razorback

is that a mopar 8 3/4 rearend i see?

13B-RX3

iTrader: (2)

It sure is. I thinks the 9" ford is too inefficient and a bit overkill for my application.

razorback

i think it is as well. usually ford 9 inch rears are for those high horsepower bigblock v8s. when i upgrade my fb rearend im putting the 8 3/4 and if i go solid axle in my fc ill use one (i have 2 of them, so thats not an issue) there is a guy in the low 9s with the 8 3/4 on here in an fc, good for rotary apps, because well rotaries dont have that axle bending torque.

tearbo2

iTrader: (2)

THAT would be me !!!!!!

razorback

do any of you texas guys plan on going to the meet in tulsa during memorial day? pm me if you want the website/forum address.

twomucboost4u

iTrader: (9)

I am currently biuldning a RX-2 very similar. I was wondering what your thoughts are on a ford 8.5 rear end. I already changed the front suspension to the GSL-se and I wanted a rear end with matching lug pattern. Is the mopar rear end better for whatever reason?

razorback

the mopar rear is the common rx7 bolt pattern (mustang too, etc) but if you use the 8 3/4 rearend you will have to have it shortened, and new axles made. bout 100 bucks for shortening, and probably 300-400 for axles (moser and strange engineering both do this, good idea anyway, due to changes in tech the past 30 years) in whatever lug pattern you want. the 8 3/4 is pretty common, go to a junk yard and ask them if they have one. (you can also try www.moparts.com in the for sale section, transmission and drivetrain) i was told that a 8 3/4 rear end should last up to about 800 hp with an equal amount of torque on an auto with a big block. so they are far more than you would need.

here is a good tech article for the 8 3/4, should be all the info you need. http://www.bigblockdart.com/techpages/875axle.shtml

i can go measure the center section, housing and stock axles if you want a high general weight estimate.

"LILHEMI"

so whats the difference between the 8 3/4 and the 9" beyond the obvious? i have a 9" in my colt but thats only because i got it already shortened to the right length for $100. i want to know this for reference in the future. if had to do it all over again i would have gone with a ford 8.8. my car weighs 2180 without me in it so its light.

Jesuscookies

iTrader: (1)

I don't know too much about the 8 3/4's rear ends, but my guess is that they are just as strong as any 9 inch. And, probably just as heavy. I am using an 8.8 for my RX2 build up. They have a couple of good pluse's that make them worth using.

1. They are lighter than the 9 inch.

2. You can weld in the 9 inch axle tubes and do away with c-clip, and c-clip elimantors.

3. Tons of gears sets and parts readily available.

4. Ford Explorer rear ends are stock big bearing 31 splines.

5. You can pick them up fairly cheap with disc brakes.

Any rear end you pick up will need custom axles, so you can select any wheel pattern you want. However, the Ford Explorer is already 5 X 114.3, which is the same as later mazda, and will allow you to use the ford disc brakes.

Another thing that I heard, and I do not know how true this is, but the 9 inch, due to it's design, is less efficent at transmitting power to the rear wheels when compared to the 8.8.

I picked up a 96+ Ford Explorer rear end for $225 + shipping. It came with a 4.10 gear set, 31 spline big bearings, Trac Loc Limited slip rear end, and 11.25 inch disc brakes.

I am paying about $900 to have it shortened to length, have a set of custom axles made, a rebuild of the center section, and a new custom set of spring perch brackets welded on. I am also going to be adding a stronger rear cover for additional strength. This set up should be good for about double what my car will be seeing powerwise (500RWHP Max).

Anyways that's my 2 cents.

And good progress on your car 13B-RX3. I am jealous, and still want you to tub the back of my 2.

Doc Holiday

iTrader: (2)

Both the Ford 9 and the Mopar 8 and 3/4 are front loaders, which in my opinion, is better. No C-clips to have to eliminate, but the mopar has a better angle where the pinion meets the ring gear, supposedly soaking up less power. Its much easier and cheaper to get weird gear sets for the ford though.

13B-RX3

iTrader: (2)

Parts availability shouldn't be a deciding factor when looking at any of these three rear ends. The aftermarket will be able to supply any gear ratio, axle length, bolt pattern, spools or whatever you need for out applications. The 9" can be made by far the strongest setup but it is the most inefficient and heaviest. The reason for this inefficiency is the angle that the pinion intersects the ring gear. The pinion is very offset which in turn makes the tooth contact very large and adds friction. Also the size of the ring and pinion and it's weight take more horsepower to accelerate. The 8.8 ford and the 8 3/4 Chrysler would be a very close match. In stock form the 8 3/4 would be slightly stronger than the 8.8 IMO. But filled with aftermarket parts it would be tough to choose. I went with the 8 3/4 because i had four setting in the back yard. I narrowed myself and used the original housing ends. I cut the tube with a giant tubing cuter and had the housing ends trued up on a surface grinder. I installed a set of Green bearings, Mosier axles, and Richmond gears on a cone type posi-trac unit to round it off. The ultimate testimony for the 8 3/4 is my dads 70 Duster. He had over 300 passes on his and was still running the original gear set. This is in a 2900lb drag car that runs 10.1X at 132 MPH.


I rough fit the front tube for my header today and it turned out very good. Both front and rear tubes are exactly 16" and have somewhat smooth bends. Now i have to finish fit all the cuts and start welding it together.

RXn407

PLs. finish it Allen! Im dying to see this car go!!! The best of luck to ya'

13B-RX3

iTrader: (2)

Not half as bad as i am! You know a couple of hundred dollars would really move me along. Hahahaha

13B-RX3

iTrader: (2)

Got everything tacked together today.

SPOautos

couple hundred huh.....how about $700 and you make me a copy of your manifold lol