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Old 10-01-2022, 07:14 AM   #1 (permalink)
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David Vizard's Pressure Wave Terminator Box?? and Anti Reversion?

David Vizard's Pressure Wave Terminator/Termination Box:

You cant upload pics directly to this forum (a shame IMHO) so the pic of the PWTB is on page 10 here:
(Whole thing is worth a read)
David Vizard Exhaust Article

So basically the PWTB is put at the end of of your Tuned Length 4 (into 2) into 1 Exhaust Manifold
and
Fools the 'Branch' into thinking it's exhausting into open air by cancelling out all the pulses in the exhaust before they go through the muffler/s.

NB
That the rule for the PWTB is that it must have a volume of at least 8X one cylinder.
Preferably 11 to 15X the volume of one cylinder.

Here is some talk of how well it works:
https://www.460ford.com/threads/pres...on-box.103437/

Here is a video, but I don't think the Box has enough diameter really.
It's more of a 'pipe' than a 'box':


NB
that both builders drilled a number of holes through the flat plates of the box and welded in short lengths of round bar to stop the flat plates from vibrating/resonating and kicking up an awful racket.

For fuel economy:
Your Tuned Length 4 (into 2) into 1 'Banana' Branch would be made of longer, thinner pipes.
(There are various calculators on the net)
The length of the last, 'into 1' pipe is also critical and thats where the PWTB would go.
Then any muffler system would not have the usual negative effect/s on power/economy..?

Has anyone here tried this??

(NB that a quick look on the net shows that for most Branches advertised the 4, 2, etc pipes are NOT the same length..!
These 'Branches' are 'tuned' to lighten your wallet! Nothing else)


ANTI REVERSION Exhaust ...er... Doodats:

Even if you have a legit Branch: (same lengths)
The rpms they are tuned for are too high for economy.

Anti Reversion doodats can help here:


Basically they act as Tesla Valves (worth a search) to alleviate reverse flow while both the intake and exhaust valves are both open at TDC at the end/beginning of the exhaust/intake strokes.
This will minimize the backflow of exhaust into the intake tract at low rpms.

Some Discussion:
https://xwebforums.com/forum/index.p...-theory.37045/

Anyone tried these??


Last edited by Logic; 10-01-2022 at 07:21 AM..
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Old 10-01-2022, 03:14 PM   #2 (permalink)
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Haven't tried but I have studied Tesla.
Quote:
That the rule for the PWTB is that it must have a volume of at least 8X one cylinder.
Preferably 11 to 15X the volume of one cylinder.
Applying the same logic, the doodat would be larger than the cylinder.

It differs from a Tesla valve in that it's a 'blind alley'. Perhaps a ring of holes at the constricted end might help.
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Old 10-02-2022, 05:57 AM   #3 (permalink)
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Quote:
Originally Posted by freebeard View Post
Haven't tried but I have studied Tesla.


Applying the same logic, the doodat would be larger than the cylinder.

It differs from a Tesla valve in that it's a 'blind alley'. Perhaps a ring of holes at the constricted end might help.


Anti Reversion 'doodats' aren't PWTBs freebeard. They're MUCH smaller.

ie: You're not trying to turn exhaust pulses into nice smooth flow;
You're trying to disrupt backward flow in the headers some with the cheapest interpretation of a Tesla valve possible.

They typically go in the branch pretty close to the head, where the pipes get hottest apparently..
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Old 10-02-2022, 01:39 PM   #4 (permalink)
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Quote:
Applying the same logic...
I left myself an escape hatch.

What do you think about the reversion trap being vented. Does it rely on back-pressure or volume?
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Old 10-02-2022, 04:55 PM   #5 (permalink)
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Quote:
Originally Posted by Logic View Post
David Vizard's Pressure Wave Terminator/Termination Box:

Fools the 'Branch' into thinking it's exhausting into open air by cancelling out all the pulses in the exhaust before they go through the muffler/s.

NB
That the rule for the PWTB is that it must have a volume of at least 8X one cylinder.
Preferably 11 to 15X the volume of one cylinder.
I'd like to offer a couple clarifications.

1) The pressure wave box doesn't cancel out the exhaust pulses. It terminates them. When the pressure pulse reaches the end of the pipe, it reverses and goes back up the pipe. The box allows you to have the benefits of tuned length header extensions, while also having a "real" exhaust system.

2) That volume calculation is specifically for an 8 cylinder engine. Hence the "8 times cylinder volume". The calculation also assumes a single pipe exhaust. Another way to look at it: the box needs to be at least the total volume of the cylinders feeding into it, preferably 1.5-2x.
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Old 10-02-2022, 06:17 PM   #6 (permalink)
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Old 10-03-2022, 02:34 AM   #7 (permalink)
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Quote:
Originally Posted by freebeard View Post
I left myself an escape hatch.

What do you think about the reversion trap being vented. Does it rely on back-pressure or volume?
I think the Anti Reversion Trap is about disrupting any backward flow aerodynamically.

Venting them into a specific sealed volume may make them more like PWTBs, but you WANT the pulses in the Branch to help pull the exhaust gasses out...
ie: If you moved them further down the pipes to get these pulses timed; you'd end up with a PWTB!

Last edited by Logic; 10-04-2022 at 06:31 AM..
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Old 10-03-2022, 02:47 AM   #8 (permalink)
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Quote:
Originally Posted by Blacktree View Post
I'd like to offer a couple clarifications.

1) The pressure wave box doesn't cancel out the exhaust pulses. It terminates them. When the pressure pulse reaches the end of the pipe, it reverses and goes back up the pipe. The box allows you to have the benefits of tuned length header extensions, while also having a "real" exhaust system.
Quite so Blacktree thx.
But wouldn't the fact that the pressure pulses are smoothed out through the mufflers be a large part of that termination effect?

Quote:
Originally Posted by Blacktree View Post
2) That volume calculation is specifically for an 8 cylinder engine. Hence the "8 times cylinder volume". The calculation also assumes a single pipe exhaust. Another way to look at it: the box needs to be at least the total volume of the cylinders feeding into it, preferably 1.5-2x.
Hmmm... I also thought so Blacktree
BUT
NB the H Pipe David Vizard specifies, preferably before the PWTB, or into it.
ie: He's already taken pulses from the other bank into account on a 2 pipe/PWTB exhaust..?
So the 8x to 15X the volume of one cylinder seems universal to me..?
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Old 10-03-2022, 12:29 PM   #9 (permalink)
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I don't think exhaust reversion is a huge issue other than at low load + low speed (I read a bunch of papers about exhaust reversion trying to figure out how to optimize my VVT).

At low load, you're pretty screwed because the intake pressure is far far below atmospheric.
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Old 10-03-2022, 01:35 PM   #10 (permalink)
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Quote:
Originally Posted by Logic View Post
Quite so Blacktree thx.
But wouldn't the fact that the pressure pulses are smoothed out through the mufflers be a large part of that termination effect?
I'm not sure what you're trying to say. But on a normal exhaust system, the exhaust pulses won't be reflected (i.e. terminated) until they reach a significant change in the exhaust pipe geometry. That might happen at the catalyst or the resonator, or whatever, depending on the design of the exhaust system. But that length of pipe won't be tuned for a power boost at any usable RPM.

The whole point of the termination box is to make a place for the pressure wave to reflect, so that section of pipe can function as a header extension. The pressure wave will reflect at the end of the exhaust pipe (the pipe coming from the engine). And the box itself acoustically decouples the two sections of the exhaust system. So the stuff downstream of the box doesn't affect anything upstream of it.

PS - I know that math is specifically for an 8 cylinder engine, because I asked David about it.

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