is it worth the time to build up a 8 inch rearend?

bikefreak600 · Jul 9, 2009

starting my street car build, im new to older mustangs. motor will lowside 500 + hp. i thinking about rebuilding the 8 inch rearend that came in the car. is it possible for a 8 inch to handle that much power with stronger axles, gears, & locker ? i have a 8.8 housing that i can resort to using but i will have to completely build it with all new parts, both axles locker n gears, just weeks before i purchased this 65 fastback, i sold all the new in box parts for the 8.8 thinking i was never going to use it again. ( yea how stupid do i feel now).
so will it be worth the time to build this 8 inch or will it just explode after a little abuse?

2+2GT · Jul 9, 2009

Currie has a very strong 8" Traction-Loc diff, but if you are going to 500hp, you should consider changing to a 9", and not some lame passenger car 2-pinion job, either.

mrmustangman357 · Jul 9, 2009

nope, 8 inch is junk at a higher build especially if you are putting down traction

Rusty67 · Jul 10, 2009

Since you have a stick shift, even a built 8" isn't going to hold up to the motor you are planning. Go with a 9" or an 8.8". I don't like the 8.8" because its got C-clips. With that much power and a stick trans, I'd go with a 9".

squidz · Jul 10, 2009

My built 8 is holding up fine so far. I have a detroit locker, motive gears and stock axles. I'm making 360rwhp and 390rwtq which puts it at about 420fwhp 470fwtq. Have taken it to the strip a few times and no problems yet.... running 12's all day long at the track. I actually opened up the pumpkin after about 2000kms and everything looks good. PLus its like 40-60lbs lighter than a 9". BTW I'm also running a toploader. its not hp that breaks things its torque.

10secgoal · Jul 10, 2009

A lot has to do with your driving habits squidz. What is your 60ft at the track ?

Buddy broke for of them, on the street making a whopping 300rwhp

Decurion · Jul 10, 2009

I have a friend that just hot-lapped for 25 passes last night in his 63 Falcon. Its got a built 302, t5z, 3.89 8", 235 drag radials, and cal-tracs. His best time was a 13.06 @ 104.8, 1.83 60'. He doesnt have anything special into the rear end, just a later model 70s pumpkin and axles. Im not sure about the carrier, but that may be a 4 pin Richmond posi or something, I know its not a stock piece. He did do some custom work to the case, and I think custom made his own caps with longer bolts. Hes pretty good at that type of custom work. Having said all that, it would still be easier to just get a 9" to begin with, especially since youre making more power that my buddy with the 8" and are running a stick.

bikefreak600 · Jul 10, 2009

i dont consider 500 hp much at all. even for a pump gas motor. this car will never have slicks on it. i will probly never race it down the 1/4 either. i understand that driving habits are main factor in parts failure. this is just going to be a wild street driver/show car. i have the original 289 engine and trans for the car also. but i would not be happy with that performance. i know a 8.8 can handle lots of power if built right. im just trying to avoid droping $2000 + on a rearend.

jcode68 · Jul 10, 2009

500 HP out of a 331 is asking alot unless you are planning for some NOS or forced induction. My 8" (4 pinion traction lock unit) is holding up fine behind my 347 which is rated for 405hp and 420 ft lbs at the crank. If 500 is a very real number, then like the others have said, just go with the 9" out of the gate and you will never need to worry about it.

rbohm · Jul 10, 2009

as long as you stay off the track and never use slicks, you can make the rear end last. you will need the later model center section, stronger differential, and stronger axles. how long it lasts depends on your driving style. if you shift smoothly, and add power only as fast as the driver train can handle it, it can last quite some time. if you are a ham handed driver though it will break on you fairly quickly and usually at na inopportune moment.

bikefreak600 · Jul 10, 2009

jcode68 said:
500 HP out of a 331 is asking alot unless you are planning for some NOS or forced induction. My 8" (4 pinion traction lock unit) is holding up fine behind my 347 which is rated for 405hp and 420 ft lbs at the crank. If 500 is a very real number, then like the others have said, just go with the 9" out of the gate and you will never need to worry about it.

change your heads to a set a big 215-225 afr's, and a solid roller cam, victor intake 500 hp is a low estimate.
mm&ff did a article several years ago with 25 mild to wild engine builds, a 347 afr 225 heads, .670 solid cam, victor jr intake made 575 hp. they got 500 hp with afr 185's and very large hyd roller, but it would have made more had in not suffered valve float. big numbers are easily made with enough port volume n cam durration. and thanks for the reply, if your 8inch holds up with your motor durning normal driving i should be fine until i can afford to build a proper rear end. as for now mony is tight so i will have to make do with the 8 inch

bikefreak600 · Jul 10, 2009

rbohm said:
as long as you stay off the track and never use slicks, you can make the rear end last. you will need the later model center section, stronger differential, and stronger axles. how long it lasts depends on your driving style. if you shift smoothly, and add power only as fast as the driver train can handle it, it can last quite some time. if you are a ham handed driver though it will break on you fairly quickly and usually at na inopportune moment.

i have a knack for braking stuff, in my 85 it went through 2 differentials, 2 t5 trans, ( broke 1 t5 tail shaft completely in half) lol and through all that the centerforce dual friction clutch still works like a champ ! matter of fact im putting that exact clutch/flywheel in the 65 lol

rbohm · Jul 10, 2009

bikefreak600 said:
i have a knack for braking stuff, in my 85 it went through 2 differentials, 2 t5 trans, ( broke 1 t5 tail shaft completely in half) lol and through all that the centerforce dual friction clutch still works like a champ ! matter of fact im putting that exact clutch/flywheel in the 65 lol

you might want to step up to a dana 70 then

j/k, in your case then o would step up and build a 9" and avoid the hassles.

runawayabc123 · Jul 10, 2009

If you do go for the 8.8 or the 9in depending on the numbers and how matching your 8in is to a '65 April car, I would be very interested in buying the 8in from you. (I am in Milwaukee and I am guessing the diff is in northern IL.)

So, my vote is you should upgrade today!

Rusty67 · Jul 10, 2009

bikefreak600 said:
i have a knack for braking stuff, in my 85 it went through 2 differentials, 2 t5 trans, ( broke 1 t5 tail shaft completely in half) lol and through all that the centerforce dual friction clutch still works like a champ ! matter of fact im putting that exact clutch/flywheel in the 65 lol

You will NEED a 9".

v8only · Jul 11, 2009

You sure you want to gamble $1500-2k on a built 8" rear, just to possible blow it up??

Fork out the $150 and get a 31 spline 8.8 rear end from an explorer, it'll hold 500 hp on slicks all day long

5.0ina66 · Jul 13, 2009

I'd build a 9". Find a truck unit cheap, get it cut and get new axles, build a 3rd member with a Torsen. Should be much cheaper than buying one from Currie or some such.

Then again, 500hp with no slicks? 215cc heads? Vic JR intake? I guess I don't see the point of it all?

bikefreak600 · Jul 13, 2009

5.0ina66 said:
I'd build a 9". Find a truck unit cheap, get it cut and get new axles, build a 3rd member with a Torsen. Should be much cheaper than buying one from Currie or some such.

Then again, 500hp with no slicks? 215cc heads? Vic JR intake? I guess I don't see the point of it all?

i used to favor the drag style cars, i now prefer mustangs with the stock apperance style. my buddy took me for a ride in his 700 hp 97 supra with stock wheels tires suspension, it is a blast to drive, so much fun, yea all the power was kinda overkill under 90-100 mph, im kinda wanting to built this just for fun and show.

is it worth the time to build up a 8 inch rearend?

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