Carb tune change with better heads?

[DrCharles]

I recently put a QF 950 (1.42 venturis, 1.75 throttles) on my 451 and went through a lot of contortions getting a good tune with my big cam.
My bowl-blended 2.08/1.74 iron heads probably don't flow much over 250 cfm, but they got me on the road!

This winter I plan to put on the PRH Stage 1 aluminum heads that do 293.5. How much is that going to change my tune? I am thinking that the air bleeds might need a tweak since there'll be a lot more air flowing at higher RPM. Also, more hp = more fuel, but does that = bigger jets with the same size barrels?

 

[496 polara]

Not a guru by any means so don't take anything I say as the gospel.
If it becomes more efficient it may need less fuel.

 

[yellow rose]

Not a guru by any means so don't take anything I say as the gospel.
If it becomes more efficient it may need less fuel.

^^^^^^^^THIS^^^^^^^^^

You can have two ports with identical flow and the one with the better shape (and with that better flow characteristics that don’t show up in the numbers unless you test for them) and the best port will make more power with less jet.

If I port a set of heads and it doesn’t make more power on less fuel I’m disappointed.

 

[DrCharles]

Thanks! I can change the fueling by swapping jets easily enough, and watch the AFR gauge.
But will the slope/shape of the curve change also? Then I have to start tinkering with the air bleeds again...

 

[mderoy340]

The booster signal will be better so plan on at least jetting. If the current curve was flat you most likely won't need to mess with the MAB.