After doing some reading about boost creep, these are my conclusions (please correct me if I'm wrong).

Creep is caused by the wastegate not being able to blow off enough gas in time and the backpressure casues the turbine to boost even more.

My guess is, with a GT35R and only running ~7psi the 38mm wastegate is simply to small for such a low psi in this cold weather. Come summer, I don't think I'll have a problem as the air will be much denser.

I also think after I raise the boost to ~15psi or so (once the headgasket goes in) I won't have a boost creep problem in winter as I'm letting the turbine compress more air (thus less air needed to exit the wastegate).

 

The wastegate is basically a valve that allows exhaust gasses to bypass the turbine. The exhaust has two paths to atmosphere with the wastegate open, through the wastegate or through the turbine. If either one is too small, additional backpressure will be generated. The 35R turbine could be considered a medium large frame housing. Its definitely not "small". It is also very free flowing (not very restrictive). My guess is that there is either something wrong with your wastegate, or it just doesnt work well with your particular setup of manifold, turbine, and WG.

Perhaps the wastegate doesn't function well at this particular operating point. A different spring may fix the issue if this is the case.

The air will be less dense in the summer, not more dense. The mass flow rates will fall with less dense air, meaning less mass throughthe system , less power, and potentially less boost creep.

 

Whops, mean't to say less dense

I've tried the 5psi spring, it works a little better then the 7psi spring but not by to much. I don't think its the wastegate as it holds till ~7k rpms then it starts to climb until hitting max creep at 9k rpms.

As I've stated, I think its because for now I'm limiting to much boost for a somewhat large turbo thus causing the problem when the air is very dense (cold nights / days).

I don't think its TOO much of a problem hitting ~10psi for a split second every once and a while *knock on wood*. I'm awaiting the warmer summer days and finally the headgasket so I can get the turbo in its operating range

Maybe Ya or John could chime in here?

 

More than likely, it's not the wastegate.

Check, double-check and then re-check the vacuum lines to the wastegate.

I was creeping hard and found that the heat had hardened and then cracked the vacuum lines on the wastegate.

I replaced them and my boost pressure was under control again.

When I replaced the lines, I also got some fire sleeve -- http://www.heatshieldproducts.com/red-hot_sleeve.php -- and covered them and have not had a problem since.

 

I'll def. have to do that.

Quick question, where can I buy vacuum lines? I'm guessing autozone / home depot / sears / Nappa? I've never actually seen them in a store before.

 

The reason why you get creep on the road and not the dyno is that the dyno doesn't provide aerodynamic load, which increases as an exponent of speed. More load will mean more air being moved by the engine, since a turbo compounds load based on demand, the higher demand of road conditions (incline, contact patch friction, etc.) and aero load allows a turbo to spin up faster. The rate of rise in ex mani pressure may be faster than your WG can take. The simple fix (band-aid) is usually a bigger WG, dumps more air quicker. But that typically requires fabrication, which can be a big hassle.

Try this some time, cruise at a low speed and allow the intake manifold to go to vacuum. Left foot brake and ease into the throttle, do you notice boost while you aren't going anywhere? That's due to and increase in load.

The GT35 is an efficient turbine (I didn't say turbo, or compressor) so it tends to produce less backpressure than older technologies such as T3's or T4's. Low backpressure turbos tend to creep more after crossover, or the point where the intake mani pressure begins to exceed the 1:1 ratio vs the ex mani press. Potentially, you are seeing low backpressures, so that there isn't enough backpressure to help open the gate. So if you go off of the cracking pressure of just the spring and diaphragm and don't add in the force on the ex mani side of the valve, you are at the actuator threshold for opening the WG. Take your WG and put it to compressed air, and it will probably open around 10-13 psi, but some people see 6 psi on their setup while others see 8 psi. The differences are all based on the value of the ex mani pressure.

 

The backpressure table on page 11 is the easiest way to show what type of conditions produce creep.

Backpressure Table

The less backpressure you've got the more boost is required to open the WG using the same spring

 

Spec how did you solve your issue? Go to a bigger WG, if so which one.

 

Boost creep, I ****ing hate it, I am not going to have problems with two Tial 38mm MVS Wastegates?

PS I think Jon got a larger Wastegate to solve

 

The GT35R is a badass turbo. But i had bad boost creeps too. (thank goodness for built motor) but exhaust does have to do with it and no matter what we creeped up to 15lbs at redline.

had a lot of difficulty keeping it lower then 15 so we just left it there as a low boost setting and that seemed to have fixed my boost creeping issues