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« Last post by JimL on April 10, 2024, 10:25:22 PM »
Yes...the Echo and Prius were basically the same except cams and pistons. The Prius will not run below about 1200-1500 rpm (it has no idle) and runs out of breath at 5000 or so. Atkinson cycle is efficient, but in a narrower range than Otto. Many of the variable valve timing engines (these days) can drift into Atkinson cycle while you are cruising at light throttle. Switching to smaller bore/longer stroke engines has made intermittent Atkinson easier to manage.
Interesting thought about salt flats racing....manufacturers have learned they can make more power than needed, using fewer cylinders and less RPM. That hot rod Corolla GR is a 3-cylinder turbo that can run 25 pounds of boost on the street, and still get traction out of the corners. This is not that new a deal....
I was sitting with Ed Iskendarian at Sema in 2004 and he told me about Model A engines he built for dirt track racing. They ran harder and came off the corners better than anybody else. He said he made them with a crankshaft that was front two pistons up, when the back two were down. He ground a cam to work with it, in order to get better cylinder fill. The more even spacing of combustion events helped traction coming out of broadslides.
I told him about Honda GP motorcycle racing, when they finally switched to 2-strokes. Everyone else were running V4 or Square 4 2-strokes. Honda ran a V3, and could set it up to fire all 3 cylinders together for tighter, slower tracks. They won world championships until they got bored of it and quit. Ed understood the concept exactly and really enjoyed the comparison.
Every time we think we are getting smart, we find out somebody already did it 100 years ago!!
P.S. Almost forgot to mention one very strange difference between Prius engine and Echo engine. VVTi engines have a "locking pin" that fixes the camshaft at retard position when you shut it off. When you start your engine, the pin does not release until oil pressure is high enough to push it back. This is done to prevent a lot of scary sounding rattling when the customer starts their engine. The Prius engine is "spun up" by Motor Generator No.1 (there is no starter) and so no combustion events occur until the engine is at "normal" operating speed. For this reason, there is no locking pin. The pin "release event" would cause bad running during an actual start, and the customer would NOT like the surge events.
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