Datsun Roadster Forum-311s.org

Shhhhhh, don't tell the Datsun what I'm getting her for Christmas!

Looking further into making an "anti-reversion" plate that will fit into the primary exhaust tubes like an additional gasket... if it works it should improve low end torque and overall performance for all U20s by blocking reverse flow on the slow side (bottom) of the exhaust port... stay tuned...

Sounds neat...hope it works!

Greg, sounds like a great idea. You could probably fab something out of thin stainless steel. The old VW beetles used something similar near the oil filler tube at the generator stand to help keep excessive oil odors out of the engine compartment (and the interior).

https://www.jbugs.com/product/113101221B.html

I've been talking some about this 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 low end torque while still gaining 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.

As I get further into this I'll likely start a thread. 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 think I'll start the thread now just to begin the community input... there's a wealth of knowledge here on 311s!).

Im pretty sure an L series head is MUCH different from a U series. The port design is different as well as the height, so before you go all in with the L series ideas, double check the differences. If I remember correctly, the U series is a better port design and setup than the L series.

I'm looking forward to seeing what you come up with.

Will