I am in the beginning process of gathering parts for putting a 2001 Honda CBR 900RR (929cc) motor into a MG Midget that was graciously donated by my father in law. I found a motor, harness, and radiator for 300 bucks with a free car that is currently motorless and ugly but generally solid. I think this think could make quite the little racer. FYI - this is NOT a street car. This is for dirt racing/auto-x (trailered) I realize that 1st gear will be useless and my top speed will be like 90mph but I cant really say I care. This is supposed to be really fun and really cheap.
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Jan. 27, 2012 9:00 p.m. singleslammer New Reader
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Jan. 27, 2012 9:01 p.m. EvanB SuperDork
I had an idea like that awhile back. I wanted it to be streetable though.
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Jan. 27, 2012 9:41 p.m. aeronca65t Dork
I bought a '73 Midget recently, for the purpose of donating its 1275 cc engine to my vintage race Spridget (after rebuilding).
But the car is pretty nice (under 30,000 miles) and very solid. So instead of chopping it up, I'm putting a 1958 Austin 948 cc engine in it (it's a direct bolt in). This engine has been sitting around in my shed for years but I know it runs.
With 35 HP, I expect it to be stupidly slow.
But probably great on gas.
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Jan. 27, 2012 10:30 p.m. RexSeven SuperDork
Bike engine swaps into little roadsters sound cool, but there seem to be a lot of challenges to it. Of course, the only one I have any familiarity with is the MotoIQ Miatabusa. Maybe it's easier with the older cars. I'd bet there's a lot less wiring involved and that a Midget should be light enough to push that not having a reverse gear is no big deal.
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Jan. 27, 2012 10:33 p.m. unevolved Dork
singleslammer wrote:
This is for dirt racing/auto-x (trailered) I realize that 1st gear will be useless and my top speed will be like 90mph but I cant really say I care. This is supposed to be really fun and really cheap.
Are you using the MG gearbox, or something? Otherwise, that statement doesn't make much sense.
If you've got 22" high tires, a 2001 900RR gearbox geared to top out at 90 mph will hit 37mph in 1st gear. I'd hardly call that useless. Granted, when you stay with a more "normal" final drive ratio (that's a final drive of 4.62:1, so let's try 3:1) you'll top out at 140 and 1st gear will take you to 57mph.
That's the great thing about sprocket cars, you can gear them to whatever you want.
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Jan. 27, 2012 11:21 p.m. singleslammer New Reader
Yeah I plan on fabbing a drive shaft. I haven't run the trans vs rear end numbers yet so the 90 MPH top speed was a guess. Frankly I don't care. This car will probably never break 60 so it doesn't matter this is solely because I can and it should be stupid cheap and fun
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Jan. 28, 2012 8:15 a.m. mad_machine SuperDork
I don;t know of the HP numbers of the CBR engine.. but gearing wise, I know my fiat spider with an almost direct ('it's slightly OD at .9 to 1) fifth and a 4.40 rear will hit about 115 just before a 6500 rpm redline
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Jan. 28, 2012 8:20 a.m. singleslammer New Reader
I see what you mean... heck no I'm not using the mg gearbox. Why would I sacrifice a wonderful, all in one, sequential shift, dog box trans for a 40 year old British box. Reverse? Nah, because race car. Haha...
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Jan. 28, 2012 8:25 a.m. singleslammer New Reader
mad_machine wrote:
I don;t know of the HP numbers of the CBR engine.. but gearing wise, I know my fiat spider with an almost direct ('it's slightly OD at .9 to 1) fifth and a 4.40 rear will hit about 115 just before a 6500 rpm redline
The main issue with bike motors are their primary reduction drive. So you have to multiply the initial gear ratios by the reduction drive, usually 1.5 or similar. In a car this means you need a very tall, numerically low, rear end to make it streetable. That is not really an issue here.
