I've ran the 492's with 14 1/2 to 1 compression on gas 20/25 yrs ago, the set i had was roll milled to increase the compression, had them flowing in the 270's in. and 73% on the ex. In fact they ran as good as a set of fully ported Brodix 10's i had. I ran both sets on a 358" and a 406" motors.
Zip.