EFI Tuning and Overspeeding Turbos

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Written by wolfems on September 9, 2009 – 11:30 pm

Hi There.

This is going to be a quick one today.

I’m not going to go into real detail here, but I want to give you a quick overview on one area of turbo charging.

Now, we know that turbos spin fast. Really fast. But there is a limit to the speed (RPM) that a turbo will work efficiently. And this RPM is different for every type and combination of turbo.

Needless to say, that when a turbo goes towards the upper end of its working RPM, it doesn’t keep pumping out more and more boost as you keep trying to increase the boost pressure.

This post is not about the specifics of that, but it is about being able to use your ECU to ensure you don’t work the turbo too hard above its efficiency curve.

Let’s say for example, you have a 4L 6 cylinder engine with a turbo on it and you keep increasing the boost pressure, and you keep making more boost and more power at 4,000 RPM, but at 5,500RPM the power is not increasing. This may mean that the turbo is no longer efficient at that engine and turbine RPM. This only has the effect of heating up the intake air more than it should, and possibly damaging the turbo.

What to do?

As the RPM increases past that maximum power point, start decreasing the turbo valve position until you just start to lose a little power in that RPM region. Now you are putting the turbo under less stress than it would have otherwise been. This is not necessarily the only piece of information you need when it comes to setting up your turbo boost curve, but as there are many variables, this will at least give you an insight into one aspect of tuning your boost control system.

PS: We may be able to put you in touch with a turbo expert/supplier. If you’d like to talk further, you can contact us as wolfemail@wolfems.com.au.

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