Ok ...Intake Pressure. What is this ...and what does this mean?
It is measured in hg/mm...or something. What is the optimum intake pressure?.....and it changes during acceleration? I basically need a definition and explination of what intake pressure is and how it corresponds to the engine. I notice mine is negative number than goes to 0 upon hard acceleration. Thanks in advance. can you have a positive intake pressure? Is this the pressure of air that the engine wants and the filter provides a negative pressure that is turned positive when the engine has enough gusto to pull air into the intake for a positive pressure...just a guess Any good books on technical data
of todays advanced cars? What i don't know I like to learn. I believe all men are created equal if the guy next to me can learn it
I can. I am dong my first brain surgery tomorrow. Geminis2k at the s2k meet in Jersey gave me a quick lesson on how too......Sorry getting carried away. Its those dam honey roasted peanuts again....superfuel for the brain

 

I believe that this is just the measure of pressure in your intake (sorry if that sounds too easy). Most people measure intake pressure at the intake manifold so it is commonly referred to as manifold pressure.

Manifold pressure is just air pressure and can be measured metrically (kg/mm^2 aka BAR) or using the American standard PSI.

I believe nearly every normally aspirated car operates under vacuum as the engine consumes air so quickly. I know my MR2 turbo idled at about -500 kg/mm^2. This will change during accelleration as the amount of air consumed by the engine changes.

Positive intake pressure is usually created by forcing more air into the manifold than the engine would normally consume - this is done by using forced induction aka turbo or superchargers. Positive manifold pressure = boost, again measured in either BAR or PSI. I am not sure if it is technically possible for a normally aspirated engine to create positive manifold pressure.

 

Don't ask me how, but Azstama had about .5% positive pressure with his custom intake/exhaust and VAFC.

PM him if you like.

 

You can do that when the car is moving, and you have a good enough intake to force air into the manifold, or with some kind of compressor (Turbo, Super, or *gasp* even a ERam or Tornado - though only when idling!)

 

On a normally aspirated car, you'll usually see a range of up to 20-22" of vacuum to ambient pressure.

At idle the engine is trying to suck air through a very small orifice. This means that it draws a large vacuum in the intake manifold. As you begin to open the throttle, the restriction is decreased, so vacuum drops. Finally, when you get to wide open throttle, you have the minimum possible restriction for that given engine combo.

I usually datalog intake pressure when I do dyno runs. At lower/mid rpm levels, you'll see an intake restriction of about 0.1-0.2 psi at WOT. As rpms climb and the air needs of the engine climb, that restriction will climb to 0.4-0.5 psi, sometimes more.

With aftermarket intakes, that restriction level drops by about half on average. Furthermore, the long tube CAIs exhibit some resonance tuning at several points, and at those points the intake pressure will actually be slightly above ambient thanks to helmholtz resonance supercharging the intake.

UL

 

Hi UL

You mentioned "helmholtz resonance supercharging the intake" is that why there is a bump in the Torque curve of the s2k? at about 5Krpm?

Also does that mean you could tune the intake to alter it's characterisitics at different rpm? Variable Intake Length?

 

Hey thanks guys....I am getting a better understanding of this. Thanks Again

 

On the stock S2K tuney there is very little apparent resonance effect in the intake tract. Honda works hard to minimize bumps and dips through airbox tuning and ignition timing control. However, you will note that a stock S2K torque dips a little around 4k rpm. That's because this is an area where the single runner style intake is less efficient in terms of resonance effects.

On cars with CAIs, the bumps at 3000 or so, and again at 6000 are definitely due to resonance supercharging from the intake system.

Variable intakes are certainly possible, but usually you'd want a variable intake manifold, or variable individual throttle bodies. Making a variable long intake pipe might provide benefits as well, but I've never seen it done.

UL