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Discussion Starter · #1 ·
I'm wondering if my 8" rear end can handle the torque of my 351W if I make some upgrades to the motor. Currently the motor is only putting out about 320hp but I want to approach the 385hp level and I think I can get that with a new distibutor, heads and maybe a new intake.

Currently I have a T-5 and a 3.50 or 3.55 rear end gearing. I was thinking of moving down a bit in the gearing as the highway hum is a bit much with a motor of this size. Something between 3.08 and 3.25 would be nice.

Will a 8" hold that kind of power? I know a lot of it will depend on the driving style. I'm not really hard on the car much but sometimes do like to let loose. I only drive it about 3k miles a year now.
 

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With the manual and spirited driving...I think you're already living on borrowed time. It would probably be best to hold off on any R&P changes or such until you have changed to a 9". The other thing about 9"s are you will find many more choices as far as R&P's go. The real deciding factor may be how much tire you want to go with in back. As long as you can't find traction...you can't hurt your rearend. If you get it to hook...I think you'll break it.

Phil
 

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Discussion Starter · #3 ·
Does the 9" space my tires out farther? I'm already running 245's back there.

Where can I find more documentation on this conversion?
 

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With the manual and spirited driving...I think you're already living on borrowed time.
Horse-poopie, if you'll pardon the French.

There are drag racers using the 8 inch to nearly 1000 HP. That C4s and 8 inchers are lightweight junk is wrong... at least, as long as you have a clean performance build on them. They're good for a lot more power than stock smallblocks, and they're a lot lighter than C6s and 9-inchers.
 

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Discussion Starter · #5 ·
Well then what do I need to do to make sure my 8" have a clean build to it? Are there special parts I need to get? Do I need to put a trac-loc or posi in the pumpkin or what?

I basically wanna make sure my rear can handle close to 400hp at around a 3.08-3.55 ratio.

Right now, I've got a little slop in the rear end and I thought, I'd take the gears out and replace them. I just took the axles out doing my brake upgrade and they looked fine.

By the way, the two posts so far leave a lot of discrepancy. 300hp is on borrowed time and 1,000 for drag applications.

Can anyone else offer some insight as to an actual number?

Also, with the tires off the ground, if I spin one tire and the other goes the same direction, do I have posi? Or would it go in the opposite direction? Gearing spins my head!

::
 

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"Old think" (that is, thinking around the time of the Mustang's heyday) was that the 8-inchers and C4s were low-end junk that real hardcore types would throw away. I recall seeing literally piles of 8-inch rear ends and C4s at junkyards - no one wanted them.

Then the racers discovered that with good builds, they were good for a lot more power than anyone had given them credit for, and were a lot lighter than the standard hipo pieces.

Have a good center section built for yours - Randy's Ring and Pinion does a pro-grade job, cheap. I had a 3.55 piece with an Auburn Gear posi built for about $700, delivered. If your axles look good, leave 'em; new bearings and seals are pretty much a duh. 400 HP on such a setup is hardly even a strain. Be sure to have your driveshaft rebuilt, too - the biggest joints that will fit and a new tube that DOESN'T have the rubber coupling. You'll be good to go for anything but the hardest, sustained drag action.
 

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400hp is about all the 8" will take with a street rebuild. If you put wide sticky tires on it...forget the 8" and the T5.

Depending on the T5 model it may take as little as 175hp up to about 330hp; slighly more if you upgrade the counter gear stabilizer and the rest of the interals to T5Z specs. So anything more than ther 320hp and you are asking for trouble if you go doing burnouts and banging gears. Look at the Tremec TKO3550 or better. The T5 can run with more horsepower on a limited lifeline, just dont abuse it. T5 has many internal problems which will limit it's horsepower abilities.
 

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I've heard the bad press about the 8 inch as well, not being able to handle any real HP. Funny thing is, when you actually talk to someone who knows their rear ends from a hole in the ground (that's humour there eh ::) they pretty much say what you do. Also, the added weight that the 9 inch carries is wasted weight in all but the most serious applications. Is a 9 inch more of a bragging right thing?
Dave
 

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proof!!!!!! an 8 inch will hold your power

13.10 at 104 at 2700 elevation with 3.55 gears... that equals a ~12.7 at sea level. i launch at 3200 rpms on a C4 with an 8 inch supporting 10 inch quick time pro's. ive hit a 1.89 60ft. and im running a C4, it was holding up until the bolts came off the 2nd/3rd gear servo and i ripped the band to shreds ::

another 69 stang is running 12.6's(~12.3) on an 8 inch and a 302. like said above, the myth that an 8 inch cant hold power is just that, a myth. same as the C4. look around and you can find c4s built and are quoted to hold over 1000 hp runs all day, look in summit for that fact. and if something goes bad theyll 'refresh' the tranny for free, for a life time.

posi weights more then a power trax but the posi is better for cornering and putting power to it. power trax, its either in or its not, there is no inbetween.
 

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look around and you can find c4s built and are quoted to hold over 1000 hp runs all day
My C4 was just built by ATO of Sacramento. Expensive, but Jim eliminated all the thrust washers and replaced them with bearings, and all seals are teflon. He says it's identical to one that's run dozens of passes in a 9-second car (except that I don't have a transbrake), and will handle 6-700 HP all day and 1000 if I don't expect an extended lifespan out of it.

And it weighs about 90 pounds. I can't even lift a C6... :)
 

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You'll never get a consensus on this issue. IMO, not one of the replies you get to this post will be worth a crap unless we also know more specifics about your car, and more importantly, how you use it. These things matter, regardless of what anybody says.
But without this information, I will say this:

1. It's not the HP or torque you make, but what can be put to the ground.

2. A stock 8" (or any other rear) is not as strong as a well built one. If you build an 8", make sure it is the one with the extra webbing, and install 4 spiders and high quality components.

3. The torque rating of a T-5 is based on a Ford durability test. It is NOT an indication of the yield strength of the T-5. In my experience with durability and strength testing, a safety factor of 2-2.5 is common. I can't say this applies to the 8" or the T-5, but it probably does.

4. The T-5 is an easier install than a TKO, and the 8" is significantly lighter than a 9", and the weight savings is in unsprung weight, which will matter to you if you want your car to handle.

5. Many things like this get blown out of proportion. Just yesterday there was a post about single versus 4 piston calipers. It's amazing how many people just blindly believe that something is needed just because it is better, more complex, or more expensive. Another little story - I once had an exciting debate with a friend about the difference in the cam gear on his Porsche and the one on my Honda. His was machined steel and mine was stamped. He claimed his was better, and I claimed that since mine does the job, and has never failed, and my Honda is actually a more efficient engine than his Porsche, his was a waste of money. I could be wrong, so you decide. When I'm desiging something in my job or personally, I always take the approach that the product used should be good enough to fulfill it's purpose to the owner, and no more. Anything else is a waste of money.

5. You have a T-5, right? My suggestion would be to use it. If you have an 8", my suggestion would be to use it. If you are starting from scratch, have the money and want to make sure your combo is bulletproof, use a stronger trans and rearend.

I'm using an 8" and a "Z" T-5 in my car. Sometime next year it will recieve a 400-500 hp engine. I'm gonna run these parts because I have them, they are well built and I'm not a drag racer. If they blow, then I'll replace them.
Most importantly, this is the internet, and you'll always get guys pretending to be experts when they are not. I'm not accusing anyone here of that, and it could just as easily be me, but it is something you should always be aware of. Just food for thought.
 

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I think Jim pretty much hit it on the head.

However, to that I would add:

1. Your stock 8" was considered insufficient by Ford for duty behind a 289 Hypo which (although rated higher) probably only put 200-220 HP to the rear wheels.

2. A Ford 9" is the "Holy Grail" of all muscle car rear ends. They are used in every brand of race car imaginable. As such the aftermarket parts availablity is tremendous. You have many more choices for both manufactuers of parts and types of parts. For instance, there are probably 5 times as many different R&P ratios available for a 9" vs an 8".

3. All that being said, I'm running an 8" in my car with an Auburn posi and a 3.55 R&P. It's a great little rearend and I intend to use it right up to the point I blow it up. I figure that will be 2 weeks after I stick a 331 shortblock under my AFR heads. That's how long my stock C4 lasted after my 289 buildup. Such is the nature of building up a car. Torque will always find the weakest link.

Phil
 

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1. Your stock 8" was considered insufficient by Ford for duty behind a 289 Hypo which (although rated higher) probably only put 200-220 HP to the rear wheels.
Okay, so I would add:
That was a "stock" 8", and it was in an era where weight wasn't a significant consideration. Weight reduction is free HP. Why carry a bunch of it around if you don't need to?

2. A Ford 9" is the "Holy Grail" of all muscle car rear ends. They are used in every brand of race car imaginable. As such the aftermarket parts availablity is tremendous. You have many more choices for both manufactuers of parts and types of parts. For instance, there are probably 5 times as many different R&P ratios available for a 9" vs an 8".
A valid point, but only if you can't find the ratio you want in an 8". My feeling is that for a street car there are more than enough ratios available in the 8" to satisfy anybody. Aftermarket parts are readily available for the 8". In fact, many of the parts are the same as the 9".


3. All that being said, I'm running an 8" in my car with an Auburn posi and a 3.55 R&P. It's a great little rearend and I intend to use it right up to the point I blow it up. I figure that will be 2 weeks after I stick a 331 shortblock under my AFR heads.
I'm thinking that if your 8" is built well, you are going to be surprised. Either that, or you are building one killer 331!


Torque will always find the weakest link.
I think you mean excessive torque in regards to the design intent of the components involved, don't you? :) :)
 
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