Horsepower/Torque required to drive 9 inch diff

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RT Machine
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Horsepower/Torque required to drive 9 inch diff

Post by RT Machine » Tue May 02, 2017 7:24 am

How much horsepower/ Torque is used to drive the average 9 inch Ford rear axle as compared to a Salisbury type axle, say GM 12bolt / Dana 60 etc I have been told it is around 50 HP loss in the driveline, because of the pinion position as compared to other axle designs, also with a 600hp engine with 4 speed manual and 3.5 :1 9 inch rear, what loss of HP would one expect to measure at the wheels on typical chassis dyno ?

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Re: Horsepower/Torque required to drive 9 inch diff

Post by pdq67 » Tue May 02, 2017 12:05 pm

I doubt if it is 50hp??

This info is out there but probably will be hard to find!

But I will say that a 9" is one tough rear end like the Dana 60 is so maybe hp vs overall strength might be worth the less eff. gear train...

And I have a stock 3.31, 12-bolt posi- under my '67 Camaro car!

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Re: Horsepower/Torque required to drive 9 inch diff

Post by Speedbump » Tue May 02, 2017 1:34 pm

There was a good thread about this very thing in the not too distant past. IIRC, someone respectable in racing, maybe Joe Sherman, said cars he had done the change to 9" lost a tenth or so with no other changes. A search should find the thread.
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Re: Horsepower/Torque required to drive 9 inch diff

Post by pdq67 » Tue May 02, 2017 2:59 pm

Big Joe 1 will know!

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Re: Horsepower/Torque required to drive 9 inch diff

Post by turbo2256b » Tue May 02, 2017 4:11 pm

mOST OF THE POWER LOSS IS IN THE PINION CARRIER GO WITH WHAT THEY call a NASCAR pinion carrier issue gone.

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Re: Horsepower/Torque required to drive 9 inch diff

Post by 1972ho » Tue May 02, 2017 5:32 pm

The ford 9 inch also has 4 ring gear tooth engaged into the pinion vice only 1 to 2 for other types.Also anybody ever ran there backlash at .015 I've heard more is faster.

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Re: Horsepower/Torque required to drive 9 inch diff

Post by 1972ho » Tue May 02, 2017 5:50 pm

http://www.truehi9.com/gears2.html Check this article out on the different rears.

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Re: Horsepower/Torque required to drive 9 inch diff

Post by bigjoe1 » Tue May 02, 2017 8:15 pm

I will step in here and re affirm that again--- I have seen it happen about three or four times-- Going from a Chevy 10 bolt or 12 bolt to a ford slows the car down EVERY TIME






JOE SHERMAN RACING

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Re: Horsepower/Torque required to drive 9 inch diff

Post by joe 90 » Wed May 03, 2017 2:11 am

You forgot to mention how fast you want it to spin.

At a snails pace it takes just over zero torque and HP to drive, the faster you want to go, the more it takes.

It's proportional to road speed.




If it's not built right, like the gears not meshing correctly, it'll take more power to drive, noisy, it'll get hotter and spit out the oil AND , worst case, spit out the seals too.

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Re: Horsepower/Torque required to drive 9 inch diff

Post by RT Machine » Wed May 03, 2017 5:03 am

Thanks for the info, cheers

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Re: Horsepower/Torque required to drive 9 inch diff

Post by MadBill » Mon May 08, 2017 8:38 pm

bigjoe1 wrote:I will step in here and re affirm that again--- I have seen it happen about three or four times-- Going from a Chevy 10 bolt or 12 bolt to a ford slows the car down EVERY TIME

JOE SHERMAN RACING
I posted this a while back; here's the proof of Joe's words.
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9 inch Vs. 12 bolt.jpg
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Re: Horsepower/Torque required to drive 9 inch diff

Post by larry woodfin » Wed May 10, 2017 9:47 pm

In my opinion, a specification is missing from the test comparison. In my experience, many drag race gear sets are built/assembled with way too much bearing preload.
With any type or manufacturers rear axle assembly it should be VERY easy to turn by hand. The preload for both pinion bearings and side bearings should be just barely, almost no preload, just take the slack out.

The first thing you will notice, the car will be VERY easy to push. With the car on jack stands the rear wheels should turn easily, just a light touch should easily turn the wheels.

I would like to see the data with a 9" rear adjusted as I described.

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Re: Horsepower/Torque required to drive 9 inch diff

Post by joe 90 » Thu May 11, 2017 1:34 am

To add to the above, the way to measure it is with an inertia dyno.

Do a run down test.


That's getting the flywheel to full speed, drop it into neutral, measure the run down deceleration.

Tyre pressures are a big variable too.

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