boost reading??

[teknetic]

hi all just installed my boost gauge. however, im having some problems with it. through 1st-4th the gauge hardly shows any boost pass zero( goes up from 14 vacumm to zero very quickly but hardly go passed) , and then reading goes wild on 5th (showing 10-15psi at almost WTO) but drops back down instantly. do i have a boost leak? the car idles fine at 14-15 vacumm. P.S. i change the tubing on the original gauge to a bigger vinyl tubing (three times the inner diameter) ,maybe that is messing up the calibration? i thought about this before i changed it but i figured the boost pressure passes through this tiny hole anyway; big or small tube is not gonna matter. perhaps it is back pressuring inside the tube. has anyone done something similar and had the same problem?
any insights is greatly appreciated.

 

[King Salami]

If you replaced the stock tubing with tubing that's 3X the inside diameter, it will definitely affect the boost reading. If you've got a bigger inner volume in the tubing, pressure will take alot longer to reach peak. I'm assuming going back to stock (or smaller), your gauge should react normally. If you'd like the gauge to react instantly (and more accurately), you could go with smaller ID tubing. Also, I don't know if I'd use vinyl tubing. It may be expanding slightly, affecting boost readings, too. Regular 3/16" fuel tubing should work just fine.

 

[teknetic]

thanks, i thought so too. however its just a pain in the ass to find a T fitting that fits the small diameter tubes, homedepot had nothing. i guess i will look around some more.

by the way, what is the normal behavior of the boost gauge?what "should" it look like with a stock turbo and stock exhaust and aftermarket BOV? i.e. should it hold at 15 psi and not drop until xxxx rpm? is it different in different gear?rpm? thanks again everyone!