Subaru High Performance Tuning - Troubleshooting & Tips

Without a doubt the single biggest barrier to high performance tuning is detonation. Also known as knocking, pre-ignition, pinking or pinging, these are all words describing a very serious engine condition. Detonation describes a situation where there is a sudden and uncontrolled increase in combustion pressure inside the cylinder and can take the form of:

- The fuel/air mixture being lit-off too early in the engine cycle by over advanced ignition timing.

- Fuel with too low an octane rating causes spontaneous ignition of the fuel/air charge before the spark plug would normally initiate the combustion process.

- Excessive charge temperature and pressure causes a spontaneous ignition of the fuel/air charge before the spark plug would normally initiate the combustion process.

- Once the spark plug ignites the fuel air charge and begins to burn, a second unplanned ignition of the fuel/air charge occurs simultaneously in another area of the combustion chamber.

Pistons and piston rings bear the brunt of detonation, but damage is not always confined to just these parts, as the constant hammering of detonation can result in; erosion of material from the combustion chamber around the valve seats, fatigue failure of connecting rods, blown headgaskets and damaged connecting rod bearings. If you haven't already worked it out, detonation must be avoided at all costs!

Detonation can be controlled by the following means:

- Efficient cylinder head, combustion chamber design and a corresponding static compression ratio;

- Sophisticated engine control electronics and matching fuel + ignition calibration;

- Sensible boost pressures;

- Controlling intake charge temperatures;

- Higher octane fuel, offering better resistance to detonation.

Subaru has done a good job designing an engine with a suitable compression ratio and base mechanical spec along with a highly advanced electronic management system. Unless considering major engine surgery (out of reach for most Subaru WRX owners), this leaves fuel quality, intake charge temp, boost pressure and engine management calibration as the easily attainable methods for keeping a lid on detonation. Juggling these changeable parameters, and translating it into a safe and powerful engine tune is the sign of a really good engine tuner. Again, does this sound like your guy?

Despite all the evidence to the contrary, some very curious attitudes towards detonation still persist. The following points on detonation are the real deal. Anything else falls into the category of old wives tales.

Brett Middleton has over 10 years experience working on Subaru's and has transcribed all his knowledge into the Subaru Performance Handbook. His company, MRT Performance has modified and serviced more Subaru's in Australia than any other workshop.
There is no other Subaru book like it! Get a valuable insight into Subaru models from just about any country.
Bonus chapters available for instant download at http://www.subaruperformancehandbook.com
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