No loss of Vac... so not extra blow by... Take the thin oil out and the power came back. I made a few more pulls checking a few other things and quit the session. I've done that test several times with customer engines and seen the same thing a time or two. Esp with big inchers... one of My own little SS/Comp V-6 engines did it too. I took it apart after I took it off my Dyno and the bearings did show signs of bumping the crank. I also called one of my buddies that works in an engine shop for a cup team and he said all their engines that use thin oil are set up with tighter bearing clearances than the engines using heavier oil. He said they had seen exactly what I had noticed. I have also had a non coated cam bearing stick with thin oil. I think Too much load with the heavy roller springs pushed the thin oil film out. I think a tight Jesel belt contributed to te load. Thats the only explanation. I polished the cam and put coated bearings in, ran the 00 oil and had no more problems. I'm pretty sure just puttimg thin oil in an engine doesn't mandate an automatic HP increase. I'm sure you should build the engine esp. for thin oil to get the most benefits fom it.
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