Sorry to drag up an old thread but I found some of the comments very interesting on this topic. The motor did make 420 honest horse without any spacers and before fooling with the lash. All dyno's are different, they are not calibrated like scales and federally watched. When my engine builder asked what dyno I wanted to use, he asked if I wanted to use a happy dyno or a sad dyno. The happy one would show 20 more horse he said. We chose the sad dyno because like he said, "when you have 420 horse, you know it's a true 420 horse. Depending on altitide, temp, and dyno, your results can be + or - 15 horse. The dyno is simply a tool for measuring changes which it does well. So while the paper out of the dyno is very interesting, the piece of paper that matters is the one at the end of the return road. That piece of paper said 12.69 @ 110 which was on F70-14 polyglas with a stock GM converter, and a single cross flow muffler. Also no spacer was used. The 454 MCR dyno'd did not have a stock GM cam and was run with 2" headers not manifolds. Have a great day and sorry to bring up an old thread but I'm new around here.
