How Many Horses does your Posi eat?

-
Blue Grey Duster

Blue Grey Duster

Well-Known Member
Joined
Jan 24, 2009
Messages
493
Reaction score
77
Location
Ohio
A drag racing buddy of mine once told me, that he had considered using a Dana rear end, but that it used too much H. P. compared to what he had. He said if his breaks down, he would rather keep fixing it than use a Dana.
I'm trying to set up my Duster's 8 3/4 and was thinking, what about all these Posi units on the market. Is there much difference in the H. P. loss comparing the Sure-Grip to the the Detroit True Trac, Detroit Soft Locker, Powertrax Lock-Right, Etc. ? How many Horses do these things eat and are they it worth it ?
 
I seen a test on I think it was hot rod TV. The difference between a small Chevy 8.5 and a huge 12 inch DANA was 5 HP with the dana eating up IIRC 15 HP to turn preety fast.

Don't beileve that hype of big rears eating up a ton of power. Also there weight difference is a moot issue since there bigger and (Key word coming up) STRONGER so you won't have to replace parts with cubic money bills that could be served else where better.
 
If you start blowing up rear ends you need a stronger rear end. Simple as that.

You don't worry about the heavier rear end eating up a little more power.

Remember……. When you blow up a rear end the pit guys running to push your car off the track are putting down a better ET than you are.
 
In my opinion going down the 1/4 mile there is no horsepower loss attributed to the sure grip/posi no matter who makes it. The horsepower loss is through the gears and bearings in other words turning friction. The Ford 9" I think is the worst cuss everything's so stiff (ya ever tried pushing a car with one in it) followed closely by the dana then the 8 3/4. I've heard of numbers between 10-20 loss through the Ford.
 
I remember they did a test between an 8 3/4 and a Dana 60. It was Steve Magnante and his Hemi Dart. He made a pass with the 8 3/4 then they put in the Dana 60. The differance was hundreds of a second. It was turning basically the same times.

Fred B
 
Yup, I saw that too. No difference, performance-wise. Strength-wise?
68 SS Barracuda's and Dart's used both.
8.75" for the Torqueflite cars
Dana 60 for the 4 speed cars

Obviously, the 4 speed cars are harder on the rears so they required the 60 to live.
The only reason's that I can think of to use one or the other are:
*power level and traction - BIG power requires BIG tough rear=Dana 60
*ease of swapping gears - 8.75" rear (keep in mind, you can build a bullet proof 8.75" nowadays)
*vehicle use - handling/road course build, lighter 8.75" will help handling through the lack of overall weight and lack of unsprung weight

Ford 9" - who cares, they just copied the 8.75"....LOL (yeah yeah, I know, great aftermarket support using zero ford parts...still don't want one.)
 
You can minimize the loss by running a lightweight spool... But you're really looking for fractions at that point and spools are not for street cars.
 
67yelodart said:
12 inch Dana?,,,,,ring gear on Dana 60 is 9 3/4.
Click to expand...

DODGESTRIKE said:
dana 80 ring is 11.50 maybe thats the one he is talking about
Click to expand...


I do beileve it was a truck rear end. It could have been a DANA 60. Forggy in the brain about it. It rates as tid bit in the brain I seen several years ago. It was something I beileved in and the show confirmed it. I just filed it in a back room folder in the brain and forgot about till I saw the post.
 
BACK IN THE 80'S, THERE WAS A 68 HEMI SUPER STOCK CUDA, THAT WAS RACED BE DeFRANK & COHEN. THEY RAN A 12-BOLT GM AXLE TO GAIN THAT LITTLE EXTRA. IT WAS REPORTED THAT THE RING & PINION WAS REPLACED AFTER EACH EVENT. OF COURSE THESE GUYS WERE THE ONES TO BEAT AT THE TIME, THEY WERE LOOKING FOR EVERY EDGE THEY COULD FIND.
 
Everybody says power breaks them but I think its the traction. if youre not running slicks or big *** meats on back the tires give before the rear.
 
The Ford 9" uses more power because the center line of the pinion is further away from the centerline of the ring gear, that requires steeper angles on the gears and more friction.

The Ford 9" is stronger than an 8.75" because there are three bearings supporting the pinion. One on each side of the pinion gear itself and the third out at the yoke end.

I have seen several articles comapring the rear wheel HP of the same car with a Ford 9", GM 12 bolt and Dana 60 (never seen the 8.75 in one of those comparisons) and there is not a lot of difference, single digit differences.
 
dgc333 said:
The Ford 9" is stronger than an 8.75" because there are three bearings supporting the pinion. One on each side of the pinion gear itself and the third out at the yoke end.
Click to expand...

The reason Ford uses 3 bearings is because the pinion is mounted so low it absolutely has to have that rear support bearing to live. That does increase it's strength over one without a rear bearing but to say it's stronger is a very debatable statement since the pinion shaft diameter is so small on a 9". Remember, it's even smaller than a 741 case 8-3/4. There are several Ford 9" cases also. Even more an 8-3/4 Mopar therefore you have to get the right one to have a stout case that don't flex.
 
hotrod magazine did an article about rear end strength a while back, and they said the 8 3/4" is stronger than the ford 9". they also said in another article that chevy ran clutches and internals that would keep enough power from the wheels so you didn't break your rear end, also springs that would twist length wise to have the same effect. doesn't bias have strange effect on the conscience?
 
The weakest thing that I have found with the 8 3/4, is the suregrip carrier. I have broken these when you get into the low 11's. A spool will fix that concern. I know that the 9 inch is the rear of choice, but to get a stout one uasully requires a few aftermarket parts. It seems that when the 9 in. breaks, it spits the pinion out of it. I seen this happen 3 times last race season.
 
mikedevore said:
The weakest thing that I have found with the 8 3/4, is the suregrip carrier. I have broken these when you get into the low 11's. A spool will fix that concern. I know that the 9 inch is the rear of choice, but to get a stout one uasully requires a few aftermarket parts. It seems that when the 9 in. breaks, it spits the pinion out of it. I seen this happen 3 times last race season.
Click to expand...

Which SG are you referring to Mike? The cone or clutch type?

I've noticed that's how Ford's usually break too. They also have at least a couple different clutch type powerlok's. One is a weak 2 pinion type.
 
A stock 9" compared to a stock 8.75"? No comparison...the 8.75" is stronger. Just look at the shaft size and bearings...Ford copied the 8.75" and in typical Ford fashion, they went cheap.
Ford has always tried their best to do everything cheap.
Henry Ford would do some pretty tricky stuff to get over. He used to have vendors send a part to them in a specifically made wooden box so he could reuse the wood elsewhere in the car. He was not stupid, though I think he was a bit of a prick.
Inventor of the assembly line? Hardly!
 
To upgrade a 9" to make it stronger you put a 489 bearing in it for beef . 9" fords are for 350 chebbys. The guys that read the magazines too much use them because they don't know the difference. 8 3/4s have been used in funnycars and diggers long before 9" rears were popular. 9" rears and powerglides that go fast have very little original parts in them.
 
Henry ford used to use dodge motors in the very beginning...

Some got it right.... The 3rd bearing in a 9" is a NEEDED piece not a add in..

When the 3rd bearing starts to go bad, the driver finds out when he needs to buy a new 9", and driveshaft and transmission, because when the 3rd bearing goes bad or the housing cracks there, it sends the pinion forward taking everything in front of it out...

But i just love hearing everyone run to the 9"

The 8.75 will handle the hp, if you feel nervous use the D-60..

I have a D-44, 8.75, D-60, and unfortunately a 9" instead of the Halibrand QC...(i still kick myself for that blunder)

My d-44 see's over 600, and there are plenty of vipers in the 8's and 7's on D-44's

Some rears break from wheel hop and tire shake, very violent issues for diffs to deal with. Some break from poor set-up, some break from wear and not catching it (9" 3rd bearing)
 
I have the same Dana/spool in my car.It was already in the car when I became the keeper almost 25 years ago.I drive about 3k street miles a year and about 50 legal 1/4 passes.Tips the scale @3850 with me & fuel.My junk ain't no trailer queen:-D
 
You must log in or register to reply here.
-

Back
Top