Formula GRM: My New Challenge Project

Why make, when you can bolster the economy? Taylor Race Engineering.

A typical Solo B Mod car will run sprockets on the order of 13F/46R that yields about a 3.53:1 ratio. My B mod runs a 12F/46R (3.83) and I end up running most courses in second and third gears with an 11,600 redline and 22 inch tall rear tires.

When calculating your overall ratio or your speed in gears using a bike engine/trans, don't forget to factor in the primary reduction ratio of your particular bike engine.

I didn't realize chain drive was an option?

I appreciate every suggestion, but don't lose sight of the fact that this was to be a Challenge build. I have $500 into a bare chassis with nothing to sell off.

I'd love to buy all the fancy bits and build a supercar, but I only have another $1510 to work with. I need to salvage and fabricate.

FJ1200 yamaha motors are used in the Dwarf series. I'll bet you can score one of those pretty cheap. Maybe with an adapter already installed so you can use a driveshaft.

Another option would be an older Goldwing motor. Flat 6 powered and driveshaft already setup. I think some of them even came with an electric reverse.

If you not afraid of the rotaries you could even slot a 13B in there and have a riot good time.

mblommel wrote:

Woody wrote:

wearymicrobe wrote: First I love the idea of this. But could you do a ford motor with the same dimensions as the formula motors. They run 1600 pintos right.

A Ford engine would be cheap and easy, but getting a Hewland gearbox in under the Challenge cap would be tricky.

Maybe make your own "Hewland" with VW bug box with a flipped ring gear? Weren't some of the first Hewlands VW boxes turned upside down with beefed internals? Kennedy makes adapters but they are $$$. If you have access to a CNC you could make your own adapter. Check out Hewland MK1

There are tons of adapters out used on the market for the VW's.

You can also use a Audi 90 box flipped like the VW's. Its a kit car trick from way back, they can be built up to hold pretty decent power (500hp ish) and they are cheap and plentiful.

The 914 guys use them with the LS swaps as well. So I imagine that with your limited weight you could get away with a stock one.

The Audi 90 box is the same as most Audi's, 924/944's up to the late eighties.

Swaps are starting to become more prevalent, but the money invested in raw material might still push it over budget.

WAIT! there is a "special class"? is this for non-road-initlaly-cars, race cars?

"5. Only Production-based passenger road cars are allowed in the regular competition. All Locosts, race cars, kit cars, Zambonis and the like are allowed only in the Special class "

In reply to Woody:

From looking at the pics of your chassis I'm guessing the tranny is a structural member and rear suspension pickup points are supposed to be located on it. Are you going to build a tube back-half ? If not a North-South VW or Audi tranny might be a better option as it would retain this type of design. Of course you can cut and weld your way to anything you want.

Yes, I plan to build a short, tube back half to carry the rear diff and the rest of the suspension. If it was not going to be a Challenge car, I'd probably mate a Miata engine to an Audi or 944 transaxle, but I'd prefer to keep it bike engined and light.

Skip the diff, just put a sprocket on a tube for an axle. Or look for a Merkur rear end, that's basically the same Sierra rear that's found in a bunch of Locosts in the UK. Since you can buy a complete running XR4Ti for a case of beer, seems to me the diff should be cheap. I don't know if they came with LSD though and I have no idea of the rear end ratio.

Keith wrote: Skip the diff, just put a sprocket on a tube for an axle.

Sure, that would be easy (and fun!), but I fear that it wouldn't turn.

What's the advantage of the Merkur vs the Miata rear?

I pretty much planned on getting a Miata for the uprights and steering and a bunch of other stuff. Maybe I should consider a Merkur.

In reply to Woody:

You'd be surprised, with a light enough car you just get some chatter as the inside rear gets scrubbed. Tires wear faster, but properly setup can be just as fast a differential.

I'll try to dig up some pictures of the chain drive diffs I built. I think it can be done simply, but since this is a challenge car, I would stick to stuff that isn't custom and can be dragged out of a junkyard for cheap.

Chain drive IRS is great, but if it takes a dump the day before challenge, you're boned.

Here's a link to some free FF bodywork: http://www.apexspeed.com/forums/showthread.php?t=37962

Per Schroeder wrote: Here's a link to some free FF bodywork: http://www.apexspeed.com/forums/showthread.php?t=37962

If the seller means Marietta, GA..I'm in Acworth (about 10min away) if you need someone to go pick it up.

RossD wrote: Why make, when you can bolster the economy?

And he's got TWO MORE DOLLARS to use!!!!

EDIT: Ooops! Sorry, Ross...I didn't see Woody's post. I wasn't trying to be a shiny happy person, I thought I was making a joke.

+chalkboard noise I must read entire thread before posting. I must read entire thread before posting. I must read entire thread before posting. I must read entire thread before posting... -chalkboard noise

Hmmmmm.............If you are going to backhalf the thing anyway: 2 moderate sized snowmobile motors, each driving a sprocket mounted to the junction of the stub axle and CV on each side of a miata diff. Use a Miata viscous diff(free or almost so) to provide a bit of overrev protection. Heck, snowmobile motors that small have to be pretty much a giveaway.

1980's Mercedes sedans have independent rear suspension and very tall (low numerically) differentials.

I restored an '87 560 SEC and it had a 2.46 with limited slip. When I replaced the original, whining differential, the complete used diff cost me $150.

There's a junkyard in Massachusetts with twenty-plus old Mercedes in the yard and the parts are practically free if you take them out yourself.

I was thinking that short gears (high numerically) might work with a 600cc engine and a six speed.

friedgreencorrado wrote:

Per Schroeder wrote: Here's a link to some free FF bodywork: http://www.apexspeed.com/forums/showthread.php?t=37962

If the seller means Marietta, GA..I'm in Acworth (about 10min away) if you need someone to go pick it up.

Per and Friedgreencorrado:

Thanks for the link and the offer to pick it up. Connecticut is a long way from Georgia, but I did send him an e-mail. We'll see how this goes.

How about an old BMW rear end? I think some of the 2002s or E21s had 4.10's.

How about an old BMW rear end? I think some of the 2002s or E21s had 4.10's.

Also, I wonder if a CRV/RAV4/etc rear diff would be lighter than a Miata diff.

I always think about that whenever I'm behind a CRV at a light. You can see the whole thing.

I'm trying to keep my parts donors to one car and one bike, though.

Hey, you're in CT. I don't really have much to offer, but I do have a CBR600F2 engine w/carbs if you're interested. I'm just outside of Middletown.