Flow bench results

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mag2555
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Flow bench results

Post by mag2555 » Tue Jun 05, 2018 7:38 am

I think I have come to the conclusion that air flow testing of heads for NA use and the power they may produce from those numbers is most accurate of what will be seen in real life during the Cams overlap period.
What say you?

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Re: Flow bench results

Post by Morgo » Tue Jun 05, 2018 7:50 am

Err... are you saying that flow in TDC at valve overlap is the most meanigful ??
Or did I misunderstand something?
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Re: Flow bench results

Post by swampbuggy » Tue Jun 05, 2018 7:53 am

Mag2555, could you reword the last 12 words (or) explain what you are meaning by those words ? remembering some of us including myself are not as sharp as some of you guys. Mark H. :D

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Re: Flow bench results

Post by mag2555 » Tue Jun 05, 2018 8:08 am

Sorry its early and I have only had 1/2 cup of the black stuff, lol!

What I mean in short is that our flow benches during a Intake test are sucking air in, when in real lift air is just falling in under whaterever atmospheric pressure we may be dealing with , that is except during the overlap period when a good tuned Exh system aided with some inertia tuning can really make for high VE numbers!

And yes I know that ram tuning has a impact on power even without looking at the high scavenging aid of the overlap period , but it can't get you VE numbers anywhere near 25% or better.

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Re: Flow bench results

Post by swampbuggy » Tue Jun 05, 2018 8:35 am

Gotcha, yea the exhaust SYSTEM pulling on the intake side during overlap at high RPM's like in NASCAR stuff really interest's me. Something else to add, i was just reading yesterday where one of the well known outfits in this business had said in an engine labs interview, flow the intake backwards (air on the exhaust setting) less flow is BETTER because that will help reduce reversion. Mark H.

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Re: Flow bench results

Post by Scotthatch » Tue Jun 05, 2018 8:50 am

swampbuggy wrote:
Tue Jun 05, 2018 8:35 am
Gotcha, yea the exhaust SYSTEM pulling on the intake side during overlap at high RPM's like in NASCAR stuff really interest's me. Something else to add, i was just reading yesterday where one of the well known outfits in this business had said in an engine labs interview, flow the intake backwards (air on the exhaust setting) less flow is BETTER because that will help reduce reversion. Mark H.
I have done a lot of reverse flow tests and it is almost never lower in reverse... normal street parts are almost always 5 % higher in reverse

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Re: Flow bench results

Post by mag2555 » Tue Jun 05, 2018 9:02 am

I am wondering if figuring out a way to factor in flow numbers that we see by sucking on the Exh port ( with the whole Intake tract bolted on . with both valves open as the would be during overlap can shed some light on things?
Of course closing / sealing off the the test cylinder to simulate piston position would be nessary .

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Re: Flow bench results

Post by Rick360 » Tue Jun 05, 2018 9:05 am

mag2555 wrote:
Tue Jun 05, 2018 7:38 am
I think I have come to the conclusion that air flow testing of heads for NA use and the power they may produce from those numbers is most accurate of what will be seen in real life during the Cams overlap period.
What say you?
mag2555 wrote:
Tue Jun 05, 2018 7:38 am
Sorry its early and I have only had 1/2 cup of the black stuff, lol!

What I mean in short is that our flow benches during a Intake test are sucking air in, when in real lift air is just falling in under whaterever atmospheric pressure we may be dealing with , that is except during the overlap period when a good tuned Exh system aided with some inertia tuning can really make for high VE numbers!

And yes I know that ram tuning has a impact on power even without looking at the high scavenging aid of the overlap period , but it can't get you VE numbers anywhere near 25% or better.
No, I think you are very wrong. Air flow works on differential pressure and is no relevance whether from a depression or pressure.

Flow testing at overlap lifts will give an even more inaccurate indication of hp potential than normal flow testing at max lift.

Rick

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Re: Flow bench results

Post by digger » Tue Jun 05, 2018 9:06 am

It's pressure differential. "Sucking" from downstream or "pushing" from upstream is the same

Scavenging during overlap is at higher pressure differentials than 28" and the suction is from the exhaust side so air going through the inlet valve must go over the piston as it's near tdc then through exhaust. The flow bench doesn't replicate this very well

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Re: Flow bench results

Post by Carnut1 » Tue Jun 05, 2018 9:07 am

Scotthatch wrote:
Tue Jun 05, 2018 8:50 am
swampbuggy wrote:
Tue Jun 05, 2018 8:35 am
Gotcha, yea the exhaust SYSTEM pulling on the intake side during overlap at high RPM's like in NASCAR stuff really interest's me. Something else to add, i was just reading yesterday where one of the well known outfits in this business had said in an engine labs interview, flow the intake backwards (air on the exhaust setting) less flow is BETTER because that will help reduce reversion. Mark H.
I have done a lot of reverse flow tests and it is almost never lower in reverse... normal street parts are almost always 5 % higher in reverse
An intake port may flow better backwards due to the pressure recovery that is improved due to the port shape instead of flowing to a more open chamber. On my Dart 215 thread I was flowing 315cfm forward and 285cfm backward and I was told the reverse flow was way high. I though that was a good number.
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Re: Flow bench results

Post by Scotthatch » Tue Jun 05, 2018 9:09 am

mag2555 wrote:
Tue Jun 05, 2018 9:02 am
I am wondering if figuring out a way to factor in flow numbers that we see by sucking on the Exh port ( with the whole Intake tract bolted on . with both valves open as the would be during overlap can shed some light on things?
Of course closing / sealing off the the test cylinder to simulate piston position would be nessary .


In my experience overlap is not the key to power ... I even had a cam that ended early to lower overlap and move the ex cycle out of overlap and it made great low end power and peak was as calculated .... I think a lot of times the mistake is thinking overlap is helping when it is really just early opening of the intake valve and valve exposure at peak piston velocity that is helping ...

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Re: Flow bench results

Post by CGT » Tue Jun 05, 2018 9:11 am

Carnut1 wrote:
Tue Jun 05, 2018 9:07 am
Scotthatch wrote:
Tue Jun 05, 2018 8:50 am
swampbuggy wrote:
Tue Jun 05, 2018 8:35 am
Gotcha, yea the exhaust SYSTEM pulling on the intake side during overlap at high RPM's like in NASCAR stuff really interest's me. Something else to add, i was just reading yesterday where one of the well known outfits in this business had said in an engine labs interview, flow the intake backwards (air on the exhaust setting) less flow is BETTER because that will help reduce reversion. Mark H.
I have done a lot of reverse flow tests and it is almost never lower in reverse... normal street parts are almost always 5 % higher in reverse
An intake port may flow better backwards due to the pressure recovery that is improved due to the port shape instead of flowing to a more open chamber. On my Dart 215 thread I was flowing 315cfm forward and 285cfm backward and I was told the reverse flow was way high. I though that was a good number.
Why would you be flowing in reverse at max lift or max cfm on the bench?

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Re: Flow bench results

Post by Warp Speed » Tue Jun 05, 2018 9:17 am

Scotthatch wrote:
Tue Jun 05, 2018 9:09 am
mag2555 wrote:
Tue Jun 05, 2018 9:02 am
I am wondering if figuring out a way to factor in flow numbers that we see by sucking on the Exh port ( with the whole Intake tract bolted on . with both valves open as the would be during overlap can shed some light on things?
Of course closing / sealing off the the test cylinder to simulate piston position would be nessary .


In my experience overlap is not the key to power ... I even had a cam that ended early to lower overlap and move the ex cycle out of overlap and it made great low end power and peak was as calculated .... I think a lot of times the mistake is thinking overlap is helping when it is really just early opening of the intake valve and valve exposure at peak piston velocity that is helping ...
Overlap is just a necessary evil! Lol

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Re: Flow bench results

Post by Scotthatch » Tue Jun 05, 2018 9:18 am

CGT wrote:
Tue Jun 05, 2018 9:11 am
Carnut1 wrote:
Tue Jun 05, 2018 9:07 am
Scotthatch wrote:
Tue Jun 05, 2018 8:50 am


I have done a lot of reverse flow tests and it is almost never lower in reverse... normal street parts are almost always 5 % higher in reverse
An intake port may flow better backwards due to the pressure recovery that is improved due to the port shape instead of flowing to a more open chamber. On my Dart 215 thread I was flowing 315cfm forward and 285cfm backward and I was told the reverse flow was way high. I though that was a good number.
Why would you be flowing in reverse at max lift or max cfm on the bench?


Reversion is always a problem and anything you can do to help minimize it is a good thing .... testing is one way to see how the port and runner will behave when the flow reverses

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Re: Flow bench results

Post by Carnut1 » Tue Jun 05, 2018 9:22 am

CGT wrote:
Tue Jun 05, 2018 9:11 am
Carnut1 wrote:
Tue Jun 05, 2018 9:07 am
Scotthatch wrote:
Tue Jun 05, 2018 8:50 am


I have done a lot of reverse flow tests and it is almost never lower in reverse... normal street parts are almost always 5 % higher in reverse
An intake port may flow better backwards due to the pressure recovery that is improved due to the port shape instead of flowing to a more open chamber. On my Dart 215 thread I was flowing 315cfm forward and 285cfm backward and I was told the reverse flow was way high. I though that was a good number.
Why would you be flowing in reverse at max lift or max cfm on the bench?
It was suggested to get a basic idea of how efficiently the port moves air in both directions.
Servedio Cylinder Head Development
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