I'm curious as to whether anyone has ported only the closing edge of the secondary intake ports. If my thinking is correct, this would add a little bit of top end breathing, without impacting overlap at all (no impact on idle or emissions or fuel economy) and with minimum impact on low and medium speed volumetric efficiency. The idea would be to extend the powerband slightly on a mostly stock setup.

Stock secondaries close at 50 degrees after bottom dead center, on an REW engine. Is it physically possible to change closing timing to, say, 70 degrees after bottom dead center, without affecting opening timing or overlap at all? Would you physically run into anything on the irons?

 

this is somewhat inspired by this chart from an old Mazda SAE paper. It's talking about the development of the 6 port naturally aspirated engines, but it got me to thinking.



Clearly first gen non turbo 6 port is different from a 3rd gen sequential twin turbo, but it's an interesting thought.

 

So in regards to VE does one shoot for maximum area under the curve or a peak number? Some combination of the two?

In the chart it looks like the difference between 50 deg (triangles) and 70 deg (circles) has a major trade-off between sub 5k VE for a slightly higher peak VE.

 

Well, Mazda did this obviously on the 6 port engines...

On the FD we have the double throttle plates (though way up in the UIM), so you could use this like the Euro 6 ports which were just throttle plates in the manifold instead of rotating sleeves.

If you just port the 2ndaries for later closing without blocking the 2ndary ports somehow the reversion will still be there to hurt low rpm power.

If you want to do this really well you could move some throttle butterflies, roller barrels or slide throttle plates into LIM or side housings for the 2ndary ports.

Throttle plates in the side housings would actually be quite easy.
I was thinking how you could do this for a j-bridge motor. Just the peripheral portion for low end/midrange power and then open the stock (but later duration ported) ports for top end power. Use valve guides/seals for the top and just drill into the bottom of the port for the shaft there.

 

as you probably know, Mazda picked both, it runs 50 degrees until the 6 ports open and then you get 70 in the GSL-SE and 80 after that.

with the FD they had the turbos, so they didn't need fancy ports.