"So if I understand you correctly Moper, that if I give you a rpm that I will call peak rpm's say 6,000 that it will show something different for say 3,000 or 4,000 rpm's? How is the port volume going to change by rpm's, unless your looking at a max rpm's. So if this is correct then a 130 cc port runner for a given engine say a 318 that turns 6,000 rpm's won't be able to use a 150 cc port because the port will be too large."
I'm saying for that one point on the power curve, yes. Because as you say below, depending on curtain, volume, intake, cam, etc, the "perfect" size via a math operation will be different for every point on the curve. 5500 is different than 6000, which is different than 6300. It's not the volume that changes.. it's the perfect volume for that one rpm point and that engine that changes. The output of this program is the volumes, both theoretical given with a min and max and stall, and actual determined by piston speed, cam lobe, and curtain area. It yields not one particular size for a given engine package, but one particular "best" volume for a particular engine size at a particular rpm taking into account displacement, valve size, and cam specs. By trying to get results for a wider "snapshot" on the curve, that is more info in terms of rpm ranges, you lose accuracy for any one spot. I believe (I'd have to ask the creator) he was concerned with the rpm of peak horsepower, not peak torque, and not a wide rpm range as that would add to the inaccuracy.
"I think that what he's looking for is what a given engine needs to have for so to speak the perfect port volume."
I agree
"I think that what your saying is a given rpm will need a given amount of air flow, this doesn't mean that the port volume will change but the airflow will."
Yes, exactly!
"I guess I should put it this way, if we have 2 heads and one flows 280 cfm's @ .600 and the other flows 240 cfm's @ .600 then the one with 280 cfm's will make more power with both being the same port cc's. It will also have more port velocity because it's moving more air through a given size port or volume. With both having the same size valves."
Yes, but I dont agree more output at the crank is always the result. I know what you meant, and I agree 100% with your intention as I understand it. However getting more detailed might end up yeilding different results at the carnk. By detailed I mean things like cam, intake, and rpm range choices.
"If both heads have different size valves then the port velocity will change due to the amount of area of the valves."
In summary, yes. The velocity will change all thru the lift range on any size valve regardless of size when measured at the seat. but you know air can be tricked by shape changes to more faster or slower. Faster is always best, up until the port stalls which can be anywhere in the lift range depending how bad the port or port work was.
"But this will also be seen in the amount of port flow in the low lift ranges from .100 to .400 lifts. The smaller valves will generally flow more at low lifts than a larger one, but the larger one will flow more peak at a higher lift something like .700 or .800 lift. Correct."
I don't ever look at .700 lift so I have to believe you're correct. But I would also think that on factory iron Mopar ports, the port will go turbulent well before that lift range on the vast majority of castings because of the pinch and short turn limitations.
I think, the most expressive word there is generally... and the more the is generalized, the less exact and less individual the result.
I hope that all comes out when it posts...lol. I wish we could do a seperate color.
