Quote:
Originally Posted by Old Tele man
FYI, exhaust gases, like motor oil, gets "thicker" the colder it is, so *keeping* the temperature as stably-hot will minimize velocity "slow-down" as it traverses through the header pipes. Won't be MUCH, but it will help you maintain the MASS-velocity-flow.
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Quote:
Originally Posted by undeRGRound
I would think that undersized cast iron "log" manifolds would benefit the most from cooler exhaust. Plenty of velocity already. The water jacketed manifolds would have their greatest benefit on a totally thermally managed ICE. There was a university that did an experimental "throttle-less engine" which basically used warmer air for lower RPMs, with less fuel to maintain the targeted AF ratios. Cooler Air Temps = Higher RPM and more fuel. Needless to say, FE (is that how they say Fuel Economy 'round here?) went up as well, due to greater thermal efficiency from the preheated air!
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Everything I've read agrees "cold exhaust gas" = bad, especially at low RPMs. A few examples I've found of people implementing WAI (vs. stock intake) on Honda D-series engines also reported neutral or negative impact on FE, so I think it depends a lot on what the ECU is doing too.
If I did want hot air, I'd probably take it from a small jacket on or just after the cat. Plenty of waste heat to be had there.
Interesting about the 'throttle-less' engine - you could probably get a similar effect by running EGR at WOT... could be a good way to set up an efficient cruise control, for example, just open the throttle and use a big fat EGR valve to control power
