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Old 03-19-2003, 07:47 PM
92V8Dakota 92V8Dakota is offline
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Join Date: Mar 2003
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Question Ported Mag Head ??

OK, gotta question here... according to my reading, if you can get 2 heads to flow the exact same numbers (230cfm) at say, 28"... one having a 153cc intake port w/ a 1.97" valve, and the other having a 180cc port w/ a 1.92 valve, the head with the 153cc port is better because it will have a higher intake velocity. IS THIS CORRECT??? OR does the intake valve size change this theory because according to hughes engines this is the way it works.... NOW if you look in the 2001 MP catalog, the 2 heads I just compared were the stock ported mag heads and the R/T heads... the stock ported being the better head. How and Why is this??

TJ
dakota52318@toad.net
1992 Dodge Dakota 4X4
Long Bed, 318, 46RH Auto
DT Headers, Functional RamAir Hood
K&N FIPK, Flowmaster Muffler
Custom Throttle Body
MP Computer
15.74@87.59
4350lbs
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Old 03-20-2003, 01:23 AM
Crank Crank is offline
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Join Date: Aug 2001
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Good question lets see ware to start ,ok on the compresion stroke the plug fires boom the piston go's down just before the piston gets to the bottom the exaust valve begins to open and the piston is on it's way up as the cylinder is being emtied the intake valve begins to openand the inertia of the exhaust gases leaving causes a low -presure area in the cylinder now opening the intake valve sooner and leaving the exhaust valve open longer the low presure will help to initiate the flow of the incoming fuel/air mixture.at low engine speeds however the velocity of the exhaust gases leaving the cylinder is too low to create the enertia needed for good exhaust scavenging because the intake valve is opened so soon and the exhaust valve is closed so late the incoming fuel/air becomes diluted with inert exhaust gases.now the way i see it the larger valve creates a lower presure at lower rpms making it harder on exhaust scavenging and with the smaller 153cc port volume would need more low - presure threw the exhaust .but at higher speeds it would flow better.now with the 180cc port the low presure would fill the cylinder faster before it would start drawing from the carb or throttle body ,this is why a 1 inch carb spacer will give you more power also.
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