Posted by George in MI on Wednesday, February 08, 2006 at 12:58PM :
In Reply to: CC'ing a flathead.... posted by Terry in Bozrah on Tuesday, February 07, 2006 at 7:55PM :
I wonder about a couple things discussed on this page. First, the situation where a piece of carbon is causing early ignition sounds to me more like what is called "preignition" and not detonation, or pinging. Preignition is usually not heard and can be serious when hot spots cause burned valves etc. I suppose however, that a hot spot could cause or aggravate pinging, but pinging can occur without any hot spots whatsoever.
Detonation, or pinging, is more akin to dieseling. Compression causes heat and the this can cause the charge to explode before the spark sets off the desired controlled burning. The higher the octane value, the more resistance there is to this problem of pinging. Carbon buildup exacerbates this problem not because of a hot spot or an ignition source, but rather because it increase the compression ratio.
Then there is the statement that for maximum power, the combustion chamber volumes need to be the same. And they recommend grinding out metal in the head to lower the compression ratio of that cyclinder so it matches the lowest one.
I doubt that that act alone would increase power of the engine....I believe it would decrease it.
Regarding their selection for a working fluid to measure the volume, I agree that water is not a good choice. It has a high surface tension which creates a big minicus and it tends not to wet things which means that bubbles are more likely to get trapped. I think I would try kerosene but their suggestion of antifreeze or alcohol/water mixtures may work very well. I think I will test that.
Without data to support either of these positions, I think we have to say that we just don't know what the effect would be.