David Vizard's Pressure Wave Terminator Box?? and Anti Reversion?

[freebeard]

it's amusing how this simple mod is considered 'UNOBTAINIUM' by everyone here.

[citation needed]

As for myself, the question is always how does this apply to the flat four boxer with dual port heads.

The valve mod is interesting, but what I take away is the exhaust header could have a plate (like a tongue sticking out) that protrudes into the head. Maybe a cone canted toward the outside of the curve.

[Logic]

Originally Posted by Ecky

Some Honda's rely on inversion for fuel economy and emissions reasons. Engines without dedicated EGR passages sometimes adjust the VVT to get intentional inversion, so as to get some inert gases back into the cylinder before next combustion.

I did think of that.
Then I thought; 'why not open the exhaust valve later and get the last little bit of work out of the expansion stroke if you want more 'free EGR'... Probably because the reversion effect goes away with increasing rpm = when you want more power.'

Then I thought about the increased low rpm torque/power seen about 25 minutes into the video...
= same torque for less throttle.

Perhaps you/we're trading reduced NOx emissions for fuel economy..?

[Ecky]

Originally Posted by Logic

I did think of that.
Then I thought; 'why not open the exhaust valve later and get the last little bit of work out of the expansion stroke if you want more 'free EGR'... Probably because the reversion effect goes away with increasing rpm = when you want more power.'

Then I thought about the increased low rpm torque/power seen about 25 minutes into the video...
= same torque for less throttle.

Perhaps you/we're trading reduced NOx emissions for fuel economy..?

I'm sure it's tradeoffs, tradeoffs, tradeoffs. The Accord (has an EGR plate) is limited to 25 degrees of VVT. The engines without EGR plates have 40 or 50 degrees of VVT, which can be a problem because I think there's a possibility of valve to piston contact. Geometric limits on what the system can do.

Throttle isn't the important thing, but the fuel used. I made a table of cam angle vs fueling, and the fueling was much lower with a higher cam advance at the same throttle position. It was making less torque, but using less fuel, meaning cruising at the same speed you'd have the throttle open wider, meaning lower vacuum and lower pumping losses and less fuel, despite needing to press the pedal farther.

I imagine the EGR also provided some quench, meaning more ignition advance could be run for the same fueling and MAP value. The 50 degree engines without an EGR plate had higher compression, sometimes 11:1 or 11.5:1, and were typically knock-limited on their ignition timing even on high octane fuel. Quench would allow them to run more timing.

As an aside, the higher cam advance also made the exhaust slightly louder.

There may be something I'm missing, of course.

[Logic]

Originally Posted by freebeard

[citation needed]

As for myself, the question is always how does this apply to the flat four boxer with dual port heads.

The valve mod is interesting, but what I take away is the exhaust header could have a plate (like a tongue sticking out) that protrudes into the head. Maybe a cone canted toward the outside of the curve.

Ye he speaks of a 'tongue' at around 30 degrees, in the direction of flow.
Best place for them are on the inside of bends, following the flow breakaway or turbulence line one always sees here.

But the easiest place to DIY put one (as you have the head off) is in the beginning of the exhaust manifold.

I think that what he is saying (between the lines) is:
The anti reversion doodats are best.
But that means an expensive aftermarket header.
This is a cheaper, easy way.


IMHO the anti reversion doodats are themselves small, cheap, easy to manufacture, mini Pressure Wave Terminators, that do a decent, but not optimal, job of turning reverse flow around so its 'blown' in the desired direction again, without losing momentum.

ie:
Imagine this PWTB is mini and one in each manifold pipe.
Imagine gas flowing in the wrong, reverse direction, against or close to, the wall.

When it gets to the upstream end; a nice rounded, half doughnut shape will turn the flow around, in the direction you want, optimally.

Problem is, or was; making metal half donuts and (optimally) cones with a divergence of 7 degrees, that then also bend in all the right (routing) directions.
That problem is a thing of the past with 3D metal printing!`