Positive pressure flowbench

[Farrell]

A number of years aga someone made a post regarding the construction of a positive pressure flow bench. Well, I've finally got mine up and running and am getting useable and repeatable readings. Within .3 of 1 percent.The air source is a blower off of a Mustang Cobra 4.6 litre motor. To drive it I sourced a Hyundai 7.5 HP,3800RPM three phase motor. As pulleyed, the blower will turn just under 8000 RPM. Ya it is loud, but in a good way. It sounds like an F1 engine. Ear protection is required. For flow measurement, I used a hot wire anemometer from the gas industry. These are a tad expensive, at just under 4K, but I can measure up to 2000 CFM. For pressure measurement I chose a Meriam digital manometer that will go up to 2000" h2o. Again,this unit wasn't cheap,@ about 1K. So far I've tested as high as 300''. I'll get some pics on as soon as possible.

[Brucepts]

We await pics . . .

[Farrell]

Pictures as promised.

[1960FL]

Very Nice,

Is the motor on a VFD, How are you recording your data?

Rick

[Farrell]

Thanks for the compliment,Rick.Ya, the blue box on the front panel is the VFD.It reads 0-60 hz. Getting the test pressure set exactly where you want it is very easy as 1 hz will vary the test pressure a few tens of one inch. The hot wire I've used is so accurate though the test pressure must be within .2-.3 of one inch to keep the readings meaningful.Keeping track of test pressure and test temperature are critical for repeatable results.Once I figured out the temp correction everything came together. As to data, I manually enter it into the computer. I have Flow Quik software for this.

[Farrell]

I'd like thank my friends Dusty Eason at Abstract Supply(asimfg.ca) and Dave Cross at Passenger Industries(passengerindustries.com) for the great deal of help they gave in the creation of this thing. I had the idea,the parts and the lay out, but they really made it all possible. Whether it was allowing me to use their equipment or actually fabbing, machining and welding, I owe these guys a lot of gratitude.They're half my age, and twice as smart. Check out their sites.

[Farrell]

I've been doing a lot of testing lately and I'm really surprised at how soon most heads can start going backwards. 2 & 4 valve, based on calculated flow at a new pressure. The flow does in fact go up,of course, but a lot of times will be 20+ CFM off what it should be. There have been times though when a port will flow more than what the calculated increase should be. Though I've only seen this on down draught multi valve heads so far. Interestingly, the above mentioned losses can start as low as 2-3 PSI. But like I mentioned,the air flow does go way up with pressure, but the quality of the flow suffers.

[200cfm]

Just found this link and interested in how this is actually used for your head research. Are you simulating boost conditions through the port? Do you have a You Tube link? What does it mean when air flow quality goes down but the flow has gone up? I've heard others use this term "air flow qualilty" but what are they referring too? Quality as in ???? Thanks.

[Farrell]

I've tested as high as 300" and found what I had suspected years ago,that the air flow paterns between N/A and boosted aren't similar what so ever.I got the idea to build this bench when I started doing high boost diesel heads.Before this the highest boost I ever saw was about 50 psi on a TAD.The heads on this car I filled with epoxy and did my damndest to finess.With a tiny 2.19 intake they flowed around 400 cfm.This was back in'87.The drag race diesel stuff I did was more in the area of 130 psi.I saw some heads from competitors that didn't flow bad,but didn't make any power either.My early Cummins 12V heads were worth 50-60 HP and 200 degrees EGT with no other changes to the motor.Later combustion chamber mods brought the EGT down up to an additional 100 degrees through more efficient burn.The motor would feel a lot less lasy too.Flow quality for me is the actual flow compared to the caculated flow at a given pressure increase.At boost the back wall,floor height and chamber shape are the most important parameters.

[200cfm]

Do you see CFM flow increases at these test pressures or just density mass increases? Do high boost pressures change the velocity pass the valve and seat?