Forged 28 spline axles?
05-04-2012, 10:05 AM
#2
1st Gear Member
Join Date: Jul 2011
Location: All around the World
Posts: 104
05-04-2012, 10:11 AM
#4
1st Gear Member
Join Date: Jul 2011
Location: All around the World
Posts: 104
05-04-2012, 02:01 PM
#7
Ok, if you're talking about new edge cobras, they all came with an IRS, and the early ones sucked. However they tend to take slick launches better than dr's. If you're talking about SN95 cobra rears, they do not have 31 spline axles or diff. They are 28 spline just like the GT's. They are no better.
OP, I'd say that you'd be fine upgrading just to forged 28 spline axles. I haven't seen any data about forged 28 vs. forged 31 ever. But chances are with only 3 more splines, there will be a difference, but how much I have no idea.
OP, I'd say that you'd be fine upgrading just to forged 28 spline axles. I haven't seen any data about forged 28 vs. forged 31 ever. But chances are with only 3 more splines, there will be a difference, but how much I have no idea.
05-04-2012, 02:43 PM
#8
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
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.
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.
