I need a vacuum pump to use for a pvc system on a 64 Nova [421 stroker with an Enderle intake]I'm building. I was thinking of using a diesel vacuum pump like the one on my 95 Suburban. The pump on my truck gave up the ghost a long while ago and I put in a Turbo Master kit. I know that the pumps (should) put out 25 inches of vacuum at idle but does the vacuum reading change as the rpms change? For my application I would need to reduce the pulley speed at the pump for two reasons. One the rpm range of the engine versus a diesel and two, I only need aprx. 5 inches of vacuum at idle and 10-15 at a higher speed. There are pumps made for racing that produce vacuum but they aren't recommended for the street and they are very expensive. Since I can't measure my dead pump, does anybody know the vacuum readings with regards to rpm.