Best scenario is a ‘383 ci’ with a ‘low rpm ,high tourque RV cam. Tranny must be of an overdrive spec-( some manuals offer more than one level of overdrive). Maximum rpm-mpg ratings are giv’n for big-block R-V’s . Given what you what I’d say if you have an all-aluminum small block pressing through a 6-speed manual overdrive you might achieve what the factory 300hp.,350ci.,t-350, 290 rear axle(non posi) ,factory original ‘70 Monte Carlo actually did for many years after it was on the road. It always got 22 mpg at 60 mph. Right rear tires had to be replaced at a 3-1 margin compared to the rest. My ‘71 Lemans got 5 mpg at best with it’s 400hp-455ci.

not good i would say about 9-10 on the 383 and 5-6 on the 502 if you want gas milage drop in a 305 or 327

well i have a 1974 nova hatchback and it has a 350 in it and it gets better gas mileage than a 1999 4 cyl. staurn 3 door
i get about 30 miles to the gallon

2-4 MPG CITI

383=15 mpg
502=roughly 10-12
540=buy a gas station…………….6-8 mpg tops…

No way to tell.. It depends on how you build the engine, the VE% of engine, transmission used, gear ratio used, how you drive the car, how hard do push on the throttle..

My camaro gets anywhere from 10 to 19 mpg.. If I’m playing around town, alot of hole shots, hard on the throttle, a lot of starting and stopping, etc I get about 10 MPG… If I’m steady on the throttle on a long straight road, no shifts needed, no stops… I get around 19 MPG..

That’s with a car that runs 11.40’s at 118 mph, 1.60’s 60′… th-400 3 speed trans, 2800 stall, 3.42 gears

8 to 10 mpg

It depends on whose crate motors you are talking about, as in what builder. GM, Shaffiroff, World, etc. and what version of said crate motor. A 383 with EFI could possibly get over 25 mpg on the highway. On the other hand a 540 with a Dominator could be under 5 mpg. The fuel system and valve train combination will determine fuel mileage much more than the displacement.

I have a 383 steroker in a 85 S10 and I dont get 15MPG with that so I would say about the same for you.

The S10 is pretty well emptied of anything un needed for racing.
I still have the exterior looking like stock – but the inside is empty. So it is pretty light weight.

yer not putting in a engine that is for economy.. probly 10-12 MPG

You’ll be lucky if you get 11mpg in the city.

There are to many variables. What rear end are you using? How is your carb tuned. Did you go with EFI. If so what injectors did you use?

Assuming you have or are spec’ing out a performance car. I will compair it to my Nova.

383 535HP
4:10 Locking rear diff
Built turbo 350 auto
6mpg in towm
11mpg hwy

12.14 quarter on premium pump gas