calib plates on exhaust? - cal plates

[cboggs]

Bruce, .. and everybody, ..

I'm working on calibrating the exhaust on my custom bench, ..
but, .. have a question about the calibration plates.

Do they flow the same on exhaust as intake???
( yes I know to turn them over so they are flowing in the proper direction )

OK, .. I think this is a stupid question, .. as the air will be heated, ..
but at the same temp as the orifice plate in the bench.
Shouldn't make a difference should it? If they are both at the same temp
I don't need to worry about any temp corrections right?

Cheers,

Curtis

[larrycavan]

You're correct. No need for a correction.

Larry C

[Mouse]

Exhaust calibration is tricky, and uncertain at best for several reasons. I know I might start a very emotional thread with this, so I am just going to leave it at that. If you want to learn more, there is a thread on Speedtalk where I discussed this. Just do a search for Mouse.

As mentioned, temp correction is not that big of an issue. Just use a small calibration orifice.

John

[cboggs]

John,

yes I remember reading that thread, .. and I don't want to bring up
all those issues again.

But, .. to set my exhaust flow ranges, .. I need to tell the PT software
what 100% is and calibrate it.
I need to flow the plate, knowing what it's "supposed" to flow so I can
calibrate the sensors, etc.

So, do I make the assumption the plate flows the same in the exhaust direction?
I don't think they do cause the air is "pressurized" into the orifice, ..

I did flow them on my SF110 on exhaust, .. and my 75cfm plate flowed
85 cfm, .. the 400 cfm plate flowed 436 cfm. Flowed at 5" and converted to 28"

I'm really tempted to use the flow rates I got from the SF110 for the plates, ..
as I know that bench has been very good.

While on this subject, .. anyone know what flowbench AFR uses?
Their heads NEVER flow the advertised numbers in my shop and I'm
wondering if it has to do with their bench calibration?

Cheers,

Curtis

[Mouse]

The person who does their bench work built his own bench I believe. There is an article on it at FordMuscle.com

[Nick]

This is a PM I sent to Curtis

I thought others my like to comment on my insanity.

Are you using your test stand to do your calibration, or is it bolted to the top of the bench?

when I built this thing, it flowed the within a few cfm intake and exhaust, with the plate on the top with no head adapter.

I just went out side and tested it again with the adapter and it flowed 177ex 189in. 4.030 adapter.

I am not using electronics, so those numbers are calculated assuming the same CD.

If I wanted I could make another CD for the exhaust, but I'm not convinced I should.

So If I wanted them to show the same number, the intake CD would be .585 intake and the exhaust would be .625.

If I put the same size pipe on top the stand above the calibration plate it would have the same CD both ways.

Interesting to note that orifices in the correct size pipe have a CD of .62 So when my bench is in ex mode the orifice acts like it is in a pipe, when it is in intake mode it acts like it is in open air.

So I don't know what is right, but I do know I will not flow the same if you are using an adapter. Even the thickness of the top is going to make a difference, because it will to some extent shroud the hole

It would also depend on your orifices being the same on both sides. Mine is a flat piece of 1/8 steel 17"x20" with holes drilled in it.


I say piss on it, I am keeping the same CD both ways.

From my understanding air speed is more important in an exhaust port than a number anyways.


Nick

[larrycavan]

Try this if you will.

Mount the calibration plate for intake calibration. Dial up your test pressure, obtain your flow reading and turn the bench off.

Now flip the plate over and don't touch anything execpt the motor switch(s). If the test pressure and cfm return to exactly what they were before, you have equal flow. If not, then you can calculate the difference and use that number as a correction for your exhaust tests.

JMO

Larry C

[cboggs]

Nick,

With the test adapter, .. I think you're forgetting something, ..
It SHOULD flow different, .. cause the test adapter is acting
like the bore of the engine, ..

No doubt I would calibrate the bench with the plate on the bench, ..
then any bore adapters that are used to flow exhaust will make
the port act and test like it does on the engine.

Try your test on a FS and see what happens.

OK, back to the calibration, .. I do feel because we have the air
under pressure when it sees the orifice it will flow different.
Did it on my SF110, .. my 75 cfm plate flowed 85 cfm, ..
my 400 cfm plate flowed 435 cfm, ..

I'm going to flow the plates on a friends SF300 in exhaust and
see what he gets, ..

Now my orifice plate in the bench is rather large with the three holes
for the ranges, .. and is quite some distance to the wood that supports
it, .. so I don't think it should have too much influence on the flow numbers.

Larry, .. that's great idea, .. and a simple solution, .. you a smart man!

Cheers,

Curtis

[larrycavan]

I must have had my head up my...well you know....because my suggestion can't possibly work the way I presented it.....Not enough coffee this morning or something...

The problem is that you'd be using two different flow control valves with some benches and that throws my whole suggestion right out the window....

I need COFFEE and a rethink on this.....sorry 'bout that..

Larry

[Mouse]

What I do, duplicate the exhaust setup while in intake mode. While in intake, place a dummy bore (if you are using a test stand) or dummy piece of plywood the same thickness as the top of your bench and with a duplicate discharge hole in it the same size as the hole on top of your bench, on top of your calibration orifice and flow test it. These numbers are what I use to calibrate in exhaust mode. The larger your cal orifice, the more it will be affected.

There are still some unresolved issues, but this is about the best you can do to establish a flow rate for your cal orifice in exhauast mode.

One other note, it's not there is more pressure in exhaust mode, the pressure differential is always the same, intake or exhaust, it is the movement of the air entering the orifice that is not the same. You just can't duplicate the air movement in your shop (virtually none) inside the cabinet of your flow bench (virtually a hurricane).

[Nick]

It "should" flow different, that was what I was trying to say.

Does anyone know what superflow suggests?

I think what we need here is a standard way of calibrating.

Say I calibrate my intake, exhaust without the adapter.

Now say Bob down the road does his with an adapter.

We are going to show different flow readings for exhaust tests.

The only problem is, if we are trying to make our exhaust port flow say 70% of the intake, who's port will be better? Mine or Bob's.

Answer: Who ever gets to the Finnish line first!

I am not going to say who is right or wrong, I would like to know what is the industry standard.

In my bench I know the orifices flow the same intake exhaust, so the difference comes down to the adapter.

I like John's Idea.

In a perfect world we would have a test plate mounted in a pipe.

So I say do what you have been doing with your 110. If that is making the HP you want, and you already have % that you work within for certain heads, then stay with what your doing.

If your new bench shows different than your 110 then you will need to adjust your % for intake and exhaust ratios.







Nick

[larrycavan]

The size of the hole doesn't change but the flow increases. As such the Cd increases. The question is what causes that. Logic states that turbulent air flow leading up to the discharge port should yield less flow than non turbulent air.

Are we seeing the effects of vena contracta being lessened here?

Are we seeing the effect of the bench top thickness increasing the velociity?

Let's not forget the actual construction of the flowdisk itself. Is it's Cd the same in both directions.

The answer is not going to be the same for all of us on any of those points.

Like Nick says, the orifice being located inside the pipe is the closest thing you'll get in achieving duplicate results in both directions...

Larry C