boost drop

donkeyboy · 09-11-2005, 04:26 PM

i hooked up my boost guage today and its showing above 5 grand it starts to drop down from 14psi to almost 10 psi, is this normal i have some other upgrades but i dont think they would affect the boost i checked all the fitting and everything is tight and leak proof i even put the stock BOV back on. now im baffled i dont recall ever reading about this before...

freakray · 09-11-2005, 04:57 PM

Yes, it's normal.

keita · 09-12-2005, 09:18 PM

Well, let me ask this then. My car's max boost is usually stuck around 0.05 MPa, no matter how hard I push it. But occasionally, it will go to 0.09MPa. I just can't figure out how in the heck the max boost is set to either of those values.

freakray · 09-12-2005, 09:57 PM

In honestly Keita, I don't fully understand why it happens myself but I've seen it happen in just about every turbo'ed car I've been in.
There's a point where the blow off will bleed off boost to prevent over-boosting is the way I understand it, but I've never actually had it explained to me.

keita · 09-13-2005, 02:39 AM

Well, ok, thanks for the response. I just didn't want to be the only one experiencing this. I was trying to see if the boost is lower when the motor is cold, when I'm driving in traffic a lot, etc., but I just can't find the relationship; it's either 0.05 or 0.09 and nothing in between. I'm planning on getting Vishnu stage 0 soon, so I'll see what that would do.

LjasonL · 09-14-2005, 07:09 AM

donkeyboy, it's all about the turbo's efficiency. Any given turbo has a certain area where it's most efficient. The small stock turbo is most efficient lower in the RPM range, so you get quick spool up, but when you get high up in the RPM range you get out of it's area of efficiency and lose pressure/airflow. A big turbo will work fine all the way to redline and beyond, but you pay for it in spool up time. Read this for more - http://cherrypicker.tripod.com/id6.html

Right_LiRrr · 09-16-2005, 09:37 AM

Quote:

Originally Posted by freakray

In honestly Keita, I don't fully understand why it happens myself but I've seen it happen in just about every turbo'ed car I've been in.
There's a point where the blow off will bleed off boost to prevent over-boosting is the way I understand it, but I've never actually had it explained to me.

I've heard that the BOV has some mechanism that lets air out once the pressure is too high, like you said, to prevent overboosting.

Isn't this the main reason people get aftermarket BOVs - cos they don't have this safety feature?

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