SaabCentral Forums banner

Boost creep...

1K views 8 replies 5 participants last post by  G96nt 
#1 ·
So I'm not sure if I have boost creep or not. I have read about it, but not sure if what i have is it. Also is boost creep a bad thing? Here's what I'm talking about. When I used to have a stage 3+ my car would boost to around 17 or so and slowly drop.91 octane here in sunny Ca. Now my car shoots up to that point and then builds up to about 21 max and will hold. I'm not sure if this just the nature of this turbo(tdo4-18t 6) and how it spools or if this is termed creep?
Thanks all
 
#2 ·
i would check with the tuner as to what level of boost you should be seeing at different rpms and gears. boost creep usually occurs if the wastegate flow capacity is exceeded . you will see the boost continuing to rise as the rpms increase, if you hit 21 psi and hold steady to the red line i don't think you are seeing boost creep.

yes boost creep is a bad thing because the ECU is not controlling the boost the wastegate housing is.
 
#4 ·
Thanks all. The car was tuned on the street for 4 hours. Plus I did not change a thing since then except put a new cat in (same type of cat). I'm going to hook up the WB and take a peak just to make sure I'm not about to grenade my motor.
 
#5 ·
Its always nice to know for sure!!! The thing is even if it was working perfectly on the day of the tune with that tank of fuel, things can go bad, a weak fuel pump for example, I had this issue, new fuel pump and the fuel pressure was good to about 20psi of boost at say 65-70psi of fuel pressure, but once I would go over 20psi of boost, my fuel pressure would go back the other way and be back to 40psi by 25psi of boost:eek: This caused a lean condition in my car!!!

This is probably rare, but Nick said he noticed some falling fuel pressure on his project ng900 with gt3071 and high boost. Its very nice
to know ecactly what kind of a/f you are running! If you run a higher octane gas or just get gas at another station you can run more boost or less boost and this will directly effect your a/f to some degree. That is what I have experienced in my car...

I love my innovate wide-band and now Nick at gs offers this stand-alone wide-band a/f kit for something like 299.00

John
 
#6 ·
yeah but i dont see a failing fuel pump causing boost to rise.

honestly i think thats what you rgonna get with your tune, because you are running conservatively on those huge injectors, and you asked for a conservative tune right?

i used to get it too under cooler temps on my 9k. initial boost to 23psi and then up to 25-26 as i passed 4k (with the 18t)
 
#7 ·
saabkid37 said:
yeah but i dont see a failing fuel pump causing boost to rise.

honestly i think thats what you rgonna get with your tune, because you are running conservatively on those huge injectors, and you asked for a conservative tune right?

i used to get it too under cooler temps on my 9k. initial boost to 23psi and then up to 25-26 as i passed 4k (with the 18t)
Yep! With 91 octane gas and all the additives, you really can't get a great tune here without really spending lot's of time dialing it in. My car is pretty fast, but not blazing fast at all. It's like I gained about 25whp. With the stage 3 + I was at 246 whp so I would say I'm around 270-maybe. It will not go above 21, and I read that boost creep with rise to infinity if it could so I think it's just the way the car is tuned. It almost feels like it has 2 steps in power.
I also ported the wastgate, but there isn't much you can take out based on the opening.
 
#8 ·
saabkid37 said:
yeah but i dont see a failing fuel pump causing boost to rise.

honestly i think thats what you rgonna get with your tune, because you are running conservatively on those huge injectors, and you asked for a conservative tune right?

i used to get it too under cooler temps on my 9k. initial boost to 23psi and then up to 25-26 as i passed 4k (with the 18t)
Oh no, I was not trying to relate my lean condition to his possible boost creep, I was only saying its nice to have a wide-band a/f kit in your car so that you know for sure what your a/f is doing and with the boost rising at the upper rpm limits, it would be nice to know what your a/f actually is at those higher rpm levels.

My falling fuel pressure example was given only to show that other things besides the tune can cause lean conditions and that if I had not installed a wide-band a/f kit and fuel pressure gage, I would have never known I had a problem until the motor went pop! I had put the car on the dyno 2 weeks before and the a/f was great, then after only 3 weeks on a brand new fuel pump, bad fuel pressure and a lean condition that could have blown my motor was discovered with my new wide-band and fuel pressure gage!!! Wide-band for the win in my opinion!!!
 
#9 ·
yes, that's "creep"

higher air-flow from higher RPM means you will eventually over-run the internal wastegate, and not be able to bypass the exducer, which keeps the turbo spinning "too fast". the result is boost pressure increase past your desired setting.

The solution? ported wastegate hole, and bigger flapper-valve.
or, if you're made of money, external wastegate. (a GIANT waste of $$ with your turbo)
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top