On an otherwise stock motor, how much boost can be expected with a 17% overdrive pulley? I'm looking for real numbers from people who have actually measured it, not guesses.

 

15-16 PSI on a stock system.

Keeping in mind that your results may vary since measured boost will be effected by ambient atmospheric pressure and ambient temperature.
Plus any modifications to the intake and charge system, not just the engine.

 

My map sensor peaks out at 215 kpa, logged it this past weekend at VIR, see link below. I run methanol (wiper fluid) to keep temps down.

VIR is 400' elevation so ~99.5 kpa, car makes 215 kpa so 113.675 kpa above atmosphere, that's ~16.5 PSI

I dont have the formulas in excel so I rounded a bit

https://podium.live/events/vir-grand...?laps[]=28

 

Thank you for the responses. I am now convinced that my MAP sensor is bad, because I'm seeing 34.5 psia at 5500 rpm, & since I am virtually at sea level (172 ft.) that would be ~20 psig.

 

It sounds like there's some kind of correction being done by an app how are you logging that I'm using the raw OBD values

 

I'm reading the raw OBDII data; no app.

 

17 psi is the high point with a 17% pulley and stock head. If the car is got some wear, higher mileage, or ported head along with other mods it will be less. But again that is just the high point as many cars will be in the 15-16psi range.

 

Check the MAP sensor of course, but don't forget, unusually high boost can also be symptoms of a restriction in the exhaust as well.

 

One more piece to add to the equation. I just got a P0420 DTC code. I replaced one of the O2 sensors about a year ago.

 

Then yes, between the 0420 and unusually high boost, you may have a bad/plugged CAT.

 

What hardware & app are you using to log your data?

 

racecapture pro mine is a mk2

It data logs canbus, obd2 and 5v sources, streams live to podium and my pi dashboard, you can see the dash here

 

Apparently, that app is free. What are you using to convert OBDII to Bluetooth?

 

the app only works with racecapture data loggers, I use a MK2

 

Oh...

 

Turns out it was a plugged catalytic converter.