power loss thru 9 " rear
 

I have read that the 9" uses about 3% more power than a GM 10 or 12 bolt. Has anyone confirmed this either on a chassy dyno or track ?

Thanks

3% ???

Why would you be concerned about 3% ??? Just curious.

It's a fact. No need to confirm by testing. If you search out some gear-train engineering info, you'll see how efficiency of a hypoid gearset varies with the fundamental design values- centerline offsets, etc. The Ford's straddle-mounted pinion attains great strength at the expense of some inefficiency.

One of my old cars lost a full tenth in the 1/4 by going from a weak 3rd gen F-body rear to a currie 9". Gear ratio was very similar 3.73 vs. 3.70.

Definitely takes more power to run one.

R70- was it worth it knowing you weren't going to blow it up?

I have often thought about this myself. There are special gear carriers allowing you to run 12 bolt gears in a 9", or something like that. I refer back to Brians question of why would you be concerned about 3%. The cost of building one of these low drag 9" rears or even a 12 bolt or Dana 60, gets expensive real fast. I think I could take the money I saved and make up that 3% in the motor a whole lot easier. I think some of this stuff has merit when building a total package within the constaints of a rule book, but like Brian says, why is it of concern in a bracket car. I'm with ponjohn, also, I'd just rather know that its going to hold together, I'll get the 3% somewhere else cheaper.

Not every 9" ford rear is bulletproof...
:rolleyes:

Especially if your refering to OE cases,you better know how to choose the right ones or you could learn about this the hard way.
:confused2

The folks most concerned with this issue are those looking for every .001-.0001 of ET,and have optimized virtually every other option available to them within the rules of the class they race in.

Say super stock or comp eliminator classes.

The area of concern in stock 9" carriers is the pinion support bearing casting,some of the stock cases are way too thin and too weak to risk in hi-po use,aftermarket cases are far superior to even the OE "N" cases,which are the best OE choice.

And yes strange does offer a drop out 12 bolt centersection to fit a 9" ford rear housing,solves the "3%" issue for those who need to be concerned enough to think about this.

Here are a couple pics to show the weak area for the 9" and such,and some info on the 12 bolt dropout deal.

No they aren't. We have built a few using a Strange case and 35 spline axles. Around here you can pick up a bare housing for next to nothing then add aftermarket everything. Although not cheap by any means, seems like a 9" is cheaper than building a Dana or 12 bolt, if you are starting from scratch.

I recently purchased a Strange differential...9" Pro Iron case with 35 spline spool and Pro gears...$1200 shipped.

I used to do parasitic loss testing at one time as part of my Aerodynamic job in Truck Operations.

We used to put torque meters on the driveshaft and the wheels and test the vehicles.

The 3% is real. GM definately has a more fuel efficient design but I will take the strength of the 9" over any 12 bolt anyday. Ford still has Sterling Axle which even today makes the vast majority of the 9" geat sets for NASCAR. Might be others stickers but the gears are typically SA stuff.

JMO

I have several of the Strange carriers and Strange was picked to machine all of the SVO motorsports pieces. Takes a lot to be an OEM supplier.

Tom V.

Thanks for the replies.. I was just checking my information.

:cool:

It was very nice to know that no matter what I did to it, there was no way I would break it. -- The exact same reason I purchased one for my current project. --> Strange pro nodular center, Back braced, 4.10 spool, 33 spline Moser axles, Wilwood discs.

What about the dana 60 is it less efficient than the GM's as well ?

How about the Ford 8.8 I hear they are pretty tuff.


Thanks

Does the front pinion bearing on the 9" help with the deflection at all? I have always thought that front bearing offered a lot of support.

I purchased the Dana60 from Strange Engenieering for it's efficient design qualities and price. Seems like a 12-Bolt exterior with a Dana60 interior. I like t.