I would tend to agree that making that one change shouldn't produce enough power to feel, but what bout those nasty ledges on the upstream ends of the LIM runners? It seems that they must be creating a lot of turbulence, esp at high RPM. I wouldn't expect a big change in performance just improving flow in the manifold, but it seems that it would become necessary as the rest of the system is improved. I wasn't expecting big gains when I modded my TB, but was pleasantly surprised by the power up top. (Gained an extra 500RPM before HP fell off)

 

If there is a sharp edge to cross then by all mean get rid of it. There is no need to go out to the gasket size though. On the middle to lower manifold junction, you should only touch the lower manifold. Make it slightly larger than the middle manifold runners. Don't enlarge the middle manifold runners though. You want a reverse lip to help combat reversion. Too many people think that gasket matching every part is the way to go. It's not. If you insist on gasket matching, only match the lower half of a junction. Leave the top alone.

 

Are you sure that eliminating reversion is a great idea? I seem to recall hearing that Mazda had managed to acheive better chamber filling by utilizing the reversion pulse from one chamber to effectively supercharge the opposite intake runner. (If I'm understanding the DEI concept correctly...) If so, then it would seem to be a good idea to allow (Or even encourage) a strong reversion pulse.