High Speed Flow Bench 1

[jturner]

I have heard that high speed flow benches have been made by blowing down compressed air through the cylinder head in a similar fashion to supersonic wind tunnels. Does anyone have any insight on this?

 

[SMOKEY44211]

Most commercially available flow benches use an iris like restrictor to achieve a constant depression of 28" mg. I built one that I monitor changes in deppression at a constant flow on the intake side. I also do this with all the conduits in place. I think that gives me better feed back if I am gaining flow. Higher vacume readings = less flow. On the exhaust side I introduce positve pressure. Higher pressure readings indicate less flow. I don't know of anyone else that does it this way and its hard to argue with a method which seems to be universally accepted. My thinking is that the more closely I can duplicate the actual working dynamics the better the data. I can also analize wet flow characteristics with this method. The best part is ready to run system is under$1000.---------Phil

 

[enginesrus]

What is the measurement method for CFM?
How do they do it on commercial designed flow benches?
Is it calculated flow ie a certain pressure through a certain size orfice or what?

 

[SMOKEY44211]

To xr7755 For my purposes I wasn't that interested in what the actual cfm flow was. I was more interested in comparison of cylinder to cylinder variations. I used a 5 hp. rated vacume cleaner to draw a deppression for intake and 3 of them to blow into the system for the exhaust.
Typical 350 cu" V8 engine draws about 75 cu' per cylinder at 6,000 rpm. When the engine is on the dyno vacume readings are near zero at WOT throughout the rpm range (2,000-7,000) I was testing. The only demonstration of commercial equipment I have seen is at trade shows. The sales people are unanimous in that all testing be done at 28"hg. which they control by changing the orifice size of an iris like device. If I question why they don't just monitor vacume readings they look at me like I'm from some far away planet. I've even seen demonstrations where they draw a deppression on the combustion chamber side to check exhaust flow reasoning being "if it flows good backwards it will flow good in the opposite direction". They monitor cfm. by placing a turbine like device in the conduit between the pump and the bench. In the end I was able to achieve the results I was looking for using the method I described.----------Phil

 

[enginesrus]

I would like to do the same. And can see what you are saying, I agree with you. I was asking the how because I don't know.
I would like to know where to get an affordable CFM meter?

 

[SMOKEY44211]

xr7755 Check out

http://www.flowmeterdirectory.com

looks like a goos source.-----Phil

 

[sacem1]

If you are dealing with small flows of up to 200 SCFH of air you can get good inexpensive flow rotameters from Key Instruments via grainger or other mayor distributor for less than 80 bucks, for higher air volumes you can build one yourself with static pressure and dynamic pressure reading gages in a tube but that works well only in very high volumes, in between maybe someone else can help.

SACEM1

 

[brucepts]

Everything u ever wanted to know about building your own flowbench is located on my forum located here:

http://www.tractorsport.com/cgi-bin/forum/cgi-bin/ikonboard.cgi

Happy surfin'