Port Restrictions

[KoNEY]

does anyone have a pic of the intake and exhaust ports off of an a20? i took off my head today that was on the extra motor i have, and tore it down so i can port and polish it, but there is very little restriction in the ports once i got the valves out. i was wondering if this was the way they came or if my head had been previously reworked......thanks

[A20A1]

I bet it came like that.

[k-roy]

One quick way to tell is if the inside of the port is smothe or not.
If it has a rough texture like the outside of the head and intake manifold its definitly stock.

[iamvandemon]

Don't port and polish your head. it is most likely big enough if not TO BIG already.

porting the intake ports (making it more caverness) lowers the ports velocity, or the velocity of the air fuel mixture as it moves through the port. this is not good for improving performance.

think about it this way. lets say that the opening created by the open valve is like a 6 inch diameter hole in the floor. and the amount of air/fuel mixture you want to get past that open valve is a pitcher of water.

now, what is the most logical way to get that full pitcher of water through the 6 inch hole? should you use a 6 inch diameter pipe positioned directly above the hole, or a 1 foot diameter pipe?

according to the "port and polish" theory, the bigger the better! right? wrong!! all of that unnecessary area only causes inefficiencies and flow reduction. the water poured down the 6 inch pipe flows directly from point A to point B, the pitcher to the hole.

now think of what happens when you pour that pitcher of water into the 1 foot pipe... the path of the water will tend to be less direct splashing off of the floor etc.

bigger ports are NOT better!! Higher velocity ports are better.

polishing the port is also not a good idea. the smooth surface will have the tendency to cause the gas in the air/fuel mixture to bead (like the beads of water that form on the smooth surface of your car when you drive through a heavy fog), and everyone knows that the fuel needs to be suspended in the air to result in the most efficient and powerful combustion.

the slightly rough surface of your intake port allows for a small amount of turbulence to keep the fuel and air mixed well. resulting in more power.

van

[KoNEY]

i already know that, im not porting the intake side, im porting the exhaust side, and polishing my exhaust ports and chambers, and simply cleaning and lightly scuffing the intake to increase mixture. think of your hole in the floor example, and you have a 6 in hole in the floor with a pipe connected to it. you want drain a 40 gallon drum trhough it. would you move more of the water out through a six inch hole, or a larger 12 in hole???? and thats what its about, besides, i know what my limits are, and i have a mechanic for a father who does custom headwork and such for a living, so relax, if it runs better than my current stock head, im happy...