Can You Convert Kpa to lbs of Boost?

[Vettepartz]

First off, I am at an elevation of 5300 ft. When tuning a normally aspirated LS2, My MAP usually maxes at about 80 kpa. I recently did a blown one that maxed at 103 kpa. Is there any way to figure out the max pounds of boost from these figures?

[Bill@HPTuners]

~101kpa is equal to atmospheric pressure, any more than 105 is boost, any less is vacuum.

[Vettepartz]

Does the altitude here figure into that in any way?

[Bill@HPTuners]

Yes, you can read more about atmospheric pressure here http://en.wikipedia.org/wiki/Atmospheric_pressure

[John_D.]

boost = map - baro / 6.9

A lot of people just plug in 100 or 101 for baro, but if you have the bytes to log it, then you'll be exact for the conditions at that moment.

For example, 170kpa - 101kpa / 6.9 = 10.0 psi

Baro at your location(elevation) does make a difference.

[John_D.]

p.s.
If you're running a 1-bar map sensor, you may never see more than 103kpa reported, even though it may be making more than that.

103 would be about 3.3 psi for you.

[2xLS1]

This one has a converter at the bottom.

[Bill@HPTuners]

Unfortunatly the original poster sounds like he's trying to somehow come up with a boost figure using the stock 1 bar map which will not read boost.

[Vettepartz]

Thanks for the answers guys. I did not realize that the stock sensor will not read boost, as Bill says. My main idea here was that since the most I read on a naturally aspirated motor is about 80 kpa, can I assume that is the figure to use for baro at this altitude? I was assuming that anything above that was considered boost on a blown engine, but I guess not from reading the answers to my post. BTW, the HP editor also has a conversion table under 'Tools' to go from kpa to lbs per inch.

[Bill@HPTuners]

BTW, the HP editor also has a conversion table under 'Tools' to go from kpa to lbs per inch.

Correct and you can also switch the reading in the scanner for just that parameter, however remember whatever reading you see in the conversion you would need to subtract atmospheric pressure from to get you'r actual boost.

For instance if you're seeing 80kpa that is equal to 11.6psi, that doesnt mean you are running 12psi or a supercharger since you need to subtract ~14.5 psi off of that 11.6, meaning your still in vacuum.

[John_D.]

Thanks for the answers guys. I did not realize that the stock sensor will not read boost...

A stock supercharged cobalt 2-bar map sensor is often used in conjuction with a 2-bar OS upgrade.

My main idea here was that since the most I read on a naturally aspirated motor is about 80 kpa, can I assume that is the figure to use for baro at this altitude?

There should a sensor/pid for baro. Log it one time and see. Or just see what your map says with the key on but the engine off.

I was assuming that anything above that was considered boost on a blown engine, but I guess not from reading the answers to my post.

Anything you make, over and above normal atmospheric pressure (at your location/elevation) is indeed boost. Without a blower or turbo, you wouldn't be seeing those kpa values above 80.

14.5-14.7 only works at "sea level". The column of air is shorter (and lighter), the higher up you are...

[BBA]

The formulas work if you read the MAP sensor before you start the engine and use that as the starting point, but without a MAP sensor made to read boost (IE: use a Cobalt SS SC MAP sensor), you still will not be able to tell.