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Old 09-17-2004, 03:47   #1 (permalink)
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Port match

Should I port match my air gap manifold to suit my heads?
The intake ports on my heads are bigger than the manifold so there wont be any issue's there.The question is will it make a difference if I match them or not?
The runners are a bit rough on the inside.Is it worth cleaning them up? If so whats the best way to do it?
Any of you guys running air gaps what did you do to yours?
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Old 09-17-2004, 04:00   #2 (permalink)
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Re: Port match

Cleaned mine up (not quite air-gap but crosswind) with medium abraisive roll without enlarging much, slight mismatch helps with reversion, not sure it would be a good thing to make too big as then even minor misalignment would spell airflow disaster in the port. Want to power port mine (extrude hone) think it would provide good gains. Vr jnr opening size is 1.08 by 1.9 and is enough to pass between 250 and 280 CFM, so I think the size is not the issue, it's more the turns and shape in the manifold.
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Old 09-18-2004, 03:42   #3 (permalink)
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Re: Port match

Quote:
Originally Posted by blue66coupe
Cleaned mine up (not quite air-gap but crosswind) with medium abraisive roll without enlarging much, slight mismatch helps with reversion, not sure it would be a good thing to make too big as then even minor misalignment would spell airflow disaster in the port. .
I'm running a crosswind too. I opened out the ports slightly so they were larger than the runners to take advantage of reversion i just ran a flapper wheel up the runners of the manifold
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Old 09-18-2004, 05:21   #4 (permalink)
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Re: Port match

My inlet manifold (efi) has a smaller diamter than the ports in the heads. Is this a good thing? We are talking 2-3mm here. What is reversion?
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Old 09-18-2004, 08:05   #5 (permalink)
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Re: Port match

Air bouncing back off valve when it closes...
Also overlap in some cams...
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Old 09-18-2004, 17:01   #6 (permalink)
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Re: Port match

I would have thought matching the manifold ports to the head ports would assist rarefaction and reduce bog from air damming? A votexing laminar flow as opposed to a turbulant one at the ports is much more attractive IMHO.

Personally, I wouldn't polish the runners on a carby manifold, just knock out the casting seams. This will allow better mixing

I take it the air gap manifold reduces "reversion" through the carby, by allowing the unused rarefacting air/fuel mixture to be used by the other half of the manifold?
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Old 09-19-2004, 05:49   #7 (permalink)
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Re: Port match

Quote:
Originally Posted by AU2XLSV8
My inlet manifold (efi) has a smaller diamter than the ports in the heads. Is this a good thing? We are talking 2-3mm here. What is reversion?
the valve opening and closing with the flow of air in the port creates preasure waves in the manifold/ port By having the step at where the head meets the manifold it helps to reverse the direction of the wave (well thats the theory as I understand it)
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Old 09-20-2004, 02:18   #8 (permalink)
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Re: Port match

Reversion is exactly what the name implies, reversal of gas flow in the runners, usually including exhaust gas ,ie black runner walls and in the carb, too many causes to get involved in debate but big cam with low rpm is no1 on the list. A step in the head to manifold flange will not help a great deal but like with anti reversion header it must help a bit!
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