Now that I have more of the details tied down I can be more certain of the final compression ratio. The only unknowns are the installed timing of the cam and the combustion chamber size.
As I retard the cam timing from 4 degrees advanced (IVC=69 or Dot-Dot) to 0 degrees the CR drops, but when its installed with 0 (IVC=73) advance, I could possibly go with the smaller chamber. I have the choice of the Brodix IK200 heads with a 64cc or 70cc chambers. I figured that with the smoothing and polishing of the combustion chambers I would gain about 1cc, therefore I have used 65cc and 71cc for my calculations.
As you can see from the table below the first 3 engines have a 71cc chamber and each one is 2 degrees retarded from the previous engine. Engine #4 has a 65cc chamber and the same 0 degrees advance as engine #3, witch bumps the DCR from 7.92 to 8.44 . If you assume engine #1 is Ok at 8.2, then this is only 0.24 points higher.
I used DynoSim5 to plot engine #3 versus engine #4. It's so close up to 5500 RPM that I'm thinking it would NOT be worth the chance of running into detonation by using the smaller 65cc chamber, although the DCR only went up by 0.24 points.
The smaller chamber would have a shorter burn time, but would it be enough to counter the 0.24 bump in DCR ??? Am I missing anything ???
I know I'm splitting hairs again, but it's interesting to think about.
As I retard the cam timing from 4 degrees advanced (IVC=69 or Dot-Dot) to 0 degrees the CR drops, but when its installed with 0 (IVC=73) advance, I could possibly go with the smaller chamber. I have the choice of the Brodix IK200 heads with a 64cc or 70cc chambers. I figured that with the smoothing and polishing of the combustion chambers I would gain about 1cc, therefore I have used 65cc and 71cc for my calculations.
As you can see from the table below the first 3 engines have a 71cc chamber and each one is 2 degrees retarded from the previous engine. Engine #4 has a 65cc chamber and the same 0 degrees advance as engine #3, witch bumps the DCR from 7.92 to 8.44 . If you assume engine #1 is Ok at 8.2, then this is only 0.24 points higher.
I used DynoSim5 to plot engine #3 versus engine #4. It's so close up to 5500 RPM that I'm thinking it would NOT be worth the chance of running into detonation by using the smaller 65cc chamber, although the DCR only went up by 0.24 points.
The smaller chamber would have a shorter burn time, but would it be enough to counter the 0.24 bump in DCR ??? Am I missing anything ???
I know I'm splitting hairs again, but it's interesting to think about.
