Boost Level

[yangjiesheng]

Dear Guys/Gals..

I'm currently running on 1.0bar..
Using Blitz SSBC
Tuned with UniChip (Gold)

Whenever I full throttle..
The boost Meter will show a smooth and fast
stable boost to 1.0bar.

But once the RPM shows above 5500rpm +++.....
The Boost wills slowly drop down to about 0.9.. then 0.85...

But once gear up a level... (Autotransmission)...
The boost will again rise fast and stable to 1.0bar..
and again.. slowly drop upon reaching 6000rpm..

Is it normal?


Sincerely
Jason

[ako]

Its normal. The turbos are that small, they just can't keep up the airflow to the engine at those boost levels. Try an electronic boot controller if you're worried - in reality, chances are its better for your engines reliability.

On the downside.... Boost is good, less of it is bad. Up to you ;)

[enigma]

Yep, perfectly normal!

The turbos are weeny and run out of puff. I have found a solution, it involves a gas bottle and some solenoids....... ;)

[yangjiesheng]

Wow!..

What is that gas bottle...?
Care to share..?
Hahahaa..

ok.. thanks for the wonderful enlighten.. bro :)

[pjjohnson]

There is one thing about this boost drop off I've never been ale to get my head round. No matter what boost I set, it always seems to drop by about .2 bar over the last 2000rpm.

So when its set at 1 bar, it only achieves .8 at 7000rpm, but if I set it at 1.2 bar, it will hold 1.2, then go down to 1bar at 7000 rpm. The same happens if I set 1.4, it will hold 1.4 then drops to 1.2 by 7000rpm.

Anyone had teh same experience or know why won't it hold 1 bar all the way through ? Or could the readings be wrong ?

[simpsonm]

Could it be the actuator(s) that cannot sustain the boost levels?

[pjjohnson]

Could be, but I thought the actuator was spring type thingy, and a springs a spring, and pressures pressure isn't it ?

Still don't understand it -and if I understood it I might be able to adjust it. Or get someone to do it for me as I don't DTM.

[simpsonm]

From what I've seen the actuator is a spring loaded diaphram similar in construction to the dumpvalve. These have been known to weaken under higer than normal boost. I had a weak actuator on a Pug 406 turbo, its normal boost was 7psi it got to this at peak then dropped to 5psi.

[ako]

Its nothing like that - I'll try and explain it as best I can -

The turbo is trying to feed in this amount of air - call it X cfm. Now to rev at 7000rpm takes a lot more CFM of air than it does to rev at 5000 - unfortunately, because the turbos are that small - they can't "keep up" with how much the engine is demanding - hence the boost drop.

I can't put it into words well enough - suffice to say, the car is severely undernourished in terms of forced induction.

Two options - Go for bigger twins - from all I've read and been told, the only tihng remotely close to a bolt on proposition for the 6A12 or 13 is a td04 from an early wrx (Go figure). GTO turbos do NOT bolt on, the flanges need to be changed to suit - in which case you'd might as well go for something better anyway. The other option is to switch to a medium sized single turbo - this CAN be done for under $3K NZD, depending on how you want it done. It's been done, successfully, on a few cars - apparently with TOTALLY different driveablility. You can actually use all 7000+ rpms for a change :D

[yangjiesheng]

Wow!!!... Single Med size Turbo???
:p~

I'm wondering around for my turbos too..
Since one behind has a weak oil seal..
And a little dirty oil can be found on the Y pipe metal pipping.. :(
sign..! :(

SO.. i'm considered wanting for a Upgrade...

How to mod to a Single turbo?..

Having the Single Turbo at the end of our Down-pipe (2 to 1)
and then link all the way up to the front for intercooler and then back to
the throttle?

Man... how can this be done???

[ako]

Ok - one way I've seen it done - this is the "Cheap DIY method" mind you - was to use the manifolds from an N/A V6, and in a nutshell just joining them in the middle, then leading up to where the front turbo currently sits. There's enough room there. The turbo used was an ex - Evo 3 one, however anything could be used really. Up to you. From there, new i/c piping had to be made up, naturally, and that was essentially all thats changed. Fuelling is still quite safe, and the power curve is pretty much the reverse of now - not a lot before 3000rpms, then a huge top end that was never there before. Its nowhere near as hard as you'd think - and a lot easier and better than stuffing around with twins in the long run.

[-LegnumVR4-]

lot of work but i would say the cars would haul very hard. Just waiting for my turbos to go 'pop' and the trans so i can get a manual :p