I've been talking some about an anti-reversion plate elsewhere on 311s regarding headers and design. The plate "idea" is from a David Vizard YouTube posting on reversion. At about 18 minutes or so into it he uses a U20 or more likely an L-series head to demonstrate how much less flow velocity there is at the bottom of the port (he calls it "terrible"). As the cam overlaps between intake and exhaust a pulse wave can travel back or "revert" into the combustion chamber, especially at lower rpms. This plate would insert a tongue into that area creating a dam that blocks the reversion without interfering with the other areas of flow. Figuring out how tall and what angle is best is where the challenge sits and may need a flow bench and some time (working on that). This anti-reversion method is already adapted on some headers and exhaust systems with offset "cones" or steps in the pipe but that influences the entire flow path in the port or tube. Some head/port designs don't need this (he mentions earlier experiments with other engines) but it was pretty motivating when he went direct to the Datsun head specifically. I also believe I am seeing data on the datalogs I can collect/analyze that suggests reversion is occurring. Another advantage he mentions is that this will allow one to use a higher duration cam (think B or C cams) without losing (would actually gain) low end torque while still keeping the higher rpm advantages. BTW, I've spoken with some well know experts who have said the primary reason why this hasn't already been done for engines like ours is that it is generally against various racing rules that their customers had to adhere to, so they figured out how to address reversion in other ways that usually require significant head mods but that were still within the rules.
I'm not pretending that I know exactly what I'm doing, but I do hope to be able to work with others who can fill in the gaps and get to the point of "before and after" dyno runs to test the concept. I started the thread now just to begin the community input... there's a wealth of knowledge here on 311s and I'm very open to input. I do think this could be an easy mod to add to the engine (like installing a manifold gasket) that could benefit all U20s with more torque and make running a B or C a better option for all.
