Someone asked where the correlation between DCR and octane was made: David Vizard, well-known engine tech writer, has a chart he's used in articles and his books that I posted below.
I own a LOT of DV books and have learned a bunch from him, but this stuff can't be interpreted as a One Size Fits All thing. You can't even get people to agree on what cam/lift point to use for setting the IVC point, so how can you derive anything about a value for which 5 different people might get an equal number of different answers?
Thanks, I was the one wondering where that came from.
Your right on the IVC point also, some say to use 0.050 duration numbers, others advertised duration (0.006" hydraulic, and 0.020" solid?) At least the chart does show a difference for different temperatures, usually totally ignored in most discussions.
There is also the topic of "quench" distance, but usually no discussion of the "quench" area. There is a good difference between the "closed chamber" RPM / Stealth type heads with a "D" type chamber, and the Victor / Trick Flow heads with a heart shaped chamber. Not to mention the difference in spark plug locations and bore size.
For me, I use the advertised duration numbers to estimate IVC, and usually if the effective compression ratio is less than 8:1 I believe that I am giving up some low end torque and efficiency that could be improved with more static compression?
