dphc18

iTrader: (5)

I need to upgrade rear end in 99 T/A 10 bolt keeps breaking parts, what would be the best rear for road course/ autocross?

9inch, 12 bolt, S60, fab 9

also true trac or locker?

STFU racing

iTrader: (13)

also, to add to op's questions...How many people change gear ratio from 3.42s for autocross? say 3.73s or 3.90s?

1981TA

iTrader: (7)

I bumped from 3.23 to 3.73. The diff unit is an Eaton Posi. I'm lucky in that 2nd gen F-Bodies have a 8.5" 10 bolt which happens to be pretty solid.

My understanding is that lockers aren't really intended for the kind of constant and hard wheel differentiation that road racing and autocross present. Check out the Eaton.com website for descriptions of each style of diff unit.

dphc18

iTrader: (5)

anybody else have any input about which housing may be better and why?

94 White T/A

The housing shouldn't make much of a difference itself, but I don't know much about this stuff. I'd also stick with a limited slip setup vs a locker

dphc18

iTrader: (5)

The reasons i'm asking are b/c the diff housings weigh more than one another and have more power loss than the other. I read somewhere by adding a heavier rearend to an fbody it will really hurt its handling capability.

Cape T/A

12 bolt is 25lbs heavier than stock
9" is 35lbs heavier than stock
dana 60 is 50 lbs heavier than stock

(these weights were in the latest issue of gm high-tech performance, where they swapped a dana 60 into project STI killer)

personally I think I'd go with a 12 bolt, but a 9" would be nice because of the ease of changing gear ratio's by just swaping center chunks out.

Cape T/A

also, i dont think the added axle weight would effect handling all to much because it is unsprung weight and it is also low to the ground.

1981TA

iTrader: (7)

Actually, it does to some extent, because it is unsprung weight. It sounds a bit counter-intuitive, but think of it this way: Higher unsprung weight generally translates to slower suspension reaction times to changes in road surface. It also means faster wear on shocks and more stress on other points with "give:" tires, bushings, etc. So, given the weights you listed off, I'd second your recommendations: 12 bolt or maybe a 9" with an aluminum center section.

CTSmechanic

iTrader: (2)

9 inch.... power loss shouldnt be a huge concern over durability.... look into a investment cast steel center section.... lighter than Nodular and stronger than alum....lockers are fine.. every NASCAR car runs a locker every race including road courses...they are very rarely a problem..its usually wheel hop that kills everything

speed_demon24

iTrader: (6)

Unsprung weight has a huge effect on handling, and you can get a 9" as light as a 10 bolt if you have the $$.

Cape T/A

More of an effect than sprung weight?

1981TA

iTrader: (7)

Didn't say that A heavy car won't handle as well as a light car, all other things beside weight being equal (like, for instance, if you put 500 pounds of concrete in a Camaro, and compared it to another Camaro). Now, say you have two cars that are exactly alike, but with the only difference being their unsprung weight...

Quote from the WIKI on "Unsprung Mass:"

"The unsprung weight of a wheel controls a trade-off between a wheel's bump-following ability and its vibration isolation. Bumps and surface imperfections in the road cause tire compression—which induces a force on the unsprung weight. The unsprung weight then responds to this force with movement of its own. The amount of movement, for short bumps, is inversely proportional to the weight - a lighter wheel which readily moves in response to road bumps will have more grip and more constant grip when tracking over an imperfect road. For this reason, lighter wheels are sought especially for high-performance applications. In contrast, a heavier wheel which moves less will not absorb as much vibration; the irregularities of the road surface will transfer to the cabin through the geometry of the suspension and hence ride quality and road noise are deteriorated. For longer bumps that the wheels follow, greater unsprung mass causes more energy to be absorbed by the wheels and makes the ride worse."

1981TA

iTrader: (7)

I saw the effects of this firsthand when I replaced the front brakes on my TA with 12" Wilwood Dynalites. It was a weight difference of 20 pounds on each corner. There is a cloverleaf-style highway exit near my house with a few modest "imperfections" in the road surface. Before the switch, the most I could take the corner at was 45 MPH. Above that, and I'd need to clean my pants out. After the switch, I could take it consistently at 52 MPH.

Cape T/A

Thanks for the explanation!

ND2RACE

I don't autocross my camaro because I have a Miata for that, but with the Moser 9" in my Camaro I noticed a few things. The suspension gets put on somewhat of a bind using the stock style BMR torque arm so that would need addressed to keep thing moving freely for handling, for drag racing I don't have a major issue with it because it isn't much. The other thing is weight as guys have mentioned and in my opinion having the right shocks to control that weight is the big issue, just having the extra weight there will effect handling but it would not be a huge difference with proper set-up.

Personally I'd go with the lightest weight feasable option, to me that would be a 12 bolt or I'd look into the 8.8 converstions that have been done although that would be fairly advanced to get the design right.

djsanchez2

iTrader: (14)

For what it's worth, Sam Strano has one multiple championships with the stock 10bolt, and stock 1LE LCA's......

http://www.gmhightechperformance.com...o/viewall.html