flow decrease vs lift

[windford]

I am new to this forum but have been very impressed with the information shared in the threads. I would appreciate any advice on cam lift vs flow figures. I have a set of old ford motorsport a3 heads that i have welded and reshaped the ports. They are flowing on the inlet 390 cfm @28 but they fall over at approx .740 lift and drop to about 375 and stabilize up to .850. The valve dia is 2.24 and the throat 2.010. I am running a 45 deg seat and am yet to test anything steeper, but i still would like some input on how far fast max flow lift i can go. Is it feasible to lift higher than this as i believe the gas flow dynamics may produce differing results on a running engine than they do on a steady state flow test. The flow results obtained were on a self made flow bench calibrated with a superflow calibration plate and the accuracy has been backed by flowing heads with known values. The engine is 9.5 deck windsor with 4.125 bore and 3.85 stroke and is for drag racing. Thank you for any advice.

Regards,

Ray Fuchsbichler

Windford Engineering

 

[Fabrico]

What type of cam are you running?

 

[windford]

The cam that will be running will be a mechanical roller approx 280 @ .050 and .500 lobe lift with 1.8 rocker ratio

 

[stout1]

This topic is an all day discussion, there are just so many variables here. Here are a couple things I watch for when flowing heads, one thing is to listen for turbulence and eliminate that, another thing to try is to make a clear extension tube for your bench and use some colored liquid and use that to flow so you can see what it will be doing in the cylinder on the engine. You also want to match max lift with max flow potential in the engine the best you can, generally speaking you do not want the max lift of the cam to match the max flow/lift of the heads (your air speed slows as the piston reaches BDC). Sorry for not being very clear, it's early yet). Good Luck

Michael

 

[Greenlight]

The problem that you are having is common. The air speed at the "short side radius" (SSR) is too high and is experiencing flow separation at the SSR.

Try flowing the heads at 36" H20 or even higher. You will here the port begin to "whistle" as the velocity at the SSR reaches the speed of sound (Mach 1).

Your throat diameter seems correct (~90% of valve dia.), but you need to pay close attention to the radius/angles above and below the valve seat.

If you have a pitot tube, perform a velocity "map" of the port. It you have any points in the port that exceed 60% of the speed of sound the port will be "choked" in that area. These are the areas that will need work.