28 or 30 spline?

[balljoint]

just snagged an 8.5 with 28 spline axles from a 73 Nova for my 68 Camaro. I want to put an Eaton Posi in it. There are 2 eatons available, 28 an 30 spline. Do I need the 30 spline for a 325 HP engine? Is there a 30 spline axle for the 8.5. confused. Thanks in advance

[Samckitt]

http://moserengineering.com/Pages/axletech.html

You can calculate axle torque here to determine what you need. According to their example with 600 lb/ft of torque, with 1.86 first gear tranny & 4.88 rear you can do with 28 spline.

That is with their alloy axles.

[GetMore]

There is a 30 spline 8.6" diff which was used on pickups and fits right in place of the 8.5" units.

I would think that 325 hp will be fine with the stock axles.

If you are planning or replacing axles with aftermarket ones and replacing the diff then I'd would definitely upgrade to 30 spline, since it doesn't cost any extra and will be a little stronger.
If you are only going to change one part then I'd stay with the 28 splines.

[Skip Fix]

FWIW my 78 is running 550 hp and high 10s with stock 28 spline axles, but will get upgraded to 30 splines. It does have an Eaton posi.

[big gear head]

If your axles need to be replaced because of wear then got a 30 spline Eaton and 30 spline Moser axles. It's the same price for 28 or 30 splines. If your axles are still good then use the 28 spline parts. Most of these axles need to be replaced anyway.