been reading a book - How to Tune and Modify Engine Management Systems by Jeff Hartman something that caught my attention as i read is that richer AFRs (air fuel ratios) result in a faster flame speed.
so, if the mix is burning faster, i imagine that less timing advance is required. another way to put it - lots of timing advance plus a fuel that burns very quickly could be a recipe for gases that want to expand when a cylinder is still traveling in the compression stroke.
another thought - perhaps running a leaner mix is better bc the flame speed slows, allowing for greater timing advance. the downside is less chemical based intercooling, so obviously some optimizing is required. the other side then would be running a richer mix results in faster flame speed, greater intercooling, and requires less advance.
anyway, let me begin from the beginning -
1. 400 wtq on a dynojet is thrown about as the max Q acceptable for a stock block 4G63, such as in my evo ix. not sure if this is a continuous number, or a peak value. practically speaking, 400wtq continuous is not going to happen on my cbrd bbk-full turbo upgrade.
2. my car runs on e85. with requisite fuel supply upgrades, of course.
3. running VDR, and confirmed on a load-bearing dynojet, the car is capable of producing in excess of 400 wtq. this is especially true when free air temp is 65F or below. at temps higher than 75F, especially on sunny days where radiant heat from the ground is effective, the VDR plots are south of 400.
4. the ecu is capable of controlling boost (and therefore torque production). i have adjusted boost to ensure less than 400 wtq even in somewhat cold conditions (55F).
logs this evening - got a set of data from a tune [23mar10] that gets around 12.3 afr. i have a version that runs more like 12.5, with 1* more timing from 7-8000 rpm. in VDR, power output from 6-8k are nearly identical.
the plan for now is to remove that extra degree of timing advance and to go for a 12.0:1 air fuel ratio.
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