Quote:
Originally Posted by Logic
For the PWTB: NO it is not.
Plz feel free to discuss that with David Vizard himself.
(You have heard of him haven't you..?)
He's active on YouTube and various forums IIRC.
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He showed up in my library. He was with HOT ROD Magazine in 1984 and 1985.
Any interest in 'reversion' would be predicated upon first establishing that the engine's camshaft(s) incorporated valve overlap.
Without overlap, there is no reversion.
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Of great interest to me were his articles on hop-ups, rigorously calibrated and tested on a dyno.
With a set of anti-reversion headers, and at engine rpms which would be germane to 'eco-modding' , virtually 'ALL' aftermarket engine modifications 'hurt' fuel economy.
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Of all my materials on exhaust systems, the only mention of 'velocity' came from Ph.D., Mechanical Engineering, Edward F. Obert, University of Wisconsin.
And 'velocity' was only used within the context of 1,227-mph shockwaves passing the exhaust valve upon the initiation of blowdown.
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Any hypothesis regarding gas-dynamic 'velocity' becomes problematic, as the internal volume of an exhaust system is 'constant,' hence 'velocity' is also 'constant', with the exception of in the immediate vicinity of valves.
And this is a variable 'backpressure' issue.
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Valve overlap/ reversion is associated with 'hot cams', high-rpm power, often with compromised mid and low-range operation, and definitely loss of mpg, due to substandard BSFC, as demonstrated by David Vizard in his reporting.
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Since David IS very good about testing, it would have been instructive, had he presented a complete back-to-back performance comparison of a specific vehicle, with, and without his 'invention.'
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'ANY' internal change within the entire exhaust system can cause ultra-sonic wave reflections, in any direction, depending on the geometry of the flow mutilation.
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And whatever's done to the exhaust must be accompanied by a 'retuning' of not only the entire exhaust system, but also the induction.
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It appears that David simply created a single reversion cone for all the cylinders, as opposed to reversion cones at the flanges of each of the eight primary runners, as manufactured by Mr. Gasket's Blackhawk and Cyclone headers.