Hey guys I have a 85 f150 9 inch rear end that I am putting into a project of mine. I have found out on this site that the rear end I have is a 31 spline. The gears are 3:50. The truck project I am working on will be a daily driver type performance vehicle with no track time just street driven. Anyways how much HP an TQ do you think this rear end will be able to handle without any upgrades? 400hp&tq, 500hp&tq?

 

Stock it should handle 400 horse on the street. Maybe 500.

What you must do is control wheel hop under acceleration. If the axle winds up too far & the axle is jumping around, things are going to break.

With an automatic and conservative driving, you should be ok.

9's are run with a lot more power than that, so you have a margin of saftey with a stocker, and an ability to go up from there.

Lots of 9" info here. Note there are not a lot of 'band-aids' for the 9, as it is very strong stock. Mostly variations and options.

Currie Enterprises 9 Inch Ford

 

I was thinking of using a high horsepower and torque engine from keith craft 500hp&500tq, dream engine, Using a built AOD. Just this setup will take a huge part of my budget and since I was just really going to drive it around town and such I figured maybe just maybe I could get away with the stock without having to spend a ton on the rear end. yeah sure I would have a little burn out everynow and then but that prolly it.

 

FWIW: I had a stock 9" last for 37 behind a 360/390 before I got the truck and overloaded it with firewood. Even then only the bearing popped off the shaft.

I never had a 9" totally fail in any of my trucks and I did not always treat them nice ...

imho, With normal sized tires I would think the drive shaft would break before the 9", I know it did on my truck. So running a drive shaft safety loop would not be a bad idea if you are running some serious HP.

 

Then again..... I could break a stock 9 inch before I ever left the parking lot

I broke several with a mild 302 with tires running from 33-38's. Mind you this was in some serious thrashing.

I went to Strange 3.25 N case and 35 spline axles and now run 42's.

I have video of Mickeys Hot Tub in Moab Utah of me literally falling off the face back down in the hole under full throttle. Landed on the rear tires , Sounded like a bomb went off.



Come to find out it was only the yoke that let go. I have run 42's and done everything from jumping to serious rock crawling and even a few rolls.

Pulled the shafts and they look new after 6 years.

If you can afford to build that high of a horsepower engine, then build the rear to match and you will not be emabarassed by it breaking...

 

The tire size I am going to use is 295/50R15 bfgoodwrich on 10x15 cragar wheels. tire diameter is 26.7
Do you think that with this rear end and tire setup do you think it would work with a 408 stroker (the 500hp&tq engine I described before) in a street driven 2 wheel drive 3500 pound truck...sure an occasional burnout but no drag racing

 

It will work fine, but as per prior post, you must control axle wrap and wheel hop. Traction bars--many varieties, probably just some slapper bars will work for you. Google it or check Summit etc.

 

...with THAT kinda muscle ya might wanna consider lookin'
into a 4-link set-up...

I researched EVERY kit on the planet until I couldn't see
straight for my '56 Effie build & almoust went NUTZ...

Then I finnaly ordered this one...check it out...

FATBAR WITH AIR RIDE-No Limit Engineering


Notice the lower bar is NOT parrellel to the top...

MY turck is gonna be ridin' on air...ya can get coil-overs
or whatever ya want...

 

With that much power on street tires you will more than likely just smoke the tires off the thing.

The factory trac loc will be the weakiest link, if you're using one. The trac locs like to blow the side covers when they see any sort of extreme loads or major wheel hope. I've only seen them break from wheel hop myself.