Join Date: May 2012
Location: Temecula, CA
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You won't be able to change the "squeeze" without removing the heads and replacing the headgasket with a thinner one and/or having the heads milled to reduce the combustion chamber size. Presently you are probably running about 9.8:1 static compression with your stock headgaskets which are .045" thick. You can get pretty close to 10.1:1 static compression by replacing the stock headgaskets with .030". If you change to the S&S 570 cam without bumping up the compression you will notice some softening of the torque below about 2500 RPM. From 2500 to about 4000 the torque will feel about the same. The S&S 570 will continue to be strong up to about 5600 before it starts to flatten out while your SE255 flattened out and started fading about 4500. With cam changes, if you don't make changes in compression you're pretty much just moving the torque curve to the right or left (in your case the 255 favors the left side of the chart). The 570 favors the middle of the chart. There are other cams that favor the right. The more the cam favors the right side of the chart, the higher you need to raise the compression to bring back some of the bottom end. In other words, cam changes moves a curve right or left on the chart. Compression changes moves it up or down on the chart. Head modifications will help torque carry longer (flattening) or shorter (peak). What I just wrote is an oversimplification, but is generally a good way to conceptualize how changes effect the torque/horsepower curves.