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Old 09-07-2017, 03:17 AM   #1 (permalink)
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Larry Widmer "Softhead" and economy

Has anyone used this theory for improved mileage before? It's not really 'his' concept (Chev used it in the 50's) but he describes it best and has adapted it for other engines.

The idea is that you run as much squish as you can, focussing the combustion chamber around the exhaust valves and spark plug, to the point of altering cam timing so that you can bring the piston crown close enough to the intake valve to get even more squish. This both necessitates and allows super-high compression ratios (as in, above 13:1 on pump fuel, 16:1 on race gas).

The theory is that:
A: Because tiny combustion chamber with minimum distance to the edges and very high squish velocity the burn happens a lot faster. As in, 15-20 degrees advance at peak power fast.
B: Because it's focussed over the exhaust valves, that bit burns first, and doesn't get the chance to absorb heat from the rest of the chamber burning, and avoids detonation
C: Because it burns so completely, so quickly, and with a higher expansion ratio you get higher average cylinder pressures, cooler egt, and more efficiency
D: Because some magic involving high compression ratios (haven't quite figured this bit out yet) ultra-lean air fuel ratios still ignite at high loads.

It's more or less adaptable to most types of cylinder heads, provided you can machine piston crowns to suit

It *sounds* like a neat theory (and most of it makes sense) but I don't know of anyone except Larry having used it. Has anyone here heard of it being used?

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Old 09-07-2017, 02:28 PM   #2 (permalink)
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Lookup american race car & engine builder Smokey Yunick and his highly modified 4 cylinder GM Fiero.
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Old 09-07-2017, 04:51 PM   #3 (permalink)
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Super squishy pistons with appropriate cam on air cooled bug. I can confirm with more compression it's easier to tune and run cooler with less timing in the area that isn't hi load.
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Old 09-07-2017, 06:25 PM   #4 (permalink)
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Old tele man: Already have. That was a super vaporisation concept, the engine itself was stock bar the camshaft

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