Ah! Overboosting!

[scottyb]

I thought I read somewhere that RB25's hold 5 PSI of boost up to 5k RPM and then 7 PSI up to redline. I don't have a working tach, but I just installed a boost gauge and at WOT I'm getting 7 PSI up to what I think is 5k and then 10 PSI up to fuel cut.

I've got stock turbo and boost solenoid wired to the ECU. Maybe someone can answer this 2 part question: How does the ECU know what the boost pressure is? Does the boost solenoid regulate boost independently and report the boost to the ECU or does the ECU know the boost pressure and then tell the solenoid what to do?

I know running 10 PSI is pretty safe on a stock turbo, but is the ECU automatically compensating for the added boost by adding fuel?

[drift freaq]

I thought I read somewhere that RB25's hold 5 PSI of boost up to 5k RPM and then 7 PSI up to redline. I don't have a working tach, but I just installed a boost gauge and at WOT I'm getting 7 PSI up to what I think is 5k and then 10 PSI up to fuel cut.

I've got stock turbo and boost solenoid wired to the ECU. Maybe someone can answer this 2 part question: How does the ECU know what the boost pressure is? Does the boost solenoid regulate boost independently and report the boost to the ECU or does the ECU know the boost pressure and then tell the solenoid what to do?

I know running 10 PSI is pretty safe on a stock turbo, but is the ECU automatically compensating for the added boost by adding fuel?

something not normal there. hahhahhahhaha max boost for the stock setup from the factory was 7lbs just like you read. It sounds like your actuator has been changed. I have heard that RB20 actuators put on RB25's create 10lbs of boost. Though I cannot verify this beyond hearing it. Your stock computer can handle 10lbs of boost.

[scottyb]

Thanks for the reply drift freaq, I'm nearly 100% positive about the actuator not being changed because I pulled the motor from a completely stock front clip. I think I read on one of your other posts about doing that with the RB20 actuator and thats what has me so puzzled....Everything that would determine boost is stock...so....:wtf:

[wootwoot]

Do you have exhaust?

[scottyb]

Do you have exhaust?
Yep, McKinney 3" DP, Catco, Apex'i GT-Spec.

[wootwoot]

Anytime you put an exhaust on a turbo car it raises the boost pressure. This might not be as true in new super sophisticated cars(Evo, STI) but in the older ones it makes quite a difference. Maybe the stock solenoid does not have the capability to control boost to this level? Dont worry about it at all.

[scottyb]

Ok, I guess I won't worry about it if you guys are sure that the ECU is supplying fuel to match the 10 PSI of boost. I'm all for more boost, but I don't want to fry my new motor.:D

Can anyone answer my first question about how the ECU knows the boost pressure? Is it from the solenoid or elsewhere?

[LA_phantom_240]

MAFS. It measures the amount of air coming in. More boost = more air.