Unsprung weight....what's it worth in the rear?

[macstang]

I had 7.5 and 8.8 inch rear ends in the garage and did a comparison.

The 7.5 weighs 90.1 lbs. the 8.8 weighs 115.5 lbs.

I assume 25 lbs. is substantial unsprung weight.

I weighed both of them as housings with gearsets, track lok, pin, cover, no axles, or brakes. The axles and brakes interchange so no effect on one weight vs. another. They both have the same mounting features.

The 7.5 is weaker, but in a CMC car will probably last. I have heard of some lasting to fairly strong drag racing duty.

Gears are avail up to 3.73. The 7.5 holds less fluid, but is it negligible?

The 7.5 actually has a tighter trak lok than a stock 8.8 because of plate stack.

Anyone ever try it? If anyone wants to, I will donate what I have to the effort. I can pass it off to someone at Road Atlanta.

[GlennCMC70]

i'de give a left ...... wellyou know, to drop 25lbs. it may be on the wrong end, but its 25lbs!!!!
a side note, all 4th gen Camaros are 7.5" diff's.

[Rob Liebbe]

Reliability is your friend in CMC - I wouldn't risk it. Ford put the 8.8 behind the V-8s for a reason. The 7.5 couldn't handle it from a durability standpoint.

That's my 2 cents.

[macstang]

Ford upgraded it to decrease warrantee claims when ppl bought new stangs and put M/T rubber on them for the strip and launched at 5500. Even our standing starts don't have the traction of a drag strip and the the resulting launch shock.

I agree that 8.8 is more durable, but is it required?

If I had another season in the US, I would try it.

Surely someone has tried it.?????

[NASA13]

I would love to try it. I am running a big 31 spline monster right now , just because that is what I had. I know I have one somewhere??
I have run some 7.5s very hard in the past with much more power than my CMC car and I have only broken one. I broke it because of improper set up and it whined for a month until one day it snapped the a tooth of the ring gear.
I think I could make it last a long time, if not forever.

[macstang]

I can pass it off to someone at road atlanta, other that that, its here in MS and its free!

I also have 4 pony wheels 4 u Corey.

[Al Fernandez]

interesting...I thought all v8 mustangs always had the 8.8.

[oz98cobra]

I think you very aptly titled the thread - what's the unsprung weight worth in the rear of a CMC car - is it actually going to translate into measurable 10ths on the track?

If CMC Mustangs were hard to get down to CMC weight, I think it would be a no brainer - but they are not hard to get down to weight, and losing 25lbs from the rear end is not going to help the front/rear balance, so any advantage from shedding some unsprung weight would have to be significant enough to offset that to start with?

AI on the other hand could definitely benefit from it - wonder how a 7.5 would stand up to 320 HP/TQ? And is there a T2R available for it? hmmmm

[CMC17]

interesting...I thought all v8 mustangs always had the 8.8.

Depends on the year/model. My wife had an 85 coupe with the CFI 302 and it came with the 7.5" :(

[CMC17]

BTW.. at times, I've had to reinstall the pumpkin weight that is attatched to the 8.8 for extra lbs. A coupe is very light and I've also left the windows in it for the weight. There's only so much ballast one can run. lol

[Al Fernandez]

You Mustang people make me sick, leaving windows in....meanwhile the GM boys have to send their cars to fat camp for three months to even come close to minimum!!! :lol:

I'm fairly sure that if I had a Mustang I'd leave the 8.8 in it since its sooo easy to get to minimum weight but its not easy to get ideal weight balance and even with our little puny tq numbers people still manage to grenade rear ends here and there.