Testing a open manifold can not give the true results of what the manifolds offer going through the heads. It would be easy to open up the manifold more and just grinding the openings of the manifolds will produce higher flow numbers on a open manifold. Having the highest open manifold flow number was never Mike's goal. The test data also says without gasket and my guess is because they made the opening larger than the gasket. Because the other manifolds are copies of Mike's work, they will show similar flow numbers. Lots of things involved in making exhaust parts. Flow is only one item on the list of factors to consider. Something to keep in mind is that the head is the restriction and no matter what, you can not flow more than the head. If you really want to look at flow numbers the ones done through a head by na300zx (OH) are going to offer a more realistic comparison because they went through a head. The post can be found here with the info.... [ http://www.twinturbo.net/nissan/300zx/forums/general/view/2169590/AMS-vs-MSP-Results.html ] Velocity is also important and going too large can actually hurt spool. Mike Smith is extremely knowledgeable and took everything possible into consideration when making the manifolds and he did extensive testing because he wanted to offer the best possible solution and offer the best possible results for the Z32 engine. It simply does not get any better and you will find it impossible to find someone that would spend the time Mike did on creating these manifolds. Most people would have said that's good enough and Mike never did! He made even the smallest of changes to perfect the manifolds many, many times. It took Mike a long time to bring the manifolds to market because he cared more about making the best product rather than how many he could sell if he just released them and called it good enough. Mike made different ports different sizes to allow for the best balance between cylinders because of the different length of the runners. Mike also uses a more expensive material than needed to make sure the manifolds can hold up to even the most extreme conditions. Mike still hand finishes (by machine) the manifolds himself because he is not completely satisfied with the way the foundry does them. The bottom line is Mike's manifolds are the highest Quality you will find in the Industry for any car in a cast design. NUF SAID
