What rear end and gearing ratio should I get for a 500hp ish engine?

 

Rear end, take your pick. A stock 9 or 10 bolt may last for a while but both will eventually fail. The most common choices are a 12 bolt or 9". Neither are inexpensive.

As for gear ratio, it depends on a lot of factors. My original 383 stroker was pushing around 500 hp and I was using a 9 bolt with 3.27 gears. It was enough to push me into the high 11's at 118 mph. Gearing was wrong for 1/4 mile racing but it worked.

For general street/strip use, a gear ratio in the mid to high 3.xx range is best although 3.73 gears with a 700R4 makes a very deep starting line ratio. For a lot of highway use, low 3.xx ratio coupled with an OD transmission will keep the engine rpms down for good fuel economy (not really a 500hp engine option). For 1/4 mile drag racing, whatever gear ratio gets you across the finish line at or just after the shift light comes on while in high gear (not OD). Engine rpm range, converter stall speed and tire size and all effect which gear ratio works best. It's trial and error.

 

This is somewhat off topic, so I hope you don't mind me asking... But at what point did your 9 bolt mentioned above fail? (As in how did it fail?) High 11's is fairly impressive with a factory 9 bolt in my opinion... I'm just curious as to what caused it to let go.

 

Match the gear ratio to the rest of the combination, cam, transmission, intended usage etc.

The rear choice depends on what you are doing with the car. As a rule of thumb they say a 12 bolt is good up to about 650HP. A 12 bolt is the lightest most efficient of the aftermarket rears. Go with a 9in or S60 if you plan on more power in the future and/or racing every weekend(lots of abuse). A 9in is the least effiecient but gear swaps are easiest on those. S60 is probably the heaviest but is as efficient as the 12 bolt and as strong or stronger than the 9in.

check out this article from hotrod, it explains the differences well and they do a dyno test with all 3 rears.

http://www.hotrod.com/how-to/transmi...ear-axle-swap/

I've had a Strange and moser 12 bolt...both are good but I think the Strange rearend was a much more complete package and I got a better deal on it.

 

Ford 9 in.

 

My 9 bolt didn't fail. In order to get a better gear ratio, it was easier to swap in a different diff. I installed a modified 10 bolt with 4.10 gears and went into the low to mid 11's. When I was finally ready to install a transbrake in the transmission, I swapped to a 9" at the same time because I knew the 10 bolt wouldn't take many transbrake launches. The stock 9" center case survived down to the mid 9's. I pulled it to fix a leak and discovered the pinion support had a crack. At any time I could have spit the pinion out the side of the case. I now run an aluminum Moser bolt through center section.

 

I'll be using a modified ls2 and I want to just drive it on the highway when I want to and maybe take it to the strip a few times each summer so I'll probably go with the S60