How much HP to an 8 inch rearend

gt500lw · Jan 8, 2007

Hey all,

I am building a 427 Stroker. I currently have a T-5 with an 8 inch rear. I know the T-5 will get munched the first time I put any power to it so it is getting replaced with a Tremec. How well would the rearend hold up? I have a 9 inch, but I am not sure if I can get it built before my deadline. Thanks.

BullittStangV8 · Jan 8, 2007

Probably not very long. Some people have had some luck.. but others have blown them up quickly. Im afraid to get on the go pedal with my 8 inch and my motor is going to be making less hp then yours..(331..400 hp?)

iskwezm · Jan 8, 2007

How many licks does it take to get the center of a Toostsie Pop? The world will never know!!!!!!!!!!!!

Some 8" have lasted with 500 HP and some have broke with 300.It all depends on if you shock it,use slicks and its still "tight".

Mine has been ok behind a blown stroker, but on radials and never launched hard................yet.

rbohm · Jan 8, 2007

a stock 8" can generally handle about 375-400hp, less when running slicks. that said, quality gears, a good differential, and quality axles and that rear end can handle 375-400 on slicks, and more on street tires. how much more depends on how the axle is treated, and maintained.

66forfun · Jan 8, 2007

Where would you suggest getting good axles at?

Pbum5 · Jan 8, 2007

66forfun said:
Where would you suggest getting good axles at?

Currie, Strange, Moser make versions for your needs.

ratio411 · Jan 8, 2007

I have wrecked 3 8" rears with a 306...
C4 stock converter on two, and Toploader on one.

Do the 9" soon as you can.
However, if you get the engine running first, well you just have to test it!

66forfun · Jan 9, 2007

^ what failed? My Auburn pro posi will most likely address the factory track lock issues. I figure the 28 spline axles will be the weak point. Mine is an auto and will probably never have slicks.

joncash · Jan 9, 2007

Actually it's the centersection that will most likely be the weak link if an 8" were to break. Remember, in nearly all car applications, Ford used 28 spline axles, even when the car came w/ a 9" rearend.

Also keep in mind that it's torque coupled w/ traction that breaks trannies and rearends. A 400 horsepower 302 will be less likely to break driveline parts than a 400 horsepower 351: reason is, that 351 probably makes more overall torque at a lower RPM than the 302 and will apply more twisting force to the driveline on a hard launch.

MickeyK65Stang · Jan 9, 2007

I've been running a 8" 355 posi with a blown GT engine for 3 years now. Just figure I'll wait till it goes before spending money on a 9".

ultrastang · Jan 9, 2007

Crunch n' Munch

This was the result with an 8-inch rear end and a basically stock 351W;

http://img129.imageshack.us/img129/484/broken8inch3rdmembermo4.jpg

Do it once. Do it right. Be done with it. --Install the 9-inch.

joncash · Jan 9, 2007

Hey how come the main cap bolts are still in place?

washMO66 · Jan 9, 2007

Currie can build you a 9" that will bolt right up and you can get it built to your specs. Detroit Locker, trutrac, 31 spline or whatever you want. If you can afford to build a stout 427 and a tremec just write another check and be done with it.

Or take the time and search for a 9" out of another vehicle and modify it,,,,

The 8" won't last long if you put some tire under the car or any kind of slick, if you run on 205 radials it will probably last you a long time.....

ultrastang · Jan 9, 2007

joncash said:
Hey how come the main cap bolts are still in place?

The top two bolts were stuck back into the mains after 3rd member was pulled and the main caps were taken off.

The bottom two main cap bolts were the ones that sheard off. After that, the differential shifted around and that's when the ring gear teeth started snapping off.

The 8-inch 3rd member wasn't mine. --This wouldn't happen to me, 'cause I don't use 8-inch rears. --9-inch Fords only for me. Period.

ultrastang · Jan 9, 2007

...a couple of other good reasons I don't have to worry about a 3rd member failure like with the 8-inch...

1. http://img150.imageshack.us/img150/1196/ncases003qx8.jpg

2. http://img172.imageshack.us/img172/7442/ncases001kb3.jpg

9-inch N-CASES, Baby!

www.ultrastang.com

66StangFastback · Jan 9, 2007

To go along with this thread,

How often is a shot of nitrous (lets say 150 shot) going to break an 8", lets say, hitting it half way down the track, behind a 300hp 289 with a 2500 stall C4, on regular ****ty street tires? I would assume it would get loose in the ass but not hurt anything?

ratio411 · Jan 9, 2007

I would like to add that the 8" 28 spline axles are interchangeable with 9" 28 spline axles... and they are not known to be a particularly weak part. Of course anything will break with enough power.
I don't think I have ever heard of an 8" that broke an axle though.

All 3 failures I experienced were pinion, gear, and differential breakage.

Also, all this talk about they only break when you hook is getting me...
I have never owned a hooking tire or slicks.
All my breaks were on street radials with a 306...
I have heard a couple of folks that tell tales of their 8" that held up to big nitrous or 5000 rpm launches every day for 7 years...
If these stories are true, they just got lucky IMO.
Dave

Vinyl66 · Jan 10, 2007

With a 427 stroker do not hesitate to swap in a 9" rear. A torque monster like that will kill an 8" rear.

That being said, I still run an 8" rear behind my 347 in my '66 Coupe. It currently runs 11.8's in the quarter on 235/60 drag radials. I run a Detroit locker which is much stronger than any open or posi case. I still have stock 28 spline axle shafts. But many 9" rears have these shafts as well. I studded the pinion support for extra reliability. That just involved removing the 5 stock pinion bolts and installing hardened studs, hardened washers, and lock nuts in their place.

My car has a C4 automatic which is MUCH easier on drivetrain parts as compared to a stick. I am currently only running 3.55 gears which keeps the torque down compared to a lower ratio (higher numerically). My car is also light at ~2900lbs. with me in it. Which certainly helps keep the 8" living.

There are many variables to consider when it comes to upgrading rearends. Engine torque, torque multiplication through gearing, car weight, auto or manual, slicks or radials, stock weak open rear or strong aftermarket locker, etc.
But for the original poster: Definitely go 9" behind a 427.

Edbert · Jan 10, 2007

Power doesn't have as much to do with breaking rear ends as traction does

Vinyl66 · Jan 10, 2007

Traction is a big variable. The 8" could possibly last forever on the street using street radials. Im betting it wouldn't take long to trash it at the strip running on slicks though.

How much HP to an 8 inch rearend

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