26.8 mpg is pretty good, I don't see you getting much more out of it, and even if you could, it seems like the money required to do so would negate your mpg increase.

 

I'm really not going to pursue the whole turbo idea. It's expensive, complex and very limiting. That is more useful on diesel engines that can withstand constant boost. I'd hate to see a headgasket on an LT1 that had to deal with boost for 3.5 hours straight.

 

That is totally true, but the money I spend on mods will also help me at the track.

I'm just curious to see how efficient this car can actually be. The #1 mod is going to be adjusting my driving style.

 

Not if the stock tune has a part-throttle A/F mixture that is pig-rich.

 

Just to be clear: Yes, I understand that the OP doesn't want to spend the kind of money that would be necessary to make something like this work. I'm just discussing.

So replace the pistons with something more heat-tolerant. Titanium, carbon... there are options. I'm not saying it wouldn't be expensive.

Put enough money into it, and you could find a way to make it work well.

I know that. That's how a 5.7L V8 gets 26-27mpg on the highway. The OP is looking for 30. I'm looking for ways to make his engine even more efficient at those low RPMs to help him get there.

 

I would say talk to trifecta performance and see if you can buy one of their tunning devices and set it up with a high MPG 87 octain tune and a performance tune.

This way you put in the high MPH tune for your weekend drive and then use the performance tune for at the track or whenever.

I have thought about it a while ago but i just bought a beater 4cyl car instead.

 

True, but it would probably still be one of the fastest 30mpg cars around.

 

Not as long as there are still LS3 M6 Corvettes.

 

Change trans and diff fluid to some royal purple. Reduce some friction, I'm sure it will add some extra miles if you have not done it yet, plus it's not too expensive and regular maintenance could not hurt. Some platinum plugs and do a BG or Valvoline intake service.

 

That's odd. I think the only factory M6s that came with 3.23s were '93s (some of which also came with 2.73s). I'm guessing your car had the rear end replaced at some point with a unit out of an automatic car.

Also, I believe the torsen differentials were not used until '99 for 4th gens.

 

he has a flowmaster...probably hurting mpgs

and the tires you have up front...are the incorrect size I think. that maybe throwing your speedo off/odometer

 

I'm sort of on this quest now, not as seriously as the OP, but I still am looking for mods that improve power as well as mpg. Looking for overall increased engine efficiency. So far, it seems to have worked with an average of 1-2 mpg increase but I'm always looking for new ways to improve.

Some things I've thought of doing:

Lighter rims/tires
Some weight reduction
Improving aerodynamics in the front of the car
Removing the cat and going to a smaller, lighter, higher flow muffler

 

I usually get 28mpg on the highway.
Do a tune up such as new O2's, plugs, wires, cap and rotor kit, and fuel filter ect.
This will bring your car up to its best running potential.
Electric water pump does help too.(less drag on the motor)
Don't bother with the UD pullies they are useless on the LT1.
If you get long tubes, make sure you get it tuned. Tuning is everything for the best MPG
The Cat back is not hurting him because he is not racing it, only driving it.
Make sure you cats are not plugging up.
Who cares what other people think.
Most self proclaimed enviromentalists drive a suv and drink coffee from a styrofoam cup.
If you are really worried about pollution, convert your car over to propane or natural gas.

 

in stock configuration, you will see better highway mileage at 80mph than 60mph. If you had straight highway driving and could cruise @ 80mph, you would get 30+

any stray from this scenario and you will see < 30 mpg

 

You could get two programmable wideband O2 sensors (one for each bank) and program the output to fool the PCM into a leaner AFR than 14.7. I'm not sure what level is safe, but if I'm not mistaken, it is set at 14.7 to minimize emissions, not for best fuel economy. Theoretically, you should be able to improve mileage dramatically this way. Of course you might melt engine parts or the cats if you go too far, but I think this would work. A tune would also be in order for this mod.