Knock vs Performance vs Engine Damage
- Thread starter tomjon
- Start date
The stock chip uses 29.9 deg for the max allowable retard while in PE mode, and I've not seen that changed in an aftermarket chip. However, I don't think retarding the timing much lower than about 5-10 deg BTDC is going to continue reducing knock, if I remember the discussion in Taylor's textbook correctly. The ecm also has a retard threshold set at 15.5 deg stock, over which it will pull 10% from the wastegate duty cycle to cut the boost a little. In my street chips I emphasize safety so I set this threshold to 4 deg and pull 100% of the wgdc. Get 5 deg of knock and the car falls on its face to let the idiot, err, driver 
, know it's past time to lift. There's just no reason to beat on an engine in a street chip situation, in my opinion. Course, I also leave that in in my race chips to make sure they run enough octane (cause when things start to go bad at high boost and high timing they go very bad very quickly).
When the ecm detects knock it starts retarding the timing until the knock stops, then it starts putting it back. When you see several degrees of retard frame after frame on scanmaster that means the ecm pulled enough timing to stop the knock, started putting it back, got knock again, pulled timing to stop the knock, started putting it back, got knock again, etc. The engine may not be knocking continuously but it is knocking a large percentage of the time. When knock occurs the power output of the engine goes down because of the inefficient use of the fuel that's burned, plus the power loss from the retarded timing. Yes it is possible to go a little faster in some circumstances (mostly pump gas) with a degree or two of retard for several frames in third gear, but you would go even faster with a chip that simply took out that amount of timing if you want to run that same boost. To my knowledge no one can say "averaging 3 deg of retard will take 10% off the life of your rod bearings", or anything like that. If you really need another .05 sec off your et then rather than tuning over the edge, get better parts (turbo, injectors, intercooler, whatever is next in your combo). I run 93 octane pump gas almost exclusively, and I tune for zero retard the entire pass. Sometimes I get a little knock, yes, but when I do I turn something down for the next pass - I like tuning much more than changing head gaskets or rebuilding short blocks. So far (knock on wood) I've never blown a head gasket or spun a rod bearing or gone into the motor for any other reason, with about 101K miles on this engine and a bunch of 13 and 12 second passes on it. Best so far is 12.026, 111.0, and 1.71 for et, mph, and 60', on different days, at 4060 lbs going down the track on 93 octane and no alcohol or water injection.
, know it's past time to lift. There's just no reason to beat on an engine in a street chip situation, in my opinion. Course, I also leave that in in my race chips to make sure they run enough octane (cause when things start to go bad at high boost and high timing they go very bad very quickly).When the ecm detects knock it starts retarding the timing until the knock stops, then it starts putting it back. When you see several degrees of retard frame after frame on scanmaster that means the ecm pulled enough timing to stop the knock, started putting it back, got knock again, pulled timing to stop the knock, started putting it back, got knock again, etc. The engine may not be knocking continuously but it is knocking a large percentage of the time. When knock occurs the power output of the engine goes down because of the inefficient use of the fuel that's burned, plus the power loss from the retarded timing. Yes it is possible to go a little faster in some circumstances (mostly pump gas) with a degree or two of retard for several frames in third gear, but you would go even faster with a chip that simply took out that amount of timing if you want to run that same boost. To my knowledge no one can say "averaging 3 deg of retard will take 10% off the life of your rod bearings", or anything like that. If you really need another .05 sec off your et then rather than tuning over the edge, get better parts (turbo, injectors, intercooler, whatever is next in your combo). I run 93 octane pump gas almost exclusively, and I tune for zero retard the entire pass. Sometimes I get a little knock, yes, but when I do I turn something down for the next pass - I like tuning much more than changing head gaskets or rebuilding short blocks. So far (knock on wood) I've never blown a head gasket or spun a rod bearing or gone into the motor for any other reason, with about 101K miles on this engine and a bunch of 13 and 12 second passes on it. Best so far is 12.026, 111.0, and 1.71 for et, mph, and 60', on different days, at 4060 lbs going down the track on 93 octane and no alcohol or water injection.
