flowbench design - floaing depression

[bruce]

I know everyone is always open for discussion on flowbench design on this forum . . . but, I think you are going to be hard-pressed to find anyone here supporting the GFN bench design using one vacuum blower no matter "who" the expert is pushing it.

[49-1183904562]

[color=#000000]Simon;

I understand what you are saying but you are confusing a few sciences, Statics, Dynamics and Fluid Dynamics. Let

[1bolt]

David Vazard's first primitive flow bench is not the issue. His bench doesn't require floating depression, and floating depression doesn't require his style bench! So can we stop throwing the baby out with the bath water?

You don't HAVE to use a primitive bench to use FDp. That bench was just his introduction to the floating depression concept.

If Pipemax and Dynomation use only the square root formula I would be surprised. If they get their data from the same place that Engine Analyzer Pro does, then they are using discharge coefficients. Probably in addition to that formula I doubt they're using only the mathmatical aproximation of air flowing through a sharp edge orifice...

The programers of those sims surely understand that the further you get from a simple sharp orifice, the more error creeps into the "model"...

Also we're talking about MAYBE a few lbs of torque or HP here, even if we could hypothetically find a sweet 10hp extra with floating depression testing; that's still a not an error number that's going to shock someone using a Dyno Sim...

If the car actually does something like 195hp and 255 foot lbs and the sim says 205hp and 245 trq. I think most people would say they are pleased by how accurate the sim is as long as the power curves look the same. heck you can sit two different guys at the controls of the same dyno and come up with more difference than that.

[1bolt]

[1bolt]

[302ford]

Am I thinking correctly
A few months ago i was told in a post that 120 inches of water equalled 3,342 psi
I have done some thinking isnt it really 28 inches of water equal to 1 psi
So 120 inchs/27.7 equals 4.33 psi equals 1psi
So it would it be 600 pounds per square foot?
Thanks
Randy

[1bolt]

Randy I don't know so I'll let someone else field that.

I did want to add that since my last post on this subject I've been playing with Engine Analyzer Pro more. EApro uses Flow coefficients, not the square root approximation.

The square root formula is only a good predictor of flow through a square or sharp edge orifice. The flow coefficient of either is usually around .62 right? Well a good port especially at low lifts can be close to .80 (a valve with the same opening as a sharp orifice is going to be considerably more efficient much like a nozzle is) and at higher lifts can often be lower around the .5 range

Not only do ports not behave like a sharp edge orifice which is what the square root forumla is supposed to approximate (it's a model), they are usually considerably better or worse depending on lift and how well done the porting work was.

If you're using that formula, for example; to convert CFM at one lift/depression to another, then you will be applying a model that assumes .62 Cd at all lifts when in fact they are likely to be considerably better or worse on each end of the valve lift range. Thus your CFM conversion is okay looking in the middle lift ranges. And that is why you can see differences (sometimes big ones like earlier in this thread) they are magnified at low and high lift as the Cd of the port gets further and further away from the .62 assumption of the Square root formula.

CFM isn't the only thing we could be measuring. One way to look for differences at the same lift with more or less depression (or floating depression) would be velocity maping. I haven't done it myself but I'd be curious to map velocities (looking for relative differences between areas of the port) with higher and lower depression.

[302ford]

Hello
I was discussing test pressures with a friends a few days ago and there is no simple answer.
For example a good exhaust can pull almost 200" of vacuum at TDC and a well tuned runner can produce over 100" with the location of peak depending on runner lenngth.RPM, carb size etc. combine this with the natural depression produced by the piston desending the bore and the restriction of the port at each valve lift and u have a mighty complex situation.
So what is the best way to test and at at what test depresion. Just some thoughts to concider

[302ford]

I have a question on a post on dec 9 regarding vizards education as basic and prosenting a diffucult theory to prove insteady of building one and proving it.
I have known David for a while and trust his experence. He has told me personally that this procedure does work. I am hoping to have such a bench designed and working in the near future. But it will have 6 or 8 vacuum motors as the vacuum sorce instead of the single shop vacuum.