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Tuning for fuel economy and increased power

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Hi everyone!

Im a beginner tuner from South Africa and my first customer is a Subaru Forester XT SG9. He’s asked me to improve fuel economy as well as increase the power slightly. Would I be correct to lean out fuel in the cruise zone and then advance some timing in the boost zone under heavy acceleration?

The Car is completely stock.

I look forward to receiving any other advice that may help me on my journey.

Regards, Jeremy

Hi Jeremy, have you done any of our tuning courses we explain fully what you need to do to correctly tune the engine i would do nothing to the tune in the car without fully understanding what the engine needs, have a watch of the webinars first to help you find what is the best plan.

Regards Ross

Hi Ross

yes I have done the EFI tuning fundamentals, understanding AFR and the practical reflash tuning courses.



I will have a look at the webinars

As Ross suggested, it would be unwise to start making changes without a complete understanding of what you're starting with, especially as the OEM is usually pretty darn close.

While they seem counter productive, both can be achieved by increasing the overall efficiency of the vehicle, with numerous small improvements adding up to significance.. This isn't just limited to the engine but the vehicle as a whole - and for the economy the driver is a BIG factor!

Small gains with the correct viscosity synthetic engine and transmission oils can reduce drag, increasing efficiency. A full tune and emissions check can help identify if some parameters are out of range for fuelling, checking if the engine is reaching the nominal factory boost level could reveal an exhaust restriction, etc. Tyres can be a big factor in overall drag, a small increase in cold pressure of 4 PSI can make some difference in reducing drag and improving steering response, as can using oversized, softer compound and/or agressive tread tyres hurt drag.

As stated already, it's not really viable to approach every tune with a specific goal in mind of what the engine will need. Instead you really need to test and find out what the engine wants and what it responds to. What you can achieve will also depend on the starting point.

However some rough generalisations - You will most likely find that the biggest gains in power and economy come from leaning out the WOT operating area. Most OE calibrations are excessively rich in this area which hurts power and economy. Subaru engines in general are quite knock sensitive on pump gas so tread carefully. There can be some small improvements to be had by leaning out the cruise areas but this is normally minor - In the region of perhaps 1-2%

Thank you very much for the help guys!

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