having boost creep/spike in cold weather

[zatomz]

Here's the deal, when I come home late at night, when it's cold out, I get it to WOT and at about 4000 rpm my VDO boost gauge creeps from 16 psi to 20 psi which is not good b/c I'm not set up for 20 psi. When it hits 20 psi The whole car jerks wildly, I'm assuming b/c there's not enough fuel to compensate. What i need to know is why, why is it doing this in the cold weather and not when its warmer outside. Next I would like to know, besides a leak test which I'm working on finding the time to do, what i can do to solve the problem. Thanks for any advice you guys are awesome.

 

[MyBeatGSX]

The 2+ hours of math and figuring it took to arrive at the engines approx. flow is completely lost to me all these months later. Getting a reasonably accurate pressure ratio isn't too difficult if you take an educated guess at the intercooler pressure drop (which you can also look up online).

Honestly I wasn't too concerned about atmospheric conditions. I live within a few hundred feet of sea level and the barometric pressure changes daily anyway.

Its just about getting a reasonably accurate estimate to put a dot on that compressor chart. Obviously its not perfect, but it doesn't need to be and never will be. Its enough to tell me that a s16G works just fine at 19psi and has enough head room to be safe.

If it means anything. I came up with the engines airflow at redline as 0.25kg/sec. The pressure ratio for 15psi was around 2.1 and for 19psi (or maybe looking back now it was 18) was 2.3. Plotting that out on the chart, at 19psi its dead in the center of the 72% ring. At 15psi its just into the 70% ring.

Here's the pictures incase that didn't make sence.

S16G (red = 19psi, yellow = 15psi):

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My apologies for the complete hijack and slightly off topic discussion...

 

[Dorifto]

I think it's a good time to bust out the old SportCompactCar articles about turbo sizing and flow charting.

-Dave-O