Port Velocity??.... Dennis Moore
11-05-2002, 04:29 PM
#13
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Location: Holland MI
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Tick-tock, Jim. We ain't getting any younger and you can't make any money off the intake until it's done. The party starts any time you roll into the driveway over here. I don't drink so you'll have it all to yourself. Bring Rachel and we'll do burgers on the grill.
11-06-2002, 09:16 AM
#15
velosity
I would agree that port volume has a direct effect on overall port velosity however pressure is not equal in the port. At every bend in the runner there is a change in pressure thus changing velosity. If it were equal we wouldn't have any problems with fuel falling out of suspention. The fuel trails you see in a port or manifold result from low pressure, there is an obstruction in front of it, example would be the bend at the pushrod. The short turn radius has the most pressure difference. Using a pito tube, I have seen 40+" of pressure on a short turn radius with the bench test pressure at 28.0"
As what Dennis said about the pro stock guys learned that bigger is not better holds especially true for boat engines. What always works the best for me is the port that flows the most air with the smallest volume. Adding volume with no increase in airflow is taking a step backwards.
As what Dennis said about the pro stock guys learned that bigger is not better holds especially true for boat engines. What always works the best for me is the port that flows the most air with the smallest volume. Adding volume with no increase in airflow is taking a step backwards.
11-06-2002, 06:18 PM
#17
Tomcat
The pitot tube was pointing into the airstream. In other areas of the port the manometer would read much lower. I am sure there is some margin of error, it doesn't take much movement to change the number. If I get a chance I will try to measure air temp on the low pressure side of the short turn
The pitot tube was pointing into the airstream. In other areas of the port the manometer would read much lower. I am sure there is some margin of error, it doesn't take much movement to change the number. If I get a chance I will try to measure air temp on the low pressure side of the short turn
Last edited by JimV; 02-10-2003 at 07:07 PM.
11-07-2002, 08:33 AM
#18
Registered
JimV
That's very interesting...a velocity pressure of 40" works out to about 25,000 fpm air velocity. This was a max velocity and the average across the port would be lower. Do you remember what CFM the port was flowing when you did this, and what the cross sectional area of the port was where you were measuring?
When air is moving that fast and then changes direction, the fuel droplets suspended in the air can't make the turn. Their momentum carries them, so if the air makes a sudden 90 degree turn, the fuel droplets might only manage a 60 degree turn and impact the port wall. Does the location of the beginning of a fuel trail make any sense when you consider this mechanism?
That's very interesting...a velocity pressure of 40" works out to about 25,000 fpm air velocity. This was a max velocity and the average across the port would be lower. Do you remember what CFM the port was flowing when you did this, and what the cross sectional area of the port was where you were measuring?
When air is moving that fast and then changes direction, the fuel droplets suspended in the air can't make the turn. Their momentum carries them, so if the air makes a sudden 90 degree turn, the fuel droplets might only manage a 60 degree turn and impact the port wall. Does the location of the beginning of a fuel trail make any sense when you consider this mechanism?
11-07-2002, 04:32 PM
#19
Tomcat
Thats a pretty radical bend. I could see atomized fuel forming into droplets in the low pressure of the vortices, forming a fuel trail. The fuel aimed for the wall is heading into higher pressure the closer it gets to the wall. If the fuel were marbles I'm sure they would shatter. Visualizing your bend as a port on a flow bench, the test pressure would increase 5" plus once it reached the point where it gets turbulant.
I smoked tested that same port, interestingly enough the smoke did not break up as I thought it would. It stayed in a stream about half way in the port dipping down towards the shorturn radius turning down to the valve. I know its not the same as fuel but it tells you what the air is doing. My opinion
Are you the same Tomcat that was at the Smoke on the Water poker run?
Thats a pretty radical bend. I could see atomized fuel forming into droplets in the low pressure of the vortices, forming a fuel trail. The fuel aimed for the wall is heading into higher pressure the closer it gets to the wall. If the fuel were marbles I'm sure they would shatter. Visualizing your bend as a port on a flow bench, the test pressure would increase 5" plus once it reached the point where it gets turbulant.
I smoked tested that same port, interestingly enough the smoke did not break up as I thought it would. It stayed in a stream about half way in the port dipping down towards the shorturn radius turning down to the valve. I know its not the same as fuel but it tells you what the air is doing. My opinion
Are you the same Tomcat that was at the Smoke on the Water poker run?
Last edited by JimV; 11-07-2002 at 04:44 PM.
