Re: 8 1/4 rear....what HP limts
[Re: Neil]
#2405326
11/18/17 04:16 AM
11/18/17 04:16 AM
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Joined: Jan 2011
Posts: 15,938 Central Florida
larrymopar360
Stud Muffin
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Stud Muffin
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Central Florida
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582 hp is fine so long as it never gets any traction, BUT if it does then that is more than enough to destroy it.
You need at least an 8-3/4 axle with that amount of power. I agree. Unless you're slicks or similar and just driving on street tires and smoking them once in awhile you'll be fine. Currently I have one with close to 500hp and over 500tq and it's been fine for quite awhile. 3.21 gears. I've had three HP 360's with 8.25 rears and street tires with sure-grip and they held up fine for thousands of miles.
Facts are stubborn things.
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Re: 8 1/4 rear....what HP limts
[Re: larrymopar360]
#2405643
11/18/17 08:55 PM
11/18/17 08:55 PM
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Joined: Oct 2005
Posts: 4,958 WI
Dcuda69
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master
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WI
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582 hp is fine so long as it never gets any traction, BUT if it does then that is more than enough to destroy it.
You need at least an 8-3/4 axle with that amount of power. I agree. Unless you're slicks or similar and just driving on street tires and smoking them once in awhile you'll be fine. Currently I have one with close to 500hp and over 500tq and it's been fine for quite awhile. 3.21 gears. I've had three HP 360's with 8.25 rears and street tires with sure-grip and they held up fine for thousands of miles. I agree also. Mine is behind a 470" 4spd(500+ HP) It's a street toy running 245-60/15 BFGs. They don't stand a chance but the diff has been fine for a few years. If I don't put sticky tires on it I suspect it'll live a while. 3.73 gears with a sure-grip.
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Re: 8 1/4 rear....what HP limts
[Re: dynamite]
#2405764
11/19/17 01:37 AM
11/19/17 01:37 AM
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Joined: Feb 2009
Posts: 892 Illinois
StrkrDart69
super stock
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super stock
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Illinois
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I run one in my Dart. Do not know HP but I run 11.5 on slicks, 3500 stall. No problems at all. 4.10 gears. I do have the aluminum cover with the bolts for the carrier bearing caps. 3000 lb
Last edited by StrkrDart69; 11/19/17 01:41 AM.
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Re: 8 1/4 rear....what HP limts
[Re: dynamite]
#2405790
11/19/17 02:56 AM
11/19/17 02:56 AM
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Joined: Jan 2003
Posts: 6,840 The Swamp
Sixpak
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master
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The Swamp
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how much power will an 8 1/4 rear take...3000 lb car with 582 HP Depends on how much maintenance you're willing to do on it. Dunno if it's still true but there used to be MANY NHRA stockers that ran the 8 1/4 because they were the lightest and those guys were able to make them live. They had a specific need to run that rear - if you do not have to run that rear, there are cheaper alternatives with less maintenance.
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Re: 8 1/4 rear....what HP limts
[Re: Sixpak]
#2405816
11/19/17 04:45 AM
11/19/17 04:45 AM
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Joined: May 2012
Posts: 1,848 South Bend
John Brown
top fuel
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top fuel
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South Bend
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Billet caps and longer bolts will go a long way towards making many rear ends stronger.
July 19th should be "Drive Like Rockford Day". R.I.P. Jimmie.
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Re: 8 1/4 rear....what HP limts
[Re: StrkrDart69]
#2405893
11/19/17 01:17 PM
11/19/17 01:17 PM
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Joined: Oct 2005
Posts: 4,958 WI
Dcuda69
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WI
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I run one in my Dart. Do not know HP but I run 11.5 on slicks, 3500 stall. No problems at all. 4.10 gears. I do have the aluminum cover with the bolts for the carrier bearing caps. 3000 lb Do you have a source for those covers with the bolts to support the carrier caps? I did a quick search but didn't stumble across any for the 8 1/4.
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Re: 8 1/4 rear....what HP limts
[Re: Dcuda69]
#2405982
11/19/17 04:51 PM
11/19/17 04:51 PM
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Joined: Feb 2007
Posts: 2,578 sweden
1Fast340
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master
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sweden
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I run one in my Dart. Do not know HP but I run 11.5 on slicks, 3500 stall. No problems at all. 4.10 gears. I do have the aluminum cover with the bolts for the carrier bearing caps. 3000 lb Do you have a source for those covers with the bolts to support the carrier caps? I did a quick search but didn't stumble across any for the 8 1/4. I found these thanks to that post http://g2axle.com/pages/view/torqueUntil i read this thread i didnt have a clue those covers where available and nice to see that they are made in the USA:D One of those are on my to buy list now!
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Re: 8 1/4 rear....what HP limts
[Re: 1Fast340]
#2406640
11/21/17 02:31 AM
11/21/17 02:31 AM
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Joined: Feb 2009
Posts: 892 Illinois
StrkrDart69
super stock
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super stock
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Illinois
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I run one in my Dart. Do not know HP but I run 11.5 on slicks, 3500 stall. No problems at all. 4.10 gears. I do have the aluminum cover with the bolts for the carrier bearing caps. 3000 lb Do you have a source for those covers with the bolts to support the carrier caps? I did a quick search but didn't stumble across any for the 8 1/4. I found these thanks to that post http://g2axle.com/pages/view/torqueUntil i read this thread i didnt have a clue those covers where available and nice to see that they are made in the USA:D One of those are on my to buy list now! This is the cover I use. Nice quality. Highly recommend.
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Re: 8 1/4 rear....what HP limts
[Re: dynamite]
#2406850
11/21/17 03:05 PM
11/21/17 03:05 PM
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Joined: Jan 2003
Posts: 13,613 md
mopars4ever
I Live Here
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I Live Here
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md
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Re: 8 1/4 rear....what HP limts
[Re: 1Fast340]
#2407046
11/21/17 09:53 PM
11/21/17 09:53 PM
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Joined: Oct 2005
Posts: 4,958 WI
Dcuda69
master
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master
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WI
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I run one in my Dart. Do not know HP but I run 11.5 on slicks, 3500 stall. No problems at all. 4.10 gears. I do have the aluminum cover with the bolts for the carrier bearing caps. 3000 lb Do you have a source for those covers with the bolts to support the carrier caps? I did a quick search but didn't stumble across any for the 8 1/4. I found these thanks to that post http://g2axle.com/pages/view/torqueUntil i read this thread i didnt have a clue those covers where available and nice to see that they are made in the USA:D One of those are on my to buy list now! Thanks!! I did stumble on that one....agree,love the fact it's USA made! It's now in my ebay cart. Thanks guys!!
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Re: 8 1/4 rear....what HP limts
[Re: dynamite]
#2407101
11/21/17 11:23 PM
11/21/17 11:23 PM
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Joined: Jan 2011
Posts: 15,938 Central Florida
larrymopar360
Stud Muffin
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Stud Muffin
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Central Florida
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Great, something else I've just got to spend money on!!
Last edited by larrymopar360; 11/21/17 11:23 PM.
Facts are stubborn things.
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Re: 8 1/4 rear....what HP limts
[Re: dogdays]
#2407408
11/22/17 04:03 PM
11/22/17 04:03 PM
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Joined: Feb 2007
Posts: 2,578 sweden
1Fast340
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master
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sweden
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Dudes, the original question is so bogus! The only HORSEPOWER limit on a rear end would be the horsepower that would generate enough BTUs to cause the rear end to overheat. Example: NASCAR, where the Ford 9" they used required an oil cooler of its own. I don't know what they are doing nowadays.
What the OP should have been asking is how much TORQUE the rear end can tolerate. That's how axle manufacturers rate their axles, torque capacity.
Shock loads are also important and I think there's usually a factor for shock loads included in the calculations.
Why not use horsepower? Because an engine with rated horsepower at 5,000rpm will produce roughly 3 times the torque as an engine producing the same max hp at 15,000rpm.
R. However that 15000rpm peak hp car would probably use 3 times as much gear ratio and at that point just as much torque would be trown at the axleshafts anyway and at that point you are back to squareone again.
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Re: 8 1/4 rear....what HP limts
[Re: dynamite]
#2407784
11/23/17 11:51 AM
11/23/17 11:51 AM
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Joined: Jan 2003
Posts: 5,895 Florida
Locomotion
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If you concerned about the strength of an 8 1/4" rear, step up to an 8 3/4" because you'll be spending extra to strengthen it. Same philosophy when concerned about an 8 3/4" - move up to a Dana 60.
I know of some 8 1/4 rears that have been used in 3,600+ lb cars running mid-high 11's in the Stock class. But they spent a lot on them and at least one did eventually upgrade to a Dana 60.
Weight and gear ratio are also big factors in durability. The lower the ratio (higher numerically), the weaker the teeth because they are smaller. Between an 8 3/4" and Dana 60 - it's the gears that are the weak link in the 8 3/4. In many cases they both use 35 spline axles. Not only is the same ratio in a Dana 60 stronger, because it's bigger, but it's also more efficient because of the pinion position in relationship to the ring gear.
I would think that the ring gear would be the weak link in an 8 1/4" rear, but the caps wouldn't be far behind. Same with an 8 3/4'. I've broken some 8 3/4" ring rears over the years, but no caps (knock on wood). I am looking at a Dana 60 for peace of mind.
Even if it's built "right", it's not just how much power/torque the rear will handle, but for how long. And if you're not sure what the weak link is in the rear you choose, it can eventually show you.
Last edited by Locomotion; 11/23/17 11:53 AM.
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