Stagger jetting question

318willrun said
ok, but how do you tell #7 cylinder to pull from the 76 jet rear throttle plate on the drivers side and #5 cylinder to pull from the 78 jet rear throttle plate on the passenger side on an open plenum ?? I'm not being sarcastic at all, but I don't understand.

I don’t have an answer for that except to say what happens in a plenum is almost an uncontrolled chaos. There are two reasons why the firing order gets changed. One is because the 4-7 swap significantly reduces the torsional loads on the crank and the engine is noticeably smoother. If you do the the other swap which I think is 4-7-5-2 but I just don’t remember the other two cylinders for sure, you get an even smoother engine. The other thing that happens with firing order swaps is it changes the distribution in the plenum. Even at very high rpm there is air and fuel moving towards and away from the valve. And, even if you have the A/F mixture as good as you can get it, and it comes out of the booster clean and you get good shear off the throttle blades the fuel will still be heavier than the air and it is less responsive to changes in direction. When that happens the fuel falls out of the air and hits the floor and the walls. Then it runs into the cylinder. But not always the cylinder that it was headed to. That’s the best guess I can give you, because that’s what my limited experience allow me to understand. I do know at one point in pro stock they were moving the carbs forward as much as .600 to help control fuel with a 3g launch. I only know that because I had a friend that was working with an engine builder doing some of that stuff and he told me. Otherwise I wouldn’t know that. That’s with carbs. With EFI and the injectors at the valve cover rail it’s a bit different. I just saw the EFI guys are starting to move the injectors up. Doing that will make tuning EFI more like tuning with carbs as far as distribution and such is concerned. I’ve only read and never witnessed that some are putting the injectors right in the plenum and they are making more power. In my opinion that means that anything you would do with carbs as far as distribution is concerned you’d be doing with EFI.