I've read about guys using the .020 shim gasket even with aluminum heads. I'm still skeptical about it all though. The .020 gasket moves my CR to 11.22 to one. Quench or no quench, thats still a lot of squeeze. It seems impossible that I could add a half point of compression and eliminate the knocking in one move. I'm still worried that the high CR leaves me with too little wiggle room if I get a crappy tank of gas or if the weather is especially hot. I do not want to just barely be safe from pinging.
