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Flow Balls

5K views 4 replies 2 participants last post by  dogwater 
#1 ·
I found this very interesting...
This move is helpful if you don't have a flow bench to verify your work or you are confronted with a head that you have no experience with and are looking to make gains as quickly as possible during the first stages of the heads development.

All this deals with minimizing the shrouding of the valve in the first 0.250 lift.

At this point let me refer you to the first illustration #1. Here you see a 0.250 dia. flow ball positioned under the intake valve in part of the valves circumference that is not shrouded i.s. adjacent to the exhaust valve.. From here the flow ball is pulled up thus raising the valve until the flow ball slips out from under the valve. At this point there is obviously a gap between the edge of the valve and the chamber that is totally un-obstructive for a .250 diameter ball to pass from the port into the chamber. Hold the valve at this lift point.

Next push the flow ball under the valve and try and draw it out around the chamber where the chamber wall can shroud the valve. That's basically from the plug around to the position shown in #3. Conversely you can, while holding the valve in position, try pushing the flow ball between the wall and valve. After noting where the flow ball touches the chamber take a suitable cutter and relieve the chamber. Do this progressively so you don't overdo things. When the ball can slip between the valve and chamber wall on down over the seat and into the port you can reckon the valve is un-shrouded as far as possible.

If you want to get fussy over this you can start with an 1/8 dia flow ball and work your way up to the 1/4 diameter one.

This process works about 9 times out of 10. On most stock style castings for SB Chevy's and SB Fords it works almost 100% of the time. On some chambers, usually BBC you can go up to a 3/8ths flow ball and still see positive results. The bottom line is that this process is much faster than cutting the chamber a conservative amount and then testing. In short it is a useful starting point that will get the chamber shaped much nearer where you want them first time around.

Once valve ;lift gets much over 3/8 this method loses it’s ability to return positive results because the velocity of the air in the ports starts to play a role by directing the main body of air. When this happens making gains from purely geometric moves becomes a little dodgy.


This is just simple porting for some pretty decent numbers. The BMP 200 cc port SBF head shown here made just on 180 cfm at 250 lift through a 2.02 intake valve. That is above average and was arrived at first time around. Flow at 700 with the intake guide slimmed and little else was 288 cfm and just a tad under 200 for the exhaust.

These are some pretty good numbers for a head porting that is not using a bench to develop the numbers but to just ratify results This shows that some simple moves to these heads nets some good results and can be done at home.

DV
ATTACHMENTS
flow ball positioning.jpg
#1 setting the valve lift. #2 & 3 checking flow clearance around valve head
#5A lo res.jpg
finished chamber
Last edited by speedtalk on Tue Apr 19, 2016 7:44 am, edited 1 time in total.
Reason: Promotion
David Vizard
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#2 ·
Add a link from where you found this information Dogwater, it is against copyright to cut and paste from another website without giving credit.
 
#4 ·
As I understand anywhere the ball won't go thru or fall thru the gap between the valve & seat is where unshrouding could be done from the spark plug hole on around to the position marked in photo 2. Instead of guessing this would show where unshrouding should be done.
 
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