Highway MPG

[baddog671]

Originally Posted by Mr Incredible

My 98 Z28, 350hp, auto, 3:43 gears will get 20-21mpg in daily driving with the A/C on. 24mpg on the open hiway.

My 98 Mustang, 150hp, 2.79 gets 18-20mpg w/o AC. Hmm, the polar opposite of what you would expect...

[mjswan]

Originally Posted by baddog671

My 98 Mustang, 150hp, 2.79 gets 18-20mpg w/o AC. Hmm, the polar opposite of what you would expect...

In comparison, my '88 Mustang 5.0 5 speed with 2.73 gears has averaged 29.1 mpg over the last 15 fill-ups. Over 95% highway miles @ 58-60 mph. I believe it is the low rpm's which is a function of gearing.

[slurp812]

Originally Posted by dkjones96

People report getting over 22mpg in everyday city driving in their vettes.

Imagine the P&G that sucker probably does? Pulse for 3-4 seconds to 45 and glide for 20-30 seconds down to 30-35 mph.

Well, at least avoid smoking the tires!

[fumesucker]

Originally Posted by theholycow

Imagine a 5 liter V8, and a 2.5L I4 made exactly the same - same bore, stroke, even the same head, just appropriately different cam and crank to keep the firing order even (unlike 1970s Buick V6 oddfire). At any given RPM, the V8 would have to make approximately double the power; and at any given amount of power, the V8 should run at half the RPM. So, given twice as tall gearing, the V8 should use approximately the same amount of fuel to cruise at the same speed.

Engine friction rises non linearly with engine rpm.. I suspect it's close to a square ratio like aero drag. This means the four cylinder turning twice as fast will have more than twice the friction.

When BMW set out to design a fuel efficient version of an existing model in the very early 80's, they used a six cylinder and actually increased the displacement from 2.5 to 2.7 l. Low spring pressures in the valve train, fewer bearings, low rpm torque and high final drive ratios.

In addition to engine efficiency, the Corvette's drag coefficient is .286 vs. the WRX's is .33 to .35 (depending on trim level).

For P&G a Corvette can be thought of as a kinetic hybrid with a large storage system and a very powerful engine.

[theholycow]

Originally Posted by fumesucker

Engine friction rises non linearly with engine rpm.. I suspect it's close to a square ratio like aero drag. This means the four cylinder turning twice as fast will have more than twice the friction.

Well, that pushed the result of my thought experiment far in the opposite direction of what I thought would be realistic, into the optimism zone.

I was thinking it might be useful to start a thread trying to collect a list of where fuel's energy potential goes (mainly, a list of points of inefficiency). It would start with obvious ones -- actual energy required to move the mass of the vehicle, heat produced, aerodynamic drag, engine friction, energy lost reversing pistons, tire rolling resistance, friction in wheel bearings, friction in the drivetrain, parasitic losses to accessories and alternator, etc...

[red91sit]

a little out of context, but can you imagine the gas mileage you would get out of a tiny modern corvette with a Honda 1.6 coupled to it's 5th gear ratio of .5!!! Loost a few hp of course, but ooh so worth it. Maybe turbo it, and get about stock hp with an incredibly empty engine bay haha. Yes there is a mob outside burning honda symbols already...

[baddog671]

Originally Posted by mjswan

In comparison, my '88 Mustang 5.0 5 speed with 2.73 gears has averaged 29.1 mpg over the last 15 fill-ups. Over 95% highway miles @ 58-60 mph. I believe it is the low rpm's which is a function of gearing.

Geez, I got screwed, huh...

[GasSavers_ALS]

Originally Posted by red91sit

a little out of context, but can you imagine the gas mileage you would get out of a tiny modern corvette with a Honda 1.6 coupled to it's 5th gear ratio of .5!!! Loost a few hp of course, but ooh so worth it. Maybe turbo it, and get about stock hp with an incredibly empty engine bay haha. Yes there is a mob outside burning honda symbols already...

I'd love to see the gas mileage of a Saab Sonnet (Cd.32) with a modern 1.6L turbo diesel and a transmission with an over drive. They weighed 1800 lbs with a Ford V4.

[GasSavers_RoadWarrior]

By the way, something the mopar folks notice when they use Ford throttle bodies is that the TPS if it can be used at all it frequently glitchy and is kind of all or nothing, and that the idle bleed screw lets in wayyyyy too much air for MAP metering ECUs, so that might be the cause of some FE issues on some fords. Try hitting the TPS with contact cleaner if you can get it in anywhere and try adjusting the idle screw. Also the MAFs are prone to gunking up, and the 4 pintle injectors Ford use need great care with fuel system cleanliness and biannual fuel filter changes should be a minimum.

[eugeneg20]

its all about the torque the larger the decplacment the greater the torque(usually), and the more torque you have the higher the final gear that you can have. many off the large v8 cant even get good gas miliage below 60mph. so there is an advantage in a larger engine on the highway just like said by the guy that owns owns the corvette, try to get over 30mpg while driving at 75pgh most small decplacment cars cant do it.

i would love to get a corvette since i drive mostly on the freeway and get abo the same mpg