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Power limit/capacity of the 7.5 Posi-Trac

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13K views 24 replies 11 participants last post by  ESG-642T  
#1 ·
I've heard a few different replies anytime I ask what the horsepower/torque limit is on the Ford Racing 7.5" Posi-Trac. I've heard everything from "Don't go over 300hp with one," to "Don't even bother with one, you'll be lucky to keep 250hp in one", and I've also talked to a guy who had a supercharged 2000 V6 making 450 at the crank on the 7.5" rear.

Anyone have any more info? 450 sounds like a lot to run through the 7.5" without getting an 8.8" instead, but the guy owned the car and said it's been rock hard reliable for him, so I won't doubt him. But if I get to those power levels I'd like to know at what kind of power I should ditch a 7.5 and get an 8.8
 
#3 ·
well it would probably be alot less hassle and cheaper to just swap to an 8.8. plus with an 8.8 you know that you have plenty of room to work with as far as power levels go. you would probably be nervous on every launch if you kept the 7.5 and that wouldn't be any fun worrying the whole time.

and your friend with all that power probably has some pretty pricey upgrades. most likely a Detroit locker and possibly some stronger axles, which in the end would cost you alot more then just swapping in an 8.8
 
#5 ·
The differental is the real weak point. A Ford racing t-lok, I don't know what they'll hold up to. The detroit tru-trac should be good to around 450. A stock 8.8...well I don't think they're all that amazing. Sure a little stronger, I might say 375. But swapping for just a stock 8.8 is basically less of a benefit than swapping for a detroit differentail. Though, once you upgrade the 8.8, it would be out of the question which is stronger.

I do believe the 7.5 and 8.8 share the same axles though.
 
#6 ·
I do believe the 7.5 and 8.8 share the same axles though.
They share everything but the center-section.

+1 on just swapping out the carrier for a stronger unit and keeping the 7.5. Upgrade to some stronger half-shafts while you're in there, and you'll end up with a plenty-strong rear axle that weighs less than an 8.8 and causes less drivetrain loss.
 
#9 ·
I agree with everything on here. A tru trac is more than strong enough for the majority of ppl on here. JT launches with a high stall convertor, DRs, and 17 psi procharger using a 7.5 and a tru trac and he has no problems. He said the only thing he is worried about is breaking an axle, and they have aftermarket harder ones for when that happens.
 
#16 ·
If you are going for those numbers get an 8.8. Sure you can make the 7.5 work. But if you are making that steam you wont be able to launch hard at the track even with a tru trac. Just get an 8.8 and add gears. Then when you start making more power update and add the tru trac with 31 spline axles.
 
#19 ·
That is true on the ^. I just wanted OP to see both sides.

And if you can find a cheap 8.8 then go for it is what I say. But I could not find a cheap one.
 
#21 ·
Ah, Mr. Stangcharger, I remember looking at your website a few months ago. I never realized you stayed with the 7.5 rear though. That being the case it kind of swings me back towards doing the 7.5.

I'll just have to see what type of prices I can get between 8.8 and 7.5 to see which way I'll go with it. Thanks guys.
 
#22 ·
If you can get an 8.8 cheap with the gears you want for 500 bucks go for it because parts will almost cost you that for the 7.5. But if you can't find one for cheap go with the gears you want and a tru trac.
 
#23 ·
So far I'm only finding about a $70 difference between the 7.5 and the 8.8 differentials, and the gears for each are running the same price too. And installation wouldn't be any different for each.

But wouldn't I also need to get 31 spline axles along with the 8.8 differential? The Ford Racing 8.8 I've been looking at says it is for 31 spline axles, and the V6 rear end is a 28 spline, correct?