Motorcycle vs car engine

[sgtlethargic]

Hmmm. Well, the thought I'm entertaining is that grafting the back half of a motorcycle to a passenger compartment (to make a reverse trike) might be easier than and have benefits over a 4-wheel ... errr.

[sgtlethargic]

Originally Posted by Frank Lee

...

That reminds me of another point: motorcycle drivetrains appear to me to be quite lossy. By that I mean, unlike in most cars where the power goes from engine to trans input shaft to output shaft to differential to wheels, bikes usually (always?) employ chains or belts between engine and trans, and after trans too. More chains and belts and shafts and **** means more drivetrain losses.

I don't know, but I did recently read that chain drives are efficient. I'm guessing a motorcycle driveline is also more efficient because the transmission is smaller and lighter, and there's no 5-foot driveshaft or differential (RWD).

[Frank Lee]

Chains are efficient but to my thinking, no chain would be better yet! The GoldWing, for example, has a chain between the engine and trans, then there's the trans, then there's another chain leading to some gears that change the direction of power 90 degrees for the driveshaft, THEN there's the final drive gears which if hypoid really suck up power. And all those whirling shafts on bearings! Sheesh. But yeah you're right about the smallness of the bike trans; small gearsets should consume less power than big ones.

[Ryland]

Motorcycle engines also tend to be air cooled (again, not always the case) and with an air cooled engine it's best to run rich as fuel as a cooling affect.
Motorcycle engines also have very short intake runners, there have been a hand full of people who have made longer intakes on motorcycles and seen low end torque increase and gas mileage increase but they take up space so they are not often used.
But what it boils down to is that even tho a motorcycle engine is a small displacement engine there are a lot of compromises that are made to make it smaller, lighter and produce more HP for the size/weight.

[darcane]

Originally Posted by Ryland

Motorcycle engines also tend to be air cooled (again, not always the case) and with an air cooled engine it's best to run rich as fuel as a cooling affect.
Motorcycle engines also have very short intake runners, there have been a hand full of people who have made longer intakes on motorcycles and seen low end torque increase and gas mileage increase but they take up space so they are not often used.
But what it boils down to is that even tho a motorcycle engine is a small displacement engine there are a lot of compromises that are made to make it smaller, lighter and produce more HP for the size/weight.

I think that may be why even the water cooled engines tend to run rich too. My water cooled motorcycles won't stay warm in temps below about 50-60°F. At that point, there is so much airflow past the engine that the radiator is uneeded at highway speeds.

[BHarvey]

I'd say take a Metro engine, tuned for torque at low revs, gear it tall, and build a rear engine/rear drive car similar to a VW 1L (earlier model).

You'd have the benefit of a car tranny that can be shifted into neutral from any gear so you P&G and EOC would. (Motorcycle transmissions don't like to go from top gear down to neutral at 50mph)

Have it weight 1200lbs or less and a .15 cd should be pretty good.

If I was building a one off car, I'd copy the 1L! (except for engine of course)

[euromodder]

Originally Posted by sgtlethargic

"All else being equal", would a motorcycle or car engine of the same displacement be better for a high-MPG car? In general, don't over-analyze it, please.

All things aren't equal here

If you want to develop a high-MPG vehicle in reverse-trike fashion, I'd think it'd be a lot lighter than a car.

If you can make it light enough so that a 125 or 250cc FI engine becomes an option, it'd beat a small car engine on displacement alone .
(The smallest FI car engines you'll find are likely 1L - I doubt the 660cc Kei cars made it to the US ?)

[Michael Moore]

Most modern motorcycle engines have gear primary drive, not belt/chain and that has been the case for decades.

If you watch the races you'll see that it isn't uncommon for motorcycles to be downshifted multiple times coming into a corner with the clutch only let out once the final gear is selected. It isn't a problem to do that.

You can get in-line reverse gearboxes for use in bike-engined cars. You might even end up with 5 or 6 reverse gears as they go in the driveline after the m/c transmission.

Car engines and transmissions are often not terribly light. A complete 250 Ninja powerplant with 6 speed gearbox/clutch less carbs is 90lbf. A complete Yamaha 250 4T single MX engine is 55 lbf including carb, electrics and kick lever. An SV650 Suzuki twin without carbs but with starter motor is 120lbf and that puts out 68ish hp.

A friend has a Guzzi-powered TriKing

triking dot co dot uk (not enough posts to use a regular link)

and that is light enough that with a little planning he doesn't miss not having a reverse gear. But that can be dealt with as I think Honda did on the big 'wings, by driving the starter motor in reverse when the bike is in first gear. Instant "brief use" reverse.

cheers,
Michael

[Frank Lee]

Power transmission efficiency drops at least 1% with every chain, belt, or gear mesh between the crank and the wheel(s) right?

[jamesqf]

I'd go with practical experience. I've never gotten much over 50 mpg from any bike I've owned (most in the 650-850 CC range, but including a 350 CC Honda back in the '70s). I get over 70 mpg from the 1000 CC in my Insight.

For building a reverse trike, I'd think (on the basis of zero practical experience, of course) that it'd be easier to grab the engine, driveshafts, and all from a FWD car. Maybe look at some of the Locost designs, where there's some practical experience - on the front half, at least. Searching on "locost trike" brings up a bunch of hits.