boost drop
 

hi. in third gear and when i floor it, i hit full boost around 3.5-4k rpm. boost is set at 12psi with the help with a Profec "A". When i set the boost at 14, boost will go to 14psi, but as soon as it hits 5.5k rpm, boost starts dropping until 7k rpm. boost would drop till its at 8 or 9 psi. here are my mods

-2.5" downpipe(no cats)
-2.25" Midas shit bent y-pipe and N1 style cans
-street ported 3mm apex seal engine 20k miles or less
-intake
-Apex bov
-guages
-HKS turbo upgrade(dont know size. its pretty small with internal wastegate)
-HKS FMIC
-850cc secondaries
-Walbro pump

Im thinking it may be my BOV leaking boost. maybe but i remeber the nut on the top of the BOV was tight. How do adjust the thing and when do u know when to stop? Also my intercooler plumbing is funny. Most 7's I see with FMIC, plumbing that leaves the IC goes straight to the throttle body. mine kinda bends and bends and bends. you will see in the pic below. My IC plumbing is really long compared to others.

OK, i have another problem. When i let off the gas suddenly, the engine tries to stall and the idiot lights flicker and the engine gasps for air. Sounds like an intake leak? Before it would try to stall all the time and if i didnt put my foot on the gas when i do that, it would stall for sure. I took it to a rotary mechanic and they cant find any leaks. Took off the intake manifold and stuff too but cant find any. They put on my stock BOV and it looks like it plumbs air back into the intake. It has helped alot but it still tries. Oh and dont get it wrong, i still have the Apex bov and it is mounted between the turbo and IC. So i have 2 bov's.

here are some pics. they may help.

Pic of IC from front. see how the plumbing leaves the IC and bends 180degree then bends another 90 degree to go underneath the battery?
http://members.asianavenue.com/frankiewong/Dscf0001.jpg

then the IC plumbing goes underneath the battery and near the spark plugs(bitch changing the plugs cause the IC piping is in the way) and a 90 degree bend upwards and then another 90 degree bend towards the TB.
http://members.asianavenue.com/frankiewong/Dscf0002.jpg

Heres the messy pic of my BOV's if its any help. see how the stock bov is plumbed back into the AFM? without the stock bov, the car would stall for sure. Now it just tries but rarely does.
http://members.asianavenue.com/frankiewong/Dscf0003.jpg

Thanks for any inof guys.

pls?

nice name, can't help w/ ur problem though sorry

are you sure the turbo is upgraded? the stock turbo will drop like this since it is too small. it just can't flow enough, and it'll drop off even more with a ported engine. maybe the hks one isn't much bigger then stock.

the only other thing might be the exhaust. get a bigger one :)

yeah the turbo is upgraded with a HKS sport upgrade. it has a to4 housing but i think both the compressor wheel and the turbine side are both pretty small, not much bigger than stock. i raced a tII with a full 3" exhaust and i didnt beat it by much even though i have much more mods. i need full boost at higher rpms. i cant live with 8-9lbs.

oh and i have heard some other ppl get boost ccreeps that go up to 14psi or so. i guess their wastegate is stuck. maybe if i stick my wastegate boost will go up. maybe its my bov leaking boost. check later. thanks.

Try temporarily moving your boost gauge measuring point to before the IC and see if its 'good' at that point. Lots of bends aint good for airflow so you might be maxing your piping at higher RPMs.

Henrik
87TII

had this same problem on one of our race cars and it turned out that the combination of excessive I/C piping and and overly large intercooler the turbo just could not flow enough air to keep the boost at the desired level. also the life of the turbo was dramaticly decreased, would eventually bend the main shaft from over rev. this engine spends most of its life at full boost so street cars may not notice it as much. reducing the size and length of the I/C piping and the overall area of the I/C solved our problem. a larger turbo would also essentially do the same thing.