Tried searching, got 2-3 pages of "Gas Milage" with the contents of my TPI only gets 14 mpg, how can i make it better, and such post

So with much regret i ask, im building up a 355 for my bird, it will have a 700R4, with an unknown stall as of yet (determined depending on some economy) I have yet to pic out my heads and cam combo for it, it will get a Edlebrock Performer 600 cfm, or a holly 4150 600cfm, with an undecided intake as of yet.

Now, how big of an effect will be heads/cam on the motor, i know in stock condition with 882 heads and a quadrajet i could have gotten around 11 in city with my 3.73 gears, and stock stall, so will adding a somewhat radical cam with heads make a huge diff? or a few mpg?

Plans are to get some AFR 190 heads with a XE268 cam, with a 1800-2200 stall converter, that should put me at over 400fwhp

 

I've tried to be pretty fuel consumption conscious, and I've studied up on it a bit.
The general theory is, keeping the cam and intake runner vol smaller will improve fuel consumption. But in practice it has been proven that more cam and larger runner vol doesn't hurt much at all.
One of the members, texasLT1, runs LT4 heads (195cc) and a hotcam and I read in one of his posts that he's gotten 31mpg hwy @60.

http://www.geocities.com/texaslt1/lt1swap/swap.html

Here's another link to a thread where there's some discussion on the topic.

https://www.thirdgen.org/techbb2/sho...&highlight=442

If hwy mpg is what you want, you can go with bigger cam and heads. For in town mpg the factory L98 or LT1 is pretty difficult to improve upon.
By bigger cam, I mean bigger than stock. A lot of guys seem to be getting good hwy mpg with the 268, prolly a good choice.

 

You should be able to get OVER 20 on the highway w/your proposed combo.

W/my terrible combo (350, TFS heads, 234/244 cam, 750 Edelbrock carb, and 8.5 compression(!)), I got 20 mpg driving the car from Mass to Utah when I bought it.
6 speed, 3.73 gear.

-Tom

 

MaxxMitchell......That combination should get better fuel milage than your original combimation, because it should be more efficient if tuned properly. That is if you stay off the throttle! Another thing is that I doubt that combo would yield you at 400rwhp, maybe 300.

 

Well sounds good then, im happy to hear that i can go with a more aggressive cam and still not suffer badly on milage, makes me feel all warm inside

I expect around 400fwhp, but netting to 300+ at rear would be just fine for me.

 

One of your largest obstacles may be your choice of fuel delivery systems. Any carburetor will be difficult to tune for both power and fuel mileage. Any Holley will be even more of a challenge, since they are overly simplified and allow very poor mid-range mixture control and little thermal compensation. The Edelbrock clone of the Q-Jet is only going to be a little bit better. With no feedback to an ECM, you will likely have hours of tuning in the carburetor, and constant tweaking for temperature and density altitude variations. An old Carter ThermoQuad is probably the epitome of mechanical carburetion, but not many people have the patience and skill to tune them properly. They have various jetting possibilities, enrichment circuits, transfer (midrange) circuits, and all of it is thermally compensated by bimetallic controls. Short of electronic fuel injection with feedback, or several smaller carburetors that are easier to tune and balance, peak mileage without the risk of going lean under power is going to be difficult at best.

Regardless of the stall factor you select for a converter, get one with a lockup clutch to allow peak fuel mileage during cruise.