Quote:
Originally Posted by Irace86.2.0
If my theory from earlier holds any water then the reason why a tune can't fix the dip alone is because the motor will try to avoid knock regardless of the basic parameters set by the tune, and knock may be problematic on some high compression NA motors at low rpms where slow exhaust speeds increase combustion chamber temperatures from residual exhaust gases.
If my theory is true then trying to hard tune out the dip without a header could be dangerous or increase the chance of engine knock.
The FB20 is a stroked FA20 (minus port injection). The FB20 has a lower compression, so it would make a good apples to apples comparison for comparing the effects of compression ratio on low end torque (to demonstrate my theory true or false), but it isn't a good apples to apples comparison because the engine is undersquare (longer stroke and smaller piston diameter than our square setup). Usually a stroked motor will have more low end torque, so any dip alleviation from not being as high compressed could just as likely be from being stroked. Thus, I agree with you that the FB20 isn't an apples to apples comparison for my theory or for his theory.
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I am aware of the differences in the FB20 and not fully discrediting your opinion because there is merit to the idea. I'm just making observations based on the charts I have seen.
E85 is much more knock resistant. Still has dip.
http://www.ft86club.com/forums/showthread.php?t=52326
It is pretty easy to discredit the thought that the factory tune causes the dip, when tuned cars still have it.
There is so much more that we don't have answers for so there are a lot of assumptions. I know bore to stroke changes VE. We also do not know how the FB is cammed vs the FA which would also play a large role. I have a feeling it is significantly different just based on what red line is between the two.