I was reading another very informative post over on Speedtalk. The link above takes you to part of the conversation that I thought anyone new to building a flowbench would be interested in.
Larry C
Pro Bench Accuracy - Comparison Flow Tests
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by larrycavan » Mon Nov 28, 2005 12:17 pm
I was reading another very informative post over on Speedtalk. The link above takes you to part of the conversation that I thought anyone new to building a flowbench would be interested in.
Larry C
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by gofaster » Mon Nov 28, 2005 1:43 pm
My main concern is that the bench repeats.
Trying to compare flowbench test results to someone else's on a similar head leaves a lot of variables unaccounted for. (Or even the very same head for that matter!)
Another shop may use different entry radius plates, clay, a long velocity stack, or nothing, at the intake opening. They may use a straight flow tube on the exhaust or different size tube, or longer or shorter. They may or may not grease the valve guides and use seals to cut down leakage, they may or may not grease all o-rings, gaskets, and seals to eliminate leaks. Maybe they remembered to install the spark plugs, or maybe they didn't. Their test fixture may be very close in size to the cylinder that the head is being flowed for, or they may have a one cylinder fits all approach.
I know what my procedures are, and I can take a head that was tested two years ago on my bench, and get the same numbers back today, with only a fraction of a percent difference.
If it doesn't, the first place I look is for leakage in my set-up.
I try very hard to make sure that I test the same way every time.
When my new project bench is done, I want it to repeat.
If I take the same hypothetical head from the previous example, and put it on the new bench, I'll be delighted if it gives me the same numbers once again. If it doesn't, it's not the end of the world, and it doesn't mean one of my benches is no good.
The main thing is that it's numbers repeat on that bench.
Next summer, or two winters from now that head should give the same numbers on the same bench.
After all, the main purpose I have for my bench is to find out what is happening as I make changes in the port, valve, seat and combustion chamber.
It is just a tool, and it's just about the neatest tool in the world for my money!
Trying to compare flowbench test results to someone else's on a similar head leaves a lot of variables unaccounted for. (Or even the very same head for that matter!)
Another shop may use different entry radius plates, clay, a long velocity stack, or nothing, at the intake opening. They may use a straight flow tube on the exhaust or different size tube, or longer or shorter. They may or may not grease the valve guides and use seals to cut down leakage, they may or may not grease all o-rings, gaskets, and seals to eliminate leaks. Maybe they remembered to install the spark plugs, or maybe they didn't. Their test fixture may be very close in size to the cylinder that the head is being flowed for, or they may have a one cylinder fits all approach.
I know what my procedures are, and I can take a head that was tested two years ago on my bench, and get the same numbers back today, with only a fraction of a percent difference.
If it doesn't, the first place I look is for leakage in my set-up.
I try very hard to make sure that I test the same way every time.
When my new project bench is done, I want it to repeat.
If I take the same hypothetical head from the previous example, and put it on the new bench, I'll be delighted if it gives me the same numbers once again. If it doesn't, it's not the end of the world, and it doesn't mean one of my benches is no good.
The main thing is that it's numbers repeat on that bench.
Next summer, or two winters from now that head should give the same numbers on the same bench.
After all, the main purpose I have for my bench is to find out what is happening as I make changes in the port, valve, seat and combustion chamber.
It is just a tool, and it's just about the neatest tool in the world for my money!
Jim
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