just wondering,has anybody done any r&d on these manafolds to see which one flows the best?

I'm not going to mention names but a very repected member on here told me that EMI's stink when I asked about what exhaust to choose. Stainless Marine are very good and last forever. I had them on my engine and switched to Eickert Headers. The Eickerts certainly outflow the Stainless Marines but there a pain in the A$$ to install and are much heavier. Either way, you cannot go wrong with the stainless manifolds.

I sell both and have not had a problem with SM or EMI. I sell more EMI than SM, mainly because of the price difference.