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Re: Boost control from manifold instead of compressor
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Posted by Dean (more from Dean) on Wed, 14 Feb 2001 12:18:58 Share Post by Email
In Reply to: Re: Boost control from manifold instead of compressor, fsik, Wed, 14 Feb 2001 08:54:25
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fisk,

I had changed my system to tap pressure from the manifold for the stock BCP solenoid valve long before increasing pressures. So I used that when I went to the HBC. Then with the drop in temperatures, I got the overshoot and fuel cuts. If you stay on the throttle you will get repeated fuel cuts and overshoots. Not really a occilation, certainly not a harmonic occilation.

So I tried the TurboXS valve to try to combat this. What is needed is to have the ball valve open a bit sooner, and then open the bleed port to compensate and achieve the target boost pressures. With the cold weather, I have not been motivate to try to tune this in. But with nicer weather, the problem will go away too! And the snow tires are on the limit of their traction quite often when at 13 PSI of boost. Don't know my exact pressures as the boost guage reads about -1 at rest.

I did try to get it tuned in and concluded that the valve could not stroke the wastegate actuator fast enough. So I removed the inlet host barb, and drilled out its 1 or 1.5mm inlet to 5/32". So it can flow more. So upstream flow resistance which used to be the ball and spring plus the small opening is now reduced to the restriction of the ball and spring. That should allow the valve to stroke the actuator and open is faster in response to rapid onset of boost. So the jury is still out. I have not made any adjustments since doing that drilling.

One of the problems with tuning close to the edge like this, is that repeated tuning runs do get the turbo very hot and very responsive. So the boost onset is even more rapid which just makes the issue worse.

I can see that all of these types of controllers need a fixed upstream orifice, and a spring piston or diaphragm actuator to open a mechanical valve, combined with an adjustable bleed orifice. The controller to actuator hose lenght should be kept short as well.

So what do you think, the HBC is better without tapping to the manifold. Was it stable in the other confifuration. Did you have a guage. Can you quantify the pressure droop at high RPMs?

What is happening is that the controller sees the pressure so late, that the it cannot adjust the wastegate fast enough. Perhaps a pressure tap from some point after the intercooler would be a good trade off. That would be a good assumption if the transistion casting rework has been done. This time lag is working against us.
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