Anyone here ever have their pistons machined?
FD, as far as milling the heads an equivalent amount as the pistons are in the hole, and using that to equate CR, well, it's not that simple. If you're talking about milling a wedge shaped chamber versus a cylindrical object, geometry says the volumes won't be the same for a given distance.
I'm apparently going to have to re-read your original thread a little...
After I wrote that, it occurred to me that the quench pad affects the volume. The head milling affects about 3/4 of the chamber compared to what it would with an open chamber design.
The real test will be when the heads are cc'd. At that point I'll be able to know the true number. Looking back, I figured that the milling and carbon buidup had me closer to 11.0 to 1. I applaud those that are able to make that work. I know that I wasn't able to do it. I first tried switching from stock steel rocker arms to 1.6 roller rocker arms. This was with the 509 cam. There was no difference. I switched to a cam with more lift, duration and what I was told was a LATER intake closing. The info on the intake closing of the 509 cam is still undetermined, but it appears that the new cam closes earlier because of the increase in cylinder pressure and detonation. I tried different carb jets and power valves. Different carburetor. Different distributors, different spark curves. I installed a wideband UEGO guage to monitor the A/F ratio. I have tuned the carb to run at the highest possible idle vacuum and had the A/F ratio dang close to 14.7 at idle, 14.7 at cruise and 13.0 at WOT. I tried a 50/50 mix of 91 and 100 octane. ALL of those efforts and the car still knocked. I ran a 50/50 mix of the 100 and 110 race fuel and the car ran faster than ever. It idled the same and cruised the same but at WOT, it flat out screamed! NO detonation at all. This was with 16 degrees of initial timing and 30 degrees total. I did not bump the timing to 34 or 35 to see how much faster it would be nor if the detonation would come back.
It came down to 2 options: Raise the octane or lower the compression ratio.
Seeing and reading about others that like to drive their Muscle cars inspired me to do the same. In 2003 I made my first road trip in the car to Reno Nevada, about 225 miles round trip. This was with the first 440 I built, a standard bore, rering job with 9.2 compression and a 280/474 cam. The car ran great with zero knock and decent mileage. In 2011 I decided to drive to Los Angeles for the CPW Spring Fling. That was a 1000 mile round trip. It was also a real shakedown run. The car ran then as it has since I first built the 493: Great until I was past 3/4 throttle. Since then I have looked at many options to achieve the great street manners that I had with that 1st 440. This engine has more of everything...Cam, Compression, Carburetion, Exhaust. Maybe I have somehow overlooked a small detail that would have made a difference. I can say that if this sucker knocks after these changes, I will surely be baffled!
The combustion chambers had some carbon on them but not too much. Same with the tops of the pistons. Obviously as more continues to accumulate, the CR will rise. I figure that if I have a reasonable safety margain in terms of compression, I'll be able to run the engine longer without any detonation.
