Engine efficiency

[merccom]

so your talking about an engine that is physically the size of a big block chevy that puts out about 31 horsepower

[drmiller100]

Originally Posted by pete c

Sure. I'd prefer chocolate though.

it would melt and you might remember to breathe.

[drmiller100]

low rpm means you might get more of the energy out of the fuel. smaller engine means lighter car (and once we remember basic physics, lighter cars get better mileage).

back to an earlier question, but lets put some real numbers to it. Lets say our car needs say 22 horsepower at the wheels to go 70.

Are we better off with a 500cc engine turning 4000 rpm, or a 1500cc engine running 1300 rpm?

both numbers assuming 10:1 run from

Rough Engine Horsepower Determination Program

FWIW< the calculator is shockingly accurate as an upper goal.

[Frank Lee]

Ooooooh, I gets it nayuh!

Did da maths and my hypothetical 3.8" x 9.8" mini-MAN, at 1/1000th the displacement, has a 10x surface area disadvantage. Guess everything should be a monster single cylinder.

[user removed]

According to WIKI the 1990 Audi 2.5 TDI was 42.5%. Heck that was 22 years ago.

regards
Mech

[user removed]

Originally Posted by Frank Lee

Ooooooh, I gets it nayuh!

Did da maths and my hypothetical 3.8" x 9.8" mini-MAN, at 1/1000th the displacement, has a 10x surface area disadvantage. Guess everything should be a monster single cylinder.

Frank, you done gone from teachin to learnin. Must be the solar flare .

regards
Mech

[NeilBlanchard]

Yes, rolling friction is a total loss, and it is reduced by lowering weight. Steering and suspension geometry can be fine tuned for lowering rolling resistance.

I think that something along the lines of the Energy Return Wheel (with proper aerodynamic streamlining!) would also help reduce rolling resistance. And if those (non-inflating) are less able to absorb the small bumps, then I think that a scaled down version of the Levant Power regenerative shock absorbers could be a useful piece of an uber-efficient car.

[Ken Fry]

Originally Posted by drmiller100

back to an earlier question, but lets put some real numbers to it. Lets say our car needs say 22 horsepower at the wheels to go 70.

Are we better off with a 500cc engine turning 4000 rpm, or a 1500cc engine running 1300 rpm?

You can use the same Saturn chart. The Saturn shown produces about 120 bhp at 5500. So a 1500cc engine like it would produce 90 HP, and 500 cc engine would produce 30 (which match the calculator numbers for 5500 rpm). The chart torques would be multiplied by 120/90 for the 1500, and 120/30 for the 500.

I think you'll find the two engines very close in BSFC at that HP.

[oil pan 4]

Originally Posted by merccom

you can scale it down, the problem is making useable power in a vehicle size package.

remember that thing only spins about one hundred rpm. if you scale it down to 18wheeler engine size you'll only be making 20 or so horsepower

figure your average detroit makes around 1100 pounds of torque at 1200rpm

if you take that same 1100 ft/lbs and drop it back to 100rpm

you have 1100ft/lbs * 100rpm = 110,000/ 5250 = 20.95hp

so you have a road tractor engine that puts out 21 hp.

it would make an awesome stationary engine for a small generator.

You could put a 2 stroke diesel in an on road vehicle.
You cant turn it at 100rpm, it will barely run.
The smallest 2 stroke diesel I know of that you could get in an on road passanger vehicle would be a detroit diesel 4-71 engine and it would have to go in a big truck sized vehicle or at least a small bus since the engine is so tall.
The regular 4-71 makes about 110hp, there is a turbocharged version that makes a little more power. Max RPMs is about 2250.

[pete c]

Originally Posted by Old Mechanic

Frank, you done gone from teachin to learnin. Must be the solar flare .

regards
Mech

That's weird. I thought them solar flares only affected me like that. Why, during a particularly strong flare up, I feels like I'm almost as clever as doug.

Almost.