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Just starting to plan out a BEC and have been thinking about the different options to correct the diff rotation. Flipped diffs have their own issues. I'd love the Elite Racing Transmissions MX200 witch solves rotation and Reverse $$$ While looking at AWD front Diffs I came across the Porsche 911. Its long but it has LSD which I'm imagining is rare. Any thoughts?

https://www.redlineautoparts.com/porsch ... lIQAvD_BwE

Possibly a good find (you're to use a shaft-drive bike motor?).. I didn’t catch the Porsche ratio(?). most BEC guys end up around 3.0:1... maybe all the way up to 4.0 for track use (smaller track).. Ratio, rotation, reverse... I know it’s not at all Locost, but that MX200 addresses them all.. my next build will be my 3rd BEC, and I’m pretty sure I’ll use an Elite rear in it.

You might also look at SXS (off-road cars) front diffs, like a Polaris RZR1K or a CanAm.. I briefly researched them, and had an issue with out-of-range ratios, and they are a bit expensive..they do have a ‘locker‘ function, but it takes a bit of fussing to adapt for BEC use.

Whatever direction you go, an IRS in your BEC will be one of the projects more complex/challenging aspects - especially if you want reverse (and you do want reverse ).. That MX200 is the easy button... I’ve already started saving my pennies for it..

—ccrunner

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Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

At one time Quaife had something very similar, at a similar price I think.

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Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Hmm, the MX200 says it can only handle 250 lb-ft of torque. By my math even my R1 engine would be putting out around 300 lb-ft in first gear. Not sure what other engines are putting out but it would seem to me anything in the 1000cc range is probably out. The MX250 costs more but can handle 350 lb-ft.

While technically true, keep in mind that it's handling that torque from input to output, and tire traction will set the real limit. That is, if your vehicle weighs 500kg, the tires will very likely spin before the differential sees anything near its rating. Now, how to calculate that is another kettle of fish!

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Good point, and it got me thinking after doing a little math. When I made my original 300 lb ft comment I had just multiplied peak tq by the 1st gear and primary (internal) ratios but either the ratios I googled were wrong or I made a typo. Looking back at the spreadsheet I made a while ago, I had calculated 241 lb-ft as my peak 'driveshaft torque'. I trust that number more, so maybe the Mx200 would be sufficient, as long as it can handle that kind of power on a regular basis.

Now to go off on a tangent: As for calculating torque required to spin the wheels, as far as I'm concerned you just need to estimate the weight on the rear wheels and the force they are imparting on the pavement, with some kind of reasonable friction coefficient estimate. This assumes a lot of things, including that you are going in a straight line. In my case, 241 lb-ft x 3.45 (rear end ratio) gives me a peak wheel torque of 831 lb-ft and the radius of the tire being what it is, 856 lbs of 'thrust' so to speak. I will count both tires because I have a clutch type LSD. Being that the car weighs about 1350 lbs with me in it, and assuming a friction coefficient of 1.0 (RE71 tires) I must have at least 856 lbs on the rear wheels after counting static weight distribution and whatever else from weight transfer. Actually, even sitting still, assuming a weight distribution of 40/60 gets me almost to that number. I know I can't spin them at full throttle all the way to redline, so I must have at least that much weight on my tires under hard acceleration (and/or less torque than advertised ).