i'm slowly getting my 9 bolt ready to install, buut i presently have 3.45s in it as it came from a MT car. i also have the option of a complete posi unit from a 88 GTA, which should have 3.27s what are the pros and cons of either. and does anyone know what kind of highway RPMs i'd pull at say 70mph with either?

 

Check out the calculator on the sites main page in the tech link.

https://www.thirdgen.org/calculations

You just need to plug in the trans final gear ratio, rear diff ratio, tire diameter and speed. it will tell you what RPMs your going to be pulling at that given speed.


Just a quick calc using my tire diameter (13") got 2000RPM on the 3.27's and 2200RPM on the 3.45's. Not really a huge difference.

 

if you have very little torque and you drag the car stay with the 345s, if you want better gas mileage or you have a torquey engine go with the 327s, but keep in mind that the differences are not great.

 

What year is the 3.45 rear out of?

 

Hi Chris,
I'm currently working on rebuilding a 9 bolt as well. Please let me know if you're interested in selling the gears you're not ended up using (either the 3.27 or 3.45). Thanks!

-Stefanus

 

I think the overwhelming response to your question will be to keep the 3.45's! That's the hardest ratio to come by in the nine bolt rears. I've ran both the ten bolt equivalents to these gears (3.23, 3.42), and I'd have to give the 3.42's the edge. I ran slightly higher rpms on the freeway, but not really enough to be annoying, and they made a pretty noticable difference in acceleration around town.