My 46mm Tial had a .8 and a .3 spring in it, making 1.1 bar. The engine has been modified to run the correct AFR's etc., but for longevity, I took the .3 spring out, leaving just the .8 bar spring in. Everyonce in a while, nearer the higher end of the rm range, in 2nd gear, I still hit the overboost. I need to move the switch to a line off the intake and plug the hole on the intercooler.

Bill

I know you're all done already with your project, and give me a shout anytime you need some help. SmileWavy

Slightly off topic, goes with previous posts, but I don't like the thought of boost creep at all. This can cause serious damage if your car isn't prepared to handle the extra boost. This is one of the main reasons I'm hesitating putting on my GHL headers and a K27. My first mod was a .8 spring and so far I've hit whatever my spring is every time like clockwork. Now I've put in a 1.0 bar spring removed the CAT and put on a GHL muffler with a larger B&B intercooler. I've made sure my AFR is set correctly using a Gunson tester and I hit 1bar every single time.

I guess my question is why is there boost creep? What causes it? Does it just blow by the wastegate? I've noticed a trend being with the guys with the Tial wastegates. Anyone have boost creep with the stock wastegate and aftermarket headers/turbo?

BSiple - you shouldn't ever hit your overboost with a .8 spring. That is some serious boost creep IMO. I wonder what boost you'd have if you just used your .3 spring. 1.0 bar?

Unfortunately the Gunson is not the proper tool to check the A/F ratios on boost, it only works at idle. You need an LM-1 or similar device to check the ratios throughout the RPM range.

Boost creep can come from different sources. The inacuracy that you are referring to is a design issue. The volume and speed of the boost signal overcome the waste gate's ability to read it instantly. This is likely due to the branch off of the exhaust that feeds the waste gate not being an optimum angle (such as a y vs a T).

The gunson isn't the ideal tool, but it works. I used it to set the CO then worked with a guy that has a data logger to double check it. Basically, if the CISystem is working correctly it should automattically advance the timing and richen the mixture. Using the data collector verified that my 'system' was working right. So I'm ok, at least that's what I keep telling myself. The car runs great..

I understand what you are saying about the design. I guess I'm asking about is how to plan for it, better yet, protect my engine from damage it could possibly cause. Or do you just rely on the overboost switch?

Bill,

I do have the B&B system, so I agree that it is more of a design issue, coupled with the fact that the intercooler can see boost spikes, I think the best solution is to move the overboost sensor.

As to the protection against overboost, the records are pretty spotty and non existent on my car, but when I got it, it was running 1.1 bar worth of springs like I mentioned and the overboost was grounded out. It was running extremely rich, even more so since it hadn't been tuned at elevation (a little over 5000 feet here), I think to compensate for the massive amounts of boost. It has also been twin plugged and is running an electromotive crank fire ignition. Like I said, the info on the car was pretty vague, and my mechanic, working with Stephen K. (Porschedoc) set the cis, and tuned it with the .8 bar spring in.

On a side note, we did take it for a spin with the 1,1 bar worth of springs and WOW....

Hope that helps.

I would try a 0.8bar and see how that goes.

BSiple - But you still hit your overboost with a .8 spring after being professionally tuned? I'm curious to how much boost is required to have the engine cut out because of overboost. I'm not trying to be difficult even though it seems like it, but I just don't like the idea of not being able to control the amount of boost the engine.

The overboost switch should activate at 1.1-1.2 bar.

I'm into letting the dyno tell you how much you can get away with.

Basically everythign I have read, says that the intercooler see higher boost spikes than the engine. That is why I am going to move the overboost to a line off the intake.

+1 on the dyno.

Plus by moving the wastegate line to the intake you account for the pressure drop across the intercooler and actually operate off the actual engine boost not measured before the pressure drop in the intercooler. This may be splitting hairs, but the reason I moved mine to the intake last weekend.
I found that you could use a 1/8 inch NPT pipe elbow to fit in the intake manifold under the intercooler and run the wastegate line to it.

You ran the WG line off the intake fredmeister? I was thinking of just moving the overboost sensor. I hadn't thought of moving the wg line.

Do not move the wastegates line. Only move the switch.

Even by moving the switch there will be no protection for the turbo when the throttle is closed.

I think you guys misunderstand the new position of my wastegate hose. The switch I would not move, no benefit in doing this.
The wastegate hose is still before the throttle body but just moved to a point after the intercooler. It is basically in the casting right above the blow off valve assembly piston.....there was a plugged port there that I am using. It is in the same casting as the overboost switch.
Don't know if there is much of a difference in boost now, since in theory the pressure drop across the intercooler should be on the order of 0.5-1.0psi (guessing) but hey any free hp is good.

Gotcha.