How to choose testpressure?

[arnotoekan]

Hello, my name is Arno and i have a question regarding the height of the water(manometers).

Currently i am using a Superflow SF 300, and the manual advises a testpressure of 25 inches. But i dont have to stick with this value. How do i choose the right height for a cilinderhead? Are there calculations for it??

Thanx

[86rocco]

[Thomas Vaught]

The SF-300 bench was truly calibrated for testing using 25" of water test pressure. Says so right in the SF manual. If you test at a different value there is a correction factor they would like for you to use
with the range chart mounted on the bench.

The bench was calibrated at 25" as there is a sweet spot on every orifice where the accuracy is the best and SF used that spot when they selected the orifice sizes.

Agree that you can use the conversion chart to find the flow value but you also need to do the correction on the max flow value for each range if you deviate from the 25" test pressure.

Tom V.

[lewis]

correct me if I wrong here....but the standard test pressure is 29" or 14.7 psi.........based on the fact that if a perfect vaccum is vented to ATM the pressure would be 29" @ std conditions. Of course supercharging could drive this differential up. At higher pressure you alway got to be aware of trans and supersonic flow........generally a condition you will not find in a normally aspirated system.

[86rocco]

You're refering to standard atmospheric pressure 29.92" of mercury, a flowbench can't come anywhere CLOSE to generating that kind of differential pressure. On a flowbench, test pressure is typically around 28" WC (water column) or about 1 psi.

[lewis]

that is right ....just thinking out loud......and pulled the trigger before rereading .......so the question is then has someone and, someone must have, mapped the flows in a running engine?

As for testing in generally, its a comparison process, a comparison process to measure your efforts. I think people spend to much effort trying to match or improve on someone else "numbers" when the final abritrator is at the track.

If you measure at x and get results good or bad you are moving in the right direction........

[DaveMcLain]

I think the real secret to selecting a test pressure is to pick one where you will not run out of capacity as you open the valve farther so that all of your data points generated during the flow test will be generated at the same depression.