Alpine951

I have been starting to mod my car. I am wondering if I am wasting my time because i am going in the wrong direction or if there is a problem. lets establish the reason for what i am doing. My car can hit 18 psi initially but it drops like a two ton weight to 10 in the high rpms. I am trying to keep the boost around 15 in the high rpms. Should I be able to do this? the wastegate is a guru with a one bar spring. I have seen posts here of listers who have had guru WG and Tials not be able to hold boost. i have seen people here say get a Tial and you won't be sorry. I have seen people here hold decent boost with both. The cars has the stock afm with a Reliaboost. The reliaboost has the heavier spring and the cycling valve is not on the car and thus bypassed. I disconnected the Reliaboost and plugged the pressure line coming off the intercooler pipe. I was able to get 15 psi and then some all the way to the mid5k rpms and then I backed off. Because I was able to do this I figured my Turbo can make the power. i had some detonation occur because the chips were mapped for a shimmed wastegate not one with a heavier spring. Its now got chips mapped for a heavier spring. The boost still drops like a rock. Not sure what to do.

mideastmafia

Sounds like a tuning issue. Get the chips checked out.

Mike1982

I have the EXACT same problem!! I got the guru chip set at 15psi then about 6 months later upgraded the WG to Tial 38mm. I have an aftermarket boost gauge and air/fuel gauge so I can monitor what is going on. I know that when my rmp's get up say about 4.5 or so, the boost already starts to roll off. My air/fuel is ok, doesn't go rich or lean but by 6k it is down to 10psi. That is some SERIOUS HP lost!! Other then that, the chips work great, so I was thinking it was my turbo because my car has 130k on her.

Alpine951

Mike,

have you tried disconnecting the line at the intercooler and seeing if you can at least make and hold 15 psi in the high rpms? I think that is a way to tell if the turbo can even make 15 psi, but I am looking for help here so don't take my word as though i know what I am talking about. So you got a Tial and can't hold the boost either. Ok. makes me feel somewhat OK about not buying a Tial. My car has 60k miles on it.

Alpine951

Mike,


What kind of boost controller you using?

jimbo1111

Most people with a k26/6 can't hold boost in the upper rpm's. You will have to replace the turbo with a k26/8 or better.

J Chen

Hi Guys,
I suspect that it could be a partially block cat
or test pipe. Under high load & high rpm, the
back pressure could kill boost.

Alpine951

test pipe is clear.

J Chen

How can you be sure ? Note that the test pipe
looks like a figure S viewing from the top. If
theres a blockage after the first bend from
the turbo down pipe side, you will not be able
to see it. Being double walled, it is a know fact
that the inner tube may collapse & cannot be
confirm just by visual inspection. What about
the cat ? It could be partially block.

Alpine951

A test pipe means there is no cat.

J Chen

Sorry, do not read your sig. No cat, do you mean
the whole pipe form the turbo down section to
the cat section has been upgraded or did you
just cut out the cat & replace with a welded pipe ?

Alpine951

The whole pipe from the turbo to the muffler is one 2.5" pipe. The cat unbolts and this pipe bolts right in place of it.

J Chen

In that case, check for exhaust leaks. What's
your vacuum reading like & what about A/F
readings ?

hosrom_951

A better term would be that ALL k26/6 turbos boost fall at high rpm. I saw some dyno charts of lucky people on getting a boost loss of 0.5-1.-psi in the upper rpms with the K26/6, but they were using a Tial 38mm WG.

It is a 50/50 with the K26/8, since it would depend on the condition of the turbocharger. If i am not mistaken, i believe toddk951 is using a GURU 1.0bar spring WG with a k26/8 and holds boost to redline???

toddk911

It's your turbos folks. K26/6 WILL drop a lot of boost in the upper rpms and K26/8 wil drop about 1-2 psi or more depending on it's condition. This has been proven to happen with ALL wastegates.

Using an EBC helps, but you still will see some drop. I was holding 18psi to redline as I have an aftermarket turbo. It performs much like a K26/8, but it is not so I am able to hold more boost to redline.