Re: DIY Engine displacement change
JB has got this pretty close. The whole idea of cutting out cylinders is to get the throttle more
open and hence the engine more efficient. Like my torque comments, this will raise an eyebrow or two, but this is why they do it. Another trick I learned from the good Dr. Beck
(see 6 stroke thread)<br /><br />Pumping losses are the issue and a closed throttle increases pumping (sucking) losses on all throttled engines. Despite popular opinion, WOT is the most efficient point for an Otto cycle engine. I didn't say WOT RPM, I said WOT, which is why they continue to gear cars faster and faster, to bring RPM down at cruise and open the throttle more. Same idea with cylinder cutout. KIZ is there too. You want the exhaust valve open during the deactivated compression stroke and the intake open during the deactivated power stroke. You want zero fuel and WOT for that hole or wider open for all holes i.e. 4 holes (or more or less) working at WOT and running and 4 holes deactivated with WOT and the valve action I describe. This requires independent intake and exhaust runners everywhere to eliminate any crossover . . .<br /><br />Cadillac tried this with the infamous 4, 6, 8 thingee and now they're all at it again . . . BTW, diesels don't have a throttle and this is the
primary reason they are more efficient. The compression ratio helps too, but the ability to operate at a very wide fuel to air ratio allows diesel to eliminate the throttle and the associated pumping (sucking) losses. This is a larger factor than the higher compression. Also, the commonly held belief that diesel fuel holding more energy is the main reason is only half true. When comparing cycles or engines or fuels in a lab, we equalize their energy BTU for BTU, so when we say that a diesel is more efficient than an Otto engine it is with the difference in energy density eliminated. This still usually results in a 25% or more benefit to diesels when compared over the entire operating cycle.<br /><br />Man, I'm on an engine techy kick lately . . .
