M20 Cam charts?

[LateFan]

Those are great. So that's cut though the center of the valve stem....I wonder how you could visualize the whole 3D flow around the valve.

So are you not trying to maximize flow, but maximize velocity?

[digger]

The above plots show what happens with a steady state scenario kind of like a flow bench. All you can do here is try to maximise flow per square inch of area. This comes from having as uniform velocity gradients across each cross section and efficient transition shapes.

However you also need to target an absolute size that provides the best cylinder fill. this is dependent on engine parameters bore, stroke, rpm etc etc . At any given rpm a 3.2L engine will pull harder on the port than a 2.5L so in a stock head the velocity will be higher with the bigger engine. as the rpm rises the bigger engine may pull too hard on the ports and the head wont function well at the higher airspeeds if the head isnt ported properly. this is why a big stroker engine without a proper ported cylinder head doesnt make hp up top there isnt enough area to feed the engine. So it is the absolute size is what governs velocity in the running engine. The flow bench won't tell you the correct size because if you keep making the port bigger and bigger in an efficient manner the flow keeps going up in proportion to the area increase this is due to the nature of a fixed test depression. a given bottom end will pull a variable depression on the port with differing rpm and for the same rpm a different capacity bottom end will pull differently on the head.

So first thing to work out is how big does it need to be then maximise the flow without going bigger than that size.

[ForcedFirebird]

The flow bench won't tell you the correct size because if you keep making the port bigger and bigger in an efficient manner the flow keeps going up in proportion to the size increase this is due to the fixed test depression.

There's more to the flow bench than just the flow numbers. Using other tools in combination, you can find dead spots, where the velocity is etc. And I don't just use 28", it's just a number that is industry standard, so numbers correlate to one another. With the 2 vacuum motors here now, about ~24" at 200cfm is what I can achieve, but lower lifts can generate in the 40's. Would be nice to have a 6 motor setup with electronic depression control. :devil:

[digger]

of course a uniform velocity gradient is the goal, minimize dead/slow areas and too fast areas and the port works better at higher average speeds and pulsed flow so can be kept a bit smaller than would otherwise be the case.

in the first pretty picture you can see the high speed area over the short side. i'm sure if you widened that area or layed back the radius better it would be a whole lot better and the air would turn better

at peak hp the cylinder pressure can be 150-180" below ambient so you can never test at too high of a depression