Originally Posted by
techinspector1
Thanks Pat, for mentioning heads. I forgot to explain that, but what I do is find the published flow data from Stan Weiss or from the manufacturer or from another independent shop that has flowed the heads. I factor those numbers by either 0.90 or 0.95, depending on how much I think the fellows who flowed them are skewing the numbers and enter them into the DynoSim manually. It's the only way I have found to be REAL about the outcome. When push comes to shove, I think the only ones you have to worry about really tweaking the numbers is the manufacturers. Bigger numbers sells more heads. I factor Edelbrock down by 10% (0.90) because of the feedback from engine builders who dyno test motors with Eddy heads.
There are lots of tricks to embellish the flow numbers, you just have to figure out what the flow bench operator did, such as using a 4.200" barrel to flow a small block Chevy head. The vast majority of the cylinders on these motors that Johnny Hotrod is building will be less than that and so you just have to factor the numbers down a little toward realistic. There are other tweaks, such as multiple valve angles, undercut valve stems, bowl blending, wet/dry flow, etc., etc. that may be hidden in the numbers.
In short, it's not just a matter of getting the software and putting it on autopilot. You have to play with it and tweak the numbers to get anything near realistic. I think I have it down pretty close now and can generally get to within 2% or less of the readings from a "real" dyno. Being that close can allow you to change components and trust what happens as a result.