As part of my work, I drive a lot 45-50k miles a year. I have a nice 2010 Taurus Limited with a 3.5 na engine. It is quite comfortable and averages 26-27mpg depending how fast I drive on I95.

I have been thinking about buying a 2007 C6 and building a smaller 5.3 or even 4.8 LS that would be efficient, get better mileage, last 110K miles and run on 87 octane.

Has anyone done this or though about super efficient low compression combinations. Like light weight rods, pistons, valve train etc...

 

Easy enough to get 27+ mpg with stock M6 C6 @ ~70 mph.

 

Understood. I usually drive 80-85. The stock C6 still takes premium right?. I would like to get better mileage through less displacement and higher efficiency while burning cheaper gas not caring about how much hp it makes.

 

Toyota Prius?

 

A smaller cube engine running 80-85 mph could cause you to use more gas pedal reducing your current MPG. Maybe reduced compression on your 6.0/6.2 so you can run 87 octane?
Have you done the math on the costs of the changes compared to the higher cost of 91 octane?
One more thought. Lower rear gears to reduce the cruising rpm?

 

Prius? Thanks but no thanks. I have thought about the costs - I was just batting around the idea...

 

I think about well put together and thought out combination paying attention to quench etc well make for a efficient engine that can be somewhat octane friendly depending on cam events. Smaller engines work harder to accomplish the same results as bigger engines. Jmo

 

I understand wanting to save money on fuel. But no Corvette has ever been marketed as an economy car. I've had an LS7 in my C5 for almost 20 years. I can get an actual 23mpg on the highway. I guess my point is this; I'd never emasculate my Corvette. I'd never go from even an LS1 to a 4.8 or 5.3. If you are considering a 5.3, I'd build it for boost, a turbo. This is what the OEMs are doing for maximum power AND economy. I believe you'd be very sorry if you go to a 4.8 or 5.3 N/A.....

 

Fwiw, the best way to get a gallon of gasoline to go further is to squeeze it harder…compression. It’s why the LT’s have such a high compression ratio…fuel economy. The Gen6 coming soon will have even more, and from what my insiders are telling me, it’s going to be a Coyote engine on steroids. We shall see I suppose.

 

Does that mean GM is abandoning pushrods all together?

 

You are thinking too hard, getting the mileage out if a Vette is easy. It's all load abd rpm. You can get near 30mpg hwy with a 6.2, proper camming, proper gearing, etc. Building a tiny motor isn't the answer, it's all load based to get mpg.

 

Thanks guys.

 

I've been building a 30mpg 750 rwhp C6 in my head lately. During the slack times on the farm, the mind wanders a bit

It involves a 4.8L crank in an LS3 block (337 cubic inches?). Also, flex fuel and a TVS blower needs to happen. 12.5:1 static with a 215/236 115 high lift cam. Run it on 93 octane unleaded for the 30mpg and E85 when the 750 at the wheels is called for.

My version of what the OP is looking for.