Airflow through intake

[NSXLNT]

Hi all,
I posted this question on another forum, and thought maybe someone here could provide me with the answer I'm looking for.Thanks,
Keith http://www.nsxsc.com/ubb/Forum17/HTML/000114.html

 

[Lud]

Does anyone know how much air(in cubic feet per minute)is drawn through the intake into the engine at various points, from idle to wide open throttle? If a constant increase in CFM were to be made available, would engine performance benefit, or does the increase have to be variable with engine speed? In other words, say for instance that a stock engine draws x amount of air through the intake at idle, where x is the max that can be drawn at idle speed, based on filter and related intake plumbing restrictions. Then let's say that the same engine draws y amount of air at wide open throttle. If we introduce z, which is an increase in air available, constant from x through y, where the engine is now running x+z through y+z, do we see an increase in performance attributed to z, all other things being equal? Is this how a turbo or supercharger works? Or is z variable based on need/engine speed in a turbo/supercharger setup? How can it be determined as to what velocity in air intake is needed to provide a given increase in power? If x above provides one horsepower
and y provides ten horsepower, can it be shown conclusively that adding z will increase that HP equally from x through to y,
say by some percentage of HP? What other variables are inherent in a turbo/supercharger setup that result in the increased performance of the engine?
Thanks,Keith

I'm not sure I fully understand what you are asking here, but it all boils down to simple math.

CFM is calculated as: engine_size * RPM/3456 * volumetric_efficiency = CFM

engine_size is in CID, which is cc * 0.06102

volumetric_efficiency is used as a decimal value (i.e. 99% VE would be 0.99 in the calculation).

Air supply, aside from being a classic '80s band, doesn't mean anything by itself. What matters is how much air the engine needs vs. how much it can get.

If your setup can flow the peak CFM required at redline at whatever the maximum VE of your engine is, there is nothing to gain by reducing any "restrictions" in the intake path because the engine already has all the air it can use.

A turbo or supercharger pressurizes the cylinder. This forces more air into it than would go in at atmospheric pressure. This increases the VE of the engine to some amount over 100% depending on the PSI of the system. When you increase VE you draw more CFM at a given RPM. More air + more fuel = more power.

 

[NSXLNT]

Thanks Lud, your response went a long way towards the answer I am looking for.Based on your response, perhaps I should rephrase my question with a new twist: In an N/A motor, can we make it easier for the motor to breathe( reach VE )by introducing an increase in available cfm through some sort of mechanical means? And, if so, would the resultant efficiency in breathing provide a gain in performance? Something like a Turbo or Supercharger without the pressurization of the cylinders.

 

[ScienceofSpeed]

While additional airflow may present higher air density to the engine, I'm not sure that the stock ECU would compensate enough for the increase to notice a measureable power increase. Sounds like a fun project never the less. There is an NSX owner here in Seattle that works on Navy jets who is looking into a similar project.

Reminds me of that Toro leaf blower connected to the throttle body of a car that circulated the internet a bit ago.

-- Chris

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[NSXLNT]

So then do you think an aftermarket chip would be beneficial?

 

[dswartz]

In a normally aspirated motor, air velocity is extremely important. That is why a smaller throttly body will generate more power at lower rpm. However, at higher rpm the smaller throttle body becomes a CFM restriction. High velocity intake charge improves volumetric efficiency by providing a "supercharger" effect. Therefore, the trick is to allow just enough CFM at a given RPM while maximizing intake velocity.

I'm kind of a normally aspirated freak, so if you come up with something, I'm interested.

 

[Edo]

Get Velocity Stacks.
The Ultimate NA Intake Solution.

 

[Lud]

Originally posted by NSXLNT:
Thanks Lud, your response went a long way towards the answer I am looking for.Based on your response, perhaps I should rephrase my question with a new twist.

dwartz did a good job of answering your your question on this. Do you have all the answers you were looking for now?

 

[DutchBlackNsx]

There is this thing availble over here called 'powerrohr', which is german for powertube.
It's actually a tube with a alectrical fan in it. No HP-gain measurable.

(Maybe the fan is not strong enough???)

Very intersting project though.


Dutchy