Anybody doing the staggered jetting on there open plenum style intake as per Vizards book? And why add 2 jet sizes to the pass rear of the carb when cylinders 5 and 7 are on the driver's side? Open plenum M1 max wedge port 4150 950 ultra hp carb
I would think just like a lot of carburetors come in with two stages of primary and secondary it's making it more like it has three stages and comes in more gradual and not overloading all at once...?..Maybe my "lack of knowledge mind" doesn't understand, but on a single 4 bbl sitting on a open plenum intake, I cannot see staggering jet sizes from driver's to passenger side. I've never done it. I guess I don't know anyone that does do it.
My way of thinking, if a guy has an open plenum, all cylinders are pulling from the throttle plates so staggering isn't helping one individual cylinder. Again, I've not chased down that avenue, nor have I felt the need to. Somebody that's doing it can share their benefits. Waiting to see or hear.I would think just like a lot of carburetors come in with two stages of primary and secondary it's making it more like it has three stages and comes in more gradual and not overloading all at once...?..
Anybody doing the staggered jetting on there open plenum style intake as per Vizards book? And why add 2 jet sizes to the pass rear of the carb when cylinders 5 and 7 are on the driver's side? Open plenum M1 max wedge port 4150 950 ultra hp carb
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I was thinking about throwing a little more jet at the engine as the dyno sheet shows 13.2 a/f ratio. I would assume I'd see any improvement in mph and having just read that section yesterday I figured I'd see if any other members/racers had done that. The bottom of the M1 intake has no dams . Flat so I'm thinking it may suffer a bit from the 5-7 issue described by Vixard. I doubt it'll hurt to try. And 4.5 bore 4.15 stroke flat top diamonds 13.8 308 comp solid roller
My way of thinking, if a guy has an open plenum, all cylinders are pulling from the throttle plates so staggering isn't helping one individual cylinder. Again, I've not chased down that avenue, nor have I felt the need to. Somebody that's doing it can share their benefits. Waiting to see or hear.
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.It happens more than you think. Just because you have a plenum doesn’t mean you won’t have distribution issues. Some of them occur because the booster design is wrong. Sometimes it’s because of the position of the carb over the plenum, even on a single 4. There are issues caused by big overlap cams disrupting air movement in the plenum and also cause a rich mixture, which requires more heat to vaporize the fuel. I’ve seen several times where getting the fuel curve cleaned up also cleaned up distribution issues.
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.
well, changing the firing order is a complete different subject. But for the topic at hand by the op, I can't see staggering jets from passenger side to drivers side on an open plenum intake will cure the fuel distribution for cylinders on the same bank. I'm lost there...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.
When my Indy headed small block was on the dyno the afr’s were about two points off side to side. A 1” Super sucker brought the afr’s to a couple tenths of each other. And it made 13 more hp, no other changes.