Does anyone have any links to some info on it? On Google All I find is links to Honda forums. Mainly looking into the Intake/Exhaust ports, not the header chamber type. Here's a quick explanation: http://forums.vwvortex.com/showthread.php?5180986-Concerning-anti-reversion-porting I know the consensus is usually to gasket match, but In my head having an anti reversion step seems better for non WOT driving.
On my race motor..............this is a WOT thing............my SuperVictor Jr. is .025" less than the intake ports in the head. I personally don't think that anti-reversion does much, especially on a motor that is not at WOT. One thing to keep in mind is that a motor is nothing other than "an air pump", and although I have never done any dyno testing to prove one way or the other I believe that intake/exhaust port design needs to go hand in hand with header design. My Maverick has had stepped headers since the late 90's when everyone was saying stepping didn't really do anything......well...........it certainly does aid in scavanging on a naturally aspirated motor, a little less on a direct port injected motor, and even less on a blown motor, but each motor is different and I believe there is no magic formula that you can use as general rule of thumb.........because no two motors are exactly alike. This is just my opinion, but on a non-race motor I don't think it is worth trying to do, again, just my opinion.
If the headers are properly tuned to the port timing reversion cannot happen. You have to tune the primary pipe diameter, the primary tube length and the collector diameter and length. I go two steps further and tune the distance to the "H" pipe and muffler. Each step can be used to broaden the range that the headers are tuned for and the range that prevents reversion. There is a lot of math involved and a few compromizes along the way but the "tuned range" on my engine is a 4000 rpm range from just off idle to 5000 rpm that favors the torque curve. Mine is not the best set up for all applications but it is definitely a street friendly way to go. Paul
