I already ran a search but found nothing. Here's the situation. I was reading in one of the other forums that intake pressure should never go positive and if it does you have a problem (on a naturally aspirated car anyway). I have the Apex VAFC reading out my pressure and noticed that whenever my throttle is more than 20% that my pressure rises up to 0.12mm/kg in the positive range. Does this mean that I have a problem with my ride? In case it matters I have aem cai, fuel rail regulator, cam gear, dc headers 4-2-1 w/greddy catback 2.5" & freeflow cat converter. Any info would be appreciated.

 

I wouldnt worry about it. Mine does that to every once in a while.

 

Just cuz I do it everytime, its HEADER (singular) not HEADERS (plural). To have headers, you must have more than one cylinder head, ie. a V or W motor.

 

English never was my favorite subject. But thanks for the lesson.

 

Its not so much that it shouldn't go positive, but rather it can't go positive. Without a turbo- or super-charger there's nothing to raise your intake above atmospheric pressure. I think either your gauge isn't as accurate as you think or you've placed the measurement tube in a way to read some amount of stagnation pressure.

I don't know what 0.12mm/Kg is, but if you mean 0.12mm of Hg, that's a really small amount of pressure.

 

Isn't it possible when under WOT and then you let off of the gas. When the throttle body slams shut and the air is still moving at high velocity there may be a brief positive pressure. Not sure on that but I think it's possible...

 

Yeah - that's kind of like seeing the stagnation pressure, just for a moment till it equalizes.

 

I would expect greater vacuum if when the TB valve shuts the engine is still sucking like a pig,,,, the manifold/plenum will be under major negative pressure.

Maybe at the CAI tube in front of the TB you would see higher positive pressure. The air stream has some momentum and when it slams into a closed TB valve there is some positive pressure.

This is assuming that the valve closes all the way when you let off the throttle.

But I would suspect that the calibration of the sensor is a bit off or as mentioned earlier sensor placement is not optimal.

 

i have experienced this a few times, when i dropped it down into 3rd and get on it hard. i had +1 and 0 a few times. i have no clue how it happens.

 

OK my vafc is where I'm getting the readings from and whenever my throttle is more then 20% which is not much on the gas pedal, that's when it goes positive. I was just a little worried because of the thread that I read. I have no idea where the vafc gets the pressure reading from though. I appreciate all of your responses.

 

VAFC gets its reading from the ECU which gets its reading from the MAP(Manifold Absolute Pressure) sensor

I'd have to assume that honda put it's sensors in the correct spot...

I wouldn't worry about it to much unless the car was running like ****