primary and secondary chamber volumes

[Thomas Vaught]

Quote:

"I assume rigorous testing has come into play somewhere along the line to achieve this constant. Well I was contemplating on my latest car project to try and establish this figure in the field."

A little history for you:

A guy named Henry Yunick (Smoky to some) was doing a lot of dyno testing. He was trying to determine how he could improve his HP of his engines without massive dyno testing. Flow bench testing of heads was one thought. He tried changed on a head tested at different test pressures and found that everytime he made a change that was picked up on the bench using a test pressure of 28" of water he also saw the same improvement on the dyno. He wrote about this in his book therefore everyone took it as the benchmark to use.

Ford tested at 67" of water for years but they had very good air flow vacuum pumps. Smokeys test pressure was in the range of possible testing for the average guy who built a bench.

The old SF 110 used a much lower test pressure because it had fewer vacuum motors. SF used 25" of water as their calibration point for the benches.

Hope this helps.

Ford Motor Company records flow readings at 10", 20.4" 25" 28" and 67" so they have data at all points typically used.

Tom V.

ps Larry, Harold does the job for a living, I typically take his info to the bank.

[86rocco]

Tom,
That bit about encouraging turbulance in your earlier post definitely seems counterintuitive, care to expand on that a little?

[jsa]

[Thomas Vaught]

86Rocco, please explain your issues with the statements made and I will try to answer them or have Harold post here and answer them.

As far as the test pressure corrections go, we find the corrections very accurate if you have accurate discharge co-efficients for your benches ranges. The only other issue I am aware of is that your cylinder tube that the head mounts on must be large enough that you measure the test part and not the cylinder when making test pressure comparisons.

Tom V.

[larrycavan]

Before looking at Greenlight's chart, the turbulence being beneficial to orifice flow accuracy didn't make any sense to me at all. To be honest, my jury is still out on that issue.

The chart shows the relationship between Cd and Reynold's Number. I have to put time into fully understanding what is truly happening.

What I know [real world] is that without even considering the Reynold's Number, my flowbench works pretty darn good. I really wish someone with a clear porthole setup would tape some string sections inside their orifice plenum and observe what happens. I look at the flowpath and just can't picture the baffle helping to create, rather than to fight turbulence in the chamber.........I'm trying to Tom...but my brain won't wrap around that one.. :;):

[86rocco]

[larrycavan]

[Thomas Vaught]

Quote:

"I look at the flowpath and just can't picture the baffle helping to create, rather than to fight turbulence in the chamber.........I'm trying to Tom...but my brain won't wrap around that one."

If you take a water hose and with a minimal water pressure at the nozzle (with the nozzle focused in a single stream) you get a nice smooth water arc to the ground. This is a lot like laminar flow (nice and smooth).

If you take that same smooth stream of water and point it at a wall next to you you get a lot of "water break-up" into "turbulent flow" from the laminar flow now impacting on the wall. You get water on your shoes!

Same deal applied with the baffle inside the plenum. Initially you guys tried just having the
bore tube over the orifice hole and had a lot of goofy readings. Once you put the baffle (sf design) into the plenum your reading got much better. You ever wonder why that was? Obviously the air impacting on the baffle did not allow "laminar flow" to continue out of the tube to the orifice. Right? When it hit the baffle the air went everywhere just like the water did when it hit the wall. Turbulent flow. JMO

Tom V.

[jsa]

[quote="larrycavan"][/quote]
[color=#000000]Larry,

Along similar lines I hired a mass flow meter to test a prototype laminar flow element I made. I also tested a 5.05mm orifice with the mass flow meter.

At 46mm H

[larrycavan]

[jsa]

[color=#000000]I made a 12.82mm orifice yesterday and did some measurements on it with the hired mass flow meter to see if the Cd was more consistent for a larger orifice.

I set flow from 50 l/min to 300 l/min in 50 l/min increments as readout from the mass flow meter which is calibrated to give standard litres / minute of air.

I read off the pressure drops in mm H

[bruce]

Square edge or sharp edge orifice?

[Greenlight]

Larry, if you could post the document titled Re vs. Cd (or just the graph contained in the document) that I emailed you on 10/18, I think it would help clear up some of the confusion as to why his Cd is changing as he increases flow through the orifice.

Higher Reynolds numbers will give you a lower discharge coefficient, especially in the Reynolds number regions you are experiencing.

[jsa]

[jsa]