Repairing intake manifold fuel distribution issues

[BILL-C]

I'm interested in knowing what other shops are doing to repair intake manifold fuel distribution issues on the dyno that are not carb's fault. Single plane BBC in particular.

[mag2555]

At what rpm does the disparity first show up?
How much vacuum is the motor pulling when the disparity kicks in?
Does the disparity get worse with closed headers?
What fuel, gas?
What Intake Manifold and what Carb are we talking about.
Any spacers used?
Oval port heads or rectangular?

[user-30257]

I'm interested in knowing what other shops are doing to repair intake manifold fuel distribution issues on the dyno that are not carb's fault. Single plane BBC in particular.

Straightening the path from the venturi to the port.
You could put the carb on a good bench and measure each booster, to verify each booster is getting the same signal.

You may have to open up the base of the pad on the intake manifold.

Tell us. Is it a 4500 with 2.25" blades or is it a 4150 with 1-5/8?

What's the angle of the base pad on the intake?
Is the float too high.
Is individual cylinder timing way off ignition or cam.
Post more details

[user-30257]

Is the carb base the same angle on the dyno vs car?

[user-17438]

I'm interested in knowing what other shops are doing to repair intake manifold fuel distribution issues on the dyno that are not carb's fault. Single plane BBC in particular.

wouldnt it be ideal to fix those issues if it were in the car? Porting them seems to help significantly if we are talking about a basic single plane intake, but often times staggering the jets can help, or in some case header design, cam timing can change what you would think is an intake manifold issue.

So, how about try a different intake. a Torker vs SV565, you couldnt make a torker perform anywhere close to that manifold.

[BILL-C]

pro built 4150 carb with 1.75 plates on brodix oval port 18* intake ported by a famous nascar builder. Great power, just a little leaner on rf corner on dyno than we are comfortable with. 475 cid DIRT modified. Problem is manifold, not carb. Tried many spacers. I'm considering welding a "spivey" on spacer to re-direct some fuel. Roof is already a straight shot to head.

[user-30257]

pro built 4150 carb with 1.75 plates on brodix oval port 18* intake ported by a famous nascar builder. Great power, just a little leaner on rf corner on dyno than we are comfortable with. 475 cid DIRT modified. Problem is manifold, not carb. Tried many spacers. I'm considering welding a "spivey" on spacer to re-direct some fuel. Roof is already a straight shot to head.

That was confirmed by o2 or plug?

[user-30257]

Also, could be a carb trick. Lots of left turns.

[BILL-C]

Not much lateral grip on dirt.

[mag2555]

If you have the room for more Carb spacers then install a Brodix Turtle in the Plenum , make up for the reduction in Plenum volume with a added spacer.
Are you limited to a 4150 series Carb?
That size motor even with only 310 cfm heads wants a at least a 1050 cfm cfm by means of a 4500 series Carb!

[BILL-C]

Engines are only appx 860 hp, so not enough gain with 4500 to overcome superior driveability of big (1050+ cfm) 4150. I feel funny putting a turtle in a $ 2500.00 intake manifold on a $ 50 k engine. I always thought they were for street stuff. Never tried one.

[groberts101]

Engines are only appx 860 hp, so not enough gain with 4500 to overcome superior driveability of big (1050+ cfm) 4150. I feel funny putting a turtle in a $ 2500.00 intake manifold on a $ 50 k engine. I always thought they were for street stuff. Never tried one.

I hear ya there, Bill. In the end the cylinder doesn't care.. just see's the deficiency and sends that issue further on down the line to the crank. I've run maybe 4 turtles through the years and all were advised/designed to help soggy mixture related issues on bigger plenums/smaller CID when taking the motors well below the peak torque curve. Doubt that will help in this situation but you never know until you try it. Quick-n-dirty test with zip tied spivy will tell you if you need to dig deeper or even bother with other fixes, IMO.

[Carnut1]

I have used turtles and then designed my own using a different strategy. Since it is a bbc single plane each runner has a different length. I wonder if the runner length change as adding length with a runner extension or even a surface treatment inside intake would help.

[Walter R. Malik]

I would suspect that the discrepancy from port to port is "fallout" fuel which is not yet atomized so, somehow getting that non atomized fuel nearest the ports which can use it most, however you can get that accomplished, would be beneficial.

[MadBill]

If not already done, stagger jetting would be an obvious first step. Every combo can be different but in general, the distribution for standard F.O. Chevs with single plane manifolds is often improved by going up a size or two on the right front main jet and down on the left rear.