boost problems

[kchaazz]

hello there. im just wondering what would cause me to get 15psi in 1st gear all the way up to the redline, then get a spike to 13-12 psi and level off at 10psi through all the other gears? i did a boost leak test and got none in the ic pipes, but perhaps there is a leak in the tb area cause i do get a high whisle when hitting boost while driving? do i need to put my engine at tdc then hold the gas pedal down while doing the boost leak test in order to find a leak in the tb? and in any case, how could this cause me to get full boost in 1st and less in the other gears?
by the way, perfect compression all the way across- 160psi, no smoke ever, and car still has loads of power all the way- but more in 1st.
please help me out here, this sucks.

 

[dave99gst]

ya got a datalogger ? are you knocking ? timing may be gettig yanked-
hows the plugs etc..
your profile says custom MBC - what makes it custom ? is it homemade ?are you sure its hooked up correct.
is this a new prob ? was all fine before ? if so what did you change?

i wonder if its more like your spiking to 15 in 1st and its set to 10 for the rest.


I never put my motor to TDC or hit the gas. Ya should be able to hear a leak at the t/b if its leaking.

 

[nine5raptor]

A few other helpful things (regarding spike):

1. Does the boost act the same if you slowly roll into it in first? Other gears?

2. If you are in 2nd at ~3000rpm, what happens if you mash it?

Let us know how it reacts here as well as answering dave's questions about your controller.

BTW, how long are your boost controller hoses? And where are you getting your boost source from?

Chris

 

[kchaazz]

well, i built the mbc myself, the home depot special, and ive had it for a long time. see, usually its pretty touchy, i mean, if i were to barely turn the screw it would raise me by 3-4 psi. since i put on this new dejon tool upper ic pipe ive had this problem (about a week) no matter how much i turn the screw it wont go past 10 psi in the other gears but ive been too scared to turn it up too much cause ive been gettin 15psi in 1st but perhaps i should ease into 1st and see if the boost drops down? it seemed to hold throughout the redline.
also, if im at 3000 rpm, i get great spoolup from there too, i mean, itll hit 10 psi quick. maybe i have a bit of a pressure drop with this ic pipe? well, thanks for the posts, guys, i really appreciate it and ill answer all your questions as best i can.
charles

 

[kchaazz]

oh, and also, i have my mbc teed into my blow off line and its definetly hooked up correctly.

 

[nine5raptor]

This is pretty much irrelevant to the current situation, but you might want to try this on your mbc....

1. Find an extra fine thread bolt slightly larger than the one you are using now and buy the tap that goes with it. Redrill and retap the housing for your mbc to accept the new bolt. This way, when you turn the bolt, it will move less axially and change the boost less.

2. Experiment with a couple of different spings (I went through ~10 before I was happy with mine) and use an air compressor to pressurize it to get an idea of how much your boost changes/adjustment.

3-4 psi per wiggle is way too much.