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Old 10-26-2010, 08:43 PM   #6 (permalink)
t vago
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Quote:
Originally Posted by Frank Lee View Post
Seems like peeing into the wind to me.

Variable displacement systems shut down intake and exhaust valves on the disabled cylinders. If it was as easy as adding a butterfly valve to the intake, that's the way it would have been done OEM. If the valves are still working, there will still be pumping losses from the intake tracts and from sucking/pushing into the exhaust tracts.
Don't let the perfect become the enemy of the good.

OEMs don't use butterfly valves to deactivate individual cylinders because they cannot allow the exhaust to be contaminated at all with inlet air before the pre-cat O2 sensor(s) can read it. There will be more leakage with butterfly valves than with the poppet valves in the heads. This is the reason why OEMs tend to use the poppet valves - the OEMs can comply with EPA regulations and the Clean Air Act. Granted, some vehicles inject air into their cats, but that's a different matter.

That aside, pumping losses will offset much, if not all, of the gain provided by causing the remaining cylinders to work more closely to their full potential. Therefore, minimize these pumping losses, and you minimize the drag induced on the engine itself.

Quote:
Originally Posted by Frank Lee View Post
So the trick will be to disable valves. I believe it can be done at home, but it would be quite involved.
I would have to design some of the hydraulic lash adjusters to be able to collapse more completely than normal, on command. After that, I'd have to figure out a way of keeping the rocker arms in place, since they are only secured onto the valvetrain by the lash adjuster at one end, the cam at the center, and the valve itself at the other end. Sounds like a lot of trouble.

On the other hand, it's a compromise to put butterfly valves on the intake side. I should still see some meaningful gain.
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