I've owned my '81 Z28 for a few weeks and the gas mileage seems a little high to me. Since I'm new to the car I've driven it easily so far.

Here's the spec:

ZZ4 crate engine, trick flow ally heads held down with an arp bolt set on top of ultra thin metal head gaskets raising compression to 10.5:1, trick flow cam, trick flow hardened push rods, Weiand stealth warrior dual plane inlet with a 750DP Holley carb fed by a 110gph Holley fuel pump, upgraded Davies unified ignition HEI distributor, new rotor arm, new leads and new plugs, full length headers into 3 inch collectors with exhaust dumps, power now estimated @ 460+ bhp all kept cool by a 3 core ally be-cool rad and steel flexi fan with billet reduction pulley, also new battery and alternator just fitted

Drivetrain
Rebuilt TH350 with B&M 3200 stall converter, shift kit, external cooler, and quick silver shifter
Rear end is a rebuilt 10 bolt posi with 3.90 gears

I'm getting 4-6 mpg which I figure is too low, but then again considering the spec and gearing is it?? I will say a fair amount of town driving has been involved, and I have noticed at 70 mph the engine is around 3500 RPM.

Any ideas? Thanks

 

Have you checked the plugs since they were replaced? Using that much fuel, they should be black.

Is the torque converter locking or non-locking?

Is the fuel pump electric and how is the pressure controlled?

 

Wondering if you've ever had it tuned to see if it's running rich or not, properly jetted.

I had a plastic float sink once in a quadrajet, that caused a lot of fuel to flow. Got it rebuilt and fixed that problem. Since you're using a Holley I'll guess it's not the same problem but worth checking on. But what do I know?