Mopar 8 3/4 VS 8 1/4

[Mark Yacavone]

Originally Posted by Phillip marvetz

Can I expect a gain in ET buy switching from one to other if using the same gear ratio? How about overall weight?

I assume Philip is asking about it for his slant six/ automatic combo.

Not knowing a thing about Mopar rears, I'm still going to offer my opinion:
Do it.

[STK4340]

There was a bracket racer that raced at State Capital Dragway in Baton Rouge who used an 8 1/4" in his Dart Sport. He ran high 10's with a 360 with it. I say if you can find the ratio you need, run it. It can't be any weaker than say an old 8.2" GM...

[Gordie Kissner]

Loge's use to run one in their Volare stocker.

[magnumv8]

I've run an 8.25 for years and never had an issue with it 12 sec.vehicle....over 1000 passes with the original suregrip and 4.56 gears (they are getting replaced now)..... Moser made me a set of alloy axles when I first built it and recently I picked up a locker for it for the rebuild....I guess the the main issues would be axle retention and the fact that you can run a little shorter driveshaft with the 8 3/4 allowing more rpm before driveshaft issues....

[Phillip marvetz]

I have been using the 8 1/4 all season with out any issues and I'm sure it is plenty strong enough for what I use it for, I'm wondering if the 8 3/4 is more efficient or not. I don't really have any concerns about the ease of gear changes, Is it worth the hassle of changing the hole assembly ET wise?. Hey John, have you swapped out the rear in the mirada yet? Any one have a phone number for Loge? Sound's like he would have experiance to give me the right answer.......

[GTX JOHN]

Sold the Mirada to North Carl. family.. beleive they are still running the 8.25 with no problem. I would research gear availablity ... have not seen any gears past 4.50 since 1980. Mopar in its race seminars did not encourage us to run then in high HP stockers even in 1970's.

[Bob Pagano]

Phil I may be wrong but are you building a hemi car ? Tires and converters have changed from the old days and an 8.75 will not live, just ask Larry Hill, his Cuda with a 440-6 broke at every important run when he needed it most. If your not convinced start out with a 741 case and try Jim Bailey at Finished 330 858 1842 his treatment of rear part is the best bar none. I still think you will need a dana, look under John Shaul's Maxie.

[Eric Merryfield]

Originally Posted by Todd Boyer

Eric, does your Dakota have an 8 3/4 in it?

Sure does. The challengers 70 and 72 have dana 60's. All three 4.88 gears. Rounding out the collection is the 78 lil red stock 9.25 with a detroit locker and 4.56 gears.

You can never have too many racecars, or baseball bats. You never know when you might break one!

[Myron Piatek]

Originally Posted by Bob Pagano

If your not convinced start out with a 741 case and try Jim Bailey at Finished 330 858 1842 his treatment of rear part is the best bar none.

Don't you mean "742" case? 741 has the smallest pinion @ 1 3/8" and smallest variety of ratios.
Then there are aftermarket steel caps, aftermarket 489 nodular cases and the Mopar Aluminum 742 cases.

It might be the same Mirada GTX John mentioned, but I know of one that does run the 8 1/4".
Personally I'm happy with my 8 3/4". Car weighs 3,530+ but have only had broken teeth 2-3 times in 10+ years and the ease of swapping gears is too good to pass up. Current gears have been holding up for the last few years, but I have a set at Jim Bailey's right now.

[Jeff Teuton]

Think about this. 8.75 Any ratio you need, multiple spool manufacturers, axles to any spline, any width (we make our own housings) We run the 742 housing in both my large land barge and the GT/FA. Real easy choice to me. And get Bailey to treat them. Now at about 3600 lbs with 700+ hp, 600+ torque, the 8 3/4 will probably give up. Hope this helps.