ON BLOCK FLOW TESTING PROBLEM

[RRBD]

Earlier tonite, myself and a friend were flow testing(sf600) a V-8 cylinder head on an old block that is all sealed up, pulling vacuum through a bung which is welded into the oil pan and noticed a difference (gain) of approx. 18 cfm from prior tests which were done on the bench it self. At first we thought we had a leak some where, but after double sealing every possible leak with duct tape the results were identical. Next we took the superflow calibration orifice and set it up on the bench, as well as set it up over a cylinder in the block and this test also confirmed the same, an 18 cfm gain on the block. Next we sealed the calibration orifice to the engine block end of the hose, (now just bench and hose being compared) and yet again same results.We are kinda baffled, a person would think that it would be just the oppisite, considering we are connecting the two through a four inch hose about 6ft long. Any thoughts from you guys???
Could it be due to the additional volume of the chamber(hose), or could we be experiencing laminar flow at 25" wc and around 240 cfm?? Thanks in advance.....RRBD

[bruce]

Now this is just a suqqestion and may not be your problem at all . . . . I think you have a leak somewhere in your connection? I know you said you double sealed eveything but how did you verify that your seal is not leaking? I use a wand connected to a vertical manometer (on my bench its a digital manometer, but you can use a vertical water manometer also) You probe all your connections and look for a change in the reading, if it changes you have a leak. I had a similar problem this past week with a block/head I was checking, it appeared to be sealed but my cfm's were higher than previous tests with no changes to the block/head. I probed the sealing and I had a small 2-3" water leak at one specific area where it was connecting with the flowbench. It was changing my cfm's about 10 cfm's.

[RRBD]

Bruce, I think you are probably right there is probably a leak somewhere and after sleeping on it, I think it is in the crappy dryer ducting flexable aluminum hose we were using. I am leaning toward the idea that the ducting is not vacuum tight an the whole thing is leaking all over. Do you have any Ideas for a reasonably priced hose in a 4" dia. that will work for intake and exhaust flowing, I am personally using a very stiff hose as used in the vacuum supply for a Komo cnc router, but it is made for pulling 29" of mercury and is very expensive and tough to work with. I wonder if regular flexible dust collection hose will work both ways?? Anyway, thankyou for your input.

[RRBD]

Bruce, I think you are probably right there is probably a leak somewhere and after sleeping on it, I think it is in the crappy dryer ducting flexable aluminum hose we were using. I am leaning toward the idea that the ducting is not vacuum tight an the whole thing is leaking all over. Do you have any Ideas for a reasonably priced hose in a 4" dia. that will work for intake and exhaust flowing, I am personally using a very stiff hose as used in the vacuum supply for a Komo cnc router, but it is made for pulling 29" of mercury and is very expensive and tough to work with. I wonder if regular flexible dust collection hose will work both ways?? Anyway, thankyou for your input.

[RRBD]

Ok guys, new info: Cant be any leaks cause we checked by having valves all closed and watching for flow on the inclined manometer, didnt budge. Flexible dryer duct will work on the intake side but cant have any dings or bench will collapse it. All of this was done with a 303 cfm orifice at over 25" h20.Now I'm really stumped???