Calculating Airspeed in a cylinder head
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Calculating Airspeed in a cylinder head
Does anyone have a formula to figure air speed in a port(running engine), by using piston speed numbers?
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SW
That's the million dollar question. There are so many things that contribute to air speed in a port that it is almost impossible to predict.Piston speed is just one of the factors involved.You could name just about any other part of the engine,cam, intake, exhuast,port configuration, runner lengths,and about a zillion other things that all make up velocity in a port.There is a good program, engine analyzer pro, from performance trends, that does simulate these velocities.As far as how accurate these numbers are, I couldn't tell you. I'm sure some of the high end cup teams and F1 have documented these numbers in real time, but they are probably a little reluctant to share them with us common folk.
Shawn
Shawn
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if you look at the right-side columns you would get a good idea of the Flow need to keep up with the piston motion
that Link pic doesn't show any effects of "Lag" due to rest of induction system lags behind the exact moment of intake valve opening and closing points
if you know what CFM the piston is trying move , then you can get an idea of what "minimum" port velocity would have to be .
You have to know cross-sectional areas of various port locations , and min cross-sectional area, bowl area, valve area, curtain area, short-turn area, seat insert area, etc. and calculate the various velocities
these are simple equations that seem to give accurate enough results to give you a very good idea of whats needed for given engine RPM and size
but doesn't even come close to simulating all the dynamics of a real engine.
running data from 500 cid at 9000 RPM
Piston Cylinder Piston--CFM @ inch. H2O
Depth Vol. CCs FPM @105 @28
0.0089 2.522 965.1 115.3 59.5
0.0799 22.510 2846.3 340.0 175.6
0.3107 87.569 5372.2 641.8 331.4
0.6673 188.113 7313.0 873.6 451.1
1.1123 313.533 8502.8 1015.7 524.5
1.6011 451.316 8894.1 1062.5 548.7
1.7660 497.803 8855.8 1057.9 546.3
1.9293 543.839 8740.1 1044.1 539.2
2.0896 589.031 8553.0 1021.7 527.6
2.3963 675.486 7990.3 954.5 492.9
2.5406 716.150 7629.0 911.3 470.6
2.6776 754.774 7223.9 863.0 445.6
2.9273 825.152 6311.4 754.0 389.3
3.2341 911.652 4782.7 571.3 295.0
3.4543 973.719 3180.8 380.0 196.2
3.5862 1010.882 1581.1 188.9 97.5
3.6300 1023.238 0.0 0.0 0.0
about 549 cfm @ 28" would be needed to keep up with the piston
of course wave, inertia, lag-time dynamics will change
right-side column data in real life, but it does give you a pretty good idea from such a simple Program.
if you look at the right-side columns you would get a good idea of the Flow need to keep up with the piston motion
that Link pic doesn't show any effects of "Lag" due to rest of induction system lags behind the exact moment of intake valve opening and closing points
if you know what CFM the piston is trying move , then you can get an idea of what "minimum" port velocity would have to be .
You have to know cross-sectional areas of various port locations , and min cross-sectional area, bowl area, valve area, curtain area, short-turn area, seat insert area, etc. and calculate the various velocities
these are simple equations that seem to give accurate enough results to give you a very good idea of whats needed for given engine RPM and size
but doesn't even come close to simulating all the dynamics of a real engine.
running data from 500 cid at 9000 RPM
Piston Cylinder Piston--CFM @ inch. H2O
Depth Vol. CCs FPM @105 @28
0.0089 2.522 965.1 115.3 59.5
0.0799 22.510 2846.3 340.0 175.6
0.3107 87.569 5372.2 641.8 331.4
0.6673 188.113 7313.0 873.6 451.1
1.1123 313.533 8502.8 1015.7 524.5
1.6011 451.316 8894.1 1062.5 548.7
1.7660 497.803 8855.8 1057.9 546.3
1.9293 543.839 8740.1 1044.1 539.2
2.0896 589.031 8553.0 1021.7 527.6
2.3963 675.486 7990.3 954.5 492.9
2.5406 716.150 7629.0 911.3 470.6
2.6776 754.774 7223.9 863.0 445.6
2.9273 825.152 6311.4 754.0 389.3
3.2341 911.652 4782.7 571.3 295.0
3.4543 973.719 3180.8 380.0 196.2
3.5862 1010.882 1581.1 188.9 97.5
3.6300 1023.238 0.0 0.0 0.0
about 549 cfm @ 28" would be needed to keep up with the piston
of course wave, inertia, lag-time dynamics will change
right-side column data in real life, but it does give you a pretty good idea from such a simple Program.