Two Stock CB750 engines, One Transmission?

[Frank Lee]

The valves are held closed. Any flow takes hp.

[Angel And The Wolf]

Where is that data found. I'm willing to read it.

[Ecky]

This was worth a read:

Honda Worldwide | Civic Hybrid | 1st Generation Civic Hybrid

The New Honda IMA System employs the VTEC System to stop operation of valves in three of the four cylinders, reducing engine friction by 50%, and making possible highly efficient electrical regeneration.

VTEC Cylinder Idling System
When the throttle is open during acceleration or cruising, the valve liftmode rocker arm and the idle-mode rocker arm are engaged via a synchronizing piston. During deceleration, as soon as the throttle is closed and regeneration begins, the synchro piston is positioned inside the idle-mode rocker arm, disengaging the lift-mode rocker arm so that the valve remains at rest. Since the cylinder is sealed off, pumping losses (resistance caused by engine aspiration) that result in engine friction are reduced, and the wheels' rotational energy is effectively transmitted to the motor. Moreover, cylinder idling can be maintained at engine speeds as low as 1,000rpm, for even greater regenerative efficiency.

So, Honda chose to keep the valves closed, rather than open, the logic being that the air inside will act as a spring, and the energy used in compression would be mostly recovered during expansion. Leaving them open would force the engine to pump air in and out of the cylinder, resulting in lost energy.

So, it's better to deactivate cylinders by closing all valves, rather than leaving them open.

Honda's system is also extremely reliable. You basically never hear about failures with their variable cam system, which has been in most of their production cars since the early 90's.

[Angel And The Wolf]

Thank you, but this refers to deceleration. I'm interested in using reduced cylinder numbers to maintain speed. I will look into the V6 non-hybrid system.

[Angel And The Wolf]

This is more applicable, and yes, Honda closes deactivated valves. I may need to revise my thinking on leaving the valves open. I still prefer my rotating deactivation, giving each cylinder it's firing 1 out of 3 normal times.
Honda Worldwide | Technology Picture Book | VCM

[Angel And The Wolf]

Honda seems to be saying that compression and down stroke balance each other out in deactivated cylinders, but I believe each is a resistance, unless... the valves are deactivated at BDC with a full cylinder of air. In that case, spring back from the fully compressed cylinder might assist in powering compression in the fully expanded cylinder.
It may even help if the deactivated cylinders are closed halfway through the intake stroke.
only half the air to compress or expand.

[Ecky]

It should help either way. If the valves are closed at TDC, there will be a vacuum to overcome on the downstroke, but that same vacuum will pull the piston back up with equal force on the upstroke. Conversely, if they're closed at BDC, air pressure will create resistance on the upstroke, but it will push the piston back down on the downstroke. My bet is on vacuum being slightly better, because you'll have less heat lost through the cylinder walls if there's less air, but that might be negligible in the grand scheme.

[Angel And The Wolf]

Originally Posted by Ecky

So, Honda chose to keep the valves closed, rather than open, the logic being that the air inside will act as a spring, and the energy used in compression would be mostly recovered during expansion. Leaving them open would force the engine to pump air in and out of the cylinder, resulting in lost energy.

Is it possible that Honda didn't want the deactivated cylinders draw and blow to interfere with the other cylinders' intake and exhaust? Something that might be avoided by separate intakes for each cylinder?

[Angel And The Wolf]

OK, I want to thank Ecky*, Frank Lee, Piotrsko, cRiPpLe_rOoStEr, mannydantyla, and Grinder74, for helping to guide me through this exercise, and showing me how various parts of it won't work, Synchronizing the two engines without much cutting into the engine cases, and the staggered firing pattern I came up with because of the unbalanced deactivated cylinder pairs (two trying to pull vacuum at the same time). Seems the only promising idea is the combined clutch/shift pedal, and I'm not sure there isn't a better layout for that. Anyway, I'm abandoning this thread. Thanks guys.