How Much HP Can a 8 3/4 Handle?

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ramcharger

ramcharger

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Can a 8 3/4 with aftermarket gears, axles and slicks withstand repeated 3500-4000 rpm launches behind 550 hp? Maybe 650 with N2o? Possibly with a braced housing? Is this stepping into Dana 60 territory?

Thanks in advance.
 
mine has a 750hp big block in front of it. will be going to the track for the first time this sunday. mine is braced with yukon axles. 4.30 spooled richmond gears and a 489 case. i am foot braking the car.hoping to get into the 9's. should be interesting. i have a dana 60 if needed. but will probably go 9inch ford because of more selection of gears and lighter. will easily take the power.
 
My buddy Tim just busted his 8-3/4 behind a 800+ HP 500 inch stroker. The caps broke. He got a billet set of caps for the carrier. He could have went DANA, but stayed with the 8-3/4.

His car is very close to strickly race. Drives it to trhe local races, trailers to the track which is far, very far.

His car runs into the 9's easy.
 
I was stunned to find out that the reason my car has a Dana in it is that the original owner broke the crap out of the original 8¾ with a 383. He said he twisted the axles and grenaded the posi. It had 12.1 to 1 compression, maxed-out 906 heads, a roller cam, two Holley 650s, and no NOS or supercharger. I do not know what the HP was but he was running 10.90s at just under 130MPH launching at 5,000 RPM and shifting at a ridiculous 9,000RPM. Makes me pretty confident about the strength of my bottom end.
 
ramcharger said:
Can a 8 3/4 with aftermarket gears, axles and slicks withstand repeated 3500-4000 rpm launches behind 550 hp? Maybe 650 with N2o? Possibly with a braced housing? Is this stepping into Dana 60 territory?

Thanks in advance.
Click to expand...
Joe,

You can be on the fence real easy with an 8.75" rear depending on power/weight.

I've built 8.75" rear ends that have lived in (2800 lb.) 10 second cars with trans-brakes. Then again I've had footbrake cars (heavier) spin the ring gear teeth off in 10 runs. To get it to live--back braced housing, steel caps, billet adjusters, etc etc, you can pretty much buy a pre-built Dana 60 less brakes.

Whenever one of my customer's breaks an 8.75" 9 times out of 10 they upgrade to a Dana 60.

My opinion, go Dana 60 now, and be done with it. You'll always want to make more power, and when you do, you won't have to worry about destroying that lil 8.75" ring gear.

Forgot to mention, when that 8 3/4 does break, it can severly damage the automatic trans (see exploding torqueflites thread at top). I just did one that had a stock VB, with shift kit (low band on in 1st). It spun the ring gear teeth off, rolled the sprag in the transmission, and broke the case! The next run it would have come through the floor! This was the gun-metal grey '72 Challenger that runs out at Bandi and Pueblo. Car goes 11 teens up here I believe, off the foot brake.

HTH's
 
ramcharger said:
Can a 8 3/4 with aftermarket gears, axles and slicks withstand repeated 3500-4000 rpm launches behind 550 hp? Maybe 650 with N2o? Possibly with a braced housing? Is this stepping into Dana 60 territory?

Thanks in advance.
Click to expand...

Good question ramcharger, I'd say yes to the 489, probably to the 742 and BOOM to the 741.

Terry
 
2shelbys said:
I was stunned to find out that the reason my car has a Dana in it is that the original owner broke the crap out of the original 8¾ with a 383. He said he twisted the axles and grenaded the posi. It had 12.1 to 1 compression, maxed-out 906 heads, a roller cam, two Holley 650s, and no NOS or supercharger. I do not know what the HP was but he was running 10.90s at just under 130MPH launching at 5,000 RPM and shifting at a ridiculous 9,000RPM. Makes me pretty confident about the strength of my bottom end.
Click to expand...

Alot of folks underestimate the 383's potential... :snakeman:
 
With and auto i'd say yes...with a 4-speed i'd say your pushing it,my 8 3/4 has a "new" design 489 housing(more meat in the caps,and bearing sections),billet yoke,a moser spool w/4:30's,and moser axles..running behind my 416 stroker or 360 whichever is in the car,launching repeatedly at 2800-3000..the last thing i'm worried about if my driveline but if it does blow,you can bet a dana is going to replace it...:-D
 
74360duster said:
mine has a 750hp big block in front of it. will be going to the track for the first time this sunday. mine is braced with yukon axles. 4.30 spooled richmond gears and a 489 case. i am foot braking the car.hoping to get into the 9's. should be interesting. i have a dana 60 if needed. but will probably go 9inch ford because of more selection of gears and lighter. will easily take the power.
Click to expand...

Let us know how this works out for you once you get some runs in at the strip.

rumblefish360 said:
My buddy Tim just busted his 8-3/4 behind a 800+ HP 500 inch stroker. The caps broke. He got a billet set of caps for the carrier. He could have went DANA, but stayed with the 8-3/4.

His car is very close to strickly race. Drives it to trhe local races, trailers to the track which is far, very far.

His car runs into the 9's easy.
Click to expand...

Wow! That's a lot power behind that rear.

2shelbys said:
I was stunned to find out that the reason my car has a Dana in it is that the original owner broke the crap out of the original 8¾ with a 383. He said he twisted the axles and grenaded the posi. It had 12.1 to 1 compression, maxed-out 906 heads, a roller cam, two Holley 650s, and no NOS or supercharger. I do not know what the HP was but he was running 10.90s at just under 130MPH launching at 5,000 RPM and shifting at a ridiculous 9,000RPM. Makes me pretty confident about the strength of my bottom end.
Click to expand...

My brother in law had a 68 Road Runner 383 4 speed. Car ran low elevens at the strip with slicks in the early 80's. This kind of performance from a street car at the time was almost unheard of. 383's are bad ***.

Duster346 said:
Joe,

You can be on the fence real easy with an 8.75" rear depending on power/weight.

I've built 8.75" rear ends that have lived in (2800 lb.) 10 second cars with trans-brakes. Then again I've had footbrake cars (heavier) spin the ring gear teeth off in 10 runs. To get it to live--back braced housing, steel caps, billet adjusters, etc etc, you can pretty much buy a pre-built Dana 60 less brakes.

Whenever one of my customer's breaks an 8.75" 9 times out of 10 they upgrade to a Dana 60.

My opinion, go Dana 60 now, and be done with it. You'll always want to make more power, and when you do, you won't have to worry about destroying that lil 8.75" ring gear.

Forgot to mention, when that 8 3/4 does break, it can severly damage the automatic trans (see exploding torqueflites thread at top). I just did one that had a stock VB, with shift kit (low band on in 1st). It spun the ring gear teeth off, rolled the sprag in the transmission, and broke the case! The next run it would have come through the floor! This was the gun-metal grey '72 Challenger that runs out at Bandi and Pueblo. Car goes 11 teens up here I believe, off the foot brake.

HTH's
Click to expand...

I've seen that car. Was he using aftermarket gears? Yeah, I forgot about the damage spun teeth could do to a 727 and thanks for reminding me. That could get real expensive and real dangerous real fast. Ok, now I'm leaning toward the Dana 60. They look bad *** under an A-Body but kinda give away what I might have under the hood. Better an extra 50 lbs and piece of mind I guess. At least the weight is low to the ground and over the rear tires.

demon seed said:
Good question ramcharger, I'd say yes to the 489, probably to the 742 and BOOM to the 741.

Terry
Click to expand...

It's a 489 center section from a early '70s truck. I figured I'd start with the strongest center section availible. Chris has me wondering now though.....

mguner said:
Weight of the car? 4 speed or slush box?
Click to expand...

No exact weight as this is project under construction. '72 Duster with pretty much a full interior and roll cage, fiberglass hood and trunk lid. 727 with trans brake and 3500 stall converter.

stroked 340 said:
With and auto i'd say yes...with a 4-speed i'd say your pushing it,my 8 3/4 has a "new" design 489 housing(more meat in the caps,and bearing sections),billet yoke,a moser spool w/4:30's,and moser axles..running behind my 416 stroker or 360 whichever is in the car,launching repeatedly at 2800-3000..the last thing i'm worried about if my driveline but if it does blow,you can bet a dana is going to replace it...:-D
Click to expand...

Thanks stroked 340. This will have a stroked 360 with all forged internals. I'm targeting mid to low 500's for hp with a shot of squeeze, or at least the capacity to handle it if I so choose.
 
I think you should consider a 904 instead of the 727, I use one behind 600 HP without problems. I also use an 8.75 rear with the MP aluminum center section, better than any of the cast iron ones. I also use a pro gear which is only available in one ratio that I've found, 4.88.

It holds up with a foot brake or transbrake but a 4 speed would do it in. If I had it to do all over I would have built a Dana 60 though. Much cheaper in the long run.
 
Thanks for your input Guitar. The 904 is definitely an option. I still don't know what auto trans is in it right now. Haven't crawled underneath yet except to check for rust damage.

Looks like a Dana 60 is going in.
 
Guitar Jones said:
I also use an 8.75 rear with the MP aluminum center section, better than any of the cast iron ones. I also use a pro gear which is only available in one ratio that I've found, 4.88.

It holds up with a foot brake or transbrake but a 4 speed would do it in. If I had it to do all over I would have built a Dana 60 though. Much cheaper in the long run.
Click to expand...
Same here. I used the aluminum center, with back braced housing in my red car with a trans-brake and it's been as quick as 1.38 in the 60 ft. But like you, I would go Dana 60 in a hearbeat now, and not even consider the 8 3/4 for the cost.

Joe, also, for what it's worth, we swapped the pink b'cuda from a 8 3/4 to D60 a few years back, and it didn't change the ET.

On Larry's deal (challenger), we just ended up building another 8.75" with richmond gears, and a new 727 trans. The teeth on the ring gear will strip again in about 4-5 years, but I couldn't for the life of me talk that fellow into a D60, lol.
 
Duster346 said:
Same here. I used the aluminum center, with back braced housing in my red car with a trans-brake and it's been as quick as 1.38 in the 60 ft. But like you, I would go Dana 60 in a hearbeat now, and not even consider the 8 3/4 for the cost.

Joe, also, for what it's worth, we swapped the pink b'cuda from a 8 3/4 to D60 a few years back, and it didn't change the ET.

On Larry's deal (challenger), we just ended up building another 8.75" with richmond gears, and a new 727 trans. The teeth on the ring gear will strip again in about 4-5 years, but I couldn't for the life of me talk that fellow into a D60, lol.
Click to expand...

That pink b'cuda was consistent as hell last year too.

Larry might be thinking of resale value before the 5 years is up, lol. :-D
 
If you are starting from scratch, do a Dana!

By the time you spend the necessary funds to get a strong 8.75 together, you'll still have a rear that potentially eats ring gears for the same cost or more than a Dana. Footbraking isn't that hard on them. A transbrake or 4 speed are a lot harder on rear ends.

If you have a bunch of 8.75 parts, sell them to either partially or totally fund the Dana build. I have a Dana that I bought sans brakes with a strange spool/axles, 4.88's, forged yoke, long studs for right at $800. I built one from scratch starting with a truck rear for a little under a $1000. I know there is one, maybe two, shortened Dana units up on moparts right now for right at $1000.

There are guys running low 9's with 8.75 in 2600-2800# transbrake cars. It's the weight/torque/hook that kills them. Start geting inthe 3300+ range and it dicey.

An auto will cost more money to fix up after the rear blows too.

Good luck
 
mguner said:
Alot of folks underestimate the 383's potential... :snakeman:
Click to expand...
Yes. The original owner of my car sank cubic dollars into that 383 in 1970. He put $1,200 in the heads alone which is huge money in 1970 dollars. That short 383 stroke can wind up something fierce. The thing revs as freely as any small block but makes big block HP and torque. I love it. No need for a 440 here.
 
demon seed said:
Good question ramcharger, I'd say yes to the 489, probably to the 742 and BOOM to the 741.

Terry
Click to expand...


Why boom to the 741?
I heard on another post that the pinion in the 741 is bigger than the one in a for 9' rear
 
70 Duster with plenty of 10.99 runs never broke anything with the 8 3/4,set up suspension right,no cheap parts, pinion angle with s/s springs, and Detroit locker was my set up. Ran car 5 years 2 track championships no broken parts!
 
We twisted two 8 3/4 housing with 360 with cars weighting less the 3000 lbs...using a transbrake.
All the money in the world invested in a 8 3/4 it still will eat ring gears.....

buy once....Dana 60
 
Duster346 said:
Joe,

You can be on the fence real easy with an 8.75" rear depending on power/weight.

I've built 8.75" rear ends that have lived in (2800 lb.) 10 second cars with trans-brakes. Then again I've had footbrake cars (heavier) spin the ring gear teeth off in 10 runs. To get it to live--back braced housing, steel caps, billet adjusters, etc etc, you can pretty much buy a pre-built Dana 60 less brakes.

Whenever one of my customer's breaks an 8.75" 9 times out of 10 they upgrade to a Dana 60.

My opinion, go Dana 60 now, and be done with it. You'll always want to make more power, and when you do, you won't have to worry about destroying that lil 8.75" ring gear.

Forgot to mention, when that 8 3/4 does break, it can severly damage the automatic trans (see exploding torqueflites thread at top). I just did one that had a stock VB, with shift kit (low band on in 1st). It spun the ring gear teeth off, rolled the sprag in the transmission, and broke the case! The next run it would have come through the floor! This was the gun-metal grey '72 Challenger that runs out at Bandi and Pueblo. Car goes 11 teens up here I believe, off the foot brake.

HTH's
Click to expand...
Agree with the dana 60 , do it and forget about it .
When you start blowing a 8 3/4 every weekend , and have a violent trans explosion , u will wish you had done it earlier !!
 
I find this to be one of the most Hot/Cold discussed topics when you dive into it.
My 2700 lb dart with 620 ish HP, footbraking into the 10.40's has had the same 8.75 w. suregrip in it for probably 10 years. car pulls the wheels about 6 inches off the ground.

I called a popular drivetrain company to buy parts/build another 8.75 for my powertour car, and was pretty much talked out of a 8 3/4 for anything over 3000 lbs, and 600+ HP.
I gave the usual rebuttals...
But its an auto, but its footbrake, but its not THAT heavy...but i have one in my Dart... The guy was knowledgeable, and super friendly, but that was his firm belief.

Makes it tough :p
 
When your absolutely positive your right, then your mind is closed and everyone else is wrong or just plain dumb lucky....or telling lies...Screw him!
 
rumblefish360 said:
When your absolutely positive your right, then your mind is closed and everyone else is wrong or just plain dumb lucky....or telling lies...Screw him!
Click to expand...

Ever had a violent trans explosion because of failed 8/34 rear , I was lucky , but it didnt feel so at the time !-------3600 pound hemi , back in the day-
 
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