Boost Creep Testing Question

[travislaw]

I was testing my Big Evo III 16g Ported for boost creep this afternoon. What I did was take the wastegate actuator arm off. First I tested to make sure there was clearance for the wasgate to fully open. It had no problems opening. Then I ran the car to see if I was getting any boost with the actuator arm off. In second gear I was getting about 4 pounds of boost pressure at 5,000 RPMS. I didn't start building any boost pressure until I hit 3500 RPMS in second gear. I was in a residential area so I couldn't push it any further. Is this okay, or does this mean I have really bad boost creep? I know all about porting the exhaust housing, but I am trying to avoid doing it if I can.

Car Mods that are part of the turbo system:
Big Evo III 16g Ported
Evo III o2 Housing
Autometer Boost Gauge
1st gen BOV
Dejon Tool Upper Intercooler Pipe
Metal Intake
2.5" Catback Exhaust

 

[kenamond]

From what I've read, 4psi isn't very bad, but a well ported turbo can keep creep to under 2psi in the test you did. However, if you go to a turboback exhaust or otherwise improve your exhaust flow, you might see more. I've read plenty of threads where folks with the same turbo as yours ran into creep problems when opening up the exhaust (going to 3" w/o cat). If you plan on that, you might want to do some porting. Since yours is already ported, you probably only have to spend a bit of time on the wastegate.

I just started porting tonight. I'm doing a test run on my old T25 housing just to get the feel of the tool, then I'll go on to my mani, FP Big28 and O2 housing. Wonder if I can sell the T25 housing (if I finish it).

 

[unclesam099]

I was running an open O2 tube and with the WG arm detatched and was hitting near 20psi at redline. Is that a bad thing? I don't hit boost til 4000rpm or so, but then it climbs to ~20 by 7000.

 

[kenamond]

If you get 20psi with the WG arm disconnected, either your wastegate is sticking shut (try to open it with your fingers with the arm off) or you have a creep problem - the exhaust gasses are choosing to go through the turbine wheel instead of out through the wastegate, so you build boost even though the wastegate is open (which it should be if the arm is off and the flapper is opening). Solutions to this vary, but porting (turbine housing, O2 housing) and external wastegates are the two common solutions.

A well ported turbo with internal wastegate will get 1-2psi or less during this type of test.