how much timing is too much
01-21-2008, 07:40 AM
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Staging Lane
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well, i just learned something new though. this is my 98 trans am i am speaking of and it used to have afr heads and 224 cam and 90/90 set up w 25 degrees total timing and i put the ls6 intake and stock cam, and tsp 5.3 heads in it without tuning it and now its got 28 degrees total timing? i thought timing was something that was adjusted in tuning and didnt know swapping parts would affect it.
01-21-2008, 08:53 AM
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There are other factors to consider as well regarding the timing. Were you experincing knock on the run/scan with 25*? Could have been the gas, could have been the parts, too much heat (when did you do the first run/scan vs. the second? IAT, ECT, Oil temp, ambient temp), etc.
I agree with Phil the only way to know is to get it on a dyno. I disagree with the 'timing till it knocks' concept. In my experience, the peak torque curve is relatively flat with regard to timing when adding/subtacting a few degrees. You need to have really good dyno to do this (can hold a load and report torque live), but changing the timing +/-3* (I have seen and read several studies where the area is more like +/-5*) on a NA setup like your describing will show less than a 1% change in torque.
If the engine knocks at 29* and you make essentially the same power with 25* vs 28*, why run 28*? You are just that much closer to knock and susceptible to bad gas, excessive heat, etc.
Just my $.02
I agree with Phil the only way to know is to get it on a dyno. I disagree with the 'timing till it knocks' concept. In my experience, the peak torque curve is relatively flat with regard to timing when adding/subtacting a few degrees. You need to have really good dyno to do this (can hold a load and report torque live), but changing the timing +/-3* (I have seen and read several studies where the area is more like +/-5*) on a NA setup like your describing will show less than a 1% change in torque.
If the engine knocks at 29* and you make essentially the same power with 25* vs 28*, why run 28*? You are just that much closer to knock and susceptible to bad gas, excessive heat, etc.
Just my $.02
01-21-2008, 09:27 AM
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Timing changes with air and coolant temps as well
as MAP (dynamic cylinder air follows MAP). Anything
that drove any of these, will vary your timing. You
need to keep an eye on a lot of things to know what
is messing.
"Too much" is "anything more than makes best torque".
As judged by acceleration, in my book. Don't go by
the torque value the PCM tells you, that's all based
on a model for a motor config you left behind long ago.
as MAP (dynamic cylinder air follows MAP). Anything
that drove any of these, will vary your timing. You
need to keep an eye on a lot of things to know what
is messing.
"Too much" is "anything more than makes best torque".
As judged by acceleration, in my book. Don't go by
the torque value the PCM tells you, that's all based
on a model for a motor config you left behind long ago.
