Well the design process goes something like this.
Choose RPM for peak power
determine peak air flow at that RPM.
Determine area that will give you a air flow velocity of 690 FPS at peak
air flow, this is minimum area of the port also called choke, critical
choke, critical area.
Choke should be 1/4 cylinder volume up the intake port from the valve, so
take 571 cc's of ATF and put it in the intake port, tilt the head till
the level is perpendicular to the axis of the port and mark it in the
port wall.
The intake valve seat inside diameter should be sized for 610 FPS at peak
air flow, so the walls from the choke to the valve seat should smoothly
taper, but you need some flow bench time to design the shape. I use
Flow-Pro and potot readings to map flow in the port, I also use a dummy
valve with a hole drilled into the seat face and up the stem connected to
a manometer so as I rotate the valve the mano readings tell me where the
air is flowing over the valve. That helps shape the port, but it is
still a smooth divergence from choke to valve.
Up stream from the choke will be set by your intake runner length. A
good starting place would be size the mouth of the runner to give 350
FPS at peak flow and just a straight taper down to the choke. this
should give you a divergence of something less then 7 deg..
As for the actual grinding, I make a full sized drawing and measure
dimensions every 1/4 inch, then use snap gauges to check the work.
Chris Hall
So that is a start. It usually gives a good broad torque band.
> While I know
> there are
> many shops around that will port my head they know about top end
> rather than
> keeping the power as low as possible. I have a spare head to play
> with...
> any suggestions?
>
> Kirk
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