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Originally Posted by GreyGoose006
well 4 cylinders at inch bore and 6 inch stroke gives you 15.1 liters.
i think the sheer size of that engine might ruin any hopes of good gas mileage. just think, you need to fill those enormous cylinders with 15 liters of air and fuel.
you would have a huge problem with the flame spreading.
i dont know the technical term, but with larger bores, the amount of time it takes for the flame to spread and ignite the fuel actually becomes a variable.
you would have to use multiple spark plugs and have to advance the timing so that the flame was not still spreading as the cylinder reached the bottom of travel.
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I think the technical term you are looking for is flame front velocity, I don't think that will be nearly the problem you think.
Reason #1 direct injection sprays directly onto the sparkplug(s) so the flamefront would not have to reach into the far edges of the cylinder to catch up with all the fuel, plus with a multi-pulse injector, and a multi-spark ignition I don't think buriing the fuel will be much of a problem.
Reason #2 Since this thing is in theory swinging massive 7" pistons it's opperating speed would be much slower than a 1.6L honda I4, the flame would have several times the amount of time before we hit BDC, remember I am talking about 500-700 RPM crusing speed.
Reason #3 Last I heard a higher CR helped the air/fuel mixture burn faster, so by using a direct injection system which allows for a very high CR (and hotter spark) we should be able to keep the fuel nearly completly burnt up to our 3500-4000RPM redline, afterall if the flame front can travel 4" at 7000RPM why not 7" at 3500??
As far as the huge amounts of power it takes to move 15.1L of air per rotation, think about it this way my 03 Rodeo has a 3.2L V6 that has to turn 2600 RPM on the highway just to maintain 70mph (3.2L x2600RPM/2 = 4160L of air per min assuming 100%VE. My concept engine would be 15.1L x500RPM/2=3775L per min assuming 100%VE. Now which one sounds like more of a gas guzzler? The difference is that the larger displacement engine will loose less energy through the cylinder walls, loose less energy through swept area friction (rings rubbing the cylinder walls), loose less energy through valvetrain friction due to softer springs in the cam (remember around 4k RPM would be this things max anyway) ,and loose less energy through blowby (less ring to leak around per cubic in), so in thory the project engine would be noticeably more fuel effecent and have aprox three times the HP and over four times the torque as my modern DOHC V6!