possitive pressure? what is this?

[dsmrocker]

i know this might be a stupid Q? anyway, i just installed a Big28 last week, and for some reason i decided to go through all the instruction i'had followed, and this note caught in my attention, which am really confuse about. here you go:
!CRITICAL NOTE: Now is the time to make sure there is some source of positive pressure that reaches the wastegate actuator. If you do not connect the wastegate actuator to a source of positive pressure (such as: a "T" into the blow off valve vacuum line, or a tap in the new intercooler piping you have purchased, or, as it is with the HRC kit, the tap on the compressor housing of the turbo) your boost pressure will be out of control and you will most surely damage the engine.

i am tottaly confused about this note. i install my turbo by just doing this:......."i closed(turn it all the way down) my MBC unhook the hosing and then, take the old turbo out and put the new one on, well ofcousre with all the necessary stuff". my car runs fine with the new turbo, but i noticed my boost guage is spiking like crazy. i mean, before i raised up my boost controller, i was getting a 10 psi consistently and now my boost is set to 15psi, but when i step on the gas, it will go all the way to 20-21psi. i only did rotate the MBC five times since i install it back. so i assume thats additional five. Man, i really hope that someone here know whats going on. Thanks!

 

[GSX4LIFE]

Atmospheric Pressure at sea level is 14.7psi. This is the normal air pressure thats all around us. Its also where we get Stoiciametry from. Anything over that first 14.7psi is postive pressure or psi. Anything lower than that point is negative pressure or Vacuum. Thisd confuses a lot of people, because they see thier boost guage at 0psi. Well, they are calibrated for this. That 0psi is actually 14.7psi. What that warning was telling you is to simply have your boost controller hooked up to the wastegate actuator. If you do not have a controller, or just a line from a pressure source, the actuator would not open. Which would allow boost to rise to dangerous levals. The spiking you are expieriencing is pretty normal. Yours is a little high, but if your only seing it for a split second , it will not damage your engine. Check the length of hose that your running from the controller. Very long hose can increase boost spiking dramatically.

 

[dsmrocker]

jeezzz, thanks man! i thought am screwed! i'll keep that note you put on in mind.
...yeah my hose from my MBC to wastegate actuator were pretty long about 1 1/2 foot long. Thanks!

 

[candela]

Gsx4life is exactly right...The only thing he didnt point out (which might not even be correct), is about the boost controller. I don't know if youve tried yet, but turn it down!!! Five turns is a lot to go up when your already at 10psi. On mine (JoeP) about 0.5 of a turn is around 1psi. Are you settling at 20psi or just spiking, cause I dont know any that spike that high unless your boost is set somewhere close to that... Make sure all the connections ara correct then turn it down.

 

[froodawg]

The only correct assumption is that your MBC isn't set correctly, or not installed correcltly. Check all connections, make sure that the MBC is close enough to actuate, and try setting the boost down.

If all else fails, I'd suggest when it's down all the way you might be running a little high, but nothing to worry about. Let someone who knows their stuff look at it for you to keep from destroying your engine. On the other hand, it might be running just fine. Just make sure it's set all the way down before drawing any conclusions.

 

[dsmrocker]

well, i turned the controller all the way down again, and this time i accurately turn it up just 2 turns, but am not sure yet what the boost reading is. tonight when i leave here @work, i 'll find out. am thinking about moving my MBC closer to the turbo though, coz right now it is sitting right next to the fuse box(left side). i thought it is a bit too far from where it supposed to be and the hosing is too long. i hope this will improve and iliminate a boost spike.

 

[Eclipsed]

I installed my turboXS mbc and i had the same prob. The line was to long. I cut down the line and its fine. The radiator hose from the engine to the radiator had a plastic connector on it hold the line to the coolant dump tank so I moved the piece closer to the actuator and it holds the line great. NO probs!