[JayRow52]

Originally Posted by wookwook

"boost" is working. but this guage is gauging manifold pressure. It is slightly different than just positive boost from the turbo. You have to imagine the 0 point at 9 o'clock is air pressure at sea level, so that is really about 14.7 psi. In the manifold, there are times when engine suction exceeds the pressure from the turbo and will show a vacuum. on NA cars all you get is vacuum in the manifold. in HPT its a calculated "UserMath" result. Not to say there isnt something on board the car to do that, but in HPT it is calculated.

wookwook, would you mind sharing your math for boost in HPT? I see a few channels related to the turbo bypass valve and pressure, but none seem to be actual boost pressure...

[wookwook]

I will just riff on what I have so far, hopefully its close to a good answer.

On this chart - the pressures all pretty much track the same, so
depending on how you wanted to use them for tracking effects of changes like CAI or DP they would react the same. The sensor pressures are MAF, MAP, Absolute (in psi), and 2 are derived, Manifold psi is a User math senso wanted to use them for tracking effects of changes like CAI or DP they would react the same. The sensor pressures are MAF, MAP, Absolute (in psi), and 2 are derived, Manifold psi is a User math sensor here, and the last one is Boost/Vacuum, which I believe is ECU derived. But in the end they all tell the same story. Manifold pressure will go negative reflecting transient suction in the manifold. the last one 'Turbo boost' is the classical positive only gauge that most people think of as turbo pressure in the intake hose that doesn't go negative at all, there's always at least a little pressure in the intake tube. So in transient if the throttle plate shuts down, there's potential for a little negative pressure in the manifold, but that's referring to 14.7 psi absolute psi as zero.r here, and the last one is Boost/Vacuum, which I believe is ECU derived. But in the end they all tell the same story. Manifold pressure will go negative reflecting transient suction in the manifold. the last one 'Turbo boost' is the classical positive only gauge that most people think of as turbo pressure in the intake hose that doesn't go negative at all, there's always at least a little pressure in the intake tube. So in transient if the throttle plate shuts down, there's potential for a little negative pressure in the manifold, but that's referring to 14.7 psi absolute psi as zero.

[wookwook]

But that really isnt the coolest thing. The cyl air mass and VE which can go into the 1900's is really the story, we get about 92 percent volume efficiency which is really good for a production car. Over 100 percent is really the stuff of rocket science.

[cooper1965]

Absolute manifold pressure is what ya wanna look at. Depending on your OS, and beta or non BETA HPT version, you may or may not have to subtract 14.7... Or just create a custom math for your particular situation, and be done. (<----Easiest way)

[wookwook]

yes- cooper that is correct. after I thought about it for a sec after I posted it, the PIDs are misnomered. I actually knew that but when I posted I did'nt clarify. The blue one is the map minus measured baro pressure. In HPT there is a boost/vacuum PID that one would assume is manifold abs pressure but its just derived positive boost. I am seeing you really have to figure out what the OS is mapping, and not assume anything. Thanks!

i.e. the car is a rolling weather station, lol.

[wookwook]

also.. fwiw, the rambling paragraph looks like the edit spliced itself....sorry about that. the pressures all generally track the same is what I was saying. it was a long day.
\W.

[wookwook]

I also see I used pressure ratio... I will fix it. Attention to detail wookster....

[JayRow52]

Thanks guys! This conversation was way informative. I’m just getting started with logging via HPT and it’s easy to get lost in all the channels and chart series.

[wookwook]

its been a big learning curve. i was the kid who did all auto tech in highschool. so i am bascially learning all over again but its been a good ride so far. don't neglect learning the histogram section. if ur going to eventually work the hp tuner thats where the tabled chart data resides. for a suggestion- look at AFR tuning demos, (basic CAI tuning) see if you can find any HPAcadeny freebies on utube. our car has a built in wideband. thats about where im at.

as a personal observation, you can road tune if you have access to long steady
on ramp. also avoids standing heat soak. and if dont mind doing it over a period of time making small ajustments.