Quote:
Originally Posted by Ecky
I disagree. This way, OP will still get pumping losses. Plenty of manufacturers offer systems to close valves completely and quit firing several cylinders when cruising at low load, because the air inside acts as a spring, rather than simply sapping power by being pumped through.
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I disagree with your disagreement...
(that doesn't even sound right)
But seriously, I can understand the rational, and I guess it makes some sense... And although I respect your opinion, I don't think the line of thought is completely accurate. Let me explain my position, and please feel free to counter anything I say, after all is only my opinion...
-If you keep the pistons in the equations it is a given the there will be pumping losses, because that's what the piston does - pump air. This part of the suggestion was
not an attempt to eliminate losses, but simply to minimize them. I would prefer no pistons at all as I stated in prior post... that would in fact eliminate the pumping losses of the useless pistons.
-If for whatever reason the pistons are not removed, they would be practically useless on this particular application... And with only two other pistons to carry the load, the obvious next best would be to minimize as much of those parasitic power losses as possible, and with this in mind...
-It is a fact that it takes more power to compress air than to move air. The syringe example is almost as good as any for this purpose. Try pushing air through the syringe with the orifice plugged w/ your finger, and then with the orifice unplugged. Compression takes much more force... But also if you increase the size of the orifice it will reduce the amount of force required to push the syringe piston.... and that was the premise behind leaving both ports fully open, greater orifice sizes... bigger orifice size = less airflow restrictions = less power consumption per rev. But for practicality I suggested to only leave the exhaust side open just so that minimal modifications have to be made to engine and it can be reassembled easier if he decides to do so.
-As far as the OEMs using a closed valve method, in my opinion it has nothing to do with a benefit of "spring" action... But rather with practicality, pricing, manufacturing challenges and the like.
Because before they can "spring" into action, those air molecules have to be compressed... And again, it takes more power to compress than to simply blow to the atmosphere... And I'm sure OEMs have calculated these power losses into their equation, after all that's what they are after, they are after lowering the power output at specific scenarios so that the engine can operate at higher percentages of power output... lower the power, the percentage increases.
But it really makes no difference because you can electronically cut them on-and off as needed to offset any power losses instantly.... vs. the car in question will not have that option, and with only two cylinders to carry the load, he needs to get rid of as much losses as possible.
What you think?