Mine is BBC w/ Lunatti all roller & solid... motor must run well over a thousand RPM for starters. It's hard on the valve train under a thousand RPM w/ a bigger cam. What about timing? I have seen motors jump around @ idle with incorrect timing too. Do you have solid motor mounts? If not, it's definately not a bad idea.... Stock, sloppy motor mounts w/ high compression & larger cam BBC will jump around some... especially w/ 800RPM.