Quote:
Originally Posted by Andyman
Honda seems to think it's a good idea to close half the intake valves. Their VTEC-E engine uses one intake valve for low speed operation and both intake valves for high speed operation. I'm not sure what RPM activates the second valve. I would think it might be about 4000 RPM. This engine is very fuel efficient and I think the closed intake valves give it an economy boost. The faster air flow into the cylinders helps to speed up combustion and that will cause more of the energy in the gasoline to make mechanical work instead of exhaust heat. The extra restriction doesn't do much to change the vacuum on the piston except at full throttle and high RPM. A little extra restriction at the intake valves can be compensated for by opening the throttle a little more. Then you don't have a higher vacuum at the pistons. At high RPM you need the other intake valves working to get maximum power.
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The closed valve at low rpm keeps the velocity across the valve up at low speeds. Not sure where I saw it but aparently as the flow approaches sonic it does amazing things for atomizing the air fuel mix.
I partially see your point about low engine load, but I dont agree that retarding the intake event will reduce pumping loss. Widening the LDA will reduce the overlap and internal EGR which will increase pumping losses.