too much boost

[Beecha91]

Hey guys,

My car still just has a mbc on it, and its fine when its warm out, but when its cold obvously it makes more boost. It makes too much boost when its colder out. I turned the mbc all the way out to the point where all the threads are almost out of it, still wouldnt lower it. I have it at 20psi on 100 octane, and if I keep in it on a cold night itll shoot to 24 25psi if i dont let off. Any way to solve this. I know the turbo smokes and needs a rebuild would that have any affect? Any info would be great. Thanx

Don

 

[klrv6]

post MBC

Stick one of these after the MBC http://www.gleempaint.com/air-regulator.html

 

[OneLethal87GN]

I don't understand why it makes more boost just because of cooler temps. If the boost controller is set to a certain psi then it should stay there until changed. Maybe the wastegate needs replacing or you have a leak somewhere?

 

[Beecha91]

Well I know when I had a mbc on my wrx when it was stock the boost would vary depending on the weather. Just my experience. I have an external wastegate would messing with the nut on it help, which way would i turn it? thanx

Don-

 

[murphster]

Originally posted by OneLethal87GN
I don't understand why it makes more boost just because of cooler temps. If the boost controller is set to a certain psi then it should stay there until changed. Maybe the wastegate needs replacing or you have a leak somewhere?

I have a good guess, not sure if its correct though. When air is cooler it is more dense. If you have the same volume, the pressure will be less. Just like a sealed gallon jug expands when it gets got and shrinks when it gets cooler due to higher and lower pressure. Boost is controlled by pressure. The lower pressure exerted on a puck or some kind of valve in cooler weather means more volume of air will flow before the pressure rises enough to open the puck or valve. The higher air flow results in higher boost in the cooler weather.

In hot weather, pressures are higher so the puck or valve opens sooner, letting excess pressure out earlier and not letting you build up as much boost.

Sounds like a good theory right?

 

[MSDGN]

These cars will always make more boost as the temp cools but usually only a couple PSI...I believe it's because cooler air is more dense...that's why you have to be careful with the boost when the temps get cooler...I always have to add more fuel when temps cool down and take fuel out when it warms up...

 

[Beecha91]

So I just took the car out after I adjusted the nut on the external wastegate about three turns out, and I still have the mbc on its last threads almost outta the threads. I still get like 24 25lbs if I stay in WOT. Since i dont have a scan tool yet, I was playing it safe and keeping it at like 20lbs max on 100 octane. What should i do? help would be great thanx

Don-