quote:
Originally posted by moribundman:
I find it the gas mileage some of you guys get out of relatively large engines amazing. While my old VW Scirocco (1.8l 95 hp) got about 33 mpg, my Chevy (2.8 V6) and Buick (3.0 V6) got maybe 20 mpg. And my Audi (2.8 174 hp V6) rarely exceeds 28 mpg. Do you all coast in 5th gear at 40 mph or what?
Why limit yourself to 5th gear
On my 96 Corvette LT4 6 speed, the engine only turns about 1600 rpm at 70 in 6th, which is a 0.49:1 overdrive! It's strictly an economy cruise gear. Gearing makes a big difference in economy if your engine has broad power range and can pull the gearing.
I run right about 27 mpg on a long highway trip at about 70 mph. I have to go to take me directly to jail speeds, or run in too low a gear to get below 25 mpg on a long highway trip.
On my last highway trip I tried running in 5th (0.74:1) a couple of times at 70 mph and about 2400 rpm and mentally averaging the instantaneous mpg readouts. 5th looks like it gives about 3 to 4 mpg less than 6th under those conditions.
I'm not a GM fanboy, but GM has done a very good job at getting fuel efficiency out of some of their engines.
At 1600 rpm, friction loses are lower, and the engine is only trying to pump 2/3 as much air. As long as they can tune it to run right at those speeds, the engine is acting like it's only 2/3 as big in 6th as in 5th.
It also helps that Corvette is relatively light car at 3200 lb, has a small frontal area and low coefficient of drag. Those economy features are partly off set by the steam roller width tires
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