|
Proven strength of 8 3/4 diff
#2569253
10/25/18 08:55 AM
10/25/18 08:55 AM
|
Joined: Jan 2005
Posts: 4,243
Charlotte, North Carolina
sgcuda
OP
master
|
OP
master
Joined: Jan 2005
Posts: 4,243
Charlotte, North Carolina
|
Due to Dominic Thumper's lack of computer savvy, he has asked me to post a pic of his Dart time slips over the years. Although it started out as a small block, it has been equipped a long time with a 470 low deck, Edelbrock heads, roller cam, fenderwell headers and carb of the day. He might have banged his head one too many times, but he has never hurt the rear axle assembly.
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: sgcuda]
#2569286
10/25/18 11:30 AM
10/25/18 11:30 AM
|
Joined: Sep 2014
Posts: 4,457
Washington
madscientist
master
|
master
Joined: Sep 2014
Posts: 4,457
Washington
|
If Dom is like me, he will still be running with a flip phone. That's all I have. And when this flip phone junker dies, I'm back to a land line.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: sgcuda]
#2569287
10/25/18 11:31 AM
10/25/18 11:31 AM
|
Joined: Jan 2003
Posts: 8,028
Tulsa OK
Bad340fish
master
|
master
Joined: Jan 2003
Posts: 8,028
Tulsa OK
|
That looks like a bunch of passes in 2018 or just a few passes over 10 years lol. I don't race as much as I would like either.
68 Barracuda Formula S 340
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: sgcuda]
#2569296
10/25/18 11:52 AM
10/25/18 11:52 AM
|
Joined: Oct 2007
Posts: 4,209
New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,209
New York
|
And the car weight was...
And the weight transfer was...
And the effective torque multiplication to the pinion was...
And the tire contact patch was...
A 1,000 hp car with 1,500 stall speed and 6.50-13 tires can use an 8-3/4 for 50 years.
A 500 hp 4,000 lb. car with 80 lb. flywheel leaving at 8,000 RPM on 14" tires can't do it once.
What does this mean? We don't have enough data to draw a conclusion, other than YRMV.
Boffin Emeritus
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: Bad340fish]
#2569346
10/25/18 01:29 PM
10/25/18 01:29 PM
|
Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
I Live Here
|
I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
|
That looks like a bunch of passes in 2018 or just a few passes over 10 years lol. I don't race as much as I would like either. This year maybe 10-12 passes but some are from the 90's and this was for fun but to prove I have beat the snot outta my junk and it's still going strong when some HOPED it wouldn't and even heard a few had bets on WHEN it would grenade..........  In the last 10 years most of my 60's were in the low 1.3's and that's with a stock 8 3/4(minus new gears of course)and stock caps between 3050-3150 lbs roughly......... 
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: polyspheric]
#2569356
10/25/18 01:49 PM
10/25/18 01:49 PM
|
Joined: Nov 2010
Posts: 3,696
jersey
Spaceman Spiff
master
|
master
Joined: Nov 2010
Posts: 3,696
jersey
|
And the car weight was...
And the weight transfer was...
And the effective torque multiplication to the pinion was...
And the tire contact patch was...
A 1,000 hp car with 1,500 stall speed and 6.50-13 tires can use an 8-3/4 for 50 years.
A 500 hp 4,000 lb. car with 80 lb. flywheel leaving at 8,000 RPM on 14" tires can't do it once.
What does this mean? We don't have enough data to draw a conclusion, other than YRMV. 4600lbs wagon. 526 stroker, close to 700lb ft 2600 stall. 275/60/15 8 3/4 still alive.
526 cubes of angry wedge, pushbutton shifted, 9 passenger killer!
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: Spaceman Spiff]
#2569368
10/25/18 02:06 PM
10/25/18 02:06 PM
|
Joined: Dec 2003
Posts: 22,696
Bitopia
jcc
If you can't dazzle em with diamonds..
|
If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
|
And the car weight was...
And the weight transfer was...
And the effective torque multiplication to the pinion was...
And the tire contact patch was...
A 1,000 hp car with 1,500 stall speed and 6.50-13 tires can use an 8-3/4 for 50 years.
A 500 hp 4,000 lb. car with 80 lb. flywheel leaving at 8,000 RPM on 14" tires can't do it once.
What does this mean? We don't have enough data to draw a conclusion, other than YRMV. 4600lbs wagon. 526 stroker, close to 700lb ft 2600 stall. 275/60/15 12 year old 600 TW?  8 3/4 still alive.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: sgcuda]
#2569401
10/25/18 03:05 PM
10/25/18 03:05 PM
|
Joined: Dec 2005
Posts: 11,608
Fulton County, PA
CMcAllister
Mr. Helpful
|
Mr. Helpful
Joined: Dec 2005
Posts: 11,608
Fulton County, PA
|
Pro gear and ratio availability, aftermarket support, large diameter pinion, high strength aluminum cases, housing availability, etc., etc. 8.75s and D60s in Mopars are nice, but...
Last edited by CMcAllister; 10/25/18 03:05 PM.
If the results don't match the theory, change the theory.
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: CMcAllister]
#2569413
10/25/18 03:24 PM
10/25/18 03:24 PM
|
Joined: Feb 2005
Posts: 20,185
PA.
pittsburghracer
"Little"John
|
"Little"John
Joined: Feb 2005
Posts: 20,185
PA.
|
My thoughts are I would never run an 8 3/4 rear-end in any of my cars running the times I am BUT my Sons Duster at 3200 pounds is. Its a non-back-braced 8 3/4 with 4.10 gears, stock caps, 35 spline axles and spool, trans brake car with 5600 stall and 727 transmission, 275 radials used to be 10.5 slicks, 1.38-1.42 sixty foot times. Approximately 200 passes since gear change with zero issues. Moparts member Tim Bowman of Bowman Performance helped set the gears up for him. He's stepping up to a 4.56 gear for next year since our class (box class) strictly runs 1/8 mile only. Car number 3X97  Untitled by John Cadamore, on Flickr  Untitled by John Cadamore, on Flickr  Untitled by John Cadamore, on Flickr
1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27
Livin and lovin life one day at a time
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: humpty]
#2569422
10/25/18 03:41 PM
10/25/18 03:41 PM
|
Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
I Live Here
|
I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
|
I agree on the weight factor. I hacked on a stock 489 rear for 250+ passes, and who knows what it went through before I got it. No issues ever. I'm 3160 at the line, running a spool, drag radials, and a brake. 60's in the mid to low 1.4's.
My friend runs a 3800lb Road Runner that had an aluminum 8 3/4 housing. The car used to run 10.8's until he had the motor rebuilt this year and picked up 140+ HP and a bunch of torque. It picked up 1/2 tenth in the quarter. It lasted about 6 passes and disintegrated the case. This was foot braking.
I borrowed him my nodular 489, new this year, that had 3 weekends on it. It last about 6 passes and broke. We don't know what yet, but it broke.
I'm planning to bump up my program next year and drop a little weight in the process. I plan to run the nodular 8 3/4 next year. I'm more concerned about the stock 904 shafts than I am the 8 3/4 so those are getting upgraded first :}
That THUMPERCARBS power has a way of tearing stuff up............
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: sgcuda]
#2569473
10/25/18 06:17 PM
10/25/18 06:17 PM
|
Joined: Aug 2011
Posts: 2,864
Pattison Texas
CSK
master
|
master
Joined: Aug 2011
Posts: 2,864
Pattison Texas
|
Put Drag radials on & broke the ring gear, 4050lb auto 68 Charger, that was when the car was slower than it is now.
1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: justinp61]
#2569493
10/25/18 07:23 PM
10/25/18 07:23 PM
|
Joined: Oct 2004
Posts: 16,479
Canada
CrAzYMoPaRGuY
I Live Here
|
I Live Here
Joined: Oct 2004
Posts: 16,479
Canada
|
I'll go there. I had a Ford 9" in a street car. MILD 440. Took out six sets of gears in 11 years on the road. Street tires, 3100 pounds. I had WAR cases, nodular cases, Richmond gears, US gears, you name it. 31 spline 4 spider posi and a spool. No gear set lasted very long, set up by four different people very knowledgeable IMO. NO THANKS!!!!
CrAzYMoPaRGuY
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: sgcuda]
#2569542
10/25/18 10:24 PM
10/25/18 10:24 PM
|
Joined: Oct 2007
Posts: 4,209
New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,209
New York
|
I wish we had enough hard data on the stress points:
1. weight
2. G force on launch
3. contact patch
4. stall speed vs. flywheel mass + launch RPM
5. ring gear deflection (larger ring gear isn't always the best design)
etc. to assign a point value to each (as a multiplier) and get a total for "what will break it".
Boffin Emeritus
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: polyspheric]
#2569549
10/25/18 10:35 PM
10/25/18 10:35 PM
|
Joined: Dec 2003
Posts: 22,696
Bitopia
jcc
If you can't dazzle em with diamonds..
|
If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
|
I find it hard to see how this would be fruitful for all the needed effort.. There are likely 50? other pertinent variables, GIGO is still relevant, and only three solutions, and confirmation bias still trumps them all.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
|
|
|
Re: Proven strength of 8 3/4 diff
[Re: sgcuda]
#2569556
10/25/18 10:53 PM
10/25/18 10:53 PM
|
Joined: Jan 2005
Posts: 2,540
Milwaukee WI
TRENDZ
master
|
master
Joined: Jan 2005
Posts: 2,540
Milwaukee WI
|
You can bulk up the housing enough to stop any deflection that causes problems. But that just gets you to the next weak point. The pinion shears off at the yoke.
My 8 3/4 took my 3700 lb trans brake car into the low nines. The housing was back braced, had cap load bolts in three directions with extensive internal bracing. Probably around 50 passes at the track, and who knows how many on the street. Started working on the sixty ft, and sheared off 3 different sets of gears at the yoke. Once the pinion shears off, you’ve done all you can, and need to move on.
I ended up going to an ultra case 9” with the large diameter pinion gear (3.50 ratio) and it took everything I could throw at it.
I would think with a lighter car and a higher (numerical) gear ratio, I could get an 8 3/4 to live for a pretty long time.
"use it 'till it breaks, replace as needed"
|
|
|
|
|
, but I wasn't going there. 
