The Quick-Change for the jitney project came in yesterday morning. I didn't know what the deal was going to be as far as how it was going to be delivered but I got a phone call on Wednesday from the shipping company - straight truck with a lift gate some time between 8:00 and noon. All I needed to hear. The driver put it on the gate with a pallet jack and then rolled it into the garage for me. Nice guy, great service. Thank you, Dayton Freight. I did get a chuckle out of the fragile sticker on the carton. This thing is supposed to be good for 600 horsepower. Not what I'd consider fragile, but it made it here safe and sound and that's all that matters.
Page from the 1972 Motorcycle Repair Manual that I've had since 1972. There's a wealth of knowledge in the book. While much of the stuff for individual bikes is outdated, unless you happen to be restoring one of those particular models, like a BSA 650, the math in the back is most helpful. And math never goes out of date. So it's time to do some cipherin', Jethro.
The ring and pinion in the differential is 4:33. The transmission is 1:1 in high gear and the rear tire is a tick under 32" tall. According to the formula MPH = rpm x effective rear wheel radius / overall drive ratio x 168. That gives me 5000rpm x 15.75 /4:33 x 168 = 108 MPH. The effective rear wheel radius I figured for a tire 31.5" tall to account for it getting a little shorter with the car weight on it. So if I put quick change gears in the differential with a 1:1 ration, that's what I'd be looking at.
23/25 gears would give 117 mph on the high side, 100 mph on the low side
22/25 gears would give 123 mph on the high side, 95 mph on the low side.
All of these numbers are figured at 5000 rpm and make no allowance for horsepower numbers. The car is going to be pretty light, so the Slant Six should be able to pull to a 5000 rpm redline in high gear. When I looked into going to Bonneville, as long as you stay under 125, a regular operator's license is adequate, so the 22/25 change gears would be right in the ballpark.
Even though the diff is tagged as having a 4.33 ring and pinion, I'm going to double check that. The catalog listing says3.78. When I'm sure of what I've got I'll order the change gears, a couple of gaskets and some oil. I've already got the brake parts and axle studs, so I don't need much more to get it under the car.
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