When we dyno the engine we do run the water pump with a belt. It is hard to similate every sidepipe as well as have it fit the dyno. We use a 1 7/8 into 2 header into a 3 1/2 collector. The header runs into a 5 inch pipe that is tied into a large industrial muffler. I am sure most of the sidepipes will hurt the power some. We have seen as much as 50 HP at the rear tires with different sidepipes on the chassi dyno on the same engine.
We can normally run the engine a little leaner on the dyno but they are pretty close when installed in the car. The other problem is that we are at about 300 feet above sea level and if the engine goes to a higher altitude you need to lean it down. I use 1 jet size for every 1000 feet of altitude.
We also mark the damper with a red mark where it makes the most power. We do a dyno inspection sheet with each engine. We double check the torque on bolts, check for
oil leaks with dye and black light, do a leak down on the engine, use a system one filter for inspection during the dyno sesssion and after we are done. We inspect the exhaust ports to see if we see anything out of the normal.
We do find carburetors that do not work as good as they should and send them back for replacement. With the CNC heads and blocks we know the power should be within a few HP of the same engine. Hope this helps a little, Keith Craft