Hey guys, I've got a boost creep problem that I'm working through, and here's my plan. I just wanted to run it by you guys to make sure there's nothing flawed in my thinking.

I've got a stock IX turbo on my 06 MR, and I've got a ported intake, exhaust, head, valves, Cossie M2 cams, Forge MBC, nessi intercooler & piping, K&N w/ stock airbox, silicone intake pipe (maf to turbo), and a full Nvidia O2 back exhaust & Forge 18psi wastegate actuator.

I've been on the dyno many times trying to get rid of the boost creep at 5k rpms which goes to ~30 psi and drops to 18-20 by 7000-7500. In order to 'control' the boost creep to 28 psi we've had to loosen the wastegate actuator to the point where it rattles on idle and deceleration. This has also subsequently made it spool like a 35r which kinda sucks right now. When we tighten the wastegate so the spool is great and there's no rattle, the boost will spike well over 30, and I don't really like that as I'm sure the IX turbo is a blowtorch at 30psi anyway.

So here's my plan:

I want to make the wastegate have more "travel" from it's closed to open positions, and to do that, I want to move the wastegate stop ring so the wastegate actuator will retract further into the spring & diaphragm cylinder of the wastegate. This should allow me to keep my spool, not rattle, and still open the wastegate enough to maintain boost levels less than 30 psi.

Has anyone tried this?
Have any thoughts on this?
See any problems with this?
Etc...?

Thanks for the input.

-Eric

 

What about a problem with your MBC not controlling boost properly?

 

Sorry, I should have mentioned this.

We tested this two ways, we changed MBC to a Halman which had the same problem, and then hooked the wastegate directly to the compressor which should result in straight 18 psi, but we still got a nasty spike at 5000 rpms.

 

So why not just tune for the 28psi?

I run that same boost with no problem.

 

I had a similar issue a long time ago....My solution was to get a new wga - problem solved. On another car, I saw a similar problem, but it was a bad aftermarket O2 housing that was creating backpressure...

I would start with either of those paths before doing your idea...

 

I've actually done both of those. I started on the stock WGA, which couldn't hold boost up top, but still had mild creep, not this bad though, so we swapped that out for the Forge.

Then we had problems with my Megan Racing O2, which was very restrictive and had boost creep at 6k +, so we went with the invida O2 which solved that restriction.

 

I am currently tuned for 28 psi, and i'm running there with great results, except for the absurdly slow spool.

When we tighten the WGA to get the spool back and stop the WG rattle, it starts boosting 30+ which is where I'm afraid to go.

 

there's some other problem somewhere. There should be no reason why your getting boost creep if everything is set up right. Or in properly working order.

there's got to be something...

 

The only thing I can think of is I shouldn't have ported everything upstream for the stock IX turbo, or I should have also ported the wastegate ports on the turbine housing.

I'm thinking it's just flowing too much air to get rid of... but then why does it stop over boosting after 5.5k? Is the turbo just running out of steam?

 

Just to share my .02 cents. I had a boost creep issue when I put on my o2 housing. It would boost crazy high after a bit over 5.5k rpms. After doing a lot of reading I concluded it was the wastegate side of the o2 housing being too small causing all the exhaust to bottle neck and continue to spin the turbo to escape.

First attempt my friend ported the o2 housing and it helped a little but the creep was still there. Then we ported it even more as far as he could reach and wide as we can and it completely fixed the issue.

So I say double check the wastegate to turbine merge port on the o2 housing and make sure its not too small.

 

Before you start porting more, take a look at the O2 housing again. It's definitely worth a look. It might be your problem.

Some aftermarket O2 housings have an issue where they don't open up the area enough, where the wastegate portion flows into the exhaust stream. The wastegate tube is quite large but they barely open up a big enough hole for it to flow into the exhaust stream. The flow from the wastegate portion runs into a wall causing backpressure and reducing flow.

My aftermarket O2 housing had the same problem. I fixed it by porting out the wall that would have caused a restriction.

Here is a drawing of what I'm talking about:


On mine, this wall was huge. It wasn't even close to being a smooth transition. The wall on mine was almost 1/2 inch tall.
Good luck

 

Try porting the merge(crossover) opening in your O2 housing, as BLUEvoIX, and, INEVOIX advise.Make it about golfball size.

EDIT: If porting the O2's crossover hole doesn't fix the creep issue then you may have to pull the turbo's turbine housing and radius the entrance to the wastegate bypass port(s) in the turbine inlet area of the housing.

 

As far as your proposed WGA mod....I would have to see a drawing, since I don't quite understand what exactly you are thinking about doing. I would not mess with that myself though.

 

Giving the WGA more travel should be ok but there may be some point where it won't retract again properly if over extended. I guess it depends on the design and you may have to experiment.

You can try applying 25 psi to the WGA and see how much travel there is. Usually the Wastegate flapper in the turbo only opens up halfway so much of the air is diverted at an angle towards the O2 housing and that can be restrictive. If the flapper is unable to open wider due to material in the turbine housing being in the way then porting that slightly can help. I can't confirm the setup is the same on a 9 turbo but the flapper could also be hitting the O2 housing wall if it wasn't designed right either, restricting opening angle.

Porting out the Wastgate opening in the turbine housing can help flow where the flapper seats but make sure to mark the edges knowing that there is some play in the mechanism. No sense in creating a permanent leak and slowing your spool! Back in the DSM days it was also common to remove the stock flapper and weld in a larger one so that you could port the WG hole bigger. You just had to make sure it didn't bind up and that it seated perfectly.

 

Port the O2 housing wastegate/exhaust stream merge, and retest before you mod the WGA...