boost dying off

[Lonewolf]

Right, sr20det red top.
3" turbo back exhaust
FMIC
pod filter
ball and spring boost controller

car boosts fine to 12psi or so, but after about 5000rpm dies in the ass to 5-6psi....
now i expect that the turbo isnt going to hold 15psi etc to redline, in fact i dont care if it dies off to 5psi at 6500rpm(peak power).

Is the turbo completely out of flow at that level (t25g?), or what else should i be looking at?

will be getting dyno'd tomorrow, i guess it makes for a good diagnostic tool...

[upgarage]

stuffed boost controller maybe

[EYEH8HSV]

yer i agree...boost controller...u get wot you pay for man.

[doriae86]

shouldent drop that low

[180SXTCY]

i rekon its just the t25g passing its efficeny range at around 15 psi..

[Jazza]

T25g should support at leasttttt 10psi with an average boost controller at 7000rpm. 5-6psi is impossible as the standard wastegate opens at 7psi... and you can't have less than that at full throttle on full boost!
Somethin is abit of a miss i think hehe :)

[Tre-Cool]

manifold leak to boost guage?

[Lonewolf]

not a leak to the guage, as had it dyno'd today and their boost meter goes straight to the manifold...
after some tweaking, i got it to just under .9bar at peak, dropping to just over .6bar...
will post up the graph on monday when i get to work to scan it in.
might have to look at an EBC to get it a bit smoother i guess

[Milhouse]

pull the vacumm line off the wastegate :D

run whatever boost you want :D

[Oggie]

Maybe the catalytic converter has collapsed and blocked off exhaust flow?

[Lonewolf]

car has no cat...

[Lump]

freeboost:)

i only have a gfb bleed valve & it holds 10psi to redline fine, will see how it goes holding 20..

[180SXTCY]

spikes for the wins..

[Lonewolf]

doh forgot to take graph to work, will do tomorrow...
definitely not the boost controller, a turbosmart bleed does the same thing.

[Lonewolf]

http://members.iinet.net.au/~lonewolf3/temp/boost.jpg

note the dip in power and boost at 140km/hr

[upgarage]

wat did hyperdrive say?

[Lonewolf]

said it could be the turbo, or other things. would need some investigation.

ive also drawn a diagram of the way all the boost lines are teed up, has this been done incorrectly?
Note the "open lines" have been sealed by shoving the ends under an intercooler pipe hose clamp...

http://members.iinet.net.au/lonewolf3/temp/lines.JPG

[Lonewolf]

after getting sick of this problem, i today decided to to remove one of the tee's from the vac lines, and take the BOV out of the equation.
Boost seems to hold up now through the rev range (havent had a chance to really test out the theory), but is a buggered atmo BOV a potential cause of my issue?
I guess its possible the removal of the tee fixed it...
I'll be testing this out further tomorrow i think, your thoughts?

[bodybodyrock]

usualy the only problem caused by a atmo bov on cars with afm is the suden over fueling when boost released to atmo..

maybe it was ur bov leaking at about the 5000rpm range under the presure?

[MMM]

makes sence that it mite be the bov i doubt the tee peice had anything to do with it

[SLEEKA]

if your bov was leaking that bad under full boost with a afm engine you would know about it, would probably be missing and spluttering.
What brand bov is it? With out the vaccum line going to the bov that could cause it to leak more cause the boost will just push the piston in the bov open when theres no pressure coming from the other side.
Wastegate may be cracked and not sealing?? How many km on the motor/turbo?

[Lonewolf]

well the car does seem to be running a bit smoother with the bov out of the equation... wont be able to tell full boost til tonight down roe hwy...
its a turbosmart type2 (vee port), connected just after the turbo (ie before the FMIC).
I thought disconnecting the vac line will keep the BOV permanently shut?
turbo and motor are 180,000km, so getting on a bit.

[SLEEKA]

well the car does seem to be running a bit smoother with the bov out of the equation... wont be able to tell full boost til tonight down roe hwy...
its a turbosmart type2 (vee port), connected just after the turbo (ie before the FMIC).
I thought disconnecting the vac line will keep the BOV permanently shut?
turbo and motor are 180,000km, so getting on a bit.

180K on the turbo? Its never been rebuilt?? Thats pretty impressive.
The turbosmart bov, like most bovs, have a piston which is held down by a spring. So at idle the spring keeps it shut, but when you start putting boost through the system the piston pushes against the spring and can open it up. The vaccum line, when your on boost, is pushing the piston closed with the springs help (the boost in the line and your intercooler piping are pushing against eachother). When you back off the vaccum line turns back into vaccum and sucks the piston open and thats when you vent the charged air.
With out that vaccum line connected the charged air is pushing against the spring and depending on how "tight" you have that spring set it will most likely open up. You probably wont notice it on day to day driving, and if the bovs really set tight you might not notice it all even on full boost.

[SLEEKA]

try disconnecting the bleed valve and put it back to stock boost. See if it holds 7-8psi all the way through the rev range. Might be a dodgy controller as well...

[bhappy]

sounds like a turbo or bov valve prob.. try using another bov mate... there will be a leak in it for sure