Boost tuning: question

[christianreid22]

Not sure if this is the proper place to post this question. This question is something I have always wondered and I am sure other tuners in training are interested in as well.

Well adding boost (SC, TC, PC ect) how do you control the boost output of the engine? For example, I see a lot of ?set to max 6psi? or ?made X amount of power at 12pm I, but we turned it down to 10psi for safety?.

How are they turning down/up the boost? How does the pulley size affect what is commanded?

[white1]

rotor/impeller speed and blow off will control boost. Easiest way to control rotor speed is with pulley size

[PurpleRam]

Turbocharged, is mostly watergate (yes different inlet and housings size also).........electronic waste gates make things so much nicer now for turbo and procharger , on positive displacement(whipple , kenn bell) pulley size does most of it, blow off plates is how we control the old school dryer’s and bds screw types

[LilSick]

Electronic boost controller, mechanical gates, and a c02 bottle/regulator to open them.

[christianreid22]

So how is boost calculated then? I recently just saw a Facebook post where they claimed they are only running 6 pounds of boost utilizing a Magnunson Blower on a 5.7. Does the car max at 6psi then?

I initilally thought there is some kind of calculation to be made to solve for how much boost is being used (like baro, map, ect)?? Is this not the case?

[white1]

Boost isnt exactly calculated. Pulley ratio and engine rpm determine rotor speed which results in boost.

MAP reading minus atmospheric pressure (100kpa or 14.7psi at sea level) is your boost pressure.

Boost is "set" by pulley sizes in the example of magnuson. If you want more boost, increase rotor speed by a larger lower pulley, or a smaller upper pulley.

[fixit]

for turbo applications is base on torque, usually gear
in other words, a table provides a torque per rpm and boost, the other says what tq is desired in that gear

[christianreid22]

Boost isnt exactly calculated. Pulley ratio and engine rpm determine rotor speed which results in boost.

MAP reading minus atmospheric pressure (100kpa or 14.7psi at sea level) is your boost pressure.

Boost is "set" by pulley sizes in the example of magnuson. If you want more boost, increase rotor speed by a larger lower pulley, or a smaller upper pulley.

I think this is the answer I was looking for. so whatever MAP is reading in the log during a WOT Pull at a given RPM.... I take this number and minus 100kPa and this is the boost?

[LilSick]

make it read in psi and it will make more sense

34.7 absolute minus 14.7 atmosphere = 20 psi boost

[christianreid22]

does BARO need to be read in psi or is MAP the PID that is used?

[PurpleRam]

I use map and convert, you can also create a “user math” parameter to convert., I do it the old fashioned way because baro is always moving between 14.4-15 where I live.

[calgarylsswapper]

Use your MAP minus your Baro because 120kpa at 100KPA Baro is different than 120KPA at 90KPA Baro.
Thats why Dodge uses Pressure Ratio, related to Baro.

Rick