8.8 strength for >393 engines

Ant · #1 (**permalink**) 12-08-2003, 12:36 AM

I am curious if anyone has any trouble with the Ford IRS 8.8 rear end?

Some of these serious 408 engines and bigger, claim550 - 650bhp, so these engines are delivering a lot of power and claimed on pump gas!

I would prefer to go to 393 or bigger, but at present settled my ideas on a 347 for three reasons light weight and under hood clearance, and lastly easier on the drivetrain. Having said that I am wondering that the smaller engine might not have enough grunt, and they are still making diffs etc.

blykins · #2 (**permalink**) 12-08-2003, 06:11 AM

Nah...you should be fine with it. SPF uses an IRS 8.8 in their cars...and you can see the kinda power some of their cars are putting out. You should have no problem.

In fact, didn't the originals have close to an 8.8" ring gear? Maybe I'm wrong, but I thought so.

Ron61 · #3 (**permalink**) 12-08-2003, 06:54 AM

Ant,

My 416 stroker puts out over 500 ft pounds torque and I have ran the 8.8 in it since I built the car with only one problem. I broke the Ford posi. I then had it upgraded to 31 spline axels with a heavy duty Eaton posi in it and it is almost bullet proof. A couple of others around here run them with more power than I have and they haven't had any problem.

Ron

grumpy · #4 (**permalink**) 12-08-2003, 08:23 AM

ANT,
I have a few friends in "outlaw class" mustangs that run above 800HP with slicks and a lot more weight/traction items than a street/autocross COBRA will have, with no failures, and only one "misbuilt" failure.
grumpy

Ant · #5 (**permalink**) 12-08-2003, 10:55 AM

Well guys thats answered my question!

I have a 28spline unit, uprated the Ford posi to an Eaton, in which I have machined the sidegears to take the "c" clips, as they dont supply Eatons for IRS.
There is maybe one weakness with my setup, which might be the axles they are made in Aussie by ROMAC, but I think from a previous post 750bhp said he lived not far and they are bullet proof - hope he is right!

I suppose serious competitors go for the 31 spline setup, or do they get away with the 28 spline?

blykins · #6 (**permalink**) 12-08-2003, 11:17 AM

I'd say serious guys go for the 31 or 35 spline axles...

Ant · #7 (**permalink**) 12-14-2003, 11:55 PM

Ron61,

I am going to run with my 28spline setup with the H/D Eaton posi and Romac axles, but am going to accummulate parts so I can uprate to 31spline later!
What was necessary to uprate your rearend to 31spline, apart from Eaton having a 31spline sidegear , and I assume the Upright/splindle is same for all axles!

CV Joints
Axles
outer splined wheel bolt flange, that goes into upright bearings.

Probably to cut a long story short its everything apart from the alloy Upright, and wheel bearings?
Suggestions on parts availability, I suppose most wreckers have em?

Ron61 · #8 (**permalink**) 12-15-2003, 06:22 AM

Ant,

I looked around the auto wreckers for the axels and stuff and then was fortunate enough that the guy who is doing my big block does rear ends. He got everthing brand new for me for about $45 dollars more than it was going to cost to get the stuff from the autowreckers and then as he had all the stuff in his shop to set it up right. I just paid him $50 and he did all the work and set everthig up and I have never had a problem. My one lucky break in life I guess. And I took the rear end out one day and put it back in the next.

Ron

gsharapa · #9 (**permalink**) 12-15-2003, 08:58 PM

If you ever could get the power to the ground you probably would break some axles on the 8.8 IRS. My SPF has over 600 ft lbs of tork but unless I put slicks on it I'll never hook it up enough to break anything.........

Ant · #10 (**permalink**) 12-16-2003, 02:56 AM

gsharapa,

What size axle are you running 28 or 31spline with your stroker?

My last Cobra now owned by Bevan Wright (CC) he removed the spool and replaced it with a LSD on the 9" Ford custom built IRS, when I raced it I had to fit new 1-1/8" Jaguar outer short hub axles every second race meeting as it twisted them. Having said all that the spool probably contributed to the problem and BB injected Chev 454 made serious 600+ horsepower, mind you it never hooked up that good on the 17" radials wheelspun at 120mph plus!