just picked up a 3.27 posi 9 bolt . i'm puttin out around 300hp with a built up 700r4 behind it. now my question is should i stick with the 3.27s or would it be worth it to do the jump to 3.73s ? i shift around 5000 rpms so i dont know if maybe the 3.73s would be too extreme. maybe 3.45s ? gimme some advce, thanx.

 

depends what kind of cam your running. The cam is what dictates what gear you need. If your running a very mild cam, and then use 3.73 gears, every time you upshift, your moving out of your powerband prematurely.

 

as of now i have a very mild cam, i plan to swap that for a better one soon, still wont be an extreme cam . what kinda cam to gear advice can ya give me, like whats a good cam to go with 3.73s , just a general idea.

 

I can't just "give" you a cam recommendation, because it's going to be based on the rest of your setup as well. but, every cam manufacturer usually lists a recommended gear ratio for each of their cams. So you could start looking at what type of cam you want, ie. hyd., mech.,roller, or flat tappet. decide on what power band you want most of your power in, and then go from there.

general rule of thumb, usually, when you run more duration your gonna want more gear.

 

3.27 would be the "performance axle ratio" for a 350 with a TH700R4 for the G92 package.

 

9-bolt gears can be expensive to purchase. About the cheapest I could find was $300+ for new 3.70 (3.73) and install kit. So you would be spending $300+ for the parts and then more for the installation fees. You could always try looking around junk yards. Most places will argue with you over you didn't count the number of bolts right though.

TPIs have a rather low powerband also, until you start porting, changing bases, runners... etc. Mine worked well with 3.27s and a 2400 RPM torque converter.

Waiting for the new solid roller motor to get done before I swap out gears.

 

i found 3.70's for the 9 bolt for $170 from jawsgear.com they are made by motive gear and they have install kits for like $45 for the basic shims and crush sleeve they also have complete kits with bearings and stuff for $140

 

I also just found out I have a 9-bolt in my 85 IROC. The only place I have found so far that has r & p for it is Reider Racing. Is this axle worth putting money into, or should I go junkyard diving for something different?

 

It'll hold up better than a 10 bolt. You do need to figure out what carrier series you have before buying gears.

 

How would 4.10 work on this case?

 

A 9 bolt is alot stronger than a 10 bolt. They have been compared to a DANA rear, and have been run in 9 sec cars quite often. problem is it's hard to find gears for. I got a set of 4.11's waiting to be installed, thanks to another member on this board. But installation kits can be found at most local drivetrain places. And there's enough at wreckers and such, that you could find axles and posi units if need be.
Go through the headache, and build a 9 bolt up once, or rebuild your 10 bolt every other year, it's up to you.