MG Sports Cars

Any idea the amount of power the factory Midget rear end can take with a limited slip installed?

This may seem like a dumb question but I tried finding an answer pretty much everywhere but here so far. I know it probably isn't much, but it's one of those nagging questions to me. Thanks!

James,

The halfshafts are the weakest part of the axle and can break with only a modest increase in power with the original engine.

kevin.

James, as Kevin points out the half shafts are the weak link, but even the center section ring and pinion aren't very robust. Wheither you have a limited slip differential or not the overall strength isn't really affected very much in that area. My general rule of thumb for rear axle torque capacities comes from what the various factories used over the years and comparing those to the torque outputs of the largest engines available with that rear axle. For a modest V8 similar to a stock 302 or that usually meant a diff with a ring gear diameter around 7.5". The Chevy Vega small axle for that 4 cylinder was about 6" in diameter, similar to the MG Midget rear. I'd run at least a 7" ring gear with a small v8 or V6 just to be safe. I figure it's about the same cost to have the larger rear axle modified to fit the car than to buy all the high performance and high strength axles and gears for the smaller rear end and you get some insurance torque cushion with the larger rear.

Bill & Kevin, thank you for your responses, very helpful.

I have one more question then... about the factory MGB rear end. I realize I would have to modify it in order to fit it under my Midget, but would it be worth it? long story short the engine I plan to install (not anytime soon however, this is going to be a long build) should produce roughly 220 hp and somewhere in the neighborhood of 160 lb-ft at the flywheel. I would really like to use a rear end that I have available here, however with your answers I beleive the stock rear end, even built with stronger axle shafts, simply isn't going to be strong enough. I have a 74 MGB rear end though which I could use, any input on this idea? I'm just trying to get the ball rolling so I can start designing the rear suspension.

James, while the MGB rear would be strong enough the available ratios aren't the best and since the cost to narrow the housing and have new axles made up would be about the same as for another axle I'd suggest going with something else. There have been a variety of axles used in Spridgets from Mazda RX7s to Chevy 10 bolts. Your choice. If you want to keep the cost low then you might consider the Chevy 10 bolt from a Monza or Vega if you can find one. They shared the same lug pattern as the Midget and also used 13" wheels so the rear brakes will clear. You might find a deal on a Ford rear from a Mustang II which used 13" wheels as well, but the pattern would be different. What ever you select you'll probably find that having ratios available from around 3.5 up to 3.08 would be helpful in dialing in your combination for best performance. For my V6 with T5 combo I'm running a 3.43 but a 3.2 would be just a slight bit better for mileage.
FYI the Monza housing will take later Camaro gear sets if the pinion shaft is ground down to the size of the Monza pinion bearing, so using that housing which usually came with gears in the 2.78 range it's still easy to get a wider selection of ratios with a little work at the machine shop.
Downside of the Monza or Camaro housing is the large casting for the connection of the torque arm used on these cars, adds a lot of weight to the housing compared to the S10 housing for example.
If I was building my Midget these days I'd probably go with the S10 rear as they're plentiful in the salvage yards and a lot of inexpensive limited slip differentials are available for this housing from Camaros and Firebirds. If you want rear disc brakes, then perhaps a RX7 rear would be better, but I'm not familar with the available ratios or limited slip diffs available for that one.

Bill, you are the man hahaha. You answered my question and then some! It looks as though I will be looking into the available gear ratios for various rear ends b/c either way I will have to have it narrowed.

Appreciate the guidance!