Went for a 3 hour drive today (highway). Got 26.8mpg! I have an 83 Z28, stock LG4, stock exhaust, 105K miles. (see signature below). Very pleased.

 

Sweet..I don't even get half of that...

 

Going to thirdgen nationals I got an average of 18. That was with 2.73s and a 700r4 before the cam swap. I get better now actually. Now that I actually learned to tune my carb.

 

Before you get too excited, are you sure you filled the tank to the same point both before and after? It's not uncommon for me to be able to put another 2-3 gallons in after the nozzle first shuts off. If you stuffed it full before you left and just let it shut off after getting back, you could have actually used another gallon or so that you didn't count, so mileage could have been in the 22-24 mpg range. If your mileage with the next fill-up is especially low, you'll know that is the case.

However, what you're saying isn't completely out of line. My nephew had an '86 Berlinetta with the LG4, and when driving from Iowa (where his parents lived) to New Mexico, the car quit on him just past the Colorado boarder. They had it towed to a dealer, who replaced the coil & module, along with a full tune-up, and he averaged 27 mpg the rest of the trip driving 75-85 mph (or so he said). The car had about 120k on it at the time.

I also got a little over 27 with mine before the mods on a round-trip to Nebraska, ~100 miles @ 75 mph, ~250 @ 65 mph each way, when the engine had about 135k on it (and a bad torque converter). A couple of years ago my wife & I took it on a mountain trip and averaged 20 mpg (after the mods). Those are the only two times I've had it out of town. If I fill up before and after driving to the airport (~50 miles one way, of which ~45 is freeway @ 65-70 mph), I can get 20-21 mpg. I get around 16 mpg with my daily computer (was about 18 before the mods).

The only proper way to check mileage is to keep records over an extended period over several tanks (I record mileage and gas with every fill-up). But, few of us drive a consistent pattern over several tanks to know for sure what "highway" or "city" mileage we're actually getting. You could also get one of those trip computers that actually measure the amount of fuel used and miles travelled, which can be more accurate than the gas pump.

So, just goes to show you don't have to have fuel injection to get decent mileage. Another reason I'm a fan of the CC q-jet for the driver.

 

Very good point about filling to the same level before and after. I actually went to the same service station, to the same pump (to ensure that the car was on the same grade) and as all of you are aware clicked off several times after the first click. Thirdgens are really funny about "fooling" the nozzle into think the tank is full when you can get 1-2 more gallons in. So I think it is pretty accurate. But the long term test would be better, if I could keep my foot out of the secondaries.

phil

 

I get roughly 1/3 of that

 

8mpg here!!!