If you are tuning your car yourself or simply checking for faults you may already know that Detonation - Det - is bad for your car. Det is basically pre-ignition in the piston causing Knock. Most modern engines, including all Subaru's have knock detection systems which typically consist of a piezo microphone bolted to the block which acts as a feedback circuit into the ECU. If the ECU detects Knock it will reduce your Ignition Advance Multiplier (IAM) which may then switch you to your high det map - a.k.a. limp home mode.
DIY Det Cans
The following simple procedure explains how you can make your own Det Cans allowing to hear exactly what your engine is doing.
- Start by getting some ear defenders. The author chose some Peltor Optime II for £9.95 but any will do the job really.
- Get some hard walled hose. The author chose some breather hose mainly because it is cheap to buy. 3 meters is a good length to allow a run from the top of the engine to the driver's or passenger seat.
- Get a bit of copper piping. This needs to be flattened at one end so as to attach it to a handy bolt on the engine near the factory knock sensor.
- Drill a 16mm hole in the bottom of the ear piece so that the piping can be fed into them. Insert piping and attach at the other end to a piece of flattened copper pipe. The pipe chosen above was flexible so you can change the positioning of it if needed.
Pipe Inserted into Ear Defenders
- Hey presto - You can now hear exactly what the engine is doing.
DIY Det Cans - The Finished Article
Information source - RomRaider forum thread Make your own Det Cans