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Originally Posted by ottopilot
4/5 valves per cylinder will always be more efficient than 2. Take any DOHC engines and remove 2 valves, and try to keep the same Horsepower, good luck.
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Depends on what you mean by "efficiency". Normally, it would be BSFC, brake specific fuel consumption.
The most efficient designs in terms of BSFC won't be the most power-efficient in terms of power/displacement, that's for sure.
Fewer valves and fewer intake tracts will generally give better BSFC, as for a given flow area/volume, you will have less of the flow near the tract walls. Reduced losses drawing the charge into the intake.
Also, more cams, chains, and valves => marginally greater frictional losses.
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You need more displacement for offsetting those drawback. As far as I know, pushrod engines are limited to 1 intake and 1 exhaust valve.
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You could do a multivalve OHV engine.
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It's easy to see why DOHC engines are so popular, you get get alot of horsepower(and higher RPM) more easily out of them at the added cost of weight (Which isn't a big deal at all).
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Weight is a very big deal. So is size. For a given size/weight, you can make as much or more power with an OHV V8 vs. a DOHC V8 (which would have to be of MUCH smaller displacement to be the same size/weight).
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It doesn't matter though, those pushrod GM is pumping out are nice engines, they are just not impressive as far as engineering goes
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Only if you judge "engineering" by counting valves and camshafts. The engine engineering at GM is top-notch.
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There's nothing better than the other. :happy0180:
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There's more than one way to skin a cat. DOHC/multivalve is required to get maximum performance out of limited displacement. If there is no displacement limit, the simpler, lighter, smaller, cheaper OHV/2vpc design of greater displacement is as good an engineering solution (superior on some fronts) to achieving the same power/performance.
To disparage the LS-series V8s because of their lack of valves and camshafts is to be too fixated on the means, rather than on the end result.
All said, I'm a big fan of diversity, and LOVE higher-revving DOHC multivalve engines as well.
But when it comes to figuring what's the best engine to get maximum power in a small, lightweight package, the large-displacement OHV V8 is very hard to beat...