Restrictor Plate Question

[340king]

I was discussing the impacts of running a restrictor place under the carb of a dirt late model with some racers tonight. In that discussion they claimed that a restrictor plate increased the vacuum of the engine, which I agreed with, under the plate. They said no, it increased the vacuum at the carburetor, which doesn't seem possible to me. I have heard this said a couple of times and am wondering what I am missing.

Does a restrictor plate increase the vacuum the carburetor sees? Does the engine run rich for some other reason? How can a restrictor plate increase the vacuum signal the carb sees?

Thanks in advance. I have never ran an engine with a restrictor plate on it, so this is new ground for me.

[modok]

Does the engine run rich for some other reason?

this seems to be the basis of the question.
Your guys are imagining where vacuum is and where it isn't and what amount for what period, but why? You aren't measuring it. Lets stick to the true part of the story.

So it goes rich? it may, it may not, it would depend on the kind of carburetor used.
Here is a more common question:
Will putting the same carburetor on a larger or smaller engine need a different size jet?
WHO KNOWS! it could go either way. Same reason. None of this is linear.

[naukkis79]

Restrictor plate acts like smaller venturi in carb, it increases air velocity, so yes it will increase vacuum signal.

[pamotorman]

a restrictor plate reduces the air flow into the engine. at a local track we ran different size restrictor plates on the same spec engine for the different classes. I had my contact at GM run the program for what size holes I needed to get the HP difference we wanted. NASCAR now uses a tapered spacer to restrict the air flow instead of the flat restrictor plate. the tapered spacer does not cause as much turbulence as the flat restrictor plate and increases the HP over a flat restrictor plate.

[pamotorman]

any one here remember jr johnsons "floating restrictor plate" that increased the HP ???

[pamotorman]

when we ran the modified race at Daytona with a 1-1/2" restrictor plate I did not have to change jetting that I used without the plate

[BlitzA64]

any one here remember jr johnsons "floating restrictor plate" that increased the HP ???

I remember that going on, I thought Roush was involved as well? No idea how it worked.

[pamotorman]

any one here remember jr johnsons "floating restrictor plate" that increased the HP ???

I remember that going on, I thought Roush was involved as well? No idea how it worked.

the restrictor plate was to be welded in place in the intake but was tricked up to look like it was welded in place but if floated up towards the bottom of the carb which allowed the mixture more room to make the turn into the intake runners.

[Ron E]

I was discussing the impacts of running a restrictor place under the carb of a dirt late model with some racers tonight. In that discussion they claimed that a restrictor plate increased the vacuum of the engine, which I agreed with, under the plate. They said no, it increased the vacuum at the carburetor, which doesn't seem possible to me. I have heard this said a couple of times and am wondering what I am missing.

Does a restrictor plate increase the vacuum the carburetor sees? Does the engine run rich for some other reason? How can a restrictor plate increase the vacuum signal the carb sees?

Thanks in advance. I have never ran an engine with a restrictor plate on it, so this is new ground for me.

I agree with you. More vac downstream of the restrictor, not upstream even with higher velocity inside the plate itself. But, isn't that just a local velocity due to it being the choke of the system? The carb is still big but flows less due to reduced signal. And, a reduced signal is less vacuum. I think...