Originally Posted by 94 Daily Driven 4.6L
I think you'll find that a traction lock for an 8.8 is a dime a dozen where as the 7.5 is much harder to find. Additionally, I think the gear selection for the 8.8 is also considerably better than for a 7.5. I don’t know if exterior dimensionally if they are the same though.
And what is wrong with overkill when it comes to an IRS differential? I can't imagine a 7.5 is that much heavier than an 8.8 (especially when the 8.8 is available in aluminum), nor can I believe the additional rotating weight of the 8.8 ring and pinion would be noticeable.
No Mark VIII ever came with a 7.5 nor did any of them come traction lock differentials, but all the Mark VIII housings are all aluminum.
Just my .02, but I really think you should consider the 8.8.
Yeah, I bet you're right with 8.8's being easier to find. But with all things considered, the 7.5 would be a better choice (plus, read above, 2 people already offered to sell me theirs, so it's not impossible!). This project is for a bike-engined car. I've got lots of time to find the right carrier assembly, so it doesn't hurt to shoot for the stars. Here are some considerations with my project:
- Minimize weight; sure the 8.8 or even the aluminum 8.8 for that matter might be only marginally heavier, but why not try for lighter
- Minimize size; I havn't ever seen the two side by side, but I'd have to assume the 7.5 is probably smaller. Leads to better packaging and lower sizing requirements.
- HP and Torque; I definitely won't be producing anywhere close to V6 or V8 power in this car. A typical 1 liter motorcycle engine produces roughly 75 lb-ft of torque. I wouldn't be surprised if even the 7.5" could handle upwards of 300 lb-ft. Plus, the additional 1.3" diameter on the 8.8" setup is physically tougher to start spinning because of it's greater inertia, which saps horsepower
- Torque biasing; I'd have to assume that the 7.5 has a less aggressive 'limited slip' function, as in it more closely resembles an open differential versus the 8.8, not as "locked". This car will be anywhere from 1/4 to 1/3 the weight of a conventional car, so that is less weight to force the traction lock to slip as you're going around a corner
So for many reasons, I'm not considering an 8.8