Getting 10 to 11 MPG now with a 76 390 2BBL 2WD A/T already dualed out (CI manifolds). Just swapping the cast iron manifolds for headers will give me how many more MPG?

 

Probably less since you'll be getting on it more to listen to the exhaust!

Not sure if you're really going to notice a big difference in mileage but you should get 15+ hp

 

The engine wont have to work as hard to pump out exhaust gases. I'd say 30+ hp gain, and 3-4mpg gain.

 

I didnt notice any more MPG when i put my headers on.....too bad, would be nice. Could also be the fact i have a pretty heavy foot and its always into it.
Also, sounds good with headers and straight pipes....wooo

 

I'd say 2 mpg at best as you already have duel exhaust. This is when driving with good right foot behavior and the exhaust system matched to the motor.

Carl....=o&o>....

 

You will feel a good seat of the pants feel, I dunno about 30 ponys tho....
I didnt see any gains in mileage on my rig, if anything, since it ran better, I had my foot in it more.....

 

Crazy; that was a placebo effect installing headers, it's all in your mind, seek help on the truck forum thats what were here for. Sorry, I feel better now. Headers will help if the exhaust system if designed for the motor as well as the intended use. Intake system has a large effect also. The balance of gas flow in and out will make any engine wake up and improve its efficiency. The heavy foot is another matter that will reduce your efficiency gains. Repeat, "right foot control when in traffic".

Carl....=o&o>....