Fuel Economy

[imprttuner88]

I am in the search for a clean 4 door shell to turn into my DD project and am considering a multitude of stock engine swaps. I am looking for sporty, more power than the M20 but 100% stock save for exhaust and intake. What sort of real world MPG's are you guys seeing with the OEM BMW swaps?

TIA

[george graves]

I've been curious about this as well....

....but didn't want to sound like a penny pincher - it's a bit odd to worry about gas mileage considering what this swap costs - so I'm glad you did! ;)

[dirty30]

I got 20 over the weekend driving through the mountains in WV. I've seen 22-24ish

[imprttuner88]

Is that mixed use or just Highway?

[Northern]

1990 325i/is seems to be rated 16/20MPG and a 2001 540i seems to be 14/21MPG... so in a lighter chassis, fuel mileage should be abysmal since all you're going to want to do are burnouts and powerslides.

[kevinbednarek]

My '84 M62 E30 got about 27mpg on my trip across the country with a passenger and a bunch of luggage. That's cruising about 85-90. Through the rockies I got about 23. But I was hauling ass.

[imprttuner88]

That's damn impressive

[totheredline]

Well heres what Im thinking, feel free to dispute this with me. = Part of the reason diesels get such good gas mileage is because of their good low end torque. Torque is what is needed to keep speed up on the highway, you don't need a lot of hp when cruising.
A big torqueeey V8 is kinda the same deal, couple with the wonderfully light little buttercup E30 and there ya go.

[nando]

No, its because diesel has higher energy density.

[Ryann]

^You've got it backwards. Torque translates into acceleration while horsepower translates into the ability to maintain a given speed.

[nando]

^You've got it backwards. Torque translates into acceleration while horsepower translates into the ability to maintain a given speed.

Thank you, yes!

[totheredline]

So diesels generate horsepower at lower RPMs and v8s kinda do the same thing?

[nando]

yes they make more power at a low RPM but V8s do not get better fuel mileage than 4cylinders, do they?

the reason is energy density. a gallon of diesel simply contains more energy than gasoline. just like ethanol contains less energy than gasoline, and fuel economy drops by like half with E85.

[totheredline]

^I get what you're saying about energy density. makes sense

yes they make more power at a low RPM but V8s do not get better fuel mileage than 4cylinders, do they?

Well I think at a point it requires more fuel for a little baby 1.8l 4 to work its butt off to pull a car than it does for a larger displacement v8 to barley break a sweat pulling the same weight. Im just speaking hypothetically. No you're right though, a v8 normally wont get anywhere near the gas mileage of say an m42 engine car.

[nando]

Nope - pumping losses. A 4cyl is still more efficient. Actually, an engine is more efficient at high load than with the throttle plate mostly closed, which decreases VE.