Quote:
Originally Posted by Warpick
This.
With out overextending too much the DI means that you're not taking air and fuel on the intake stroke. It's just air. So carbs are like air/fuel mixing centers port injection is shooting atomized fuel with the air and compressing it all on the compression stroke.
Fuel is a liquid and can't be compressed as much as air. So with direct injection. You have nothing but air being compressed and as the air is compressed you have all that pressure in the chamber and THEN the fuel is injected and ignited.
Compression needs to be payed attention to, but it's not as important on carb or port injection methods. Which is why you can run such a high compression. It's all air being compressed. The only thing you really need to worry about is can the internals handle all the energy happening in the combustion chamber.
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Well sorta. IN only a few operating conditions does it use statified lean combustion.
When you put you pedal to the metal,The DI system will still inject fuel during the intake event to promote a homgenous charge. The benefit of the DI is the very fine droplet size + spray that is directly in the chamber consumes many BTU's durign vaporization.
THis is what allows high static CR and also a great deal of boost.
In the LNF camp we experiance a propagtion phenomenon when we start moving past 40lbs/min and most importantly 5800rpm. THis is when the window to inject during the intake stroke becomes too small. The system, which is shooting for a specific AFR, is then injecting on the compression stroke. This wets the walls and piston crown with fuel, you see a large 25%+ drop in torque and the exhuast looks like a duramax.