boost spike

[4doorboost]

i have a big 16g and i had the boost source pulled from the intake manifold to the boost controller and the bov. i changed it so i have the bov off the intake manifold, and i tapped my compressor housing and ran a line from the compressor housing to the mbc then from the mbc to the actuator. i thought this would make the boost hold better because the bov and mbc have there own boost source and the mbc off the compressor housing is the best boost source possible. the problem is im spiking like 18.5 psi then it drops immediately to 15.5 and holds. why is this, i thought that this setup would eliminate spike.. did i maybe put the mbc lines on backward?

 

[Brunoboy]

i think spike has to due with size of o2 housing ->Turboback. Porting the exhaust housing and wastegate flapper should eliminate the creep.
-Shane

 

[4doorboost]

i mean my turbo is ported as well as i have an evo3 o2 housing and 3 in dp and exhaust. a 16g isnt that big.. could it be my wastegate isnt large/ported enough?

 

[dlesser]

Is your wastegate internal? Also, do you have a CAT?

From my experience I found that the internal wastegate can't "keep up" when the exhaust is wide open. I never fixed this problem on my 1g...I just turned up the boost to 18-20psi and tuned for it. There may be other problems such as pressure loss in the intake system. Have you had a change to pressurize the system and look for leaks?

 

[4doorboost]

internal wastegate, no cat. im pretty sure i dont have any leaks on the intake, but ill check. i do have an exhaust leak where the dp meets the o2 housing.. could this be causing the spike.

 

[dlesser]

I would say the leak probably doesn't have an effect. I forgot to ask what Boost controller are you using? I was running my DSM in 2002 with the same problem your having so I am trying to remember everything I did to fix it. Thats why I think I turned up the boost to solve the issue /ubbthreads/images/graemlins/grin.gif

I hate to slam you with questions but does this occur during a 3 gear pull....only in first...all the gears including 5th?

 

[Brunoboy]

Port the flapper...

 

[4doorboost]

im using a bleeder style manual boost controller, i think its a dejon or something. got it from rre. ill go do some pulls and see what gears its worst in but i think it happpens in all gears. ill prolly just turn the boost up also i have all supporting mods to push 24+ psi. shouldnt be the flapper, the turbo is only a 16g ive never seen any external gate 16g's out there, so shouldnt the internal gate be enough. should i maybe consider an aftermarket actuator like the forge?

 

[4doorboost]

turbo and flapper already ported i had a big wheel put in it and everything was done professsionally

 

[4doorboost]

So when I'm in second it spikes 15.7 redline 12,7 when I throw third it doesn't even want to build boost goes to like 4 pounds. Should I just use the boost source from the IM for both the bov and the mbc

 

[dlesser]

Only 4psi in third gear.....something else is wrong it appears. I tap my Hallman Pro with a "T" between the BOV and Intake Manifold. Other side goes to the wastegate. Time to find why you can't build boost in 3rd...

 

[4doorboost]

so here is more detailed info. whatever gear i stab it in ie. first second third, it pulls hard all the way to redline but when i shift whatever gear is next it wont build boost. but if i let off an re stab it its fine. its only when i shift no matter what gear. could my tap at the housing be leaking? not sure what else would cause this

 

[Brunoboy]

how is your intercooler setup? I tapped my Boost Controllers off the J-Pipe and the other side to the Wastegate actuator on the turbo.

 

[dlesser]

Got any pics from under the hood....? Did this start all of a sudden or did you add or change something to cause this problem? What you describe sounds like there is a problem with how the lines are run...hard to tell without being in front of the car.

 

[4doorboost]

ill get some pics. yes this started because i used to have my lines as follows from the IM to a tee that went to the MBC and the BOV. i tapped the turbo and run the bov from the IM and the mbc from the compressor housing now and it does this? i mounted my mbc kinda close to the rad, do you think its getting to hot? or like i said the tap on the compressor housing maybe leaking?

 

[4doorboost]

i run a stock evo 8 intercooler with all hard pipes

 

[dlesser]

Well, the first thing to do is put it back. Tap your MBC off the BOV to Intake manifold line. Cap the other nipples on the j pipe and intake. Then route the other side of the MBC to the waste gate. That how I do mine. When you do this, do a pull, shift and see if you can get more than 4psi. I would try to borrow another MBC to test with.

 

[4doorboost]

i will def try and put it back but i dont understand why it would do this with what should be a better boost source. i might just try and run a line from the wg to the compressor housing and see what happens.

 

[AnotherNewb]

Almost sounds like your wg is binding up, or your bc isn't allowing the pressure to release off your wg holding it open.

 

[4doorboost]

i agree i ordered a new boost controller. i originally mounted mine off the rad so i think it got way to hot and messed up the spring inside the mbc. i ran the line with no boost controller and it ran of the wastegate fine.