How to set and hold valve lift on a flow bench?

General engine tech -- Drag Racing to Circle Track

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ole4
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Re: How to set and hold valve lift on a flow bench?

Post by ole4 »

I currently use my bench for small engine heads I modify. They have a rather short side and unless you build up the floor you cant put much of a radius on them. I wondered about the accuracy of flowing at lower pressures and found out on these heads with about a 80 degree turn from the bowl to the runner that flow at 10 inches corrected to 28 inches was higher that if I flowed them at 28"s also some heads stock will make a horrible noise at some of the higher lifts or with the valve in upside down when I am debugging with the flowballs. If I drop the depression down from 28"'s it will clean up and I can get it to where the noise/howl is intermittent then drop depression a couple of more inches it goes away. I also when porting will raise the depression up to about 40 inches just to listen for funny noises which I think is when it is getting turbulent. I can see with the string probes that as the valve opens the air starts not following the SSR. I think that at lower depressions with a port with a sharp turn it is easier for the air to follow the SSR. That is the difference to me why higher the depression the better it will show issues. On a port like a modern bike that is almost straight it would probably not make much of a difference.
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John Haskell
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Re: How to set and hold valve lift on a flow bench?

Post by John Haskell »

Unless there is a long term project dealing with days to months. You can test using your fingers alone, add a piece of hose or a new rubber seal to act as a friction brake. Stack them if required. Add the magnetic indicator onto what ever metallic base you choose & your set.

Once you get familiar with this method, it can be done just as fast as you can step the valve & set the pressure. Write with the other hand after 3 steps are taken. Will show yourself how good your memory is as you write. You will be surprised how good you get.

But, -- when you get up into the mid 400's & up, you can get a cramp. But then if you use computers to do your work, ---- can't help you.
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