Boost cut

Pedro · Post by **Pedro** » Wed Sep 02, 2009 2:18 pm

Guys on the R34 you have the 2 boost cut settings

at present I have disabled both by settng them to max

but what i really want to do is set the boost sensor one to cut at 19psi

factory level is set to around 14 i think is there any way to convert the number so that i can set it to 19psi

Legionnaire · Post by **Legionnaire** » Fri Sep 18, 2009 1:04 am

There is a method to change boost cut level, at least one that I know of. I did not do a lot of experiments with it, crashed my car, but as far as I know, the situation is as follows (if someone has more accurate/complete data, please post here and correct me):
Stock boost sensor, the one that is located on top of #6 cylinder, is responsible for factory boost control and for boost cut. If you are not using factory solenoid for boost control, you have much more freedom to play with the sensor. The easiest way to eliminate boost cut altogether is to simply pull manifold reference hose off the sensor and to shut it. If you are after a more elegant and usable solution (you wanted to have boost cut set to 19psi), you can solder a diode inline with the sensor output signal. This move decreases voltage seen by ECU and therefore increases boost cut threshold by a fixed amount and unfortunately I cannot say by how much. My info indicates that stock sensor sets off overboost countermeasures when it returns ~4.7v to ECU. You can solder an adjustable voltage divider (potentiometer) in your signal line, then power the sensor and, using manometer for the reference and some form of air pump, pressurize it to desired pressure level (19psi), then measure voltage output, turninig pot on potentiometer until voltage reaches 4.7v. Matt is running 17 or 18 psi on his RB25, so he definitely had to overcome stock cut, maybe he can add some useful info.

Cheers,
Petros.

PS. Does anybody have factory R34 boost sensor for sale? I need the one that is located between front right wheel arch and a firewall.

Pedro · Post by **Pedro** » Sat Sep 19, 2009 9:52 pm

Im running 18-19 psi too

but i did that by setting what was then the TP limit 2 to max (255)

but i wanna set it so it cuts if it goes over 19psi

(ie if my external wastegate sticks )

Legionnaire · Post by **Legionnaire** » Mon Sep 21, 2009 8:35 pm

setting TP limit helped with the boost cut? What kind of boost control, if any, are you using, may I ask? In our case setting tp limits to 254 did not help - boost cut, which looks like it's being triggered by pressure, was still there, started at 14-15psi

Pedro · Post by **Pedro** » Mon Sep 21, 2009 10:31 pm

there are two of them

I have them both set to max

one of the TP Limits has now been renamed to TP Recovery that is the one that I changed for boost cut sensor

but Im unsure whether Ive doen the right thing there

Im sure someone will correct me if im wrong

but before i changed the TP limit 2 it would cut at 14 psi

Legionnaire · Post by **Legionnaire** » Tue Sep 22, 2009 12:48 am

Interesting. Thanks for info. I need no do some field testing