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Old 11-16-2018, 09:08 PM   #1 (permalink)
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Three Cylinder Radial For ICE In Prius?

I've read that a radial engine (Radial, not rotary) is lighter and more powerful than an inline engine of the same cylinder number and displacement.What are the objections to a horizontally mounted three cylinder radial engine in place of the inline four the Prius comes with? Any idea of the fuel efficiency comparisons? All I can find is Hours per gallon numbers.

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Old 11-16-2018, 09:52 PM   #2 (permalink)
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It wouldn't fit is the first thing that came to mind.
Radial engines have more power because they were air craft engines. Piston air craft engines were designed around being ran at 1/3 to 1/2 power for best economy.
The fuel economy would likely be pretty terrible on account of typical car and truck engines are built around best fuel economy at 10 to 20% power.
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Old 11-16-2018, 10:02 PM   #3 (permalink)
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Then, would a smaller radial engine at 33%-50% power compare in fuel economy to the 1.8 four in the Prius?
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Old 11-17-2018, 04:17 AM   #4 (permalink)
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Well the prius would probably be doing around 80 mph at 30% engine load.
So not much of a comparison could be made.
It's just the wrong application.
Really about the only thing that could be done to improve fuel economy on a prius engine by a noticeable amount would be to rip out the gas motor and drop in a turbo diesel.
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Old 11-17-2018, 12:39 PM   #5 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
Well the prius would probably be doing around 80 mph at 30% engine load.
Then, I'd need an even smaller radial engine that will give the needed HP at 30.
A flat head engine, or disk valves would reduce the physical size.

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Old 11-17-2018, 02:10 PM   #6 (permalink)
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The only 3-cyl radial I can remind by now is the proposed Zoche ZO 03A which was meant as a 2-stroke Diesel design but IIRC it didn't reach production scale.

But anyway, the problem with radials is their frontal area, plus they would be more suitable to longitudinal applications.
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Old 11-17-2018, 02:17 PM   #7 (permalink)
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Where would you find a 3-cylinder radial? I don't think I've ever seen a radial engine that wasn't for aircraft use, and AFAIK the main benefit of the radial layout is that you got all the cylinders out in the airflow for cooling*. The few liquid-cooled ones I could find https://en.wikipedia.org/wiki/Catego...radial_engines were either pre-1920s, or experimental WWII designs. (Except for one Soviet one.)

*Which of course means that, for automotive use, you have to supply the airflow somehow.
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Old 11-17-2018, 02:23 PM   #8 (permalink)
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The closest to "automotive" use I found some examples of radial air-cooled engines were small battle tanks such as the Stuart. In my country, there were some which had their radial engines replaced with water-cooled Scania V8 engines.
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Old 11-17-2018, 06:21 PM   #9 (permalink)
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I'm thinking, now, of the Revetec cam lobe engine.Similar to the following, but with another parallel to the first so that there wouldn't be the "bang, bang, nothing, nothing" of the two piston version.

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Old 11-17-2018, 10:32 PM   #10 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
But anyway, the problem with radials is their frontal area, plus they would be more suitable to longitudinal applications.
Frontal Area wouldn't matter inside the hood, and I had envisioned the engine laid forward horizontally, feeding a 90 deg case.

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