Okay, a month ago, I did a 314 mile trip one way on I-90 between West Springfield MA and Rochester NY, top down, windows down most of the way, cd playing, cruise control at 73 MPH (rolling average of 71 mph, average with stops built in 62 mph) , 4 or 5 "pit stops" with reasonable accelaration(no Vtec) to speed from the rest stops and got just a bit over 30 mpg. OEM tires and rims, no mods.Weather went from cool and cloudy to warm and sunny, no appreciable wind.

 

cruise control is the "magic word". A 62 mph average speed is damn good for having stopped 4-5 times during a 314 mile trip.


Again, the magic word is "reasonable acceleration (no VTEC)"

If you accelerated slooowly up to 55 mph, say 1st 15 mph, 2nd 25 mph, 3rd 35 mph, 4th 40 mph, 5th 45 mph and 6th up to 55 mph and held it steady at 55 mph in 6th gear for an extended amount of time, you would most likely exceed 30 mpg.

 

The engineer types will tell you that the best mileage from a conventional throttled gas engine is obtained at WOT but low engine speeds. The throttle plate blocks airflow which creates pumping losses, but running at high engine speeds increases friction. So while bogging may be bad for your engine, it is theoretically the best for mileage. In fact one mech e told me that when they used to have coast to coast mileage challenges in college, they would do repeated cycles of WOT in top gear followed by coasting. Of course you would need to coast in neutral if you really wanted to get all the benefits.

Ideally, you could get ridiculous mileage if you had a series of rolling hills. WOT in top gear on the downhills, coast up the hill, rinse and repeat.

None of this is practical in the real world though. And I've noticed my own S2000 doesn't seem to care if I use a light throttle/lower gear vs. open throttle higher gear. Probably because the engine speeds we run at for decent acceleration and engine health are too high already for optimum efficiency.

This principle is also one reason why hybrids get good mileage. Most cars have to have an engine with much more power than is necessary to maintain speed, for situations like merging, climbing hills etc. Then most of the time you are just cruising around at part throttle, choking the engine with pumping losses. With a hybrid, you can run a much smaller engine and run it closer to WOT, then the electric part comes in when you need extra power.

This principle should not apply to engines without throttles, such as diesels and BMW's new Valvetronic gasoline motors.

Peter

 

Less engine speed = less fuel used.

 

The hybrids that I have read about work the opposite, They run on electricity from 0-45 mph, then the gas engine comes into effect.

 

For some reason, I dun't think this works when doing 135 mph

 

[QUOTE=PoweredByCamry,Jun 7 2005, 07:07 PM]The engineer types will tell you that the best mileage from a conventional throttled gas engine is obtained at WOT but low engine speeds.

 

 

pick up a used tespipe for under $100. Bam, instant gas mileage increase.

 

I mentioned radio considering aftermarket high wattage systems. 250 watt comes to roughly .5% for a 75 hp average engine output.

Skipping gears does have a small impact since the car is getting 0 mpg while you are out of gear. I believe the Corvette makes this a standard feature.