So my friend has a 03 WRX with Turbo XS Stealth-back Exhaust. He also did used to have an AEM CAI and Turbo XS Type H-RFL BOV on his car too, but he took them off when I told him they were hurting his car's performance.

He recently got a Autometer Pro Comp Ultra Light Boost Gauge for his car, so he obviously can read the boost if he wanted to up the boost. However, whenever he goes WOT, the boost gauge spikes to 15 PSI, then it drops to 10 PSI, then it goes back up to 15 PSI, then it goes back down to 10 PSI, then it hits redline. And during this time, it doesn't feel like the car is gaining or losing power, just maybe something is wrong with the gauge.

His set-up looks like there's a line that comes out from under and infront of the intercooler, which loops around and used to just connect to the stock BOV. Now he has a T there, going to the BOV, and then it connecting and continueing through the firewall and into the gauge. This correct?

We played a little with the vacuum sizes, but he said the vacuum size needed to plug into the back of the gauge is so small, that he had to use small vacuum hosing for it.

Also, I tightened down all the clamps around the intercooler, and turbo area that were lose and that might be causing a leak. After I did this, we got in the car and he said his cruising vacuum is much lower. It used to be -14 vacuum ish and now it's -20 in cruising. At idle it's -18 vacuum.

Is there anything else I should try to get this gauge to work? It should hold at 15 PSI or whatever and just hold there right?

I don't know much about WRX's so I can't really help him out unless I ask you guys. Thanks a lot.

- Chris.

 

I am not sure what could be wrong, but stock psi should be around 13.6. I would say that 15 psi is not normal unless you had a reflash or a boost controller.

 

Well wouldn't the exhaust up the boost a bit being that the turbo has less backpressure and can spool quicker/easier?

 

I am fairly certain that the exhaust does not affect boos pressure. Boost pressure is mainly regulated by the ECU and the wastegate.

 

Yep, I've read stuff like that too. The 3/16" mod is certainly another possibility if he has it.

 

I have no idea what you're talking about. You mean 3/16" vacuum size? Please elaborate .. He just installed what Autometer provided him with, then matched the really small vacuum hose up with more small vacuum hose to complete the set-up.

 

Maybe this will help:
http://www.scoobymods.com/forums/showthread.php?t=1564

But now that I am thinking about this, you are saying that the vacuum hoses for the gauge are smaller than stock right? If so, you might essentially be ending up with a similar bad affect kinda like the 3/16" mod can cause.

 

Wait. So do you NOT recommend this 3/16" vacuum connector mod? Or do you recommend it?

 

Haven't done it myself but I've read posts about people that have it and have been getting weird results, boost spikes. So, I'd be cautious about it. Personally, I am not planning on doing it on my car.
Some people do report some gains (haven't seen actual dyno posts). I guess, at the end you have to draw your own conclusions. The 3/16" mod is a DIY and you have to be kinda careful with those.