GDBSTi

It happened again. BOOST CREEP on a VF35. Both my STi7 and STi8 had the same problem. On my Scoobysport Ecutek STi 8 (SS downpipe, HKS catback) even with 0% Wastegate duty cycle on Delta Dash my boost was creeping from 0.6bar at 5000 to 1.1 bar at 7000rpm .

Porting the wastegate solved the problem as per STi7, but I am wondering what is going to happen to all those VF35 equiped cars with catless exhausts ;-). VF35's with ported wastegates could be a big seller, Bob/John/Mark.

Anyone had boost creep problems with other VF turbos? A friend had with his VF23, also solved by porting. I think we need a list please;

VF35
VF23
?


Most people probably do not have this problem because they never run less than 1.1bar. I wonder how many of the aftermarket turbos have the same problem running low boost?

rupert

GDBSTi

Mark

Your right its not so bad on my STi8, my Sti7 went up to 1.3bar at 6500 then started to come down by 7000rpm to 1.1 bat. Weird
$-).

Most interesting about the non-STi engines. Cam timing?

Rupert

loscooby

Hi,
Being a non techie, Exactly what does 'porting the wastegate' mean.

/L-O

GDBSTi

Take your turbo off, plug all the holes WELL, then use an oval shaped titanium grinder to takes away some of the cast iron leading into the wastegate hole from the exhaust inlet side. On a VF35 the wastegate exit has a landing that is completely flush with the entrance into the exhaust turbine. This landing needs to be sunk on the exhaust inlet side to allow the exhaust gasses that bypass the wastegate (BOOST CREEP) to find an easier flow path out of the wastegate. I took away about 3-4mm and it solve my boost creep. Also make sure the path leading up to the wastegate is smooth, gas flowed and polished.

Hope this helps

rupert

STi M'8

Hi Rupert,

I have read many threads here about boost creep but I never made any tests before on my 8, full 3' and de-cat bell mount dp.
I had a look on my AVC-R settings in the afternoon and then went for a OFF test (fully openned solenoid).

Boost was actually 0.60 bar up to 5000 rpm and then went up to 1.18 around 6800.

Sounds similar to yours, but... as my AVC-R is running 1.10 bar boost from 6000 up to 8000, I wondered how could I have missed this issue during the last 5000kms, even with more than 100 times select monitor data logging for set up

So I went for another test using my B mode, setted to 1.00 bar constant from 3000 to the red line. Surprisingly, boost kept under 1.03 bar all the way...

Same test with 1.10 constant setting provided similar result, not reaching previous 1.18 bar...

So, do I have a "border line" VF35 turbine housing or does a fully openned gate established flow cause this creep ?

Anyway, I'll make it smooth and clean as I may use a lower boost mode for daily driving...
Anybody got pics to spot the material to be removed ? Is the removal mandatory (please don't tell me it is )

Cheers mates


[Edited by STi M'8 - 9/15/2003 8:57:57 PM]

GDBSTi

It seems that boost creep on a VF35 is so common that nobody does notice :~)

I noticed it on my 8 when the wastegate duty cycles dropped to 0% on my Delta Dash and the car was still boosting 1.1bar :-( when the boost target we set was 1 bar. So the car was trying to control the boost and ran out of possibilities, I suppose!!

I reckon it probably is fine as long as you have the right fuel, injectors, pump and an eye on your boost guage all the time to run 1.1 + bar to the redline. I am not that happy with 92%+ IDC above 6000rpm with my standard injectors. I also prefer it if there is room for movement on wastegate duty cycle. Also 1.1 bar boost creep is mild my 7 went to 1.3 bar !!!. You just do not know when it might start happening too. A friend had perfect boost control for 1 year on his VF23 and all of a sudden had boost creep. He was just running SO rich the carbon build up was influencing the exhaust gas flow!!!

I say port the turbo its not that much work. When you have it off and look down the exhaust turbine entrance you'll know what to do ;-)
You do not need to take much away, just port it so there is a landing for the exhaust gases to bounce off out of the wastegate.

Remember you're duty cycles will need adjustment after this to acheive boost with this highly effective wastegate you just made for yourself ;~). I had to scale my wastegate duty cycles up 30%
to acheive boost targets.

rupert

EMS

STi M“8,

Did you do the later tests in a lower gear or at higher outside temperatures?

Try it in 5th or 6th gear!

In my opinion there should be quite some distance (about 0.3 bar) between desired boost and lowest possible boost, to be sure the boost is not too high under all circumstances.

Mark.

Denmark

iTrader: (2)

I have had boostcreep on a VF29 from 5000rpm and up 1,4 bar

And on a TD05 over 5000rpm 1,5bar


Skassa

GDBSTi

VF23
VF29
VF35
TD05

the list continues

EMS

It“s still a mild boost creep! I“ve seen 1.4 bar @ 7000 RPM with a nice 3" exhaust at 0% DC!!! I port the wastegate on EVERY STi I get my hands on. I am 100% sure there will be MASSIVE problems with every STi driven hard without ported wastegate, when a free flow exhaust is fitted.

P.S. When the VF35 is fitted to a non STi engine the boost creep doesn“t seem to apear!

Mark.

[Edited by EMS - 9/12/2003 7:17:41 PM]