Pro-Filer 13º Wedge SBC

Cylinder Head and Manifold Discussion

Re: Pro-Filer 13º Wedge SBC

Postby Chad Speier » Fri Jan 04, 2013 9:07 am

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Re: Pro-Filer 13º Wedge SBC

Postby upsidedown » Sat Jan 05, 2013 10:04 pm

Chad Speier wrote:Basically, the taller the port, the better the mach index. So you can run the port faster via airspeed. The 23º being a low port has a bad "line of sight" for a lack of better words. Therefore you cannot run the speed as fast. That and the pushrod is will always be the killer on a 23º. This is why some, including myself, are so hell bent on making it match the amount of air it's moving. Some 23º heads move a ton of air but will never see it because you simply don't have enough area. Now a higher port can have the same area but due to the port shape, can run a faster airspeed, and still make power. Velocity is VE. The higher the VE, the faster the airspeed usually is.


Thanks Chad so lets see if I understand you correctly. Two heads a 23 degree and 13 degree. Same smallest csa. 13 degree flows substantially better.

Are the following points correct?

1.Both heads are still subject to the critical speed of 690 fps but the 13 degree head can run closer to it than the 23 degree without choking. So in effect the 13 degree might tolerate 650 fps but the 23 degree only 550 fps

2. 13 degree head has higher velocity due to the extra flow but can tolerate that because less turbulent

3. I guess depending on the valve angle there is an optimum flow / velocity for the min csa. So a 23 degree head would have an optimum cfm flow value vs min. csa but achieving a higher flow than optimum would be detrimental. And conversely the 13 degree head would also have an optimum cfm flow value vs min. csa but higher than the 23 degree

4. Is flowing the port all the way to 1" lift like you do and having the flow go down an indicator of whether the port velocity for a given head is too high
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Re: Pro-Filer 13º Wedge SBC

Postby jmarkaudio » Sat Jan 05, 2013 11:26 pm

A few things to consider. Any gas or fluid flow has three states in order, laminar, transitional, and turbulent. Of the three transitional is the worst, it's at that point flow actually goes backwards. Turbulent flow will go forward although not at the rate laminar will. Boosted engines are a good example, you can still get more air through the heads even though flow may be turbulent.

Higher velocity air has more inertia, so it fills the cylinder better. So if transitional flow can be avoided longer the airspeed can go higher.

In an engine airflow is constantly changing speed and also direction due to reversion, those dynamic changes can aggravate the situation. Choose your cam and intake wisely.
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