So apart from material composition, these should increase plenum size a bit. In my opinion the shelf spacers are too small to show any changes anything over 1 inch thickness should yield something.

What's your take on the results?

 

Well, i haven't received my o-rings yet so I haven't tried anything yet. That said, i honestly don't expect to see any differences. Cheap and easy to try though, so why not. Let's see what happens.

 

Spacer do work in general:



I think we can expect similar results on VQ37VHR.

My 2nd car is Acura MDX. I installed manifold spacer and 3D printed 1.5" TB spacer. Manifold spacer added a ton of low end torque. I am surprised nobody came with same idea for VQ37VHR engine.

 

Man, the Odyssey spacer!
I wondered this as well, I think it's just experience and awareness. Though the engines are similar the J differs widely from the VQ. Grew up with Hondas.
Js have always struggled with air, even the J37 manifolds just clearly dont cut it. Once folks found out about the Odyssey spacer and P2R plenums on the J32 intakes things started to take off again.
They also hit another roadblock which is throttle, the fastest way for this is a second throttle. Nissan proved this from 08+ you need a second throttle for anything over 4 cylinders but electronic throttle adds complication and scares the typical tuner.

I'm certain the VQ will benefit and I'm surprised as well no one has come up with a plenum spacer. I believe a Plenum spacer would be the perfect HR manifold liaison as you could design the spacer to accept the HR manifold and bottom part of it to accept the VHR.
Then the right combination of space from the Throttle and you'll have some serious air/velocity going in.

The questions then I guess are:
Which manifold would be best suited for TB spacers?
Which manifold would be best suited for plenum spacers?
Which manifold would be best for both spacers?
At that point how big of piping are we using?
How will tune affect all of this and how will it move the powerband?

PS: In my old VQ35 DE I used 1 inch starboard to make a plenum spacer and TB spacer. I have plenty of Starboard left and a VHR in the garage I'm willing to try based on what y'all find. The starboard did great with heat, just needs the right tools for cutting.