Rear-end weight difference

One other note guys. On an engineering stand point. Some rear ends as a result of the pinion to ring gear placement have power loss do to the angle and friction. This is especially true for all those guys running a 9" ford rear end. In fact we get a bad rap, but an 8 3/4 is something like 15-20% more effective than the Fomoco stuff. I am not saying the 9" is not good or not strong, but it does cause some power loss over other grears in the market place. This is true for stock setups. After market is anothre issue for another topic.

That being said, I recall years a go a study that showed an 8 3/4 to have less effort in the torque loss area than a 7 1/4. You would think due to the size of the larger gears etc it would be more, and that the extra I think it is at 60 lbs in weight would slow you down some. But in most cases there is no diff. In fact the extra 60 lbs will if anything give you a little better traction out of the hole. See the weight of the car, the diameter of the tires etc are alos forces applying to the gears to keep it in motion once it is rolling. And the added weight of these larger gears and their design also is a benifit. I have seen the same questions for a dana 60. There is a point you are correct in a lot of weigh will make some diff in performance. But I think you will be fine and the 8 3/4 is so easy to change, swap out the 3rd member for even the do it your selfer that does not setup their own gears.

The 8 1/4 is a good choice too, but you probably want to keep the 4" pattern, and if you have an 8 3/4 I would go for it! :headbang:

Lastly, we could speak for hrs. back on the pinjion and ring combos. Did you guys ever wonder why a GM and or Ford is a 4.11:1 and we have 4.10:1 ? We have more teeth and also an odd count. What is good about that is, that it is know as a hunting gear pattern. This allows the pinion to not land in the exact same ring tooth all the time. Thus the gears wil llast longer, and are more of the time quieter.

Hope this helps you some..

PS I didi an 8 3/4 years ago even when my 273 was a stock 4b motor. Went to a 3.23 dog leg, and replaced the I think it was 3.21 7 1/4. I lost no time at all in the 1/4. Car did seem to track a little better. I have played with gears from 4.86, 4,10, 3.91 etc and even had a 2.76 for circle track. These are great rear ends.

good luck!
:glasses6: