CR and Octane Rating

Stan Weiss said:

Octane needed for CR in the 2V motor. Has anyone looked or used either of the following, or have any ideas about them.

Based on the work of DR. Gordon P. Blair decreasing squish clearance and / or increasing squish area will increase Max. squish velocity. This is in turn will promote faster combustion and in many case need less octane.

In the EMC the builders have been cutting droves in either the squish area of the head or in the pistons to help fixture speed and be able to run higher CR on pump gas.

Click to expand...

I think you and I talked about this briefly in the "School us on Engines" thread, but I really can't remember and I really don't feel like reading through that thread.

Tightening the quench(squish) distance can definitely have some benefits, especially on the small bore of the 4.6. Larger bores obviously have larger pistons, and those larger piston tend to rock more at TDC than a smaller diameter piston. This allows smaller bore motors to have their quench tightened up quite a bit inducing a more homogenous air/fuel mixture, and allowing the total timing to be slightly retarded so that the peak cylinder pressure occurs slightly more ATDC.

Here is a pretty good article I think you will enjoy Stan:

http://www.chevyhiperformance.com/techarticles/94138_piston_head_clearance_guide