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RX7 Rear End in a Midget


Jedi Knight
So Im Debating on snatching up an RX7 rear rather than invest any time $ into this spridget rear. It seems they have tons of types. Anyone no which rar would be an ideal canidate / year/ brake config. for racing. I plan to shorten to Spridget specs with newly cut moser axles and whatnot, seems if Im going to invest my money it should be in something worthwhile.


Jedi Warrior
""""""Anyone no which rar would be an ideal canidate / year/ brake config. for racing. """""

first thing I'd look at is it rules allowed?

$$ wise it's a push.

Look at dwarfcarproducts.com for more ideas.


Great Pumpkin
The only rear that is useful is the first gen RX7 rear (since all the rest are IRS). A limited slip with disk brakes would be best. I've seen them for as little as $50 and as much as $300. A drum brake/open diff RX7 rear can be gotten for less than $50. They are fairly lightweight.
Gear ratios are similar to Spridgets.

Moser will also shorten your axle housing if you wish.
And you can have them redrill the stud holes to 4 X 4" (although I'd be tempted to have them redrilled to 4 X 100mm since there are so many wheels in that size). The stock rear has 4 X 108mm and there are 13" wheels in that size so you could probably run those if you really wanted to.

If you get an RX7 rear fairly cheap and have Moser do all the work, you might get the entire thing done for $750-ish.
And it would be bulletproof.
You would likely pay more than twice that for a fully set up Spridget rear with limited slip and disk brakes.....and it would probably still leak oil onto the brakes /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

In terms of legality:
For hillclimbs and auto-cross, it's really no big deal.
For road racing: It would be OK with EMRA but you might get a class bump to ST6 (but only if me, Bruce and Pete complain. We won't unless you start killing us in ST7 /bcforum/images/%%GRAEMLIN_URL%%/jester.gif ).

Most of the vintage guys won't really care (but as you know, they won't allow big flared fenders). I think with a local SCCA region, it would depend. Especially if you don't make a big deal about it. I'd guess many local eastern regions wouldn't really stop you unless other drivers complain. In some SCCA regions, the drivers are laid-back like us (EMRA), but other regions are full of drivers who'll want you disqualifed if your SCCA decal is crooked.

At the National level, it would be different and you couldn't run this setup. But unless you just won the Lottery, I wouldn't bother even thinking about SCCA National events. The local SCCA regionals, EMRA races and NASA events are far more fun.

By the way, many top SCCA Spridget racers run a rear with Ford outer hubs welded to the housing, trick axles, American disk brakes and Quaife gear sets. The only thing that is actually original BMC in those cars is part of the housing. So if you think about it, almost no one really is running a truly original rear


2007 GCR, Production Car Specifications, rule 4.b.3:

No substitution of the differential housing is permitted on front engine, rear drive vehicles.................

Rule 4.b.4:
Drive axle shafts, bearings, bearing carriers, hubs and universal/CV joints may be modified or substituted, provided the number of these parts remains the same as the original.

There's a bunch of restriction on brakes, too.

So, by the book, not legal for SCCA road racing. Wouldn't be legal at my home track, either.
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