2008, 05:31 PM
I have heard before that using a 9" Ford rear end in place of GM 12 Bolt there is a loss in power. I don't know if this is fact or not, but if it is fact does anybody know how much of a loss? Very little as in 5HP(RWHP) or greater? Also how does a IRS compare?

Thanks,
rocketman
03-03-2008, 08:01 PM
10-15hp over a 12 bolt
TwinTurboMach1
03-03-2008, 08:16 PM
This is supposedly due to the cut on the gears. You can get 12 bolt style gears for a 9" to eliminate this loss. I forget who makes em. Im sure if you do a little research you can find out easily enough.
Tom.A
03-03-2008, 09:42 PM
Thanks for the replies :cheers:
badmatt
03-03-2008, 09:55 PM
This is supposedly due to the cut on the gears. You can get 12 bolt style gears for a 9" to eliminate this loss. I forget who makes em. Im sure if you do a little research you can find out easily enough.
Strange engineering.
deuce_454
03-06-2008, 04:39 AM
the strange setup is prety nice.. especially in aluminum.. but youd have to run 33 spline axles.... just somthing to considder
MarkM66
03-08-2008, 05:04 PM
I don't think you can state a certain HP loss. Obviosly the higher rpm, the more power to turn it. You can probably turn the yoke by hand, and your not 10-15hp, ;) .

I've read 3% .
chicane
03-08-2008, 06:25 PM
This is supposedly due to the cut on the gears. You can get 12 bolt style gears for a 9" to eliminate this loss. I forget who makes em. I'm sure if you do a little research you can find out easily enough.

Huh ?? Wow... I had thought I heard everything, until now.

It has nothing to do with the hypoid cut in the gear set. And... there is no such thing as "12bolt style" gears for a 9". There is however, a bolt drop out "third member" that uses normal 12bolt components and that fits into a 9" housing. Yes... Strange makes the casting... but, no... you do not have to run 33 spline axles. The differential itself will be the determining factor in this... and the third member will accept a standard EATON, a True Track, a spool and a few other Detroit products. Spline count running from 30 to 45.

Mark is correct. You can not put a definitive quantity in specific terms for the loss. It is an approximate. The loss is relative to the pinion gear being further off the ring gear centerline... and nothing else. Mathematically it is... 3%.