Capt Hair

I searched and couldn't find any thing so heres the question

How much power can a stock rear end handle? I'm asking because I bought a set of cams, and am piecing together a S/C and am wondering if my rear end will be able to handle the power. I don't plan on going to the track every weekend or anything, this is just a street car and my DD. I might make it out to the track once just to say I have but thats it. So will my rear end be fine a little under 400rwhp or does that need an upgrade as well? Also have LCA's waiting to go on in the garage, but other than that would I be fine?

mrtstang

You'll be fine. I have close to 400 hp and over 500 tq on the stock rear end.

cliffyk

My chronic insomnia is kicking in, so bear with me here--this may be more than you wanted to know...

Drive components are rated by their torque capacity, not HP (which is RPM (time) related). For example a 200 lbft rated gearbox could handle 200 HP at 5250 RPM (200lbft*5250RPM/5250), 400 HP at 10500 RPM (200lbft*10500RPM/5250), but only 100 HP at 2625 RPM (200lbft*2625RPM/5250).

As a practical example, the gearbox in a Honda 2000, which makes its peak of 240 HP around 8000 RPM, only needs to handle 160 lbft or so (240HP/8000RPM*5250). Drive that same gearbox from our 4.6L 2V engines (260HP/5000RPM*5250 = 273 lbft) and it would not last long...

The 28-spline 8.8 rear end is rated for 1250 lbft continous output torque, and maximum output torque of 4600 lbft (Ford's specs, probably with a 70% to 80% service factor). With the stock 3.27:1 gears this would mean that the max input torque would be 4600/3.27 = 1406 lbft.

Now, assuming that launching in 1st (3.38:1) is our worst case scenario, we find that 1406 lbft input to the rear-end would take 1406/3.38 = 415 ftlb = 415 HP at 5250 engine RPM.

With 4.10s the max rear-end input torque = 4600/4.10 = 1122 lbft. This equates to 1122/3.38 = 332 lbft = 332 HP at 5250 RPM.

Taking these calulated values out to the point of failure, I will assume a 70% service factor in the ratings, and we get a max of 593 HP for the 3.27 gears and 475 HP for the 4.10s.

The 31-spline axles have a continous rating of 1360 lbft, and a maximum rating of 5100 lbft. The 5100 lbft max rating equates to failure ratings of 660 HP with the 3.27s and 526 HP with the 4.10s (in 1st gear, at 5250 RPM).

This is all number crunching of course, there are numerous other parameters that impact actual performance and capacity.

The main thing to remember is, that in the absence of specified input and output speeds, gearboxes are rated by their torque capacity not HP.

mestit3

nice.

ZW99GT

You are playing with fire there. A S/C car on street tires will likely not have problems. But a N20 car on a good sticky tire making the tq yours is will break a stock rear on a hard launch.

I snapped a 28 spline axle on a 275/17 MT D/R and a 100 shot and my car was making VERY VERY similar #'s yours was.

cliffyk

Very good point about the sticky tires, the stickier they are the more output torque you'll be demanding from the axle.

mrtstang

I agree...i know it's a matter of time. I'm just impressed the stock rear end can hold this kind of horsepower and torque. I've been doing this for over a year now. I'm still on the stock clutch too.

The one thing i rarely do is spray from a dig on drag radials (1st goes so quick anyway). This has probably helped save me over time.