Subaru COBB AP Boost Control – Am I Doing This Correctly?

Subaru COBB AP Boost Control is sometime not done correctly.

This video will show you how to set up Boost Control Tables for Subaru XTI, Forester XT, and other popular Subaru models using COBB Access Port, Race Tuner, ProTuner Software.

What most people do is that they put in what they’d LIKE to see on their boost control tables.

Unfortunately, when you try to hit boost levels that are not attainable, the ECU will try to compensate to hit those targets even if they can’t be reached. This can lead to problems down the road. Here’s the common Subaru car owner’s problem:

• Some car owners want their cars to hit 17 pounds of boost as soon as possible and then hold it there. So they type in 17 pounds of boost target at partial throttle.
• Since the turbo can’t realistically give 17 pounds until higher engine speeds, the ECU tries to compensate by adding to the wastegate duty cycle. Some car owners also edit the values here, commanding up to 5% more wastegate duty.
• When the engine reaches 3,200 RPM or similar speeds where the turbo can unspool properly and deliver the 17 pounds of boost commanded, the additional 5% wastegate duty cycle still kicks in – and an overshoot occurs.
• In short, when you try to hit an unrealistic boost target, the ECU tries to compensate. But when you do hit an engine speed that makes the boost target reachable, the ECU is STILL trying to compensate using the added wastegate duty cycle – and that results in an overshoot.
• This is a common problem with owners of Subaru’s. The vehicle works fine at 3rd to 5th gears, but when they hit it, it over boosts and cuts off on them. The cause? Improper wastegate duty cycle and improper boost target. This is why many Subaru car owners complain of their cars cutting off when they up the throttle, such as when they try to pass another vehicle on the freeway, or throttling up after rounding a corner.

The problem is that your Subaru won’t cut off in the dyno, but will cut off on the freeway. To avoid this potentially dangerous situation, follow these tips:

• It helps to have a smooth transition on the wastegate duty cycles.
• Don’t have too much wastegate duty cycle and too high boost targets on partial throttle.
• Target your boost curve to mimic what your turbo can actually do. If the turbo doesn’t spool up until 4,000 rpm, don’t command high boost levels at 3,000 rpm. There’s no benefit, and it puts you at risk of overshoot.

Proper boost control means your Subaru will have better and more reliable performance, less chances of overshoots, and less chances of the engine cutting off in critical moments on the road.

That is what it takes for the Subaru COBB AP Boost Control. Remember always take your time when adjusting any parameter in your engine management system.

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