Re: Vacuum at WOT
QC without some type of air restricting device on ANY engine that uses a constant volume fuel you are stuck in a very very narrow RPM range, period. has nothing to do with the throttle. I seem to recall some ancient JD diesels that reqired an "air valve". your statement was the throttle plate created the ineffiencency and that is not correct.Diesel and certain other heavy fuel oils are constant combustion type fuels and will burn the entire length of the power stroke. they will burn very rich to very lean. in the past detonation was not a problem as the castings were massive, heavy but who cared. gasoline,ethanol,methanol and nitromethane are all very touchy constant VOLUME fuels that if the air to fuel ratio varies much it quits burning. to rich and it wont ignite and to lean it wont ignite.<br /> when I say air pressure moves the fuel its not only that 10 mile high colum of air above the fuel bowl but as the air is compressed going through the carb venturi it is heated and accelerated, once past the venturi it rapidly cools and expands creating a low pressure area just past the venturi. thats is what moves gasoline. that is why at or near WOT on a gas motor intake pressure is about 14 PSI as is fuel bowl pressure yet fuel still flows. thats why gas motors suffer from altitude sickness.<br /> at 1 mile high the air moecules air more widely spaced due to the lower air pressure.<br /> thats also how modern EFI compensates for altitude sickness and carbs had to have jetting changes. diesels did not seem to be affected as much, gas can lose 20% of its sealevel power right off the bat.<br /> look at it this way, a High Pressure Direct Injected 250 HP yamaha, we inject fuel directly into the cyl at 1100 PSI after the intake and ex ports close.<br /> lets say we need a 4 inch opening at WOT for maintaining the 14.7/1 air to fuel VOLUME.<br /> if all we ever need is WOT(5500 RPM) we can toss the air restrictors (throttle shutters) in the creek, would not need them.<br />however now we are gonna troll for some rockfish at 600 RPM, now we gor from a 6Ms pulsewith capeable of flowing enough fuel to maintain or 14.7/1 ratio to a 2.5MS pulse if we dont make the intake tract smaller or air to fuel ratio would climb over 30/1 air to fuel and combustion would cease and the engine would get super gas mileage.<br /> that low speed long stroke Diesy juicer on the other hand, with its fuel that burns at a constant COMBUSTION as opposed to VOLUME we can close the rack retard the injector advance and idle it at 600, the air to fuel will be somewhat lean, it will detonate(rattle) at idle due to the superheated compustion air at injection but the heads,wristpins block and bearings are massive enough to deal with it without damage.<br /> this is why ford tried a variable venturi carburator. so they could vary the size and thus airflow past the venturis to maintain a constant volume of air to fuel.<br /> gasoline is funny stuff, at about 13 parts air to 1 part gas it wont burn and about 16.5 parts air to 1 part fuel it fails to burn again.<br /> so I will stand by my statement that a trottle plate has nothing to do with the inefecincy of a gas motor its the fuel and RPM range required. <br /> as more smaller lighter high revving(5000) RPM diesels are made you will most likly see air valves on them as well.<br /> with the precise fuel delivery systems avalible with modern electronics coupled with the volume of air to fuel required from 600 RPM to 5K RPM you will most likly see it. it probalbly wont be a full shutter but a restrictor, this will allow less air so the need for less fuel at low speeds and a large enough intake tract for the volume of air to fuel at high speeds. the COX .049 model airplane motor we all played with as kids is a good example of a constant volume fueled motor with no throttle. move the air/fuel needle a half a turn either side of optimum and it quits.<br />at optimum it ran about 18,000 RPM or so. they ran on methanol/nitromethane. both are constant volume fuels.<br />one is an oxygen bearing fuel but both are constant volume.
