S4/B5 Boost Pressure Tester in Edmonton

[The_Jerbel]

Re: S4/B5 Boost Pressure Tester in Edmonton

Interesting. I've never noticed anything like that before with any of the cars that I've worked with. Since the ECU is based off of MAF readings and is modulating N75 duty cycles, it should be compensating for the air density and making the same boost pressure, regardless of temperature, which is consistent with my experiences.

Interesting that you see that difference in your car.

[fazda]

Re: S4/B5 Boost Pressure Tester in Edmonton

The air is more dense, since our cars run on a MAF system, the charge air being more dense, the ECU compensates and reduces boost pressure

i always beleived this was true as well. because the air is more dense it requires less boost to reach the desired CFM.

[The_Jerbel]

Re: S4/B5 Boost Pressure Tester in Edmonton

Keep in mind that the ECU uses fixed desired boost pressure, not desired CFM. This is an engine load-based system, which determines the other variables. The MAF values and boost pressure are independent variables, and fuel injection and ignition timing are the dependent variables.

This means that your charge air volume changes with climatic variation, rather than your boost pressure. It also means that your turbos have to work a little bit harder in summer months to meet the desired boost pressure than in the cold winter months.

I've worked with a lot of different FI cars, including several B5S4's, and boost pressure has always been consistent throughout the year (assuming all else remains equal and the car is healthy). Theoretically, you shouldn't see boost pressure variation with different temperature or altitude, but because of unknown variables that aren't accounted for, reality is sometimes a bit different from what the theory would predict. Ryan's car is one of the only cars that I've seen where the boost drops a pound or two in the winter.

[Mantis]

Re: S4/B5 Boost Pressure Tester in Edmonton

My car may behave as such due to inconsistent MAF scaling, I stuck with a stock MAF when I went stage 3, this caused large boost fluctuations in differing ambient conditions, now that it is dialed in, I still see a spike of 21 in the cold, where it was 23 in the summer, the car has no boost leaks as of last week. I should mention that my car does maintain boost at the same level 19psi, it is the initial spike that has changed.

[black97]

Re: S4/B5 Boost Pressure Tester in Edmonton

Did you get ahold of a boost leak tester? i also have one, if you need to test still.
let me know.