BIG Boost Creep

[EvlEgl]

I have a small 16g. 2g ported exhuast manifold. Hallman MBC, 2g O2 Housing, Walbro 255, FIC 650's, Buschur 3in Turbo back, Pacesetter Downpipe 3 inch, GM MAF w translator, On a stock sidemount and wastegate.

When I got the car it was set at 17psi...Held steady nicely until a couple days of normal driving and occasional hard boosting i noticed it would hold at 17 then creep to 19-21 and hold there.

Lowered Boost to 14 and it held at 14 then Creeped BACK to 19 - 21 and held again. Lowered boost AGAIN and had the same dilemma. Took off the MBC and ran just the wastegate. Held at a steady ten until 4500 RPMS then it CLIMBS QUICKLY to 20psi and it would keep going if I wanted to push it.

I thoguht boost leak but that usually drops boost not make it gain that aggresivly. Couple trubo buddies of mine suggested there Might be a hole in the vacumn line and or the vacumn line is not big enough.

I perosnally think my wastegate just won't hold after a certain RPM and it gives out under the boost Load.

Anyone have a clue?

[Fastrick25]

Make sure all vacuum hoses are tight and secure.You may need to do some port work on the o2 housing around the flaper hole and the area where wastegate section joins the turbine outlets section of the housing or you could just get a housing from hybrid connection.This is really an issue if you dont have a cat along with a 3 inch exhaust.

[TROLL]

its a mechanical issue with the wastegate... its just not able to vent enough pressure through the wastegate so instead it spins through the exhaust blades and spools up the compressor side that much more. the size of the wastegate and the path leading to it are not able to flow enough to handle lower boost at high rpms. i went through the same thing... changing your boost control wont change anything, its an isolated issue with your wastegate only.
porting the wastegate is a solution but be careful to do it correctly or you'll overdo it and then have trouble even getting boost up to target. i know 2point4dsm knows a bit about porting the mitsu turbos so talk to him about it. but if you do it yourself please be careful not to overdo it. just do a little and see if it helps, if you need to do more then take the time to go back a 2nd time. you can always take more material away but you cant put any back. i learned the hard way

[2point4DSM]

Your wastegate or o2 housing is not able to flow enough. You could do some port work but why? Just tune for 19-21 and be happy.

Seriously, you got big enough injectors and there have been plenty of DSMs in the past that ran that much boost for a good while with no problems. One car in particular, my orig 90 DSM, started to run that kind of boost on pump gas at around 100k on the odo and I did that for close to another 100k.

Even with a little bit of knock the stock headgasket and head bolts are good for up to 25psi. ARP headbolts and stock gasket with a good tune and race gas is good for up to 30psi.

The only thing you have to worry about running this kind of boost is changing your oil and plugs more often. Big deal.

Btw, if you really want to fix the creep the biggest thing you need to worry about is the lower portion of the o2 housing where the wastegate dumps back into the main exhaust flow. Hog that out a lot and that should already be enough to fix your problem. Some people will even port the wastegate a bit too. It's hard to run into problems with a stock sized flapper on the 16g.

[EvlEgl]

I'm probably gonna Go external wastegate...Just to please myself mentally.

And i agree wil I have no issues running that much boost infact It it set up quite nicely to do so. I just need to get all the bugs worked out and tune it before i run around running this much boost.

I'd like to be able to set it at certain psi and nto worry about it creeping on me...Seeing it creep like that is scary to me.

Also i have arp thruout the motor and a cometec HG.

[2point4DSM]

An external wastegate is the sure fix. Even a stock o2 housing with an external dump setup will fix it.

[EvlEgl]

I have a 2g o2 housing...If thats what you meant by stock then yes it's stock.

Most likely going to go external wastegate...Simpliest fix out of the Bunch...So i've heard Just a bit mroe costly...But i'll deal with it.

[Master Mitsubishi]

Scott there are many ways you can go about the external wastegate issue, there is the expensive and the non expensive either way it going to cost you some cash. Cheap way- First of all contact mitch for a wastegate and flange. Second get prince to weld it on. Third put all parts together and enjoy. Or you can do the expensive but better way. Buy new manifold like the one jesse bought, and and wastegate. Your choice buddy buddy. The ezer way is more expensive, i know you are low on money, but you can save
PS get an AFC and wideband ill get pissed if you lean the car out too much and blow it up

[eviltalon]

Hey guys i just installed a MBC in my car a couple of days ago, and I'm having the same problem that EvlEgl has. I was going to start my own thread but i guess my question has been answered. My mods are 3" turboback exhaust, K&N intake system, 2g ported manifold, Magnacore sparkplug wires. Also i have a 2100 6 puck clutch but that wouldn't be the problem now would it.

[Silverfc88]

I had this problem on the 7. On the stock turbo it would creep with an open exhaust with mild to warm outside temps. When I got the newer hybrid with the wastegate ported to 35mm the problem went away. When it is cold out I still get some creep and I have to turn the boost way down on the EBC.

Getting the wastegate ported will help eliminate creep during mild to warm temps. During cold you still have to watch your boost.

I think even with an external wastegate you still might have to turn the boost down during extreme colds.


Get a wideband also. Cold temps = more oxygen entering engine causing a more lean condition. Example: 12psi in the summer might give you an AFR of 12.0 but during winter months might give you an afr of 12.8 or higher.

[eviltalon]

I would port the wastegate but i have an oversized 50 trim T3 ported (40mm wastegate) turbo that i will be swaping out very soon. Porting the stock wastegate seems to me like i would be working backwards. So i just plan not to ride in boost when drive my car, until i install the T3. Thanks for the help guys.