Is this just classic boost creep or something else

[Sirnixalot]

This was a pull i did from last week, i have since backed off the actuator rod a little so the boost is lower but the curve is the same

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Basically as it is now from 3500-5300 the boost stays at 12psi, from 5300-7500 it creeps in a linear fashion to 18psi.

My setup is quite the bastard, this is an Evo X turbo with a 20G compressor and a Evo 9 actuator (on an Evo 3 ). The actuator has enough open throw to buck the flapper on the inside of the O2 flange.

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This is my O2 housing. It is a 1.75" pipe for the dump tube

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This is the turbo side of the flange

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Flapper open. I can't imagine it would creep with the flapper opening that far?

I am not sure if the rod is adjusted for 18psi but the wastegate is opening too soon

OR

It's just creep

I could take the O2 housing off and open up the hole at the top so the flapper has more travel and just weld a piece of exhaust pipe to taper into the existing bend (hard to describe).

 

[JusMX141]

What boost level are you trying to run? I'm pretty certain the Evo IX actuator is stronger than 12psi from the factory....somewhere around 1-bar (14.7psi) if I recall.

I just installed a 20G on a customer's Evo VIII last weekend- it used the Evo IX turbine housing where one flapper controls boost on both scrolls like your Evo X example, and it held 18psi rock-steady during the test drives. Full 3" turbo-back Megan exhaust and recirculated Megan o2 housing on that car.

 

[Sirnixalot]

If i tighten the actuator rod any more than what it is at now (with the 12psi from 3500-5300) it will go to 14psi for the same range and then creep up to 20psi. Right now i have tightened as "loose" as i can before it leaks at idle if that makes sense.

I need to be able to run relatively low boost (12-14psi) for autocross as anything more than that and it is just too much for me and the 225 series tires i run.

If i have to run the higher boost i can learn to adjust my lead foot, its just the creep that is bothering me.


I would think that if i was fighting the actuator by trying to run too low it wouldn't creep past the "spring" pressure since the flapper is open.

 

[JusMX141]

^ But if the actuator's spring tension is too high, it may not open "quick" enough to control that initial spike right at the onset of boost around 4K when attempting to run 12psi. You may need to rig a lighter actuator on there in order to achieve consistent lower boost levels.

Have you tried unhooking the actuator altogether and seeing what happens? If you do a full-RPM pull and the turbo never makes boost, it's not creep.

 

[Sirnixalot]

I forgot to say this is with the vacuum line run directly from the cold pipe to the actuator.

I will try unhooking the actuator tonight and report back with the findings.

I would be happy if it would run the 18-20psi from the onset and carry that across the rev range.


edit**
well....its creep

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red line is with the actuator rod unhooked and the blue line is with it tighted a few more turns. I am going to crank that sunova bish all the way and see if i can get more than 12psi for that little bit. I ran out of road for the NA pull which is why it stops at 6k.

I will try tightening the actuator all the way and see what it does to the curve

Failing that this long weekend i will have to pull the O2 off and do some more work.

On the up side my car makes 174whp and 155wtq in "NA" mode

 

[Sirnixalot]

solved!

The actuator does not have enough open throw in it's current location. It is only opening the flapper barely half way

I will see what i can do to solve it

 

[JusMX141]

That's how all Mitsu actuators are- they're lucky to open the flapper 3/8" on some turbos. Definitely not the cause of most boost creep, and likely not the cause of yours if you made 4psi from with the actuator unhooked completely...giving the flapper the ability to open as far as it can.

 

[Sirnixalot]

good point.

I am going to see if there is a way i can get wastegate ports off the manifold for an external. That should solve it.

Though that is easier said than done. Sigh

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The shorter of the 2 passages

 

[JusMX141]

Could just be the design of your o2 housing, there- the factory o2 housing is just one large passage.

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[Sirnixalot]

MAP have apparently found that they creep when trying to run anything under 25psi so they offer a profiled flange and what looks like a stepped transition from a 2" pipe to a 1.75" pipe

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I will be pulling the turbine housing off and porting the wastegate passages as well as grinding the O2 flange in a similar fashion to the above this long weekend. I also found a 38mm Turbosmart external on the rock so i will be welding that up to the O2 as well.

Hopefully i can get a consistent 14psi out of it and use the Hallman to increase it from there.

Thanks for your insight and help so far!

 

[Sirnixalot]

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It won't win me any awards but it will get the job done!

I massaged the wastegate ports in the turbine housing a little more, apparently i already smoothed the entry but forgot that i did.

As you can see i went the typical DSM route on this (CHEAP!) for right now. I still want to go external but for right now this should do the job along with a "Mr Peepers" edition Evo 9 actuator

 

[Sirnixalot]

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almost....boost is now flat from 3-6k. Next step is to go Mr. Peepers on the actuator

 

[JusMX141]

If you read one of Matt's blogs, you'll see that even he was stricken with boost creep using a 14B and one of his modded actuators....which is why I was stating that the distance the flapper opens may not have as much to do with it as you'd think.

 

[Sirnixalot]

I agree with you but considering it will only cost me time to do I may as well.