8.25 vs. 8.75

I know when I turn one wheel, the other goes in the opposite direction. From what I understand, some AHBs didn't get SG, but I really wish mine did. It's too bad there isn't a code on the tag stating it.

A buddy of mine has a volare, and hes the one who I modeled my engine off of. My heads had a valve job whereas his didn't, but otherwise the engines are identical. When he ran this combo, he had 2.7 gears, and a smaller tire and ran 14.1. He figured with my 2.9, and taller tire I'd be looking 14.0-13.9. I know that means nothing until I run, (I've got about 75 pounds on me that he doesn't, so that won't help) but just to have picked up roughly 5 seconds with a mild build is impressive. He seems to think with gears I can get pretty close if I do a bit more to the 318. I've wanted a 360 for a while anyway though..just if I gear it high (numerically) than I'll need an OD..which I wouldn't mind either.

I don't know anything from anything, but several years ago one of the car magazines ran an article on rebuilding the 8.25. One of the arguments they made for keeping the rear end is it's already in the car. The writer of the article said short of an application running slicks, the 8.25 holds up well. In the article, they basically rebuilt the rear end with new parts and installed a cover with a girdle. For my money, that's the way to go unless you plan to run slicks at the track.

Slicks have little to do with it since shock loads happen regularly without them. Truth is, most guys don't have low-12-second cars (or faster) either with hard-hitting automatics or with 4-speeds they flat shift, so yeah--the 8.25" will work great for them. For the cars I'm building, an 8.25" simply won't hold together.
Regardless of what any magazine article says, unless they're recommending a C-clip eliminator setup I wouldn't run one. I will never forget the look on that Duster owner's face and I never want it to be on mine because of a C-clip (or, for that matter, running "Green" bearings in an 8.75" under a car that turns). Even if I had to spend a grand on an 8.75", that's a bargain compared to replacing a trunk pan, inner and outer wheelhouse, and quarter panel on top of the totalled axle itself.

Captain Caravelle said:

@Aspen500
Very interesting point that never even dawned on me. My buddy has played U boat commander with his Jimmy more than a few times. I wonder how much water he's gotten in his rear diff....?

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I'll bet the diff fluid looks like a chocolate milk shake and the bearings are pitted. Even if it doesn't get in through the vent, the oil seals are made mostly to keep oil in but water can get in without too much trouble if the axle is submerged. The outer seal lips really only keep out dirt and dust.

In "normal" cases, a c-clip axle is just fine. It's when a stock rear end is kept while going from a 230 hp engine to 450 or something like that without upgrading the axle shafts. It isn't the c-clip itself that fails, it's the axle shaft that breaks off (usually where the splines end) and then there's nothing to hold the shaft in place. Then again, with an Explorer 8.8" the brake calipers would keep the shaft from coming out before you could stop..............to some extent. In any case, always a good idea to install upgraded axle shafts (in any rear end) used for anything other than daily driving. They're not all that expensive so I call them cheap (sort of) insurance.

NoCar340 said:

Slicks have little to do with it since shock loads happen regularly without them. Truth is, most guys don't have low-12-second cars (or faster) either with hard-hitting automatics or with 4-speeds they flat shift, so yeah--the 8.25" will work great for them. For the cars I'm building, an 8.25" simply won't hold together.
Regardless of what any magazine article says, unless they're recommending a C-clip eliminator setup I wouldn't run one. I will never forget the look on that Duster owner's face and I never want it to be on mine because of a C-clip (or, for that matter, running "Green" bearings in an 8.75" under a car that turns). Even if I had to spend a grand on an 8.75", that's a bargain compared to replacing a trunk pan, inner and outer wheelhouse, and quarter panel on top of the totalled axle itself.

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Like I mentioned, I don't know anything from anything, but was the Duster running street tires? I don't drag race, so I don't have personal experience, but I've been told the traction from a street tire isn't enough to nreak an axle unless there's something wrong with the axle and that's why tracks only require C clip eliminators on cars with slicks.
I'm not trying to be a wise guy, just trying to educate myself. Thanks.

Nice write-up NoCar340....

I run the '657 housing in my coupe. 3.91 SG (clutch type), all new stuff with the exception of the hard-parts: housing, axle shafts and pinion and crown gears. Backup is another 3.91 gearset with fine spline and a 3.91 coarse-spline for the 3.55 geared '742 housing.

brotherGood:
Yeah, that will be a pretty stout challenge. My coupe, during my 1st outing to the track has gone a best of 13.13@102. I know it has gotten faster, especially since I moved from the single plane Holley Strip Domintor back to the Perfomer RPM intake. However, talk is cheap, butt-meter can lie, and I missed my chance to head out to the track to re-test late in the season. The goal is to get to the low 12s...being realistic I realize that I might not make it there either...LOL

Point being: I know what I have sank into my motor/drivetrain, and while 14 sec is pretty doable, by the time you get into the 12s the game start changing fast and gets real expensive.

Are you aiming to go as fast as possible, or are you looking for a streetable car that's relatively fast? I'm asking due to weight savings considerations...

It'll be a street car for sure..although I can definitely stand to lose unneeded weight. I know it'll be a task, but I kinda like the challenge. If I can find a builder, I was considering sticking with the cop 998 if I can't find an OD. I know there's an advantage over the 727 IF built properly..so we'll see.

slant6billy said:

I have to duck now as the rocks are coming at me.

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Sadly, that's what we have to do nowadays. But that's what hot rodding is all about. How many Mustang II front ends are under countless rides out there? I too have consider going outside of Mopar. Been thinking about going to GM 700R4 (if possible) for a 4 speed.

8-1/4 diff are stronger then most people realize. i ran a 500 hp stroker for a few years with a 8-1/4 with zero problems. 1.58-1.60 60's with drag slicks. i ran 12.0's with 3.55 gears in the 8-1/4

i would stick with the 8-1/4 for what your planning on doing.