Interesting. I believe that is a world record for a C5.

 

Hmmm, so along those lines.... we would need to remove several hundred pounds of weight to make the 5.3 "equal". Sorry, I ain't giving up my ac.

 

Accelerating accounts for most of you mpg number. It takes a lot of steady driving to recover from an acceleration burst that sucked a relatively large amount of fuel. A smaller engine is likely less efficient because the gearing tends to be steeper and the engine is revved more between gear shifts when accelerating. It also probably revs higher while driving a steady speed. A bigger engine is likely more efficient because it has steeper gears and is shifted sooner and also revs lower while driving a steady speed.

You actually tend to get better efficiency when you operate at a lower rpm with more throttle then when you operate at a higher rpm with less throttle.

A 4.3 V6 won't happen easily, They are based on the earlier generation of V8 engines.


Just slow down until you're running at 40mpg or try 2.73 gears in a manual car. My car would likely pull 40mpg on a flat level road with the cruise set somewhere between 50 and 55mph.

Everyone "talks" about doing "this" and doing "that" to get better fuel mileage, yet you actually can increase your highway mileage by just going slower. Going slower isn't acceptable though.

Peter

 

FWIW I got a best of 33mpg on a tank back when I was cam-only stock gears running 11.9@119. On that road trip from Pennsylvania I averaged 30.7mpg and 78.9mph over the 1500miles, ran it up to 100mph on a flat stretch and was logging 25mpg. After the stock bottom end 346 goes 10.5 this fall, maybe I'll pull it and give this a shot. 5.3 and 2.73 diff would be cheap to pick up, it's the labor that almost wouldn't make it worth it plus the car would feel SLOW. I'd like to add an UDP to my mod list as that should promote low rpm effiency along with the other things.

 

Well if you're going to do this you might as well use the latest technology. Say a 3.5 litre V6 with direct injection and twin turbos. Power went you need fuel miser when you don't. Porsches 911 Turbo S uses a flat 6 @ 3.8 litres makes 516 lb/ft buy 2100 RPM.

My last family sedan was a Speed 6, 2.3 litre direct injected turbo charged inline for. Car made 280 lb/ft of torque. I could do 95 mph down the expressways for 375 miles on one tank.

Displacement is but one part of the equation.

Now if you really want to go exotic direct injected 2 stokes are making amazing power without the emissions issues 2 strokes are infamous for.

 

 

Until you slap on a turbocharger. I think the future will see more smaller displacement turboed 4 and 6 cylinder cars/trucks. Ford is doing this with their new F150. You get good gas mileage when off boost, and get good torque & power when on boost. If done right, the turbo gives the best of both worlds. Turbo = "displacement" on demand. Of course to get good gas mileage, you'd have to baby it and stay off boost as much as possible (ie, drive like grandma to church).

If I recall, isn't GM thinking of a twin-turbo V6 as a possible power plant for the C7? If so, hopefully the big displacement V8 will also still be an option.

 

Yep one of the EcoBoost family of engines. Direct injection and turbo chargers. http://en.wikipedia.org/wiki/Ford_EcoBoost_engine

The engine in the F150 makes more torque then the V8 and comes to peak torque much sooner.

The technology is not foreign to GM either. It was used in the Pontiac Solstice GXP. "The engine's output is 260 hp (193 kW) and 260 ft·lbf (353 N·m). This is the highest specific output of any engine in the history of General Motors at 2.1 hp (1.6 kW) per cubic inch, and it is the first gasoline direct injection engine from an American automaker. "

http://en.wikipedia.org/wiki/Pontiac_Solstice

For those that know forced induction the Ford engines run 12 psi, the one in my Speed 6 ran 16. The compression ratios aren't reduced either 10:1 in the Ford engines. That's 2 to 3 times higher boost pressures then what you would normally see from an OEM. 1500-2000 psi fuel rail pressures and direct injection make it all possible.

For those of you that are tuners you'll appreciate the value of these numbers regarding the air fuel ratio in these engines. "The stoichiometric air-fuel ratio for gasoline is 14.7:1 by weight, but ultra lean mode can involve ratios as high as 65:1 (or even higher in some engines, for very limited periods). These mixtures are much leaner than in a conventional engine and reduce fuel consumption considerably."

http://en.wikipedia.org/wiki/Gasoline_direct_injection

I think Colin Chapman would have been very excited about these engines. It would have been in keeping with his idea that keeping weight down is the answer to superior handling and performance. A light weight car that doesn't have to give up power.

 

and get under 3 mpg

 

Take a look at this: http://forums.corvetteforum.com/c5-g...post1577558442