Originally Posted by cliffyk

It's called engineering...

Originally Posted by CobraFrenzy

Oh ok thx for clearing that up..

Originally Posted by cliffyk

You are welcome, you seemed to be confused.

Originally Posted by cliffyk

The stock 28-spline axles are "forged", that's the way anything expected to do that sort of job would be made. Also I would disagree that they suck as they can actually handle quite a bit more torque than the stock engine puts out.

Here are the torque ratings for the Ford 28 and 31-spline axles (from tests performed for Fourwheeler magazine):

COT: Continuous output torque rating
MOT: Maximum output torque rating

Ford 8.8 28-spline COT: 1250 lb-ft MOT: 4600 lb-ft
Ford 8.8 31-spline COT: 1360 lb-ft MOT: 5100 lb-ft

You can see that the 31-spline axle has just an 8.8% higher continuous rating, and a 10.8% higher maximum rating--so it really isn't THAT much stronger.

The aftermarket axle makers claim the splines on their 28-spline axles are stronger then on the stock axles, one maker claims 35% stronger.

That said it is foolish to ever believe anything anyone trying to sell you something says.

Getting back to the stock 28-spline axles, if we assume 4.10:1 gears then 4600 lb-ft out would be 4600/4.10 = 1122 lb-ft in to the rear end. Now if we assume 2nd gear (2.0:1) with perfect traction that's 1122/2.0 = 561 lb-ft into the tranny. If we further stipulate that the engine's peak torque happens around 5252 rpm then that would be 561 fwHP, or 476 rwHP with a 15% powertrain loss.

Now that would be pushing the axles right up to their limit, so if we include a 0.8 design buffer that becomes 476 * 0.8 = 382 rwHP--or just about what most people here would consider to be the limit for the stock 28-spline axles.

Originally Posted by CobraFrenzy

not really, it was a good lecture

Originally Posted by HamMach1

Dang nice write up. So in essence, 28 spline are ok for launching with DR's/slicks with 4.10's and not much power/torque?