Boost issue's ?????????????

[shaun850]

hello again,

i had my 854 t5 on the roller's yesterday to have everything checked out (fueling etc etc) and she was all good apart from one annoying prob.

the boost was set to .9 bar but as the rev's went up the boost was dropping off, alot.
by the time my peak power was reached (6333rpm) it was only .5 bar.
im using a MBC ( not a bleed valve ) and was wondering what could the most likely cause, week actuator, turbo , mbc , air leak ???
would i benefit from an AVCR or similar?

any pointer's would be greatly received, and thank's in advance

shaun

[lance]

Smaller turbos tend to loose boost at higher revs, I would have thought peak power on an 850 to be around 5100 rpm however they will carry on going.
My old 16 T would peak about 4500 rpm then gradually tail off.
A bigger turbo such as a 19T would see a longer boost mine stays high to the redline and longer although max power is around 5500 rpm.
Maybe your turbos past it best and a new turbo would help keep the boost going for longer.

[volvotuning]

A good 15G should still be able to hold better boost than that, at the end, so either turbo isn't very good or there is an air leak.

Adam.

[shaun850]

cheer's for the replie's guy's,

turbo appear's fine, just been out and bought a new boost controller so i'll see if that helps and get back to you.

as an after thought, would a split diaphram in the recirc cause alot of boost leak?

[Wobbly Dave]

I'd be looking like adam said for an air leak.

[madness]

its the mbc controller. i had same problem with t4. allows higher initial boost but backs off at higher revs and limits top max speed. same symptoms as an air leak. -- get a remap and will be all ok

[Rufe]

i would be checking all the vacuum hoses for air leaks first before spending out on anything. those little elbows on the magic tree are quite known to be weak point, lets face it