<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: elonblock</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: VintageMusclecar</div><div class="ubbcode-body">The 496 in my Chevelle has 11.2-1 compression with square port closed chamber heads, and runs perfectly on 92 octane. The key(s) to making it work are 1) cam timing (needs to bleed off some cylinder pressure @ lower rpm), keeping the engine coolant temps ~160°-170°, and a nice, conservative timing curve--in this instance, 14° initial and 36° total, but it doesn't come in fully until ~4000 rpm. (no vacuum advance either)
FWIW, YMMV. </div></div>
Tell me more....
1) Can you elaborate on the cam timing?
2) Please provide more detail about your experience with the cam.
Thanks! </div></div>
In a nutshell, it's all about managing cylinder pressure. The two things to consider are 1) static ("mechanical"
compression ratio and 2) intake valve closing point. Large cams typically close the intake valve later than milder cams, which has the effect of bleeding off cylinder pressure at low rpm. This reduces the engine's tendency to detonate.
A high mechanical compression ratio builds more cylinder pressure than a low one, which requires either running higher octane fuel, or using some other means to adjust the cylinder pressure.
Lowering cylinder pressure can be accomplished either with a larger duration camshaft (noting the intake valve closing point) or retarding the existing camshaft in order to delay intake valve closing point.
The latter is a common method among pure stock racers who are required to run an OEM camshaft as this also serves to raise the rpm power band slightly.
A general rule of thumb is advancing or retarding a cam 4° will lower or raise the powerband ~200 rpm, respectively.
Hopefully that all made sense.
*EDIT* Lynn's response above this one re: quench is dead-on, I failed to mention it in my earlier post.