It works...sort of...
Back in the '90s, I had an HZ Holden Wagon, with 253 V-8...it was 15-18 MPG max (Oz MPG too, not US)..
I started playing with it
* Lower hose thermostat to control coolant INLET temperatures (the trial that I had made up ended up on Gary Allan's Jeep - it works)
* The thermostatic inlet air controller on the air cleaner was bridged, so that at idle it was ALL hot air (WOT it was ducted cold).
* I routed the PCV through a coil wrapped around the Right hand exhaust manifold, and back to the carb...wrapped the coil in ceramic blanket to heat the PCV to the max...the PCV port on the Q-Jet aimed straight at the idle mixture ports, so my intent was to heat the idle/off idle/transition and cruise.
* Added EGR extension tubes to point exhaust gasses at the same point, from the opposite side of the throttle butterfly.
* drilled the EGR valve to introduce EGR at idle...functioned as a normal egr otherwise (tried full EGR at idle, and was too unstable, surving manifold vacuum.
* restricted on of the dual exhausts (full dual exhaust), to force more heat under the heated plenum.
* Ran full vacuum advance at Idle.
* as a result of the above, I ran out of bottom stop on the idle speed setting, and had to control idle speed with idle mxture...it would run way way lean.
* as a result could stick fuse wire in the primary jets to lean them out.
* and richened up the secondary metering rods.
HOT HOT HOT...but at W.O.T. all the vacuum stuff had no vacuum, so it was cold air, minimal EGR (remember the valve was drilled), and back to mechanical advance.
It didn't ping at all.
And it got 30MPG on the open highway.
But was an absolute DOG to start and keep running for the first 3/4 mile or so.
Did similar on a couple of simple pushrod 4s and 6s with similar results.
Why ????
Because I was a fan of Smokey's hot vapour cycle (well anything Smokey)
https://www.legendarycollectorcars....-and-hear-it-run-in-our-exclusive-video/
And was in constant conversation with Australian engine engineer John Bennet. Some of his articles here
https://drive.google.com/open?id=1DLcYX0Pp9zuv_u88Yxn4fUw9Mcgpg66l