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Change ignition table after resetting base ignition timing?

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After a long time of trying to diagnose a problem with my car, I noticed a couple of days ago that the timing marks on my crankshaft pulley have spun. The timing seems to be off by around 8 degrees, which seems like enough to give me some driveability issues. I'm installing a new pulley next weekend, to check exactly by how much degrees its off, but by using a piston stopper and a timing light, I can tell it's not correct. My tuner didn't check the timing before the car went on the dyno, but the car is completely tuned, so I can't just change the base timing.

Is the solution as simple as adding 8 degrees to my base timing and then removing 8 degrees from everywhere in my ignition table? Or am i missing something?

That's a tricky one as it depends exactly where the pulley timing marks were when the engine was tuned. If it is as you say (8 degrees out), then yes, resetting the base ignition timing and offsetting the timing map by the same 8 degrees will get you the same result as you have now. But the problem here is that it won't fix any driveability issues as the engine will be receiving the exact same timing for a given load/rpm. The other issue to consider is that the pulley may have moved since the engine was tuned in which case let's say it might have been 4 deg off when tuned and is now 8 deg off - Therefore you'll end up negatively affecting the timing (assuming it was optimised properly).

Personally I'd fit a new pulley, set the base timing correctly, and then optimise the timing map on a dyno again. Even if you choose to just offset the entire map, this lets you confirm it's safe and optimal.

Thank you for the reply! Will definitely put it back on the dyno to optimize the map then!