Flow bench results
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Flow bench results
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?
What say you?
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Re: Flow bench results
Err... are you saying that flow in TDC at valve overlap is the most meanigful ??
Or did I misunderstand something?
Or did I misunderstand something?
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Re: Flow bench results
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.
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Re: Flow bench results
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.
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.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
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Re: Flow bench results
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
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 reverseswampbuggy 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.
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Re: Flow bench results
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 .
Of course closing / sealing off the the test cylinder to simulate piston position would be nessary .
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
Re: Flow bench results
No, I think you are very wrong. Air flow works on differential pressure and is no relevance whether from a depression or pressure.mag2555 wrote: ↑Tue Jun 05, 2018 7:38 amSorry 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.
Flow testing at overlap lifts will give an even more inaccurate indication of hp potential than normal flow testing at max lift.
Rick
Re: Flow bench results
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
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
Re: Flow bench results
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.Scotthatch wrote: ↑Tue Jun 05, 2018 8:50 amI 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 reverseswampbuggy 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.
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Re: Flow bench results
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 ...
Re: Flow bench results
Why would you be flowing in reverse at max lift or max cfm on the bench?Carnut1 wrote: ↑Tue Jun 05, 2018 9:07 amAn 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.Scotthatch wrote: ↑Tue Jun 05, 2018 8:50 amI 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 reverseswampbuggy 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.
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Re: Flow bench results
Overlap is just a necessary evil! LolScotthatch wrote: ↑Tue Jun 05, 2018 9:09 ammag2555 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
CGT wrote: ↑Tue Jun 05, 2018 9:11 amWhy would you be flowing in reverse at max lift or max cfm on the bench?Carnut1 wrote: ↑Tue Jun 05, 2018 9:07 amAn 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.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
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
Re: Flow bench results
It was suggested to get a basic idea of how efficiently the port moves air in both directions.CGT wrote: ↑Tue Jun 05, 2018 9:11 amWhy would you be flowing in reverse at max lift or max cfm on the bench?Carnut1 wrote: ↑Tue Jun 05, 2018 9:07 amAn 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.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
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