CNC headporting for 20v head.

[quattro84]

Sonic choke occurs at 209fps @ 10" pressure drop How does this work out in the metric system?
I personally don't believe in deLaval shapes giving supersonic speed, i reckon airflow reaching turbulent levels is only going to decrease in efficiency so i estimate max. airspeed is around mach .45, transition from laminair to turbulent flow giving the fact that our delta p is such small.
Max speed will then be greatly influenced by the roughness, changing the drag coefficient making the Reynolds number stating that we work with compressable flow.

[JP]

Sonic Choke is where the cylinderhead port can accept no more air due to the shockwave created as the port airspeed passes mach1. Most production heads will reach sonic choke when fitted with a high lift after market cam. Which is why most bolt on performance cams have a less severe lift spending more time of its duration at lower lift using a wide lobe design as found in many of the later roller rocker VAG engines.

Optimum power is found sitting as close as possible to sonic choke throughout the length and cross section of the port without going over for the given cam lift profile.

Unfortunately all my formulae and programs work in fps relevant to 10", 25" and 28" which are considered the industry standard on flow bench work. 28" being the most accurate correlation between flowbench cfm gain and hp gain.

As for roughness the difference in overal flow between an 80grit finish and a 800grit finish is so insignificant it doesn't even come into play in the grand scheme of things.

[QuattroFever]

Now this is head porting, somebody really knows their stuff here.

Edit: CLASSIFIED