Has anyone designed/built a positive pressure ...

[Tony]

I agree completely with your philosophy gte.

Suction is logical for testing normally aspirated induction systems, but for exhaust systems, or forced induction, blow testing is much more practical.

My bench has two test holes, one blows the other sucks. The blow test hole is ideal for testing whole exhaust systems, mufflers, turbocharger pipework and intercooler cores. The air flowing through these components will be turbulent anyway, and flowing a lot of air INTO a pipe, blowing it in under pressure, is far easier and seems to give better and more consistent measurement results.

The trick is to measure true static pressure in a high velocity turbulent air stream. A pitot static probe works wonderfully well for this. A pair of matching pitot static probes and a U tube manometer work very well for measuring pressure drops through pipework.

[gte]

[gte]

[bruce]

[Tony]

[thomasvaught-1]

I agree that Tony's set-up in many ways resembles what I would do with the Vortron Blower set-up.

Larry M and I obviously think on the same lines about this stuff and I agree with all of his statement about the different main webs tending to block the airflow that would be in the crankcase even using a set-up for suction like Smokey Y. did.

Tom V.

[larrycavan]

[gte]

Ok, I'm trying to picture what you are describing with the stream/river scenario ... but it's tough.

I can tell you that the exit of the pipe would simulate a venturi or Bernoulli's principle. Where a fluid or air will accelerate through something loosely resembling an hour glass of some sorts where the far edges are wider then the center. You probably know about Bernoulli's principle, but if not, here is some info on it that is a better description then I could try and explain (with an animation).

As far as the entrance to the pipe, you'll notice the outer edges slow down, as the water "bounces" off of the edges of the banks and then into the center flow to go through the pipe. If you were to take a shovel, and make the banks rectangular (parallel to the pipe entrance), instead of having the angled directional entrance, I think the reversion would be even more prevalent, even though the water isn't under "pressure" , which would amplify this even more.

[larrycavan]

[thomasvaught-1]

What I have observed, in the past, with my "Blow thru" Pressure type flow bench vs testing in the normal "vacuum" Mode:

1) With the set-up I have when I suck out of the pan, as was mentioned by Larry M, the flow through each cylinder is affected by where my suction point is in the pan. Test Pressure in the pan might be the same but the flow currents are obviously different.

2) When I "Blow Thru" the Throttle Body (EFI) the velocity of the air in relation to the blade position changes the air flow distribution to the Intake Runners/cylinders.

3) When I put a piece of curved tubing before the Throttle Body, the air flow distribution changes.

4) When I install a carburetor with a bonnet and the bonnet is clocked in the 12:00 or 6:00 position the airflow distribution (side to side) remains pretty even when only the primary blades are open.

5) When I install a carburetor with a bonnet and the bonnet is clocked in the 12:00 or 6:00 position the airflow distribution (side to side) remains pretty even when all of the blades are open but the front to rear distribution will vary, just like it does on a naturally aspirated carburetor.

6) When I install a carburetor with a bonnet and the bonnet is clocked in the 3:00 or 9:00 position the airflow distribution (front to rear) remains pretty even when all of the blades are open, but the farthest primary blade away from the inlet will always see more air when only the primaries are open. The distribution will also favor the side away from the inlet when all of the blades are open. An Open Plenum Intake seems to be able to correct for this much better vs a dual plane intake as there is no divider to limit "sharing" under the carb.

7) More plenum volume under the carburetor/ Throttle body with an open plenum intake always helps even out distribution.

With "Log" type efi intakes plenums the air distribtion can be improved greatly/ corrected by tilting the throttle body mounting flange for best off -idle/part throttle distribution to all runners. Once the blade(s) are fully open the distribution will not vary much to the runners.

9) Very small changes to the Intake Port entry shape before the runner on "Log" type manfolds can improve overall flow through the range. Some runners might need a dam before the inlet to restrict air flow at lower speeds and others might need a blended trough or radiused hump to improve air flow to that runner.

That is the way I can improve the intake manifold distribution/ Carb& Bonnet distribution for my needs.

Tom V.

[larrycavan]

IMO, testing methods like Tom mentions here are a good example of the extended use of the flowbench. To this day, it irritates me when someone makes the comment " a flowbench doesn't tell you anything".

Nope...it won't...not if you don't know how to use it to your advantage.

Nice job Tom. When you going to get around to posting some photos of these "mysetery benches" you keep talking about?:cool:

[thomasvaught-1]

When the Ford Patent comes through, larry! LOL!

Tom V.

[gte]

[larrycavan]

Here's one from one of my OLD SAE papers from 1974. You guys will get a kick out of this...

Things have been scaled down a bit since those days.



Edited By larrycavan on 1205287352

[thomasvaught-1]

That pic was the first "Real Flow Bench" I was aware of. You needed a serious air compressor to run the thing.

Years ago, Larry (without seeing the Schematic and understanding it) I thought the large plenum was charged up like the Holley Carburetor Air Boxes were. You opened a control valve, the sliding drum forced the air out of the system and you took a reading.

Today I can look at the drawing and see that it is very similar to our benches in many respects.

Orifice to measure the flow, manometers to read the test pressure, etc, etc.

Tom V.