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Old 05-26-2009, 09:13 AM   #35
Drives: Rust bucket and a jalopy
Join Date: May 2009
Location: Central florida
Posts: 52
Originally Posted by MadMaxx View Post
The DI motor does have a high static CR, but you got to remember that it's making those numbers on 87 octane. The DI bit pushes the normal CR boundaries quite a bit, even under turbo applications.

Static CR itself isn't the problem, it's the ability to fine tune that defines how well a forced induction system runs. Lowering the CR gives you more of a safe-zone for screw ups vs. running right on the edge of a FI+high CR situation. Hell, I've seen some 12:1 CR port injection motors w/ full turbos put out insane numbers and still be well within limits -- it's all in the tune. One major advantage (as I see it) is the hardware already present from a computer standpoint...the Motec ME9. This little bastard is capable of a super high degree of monitoring and correction, especially compared with older technologies. It's like Atari vs. Xbox360 man, crazy stuff. That was the biggest problem w/ DI up until the last few years -- having an ECU with enough power to control the system, and still be commercially cost effective.

From a mechanical standpoint, the V6 bottom end is forged, pistons are aluminum w/ heat coating to deal with the stress of DI. They also have factory oil squirters ...

Now, if they'd only come out with the 7.2L V12 engine... that would be a hellova lot of fun to tune.

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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