Gun Jam

I also think you'll be fine Im far less concerned about the 8" than the t5 but like I said if you get the cobra or z-spec they should last for sometime...the torque ratings for those transmissions are for 100,000 miles. The Z-spec is rated for 330 Ft/Lbs and the Cobra is rated for 310. If you are ball parking 350 shaft HP I can guess based on the info provided that torque will be around there too at some RPM which for at least for a short duration will approach the rated torque. I still say you will be okay with either of those T5s....Maybe they only last 70 thousand miles who knows you might get 130,000 out of them...or it breaks the first time you dump the clutch...But that said I think you should get a decent service life from them street driven even horsing around often enough.

-Gun

jspagna1

I have an Auburn (3.55's) in mine as well. Very good quality and it's held up very well.
Ya 3.80 gears with the C4, car must be great off the line but tough on the highway.

67mustang302

I've been pushing close to 360-400hp at the flywheel in mine for years, raced it at the track, flog it on the street. The car lives at 6,500rpm on a near daily basis. Never had issues with it.

Just put a Detroit Tru-Trac in and be done, a bit pricier up front than a clutch type posi, but no gear oil additives are needed and they don't wear out like the clutch types do. You'll have years and years of trouble free, low maintenance miles.

drewsky

i would run a 3:25 even with a t5 overdrive.. 1st and 2nd are steeper than an average c4/fmx.. so plenty of go off the line and cruise through town and frwy!! ill go through my paperwork and look at the company that built the track lock device for my 8".. just some advice c4 auto with 3:55's in the back and its not cruiseable at all!

NoReins

Ok, this is a lot for me to take in and understand, so I appreciate everyone's words of advice and opinions. We talked to a rear end shop yesterday and told him what we were looking to do. He gave us a few options but definitely said an 8 inch would be more than adequate for what we were looking to do. With that being said, if we were wanting to beef up the engine in the future (400+) he said we'd be coming right back to him for a 9 inch. He gave us these options:

1. Rebuild 8 inch, hot tank, blast, etc.. add new bearings, gear set, new Trac Lock for about $900.

2. New 9 inch housing, NASCAR 3.60 gears, reuse 28 spline 8" axels, rebuilt Trac Lock and trade in our 8" for $1,000.

We like the idea of having an 8 inch that is mostly brand new, but I would be hard pressed to pass up the "bulletproof" 9" for only $100 more and know if we ever upgrade the motor the rear won't need to be touched but tranny might be a different story...

btw, that is not me in the icon. It's Angelina Jolie!

Stangatic

Both options seems to be a good steel. Do you get any warranty? and ask what type of gears they will be using in the 8".

As for what Gun Jam said about the torque rating for the T-5, there is some discrepancies there. I recently went through a disastrous T-5 swap in which I learned way too much about the tranny. To make a long story short, depending on the weight of your car and your driving style will determine how long the T-5 survives. The torque capacity ratings on all Tremec transmission for cars are based on 5,500 Gross weight cars. The lower the weight of the car, the higher the Tq capacity, and this is where driving style comes in to play in determining how long the tranny will survive.

I had a T-5 from a V6 car that had a tq rating of 265 lbs and was told by multiple published transmission shops that this tranny would definitely hold up on a car with 400lb of tq and is under 3,000lbs.

And on that note, I ended up buying a Promotion Powertain tranny that can handle a lot more tq than a TKO-500 for about $1000 cheaper than a TKO.

phutch11

Based on the work that I've seen you doing in your build thread, you've clearly got the skills to rebuild a rear end on your own. For whatever reason, it's got the reputation as the "brain surgery" of hot-rodding. It's really pretty easy on a Ford 8 or 9.

You should be able to rebuild your rear end for $700 or so in parts and that's with a high-end everything including a Ture Track, w/ a Trac Lock it would be significantly less.

That said, $1000 for bolt in 9" is a screaming deal if it's got quality parts, and it's truly bolt in. If you have to start fooling with welding spring perches, figuring out brakes, etc... it's not that screaming any more.

Good luck...

Stangatic

I agree with Phutch11

I ended up going with an Auburn Pro 3.90 in my 8"

phutch11

Stangatic,

Have you seen the aluminum chunks that Currie sells for the 8?

Its called the Alumin8 or something like that. If I had known about those when I rebuilt my rear end, I would have jumped all over it. And I may still get one.

They are something like 30 lbs lighter than the cast iron unit, and stronger too.

Just a thought for your build...

Gun Jam

I was referring to the Borg Warner T5 not a TREMEC..Tremec bought out BW around 1998..Those torque numbers I do think are correct for the BW T5 Cobra / Z-spec (1993) I am unaware of a gross weight number for the BW T5.

On a second note I have to advise against any gear ratio higher than 3.50 (for example 3.00 or 3.25) I ran my t5 cobra spec initially on a 3.00 rear end gear with a 2.95 first gear and it was a real dog...furthermore assuming you consider 2300 to 2500 a good cruise RPM with a 3.25 gear you would have to go 85 mph to get 2300 rpm in 5th or if you tried going 70 mph in 5th you would be at 1900 RPM...Thats pretty low RPM as far as im concerned and I was pretty unhappy with how it felt.

Good luck sorting all this out..

-Gun