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Quote:
Originally Posted by daren007
Bigger cam? Is there enough room for a bigger cam.
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Yes. The head of the valve typically will hit the roof of the combustion chamber before the lobe is too big to fit through the cam journal bores.
Quote:
Originally Posted by Bob Bidonde
Porting is not reversible and it reduces the compression ratio. For a street runner, I doubt porting is of any significant value, but I am guessing.
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Bob, what you are showing in the picture is what is termed as 'Relieved' which is done to unshroud the valve. It has been my experience that most port work is done
under the head of the valve and out of the combustion chamber area.
Quote:
Originally Posted by GeneBob
Jim,
Is there a guide or YouTube video or something to show where and how much porting is done? I have wanted to do some porting but don't know how.
Thanks,
Gene
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The science of this is much greater than what most people can show on YouTube. Matter of fact, most content you watch on YouTube relating to a Model-A is generally not very accurate anyway, so that is probably not the best source of information.
With regard to porting, if you want to do porting, you need to buy/build a flow bench which is basically a manometer that tests resistance of flowing air. If you have mega-deep pockets, you can even map the ports on your block and have them digitized. Then using sophisticated software, it will create a simulation of the airflow in both dry and wet scenarios. Afterwards the computer will make changes to find what is optimal for a certain RPM range. Just going into the port or bowl area and hogging out metal does not necessarily increase airflow or horsepower. Likewise there are very basic areas of blueprinting that will net gains in most areas on a Model-A block. Some of those items are port matching in the intake manifold to block ports, blending valve guide areas, and creating multi-angle valve seats to assist flowing air. Pete Samuelson would be a good one to interject his thoughts on this too.
It is mine & several other's opinion that the 1.500" Model-A exhaust valve & port is too large which cuts down on the scavenging effect it can have. Also, I tend to take the stance that most stock intake seats are damaged enough where a seat insert is necessary to have a good valve support. For the same labor expense, I can increase the seat area to support a 1.750" valve instead of cutting and installing a 1.625" seat insert (-which holds the 1.500" valve).