Roadster IRS Axle HP/Torque rating?

[lee82]

Does anyone know what sort of the power the IRS Axles are rated for? Thanks!

[mike223]

I don't know what the hardware is rated for - I just know why it doesn't generally matter.


It's pretty well acknowledged that all you can successfully put to the ground (under 100mph in a roadster) with any "reasonable" street tire is ~400/400 (maybe 450/450).

Anything above that just spins tires - not breaking axles.

If you want to go above ~500/500 and run slicks, you might need heavier duty stuff.

You're not likely to hurt the axles / IRS on street tires, regardless of excessive HP/TQ.


Hope that helps.

[Hoooper]

Ive been putting about 580hp/550ft-lb through the 2015 IRS, iron housing. How much power they can live with depends on what you are doing with them and Ive not heard FFR speak to the power limit of the axles. If you are drag racing and doing clutch drops on slicks you might blow them up at 300 lb ft, but if youre road racing or just normal street driving it will take a lot more. I have not seen any wheel hop on this at all which bodes well for longevity. Keep in mind lots of mustang guys are making a lot more than most of us, on a much heavier vehicle which is a lot more punishing on the drivetrain.

If you are looking to move more power than most around here and actually use it you need to be running good street tires like NT-01, R888R, Rival-S, etc. With these tires you will get traction at well below 100 mph even at 600 hp

[JohnK]

Keep in mind lots of mustang guys are making a lot more than most of us, on a much heavier vehicle which is a lot more punishing on the drivetrain.


True, but keep in mind that these are not Mustang axles. I believe the FFR IRS axles are custom-made for this application. No idea how they compare to the stock Mustang axles.

[lee82]

Ive been putting about 580hp/550ft-lb through the 2015 IRS, iron housing. How much power they can live with depends on what you are doing with them and Ive not heard FFR speak to the power limit of the axles. If you are drag racing and doing clutch drops on slicks you might blow them up at 300 lb ft, but if youre road racing or just normal street driving it will take a lot more. I have not seen any wheel hop on this at all which bodes well for longevity. Keep in mind lots of mustang guys are making a lot more than most of us, on a much heavier vehicle which is a lot more punishing on the drivetrain.

If you are looking to move more power than most around here and actually use it you need to be running good street tires like NT-01, R888R, Rival-S, etc. With these tires you will get traction at well below 100 mph even at 600 hp

Ok good to know. Traction so far seems to be very road surface dependent for me and I'm nowhere near 580 whp. I'm probably making ~400whp and it feels like a rocket ship already.

[edwardb]

True, but keep in mind that these are not Mustang axles. I believe the FFR IRS axles are custom-made for this application. No idea how they compare to the stock Mustang axles.

True they're not Mustang axles. They're shorter. But they are Ford CV joints. At least with mine, you could see the numbers on the parts. For my 20th Anniversary Roadster, I had a full 2015 IRS pallet. So had the Mustang axles. The ends were the same as the FFR axles. It's true one of the things the high horsepower Mustang guys do first is upgrade the axles. But for our cars, being they are so much lighter, and for the most part traction limited as stated, the OE CV joints seems up to the task. The 2015+ IRS has been used on these builds for 5+ years now. I personally haven't heard of or seen posted anyone have issues or breaking the axles.

[JohnK]

Thanks Paul. I didn't pay that close attention when installing the IRS axles, but it's good to know the CV joints are genuine Ford parts. Agreed on all of your points. I was not making any judgments on the FFR axles other than to say that they were not the stock Mustang parts.

[Jim1855]

I have friends that broke the original 8.8 IRS (Supercoupe) CVs but generally not axles. One friend did but it too 600+ hp, slicks, a prepped track and a serious clutch dump. Often they'd upgrade to 31 spline parts, this usually fixed most of the early problems.

All reports are that the new Super 8.8 system is much stronger than the old. It's a complete redesign specifically to meet the new power demands. Maybe a there's concern in a 4,000 pound Mustang running slicks and supercharging but as previously indicated not a huge concern in a 2,500 pound car.

There are lots of things to worry about, IRS parts wouldn't be where I'd spend my time.

Jim

Jim