Bottle neck? How to determine if present

[wadesns]

I have been banging my head against the wall for about two months now and cant seem to figure out if my engine is getting the air it deserves. How do you determine if it is getting the proper amount? What needs to be logged? Are there calculations involved?

Thanks,
..RJ..

[wadesns]

Maybe I didnt ask this question correctly what i am actually asking for the more general public is how do you decide when your engine has outgrown the intake or throttle body or in my case if my airbox isn't flowing enough air.

[TNT76]

Start with MAP in Kpa, should read around 101Kpa with ignition on and motor NOT running.
At WOT if it gets below 100 Kpa or so then your starting to get a restriction upstream of the plenum (Throttle opening, Throttle body, Intake filter/pipe system etc. Downstream is harder to determine without swapping manifolds or flowbenches etc.
My std car used to get down to 93-94 Kpa at WOT in the mid to upper rpm, so there was a fair bit of improving to be done. New filter setup and SD tuning without the MAF got it upto a steady 99-100 Kpa right upto 6200rpm limiter

[Black02SS]

Start with MAP in Kpa, should read around 101Kpa with ignition on and motor NOT running.
At WOT if it gets below 100 Kpa or so then your starting to get a restriction upstream of the plenum (Throttle opening, Throttle body, Intake filter/pipe system etc. Downstream is harder to determine without swapping manifolds or flowbenches etc.
My std car used to get down to 93-94 Kpa at WOT in the mid to upper rpm, so there was a fair bit of improving to be done. New filter setup and SD tuning without the MAF got it upto a steady 99-100 Kpa right upto 6200rpm limiter

I will disagree with this statment to a point. Your kPa will vary depending on where you physically live. I have seen several H/C cars with only 97-98 kPa around here and then go to the east coast find out they are 100-101.

[wadesns]

ok so i start off with my map is 98 kpa koeo then at wot the highest it ever goes is 95 kpa but stays around 92-93 kpa so does this mean that i have a restriction? If so how are you determining this on the map only? wouldn't altitude and humidity and other weather conditions have an affect on this? I am only guessing for i have no idea how to determine a restriction but i do know that your map gives a different reading depending on altitude. Also isn't your Map pressure affected by the enternals of the engine. ie the cam's duration and lift, and displacement and stroke?

[TNT76]

I will disagree with this statment to a point. Your kPa will vary depending on where you physically live. I have seen several H/C cars with only 97-98 kPa around here and then go to the east coast find out they are 100-101.

Yeah sorry, your right. I live at around 30 meters above sea level here in Australia. I nearly always see 101Kpa at key on.
What I should of said was if your Kpa falls a number of points from your base key on Kpa, then you are having a restriction.

Wadesns, your getting 5-6Kpa below your base 98kpa, so something is holding it up a little. At WOT, 'IDEALLY' you should be getting the same as your base 'Atmospheric' Kpa if you have no intake restrictions.
Also I beleive at key on the PCM gets a current barometric reading from the MAP sensor to offset for the current atmospheric conditions, i will stand corrected on this though if proven otherwise.

One last thing, a std manifold with std TB may be able to get to close to base Kpa but once you start adding a cam, headwork, stroked etc then the std setup will start to become a restriction and you might start seeing Kpa dropping off at WOT, from an undersize inlet system upstream of the plenum. Its all got to do with supply and demand, more demand needs more supply, if it cant supply enough then vacuum builds in the plenum.
I hope i've put my thoughts into words clearly.

[wadesns]

ok that makes good sense thanks
..RJ..

[joecar]

...Also I beleive at key on the PCM gets a current barometric reading from the MAP sensor to offset for the current atmospheric conditions, i will stand corrected on this though if proven otherwise...

That is correct and that key on MAP value is called BARO;

and while running, if MAP goes above BARO, then BARO is updated with this new MAP value.

[kbracing96]

That is correct and that key on MAP value is called BARO;

and while running, if MAP goes above BARO, then BARO is updated with this new MAP value.

Yep, I run into this with my turbo setup. Here at key on, I have 83kPa, but first time I go into boost, it runs baro right on up to like 101 or 102.