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hi all I've started tuning my impreza on the road with a link g4 plus, moving on from the base ign map give added about 6 degrees of timing and don't seem to have heard any knock problem is am worried to go any further, at light cruise give tried to rack up more timing just to get a feel of what it sounds like and cant hear nothing after another 5 degrees. the timing is at about 50 now at light cruise isn't that a bit high to keep going even more to try hear this knock i did seem to feel a power decrease would it take another few degrees to start to hear the knock come on maybe? i suppose it will be hard to get the engine to knock at low rpm and load
Normally the max timing is about just below 50 on Subaru's. At light load you probably are not knock limited so can go beyond MBT without a dyno.
The other question is what fuel are you actually running? If we are talking about E85 you will be hard pressed to get it to audibly knock, which would be way passed MBT.
super unleaded, when you say max timing is just below 50 i assume you mean at low loads / rpm?
It's quite likely that at light throttle cruise you won't be able to induce knock regardless of the timing you use. 50 degrees is quite likely to be advanced well past MBT depending on the specific rpm and load point. What you find is that as you begin advancing the timing from a very retarded point towards MBT, is that the torque will initially increase sharply. As we get closer to MBT though we find the torque gain tapers off, plateaus and then begins to fall away. We will often find that over a range of perhaps 5-8 degrees of advance we see little to no appreciable change in torque. This means theres little to be gained in really pushing the advance in these low load areas. In most instances I tend to end up in the region of perhaps 30-40 degrees depending on the exact engine, rpm and load point as a bit of a guide.