i want to know you guys opinion that's been there and done that...what you would do or wouldn't do

-is there any major diff. b/t the two what are the pros and cons of them




and i think i'm going with 4.56's instead of 4.10's this time....it seems my car is still actually geared high to have such a low gear in it espi. in 5th and 6th...what do you think 4.10's or lower than that in the new rear????

 

The 12-bolt is lighter and uses 3% less power to turn. If you are going to stay under 800flywheelHP, think 12-bolt. In the 800-1,000HP range its a toss up. Over 1000HP, the 9-inch has a lot more options to beef it up. Or if you are a dedicated drag racer that uses your car every weekend and makes 10 passes with 6K clutch dumps, a beefy 9-inch may be preferred, even if you are under 800HP.

Select the gear ratio based on trap speed, tire diameter, tire growth, and engine redline, avoiding a shift to 5th gear at the end of the track.

 

Also keep in mind that 6 speed cars and 12 bolts dont allways get along...if you are under 600 whp, you should be fine, but stay away from the eaton posi. I broke my 10 bolt last week, and im getting a 9 inch with 3.89's, 31 spline axles and the true trak diff because I plan on rebuilding to a 383 with about 15 psi of boost. Like stated previosly, the 9 inch will use a tad more hp, but at ~3% loss, a 400 rwhp car would lose 12 hp. Big deal...bet you anything you will never snap a 9 inch that is "setup properly" Nine inches are also easier to make gear swaps...Ive also seen some 12 bolts whine a little more after some runs on slicks, but it is to be expected on a performance rear...

 

I have been running Eatons for 20 years with no failures...The trick is to use the HD version with 800lb preload springs...Like Fred said, what are your hp levels, and goals for the car? Track car? Street/strip? Talk to some M6 guys and see what they use...

--Alan

 

I'm at 800HP on a 300-shot of nitrous, and have the HD Eaton, and its been fine so far, but then the car isn't run much any more. It was originally an M6 car and the Strange took a beating with 6K drops on a Street Twin.

A buddy of mine took his close to 1,000HP in a 4,000# convertible running 9.0x's and 1.3x 60-fts. He did go to a 9-inch when he took the car over 1,000HP but it was not a "basic" 9-inch.... it was expensive.

 

I wasn't referring to an eaton HD posi or an eaton posi with 800 pound preload springs...It seems to me the people with the standard eaton posi that moser puts in some of the cheaper combos are the ones having problems. Ive seen 3 cars with the standard eaton posi direct from moser in 6 speed 12 bolt cars that have been giving the one tire spin deal on slicks while warming the tires up. All three of these cars were primarily track cars, but still were driven on the streets. I guess I should have been more specific. Found some interesting info over on ls1tech. http://ls1tech.com/forums/showthread.php?t=357326

 

I'm in the same boat. Leaning towards the 9 for reliability and future pully change.

 

thanks guys......my future plans for the car pretty much is to be a street/strip car, mostly street. As for now i don't forsee me ever going over 800hp, so i guess the 12 bolt is sufficient enough.


I just want something that will hold up to what i'm doing to it now that's in my sig. and not tear out if i want to take it to the track. Unlike the 10 bolt i have now that i've torn out twice on DR's before the cam swap with just minor bolt-ons.

 

9, you'll be doing some fabrication, but it's cheaper and it will work for decent power. I have a Moser 12 bolt in my Z, and do like it. If I were to do it again, seing what I have seen, I would do a Strange 12 bolt instead of the Moser. Just throwing in my .02 cents.