© 2008 by Hib Halverson
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CAC: Is direct injection a Corvette possibility?
SW: If you look at our advanced propulsion roll-out, SIDI is, clearly, where we're headed.
CAC: What's the "I" in "SIDI"?
SW: Spark ignited direct injection. I don't get very many opportunities like this in my career. I get fuel economy, I get performance and I get lower emissions with it. Not very often do I get three benefits out of one technology. You watch our advanced propulsion strategies. SIDI is one of the bases we'll use on gas engines as we do this big-engine-small/small-engines-look-big strategy.
CAC: The injector is in the head and injects gasoline directly into the chamber, kind of like a diesel...
CAC...and it's very high pressure compared to....
SW: It's very high, compared to port fuel injection, but low compared where diesels operate.
CAC: A major change in architecture of the cylinder head...
SW: Oh, yeah.
CAC: ...and fuel system, fuel pump and all that?
CAC: What about direct injection which performance, fuel economy and emissions.
SW: The cooling effect of having the fuel go directly into the chamber, not vaporizing it in the inlet port lets us raise the compression ratio. That's power and fuel economy right off the top.
CAC: How is direct injection is a cooling enhancement?
SW: It gives you some volumetric efficiency improvement because you're not vaporizing the fuel in the port. The pressures and temperatures actually go up when you raise the compression ratio. Normally that would get you in trouble, but because of the cooling effect of the fuel vaporizing in the chamber, you're able to move the compression ratio up without having knock.
CAC: And, emissions?
Like the diesel guys, we can do "split injection" after cold starts.
CAC: Where you shoot one squirt...
SW:...then another one. That really helps us with cat light off.
CAC: How does that affect cat light off?
SW: That last, late timing of the injection lets you put fuel in the exhaust where it will burn and heat up the converter.
CAC: So, the exhaust valve is open when you get your last shot?
SW: Yes. Also, because of that high pressure you have the ability to tailor your combustion a little more precisely than we can on a typical port system. So it turns out we have some great potential there.
CAC: What about the fuel economy?
SW: Compression ratio and, then, improvement in volumetric efficiency because of the cooling effect. You get a little bit of both. Play those two together, synergistically and the guys usually find a little extra...almost like two-plus-two doesn't equal four. In this case, it equals four and a half. You get a little synergistic benefit of being able to tweak the cal. just a little bit. A little more spark.
CAC: What's a typical compression ratio increase over the same motor with port injection. Half a point?
SW: Yeah...maybe a little more. It depends a little bit on how you shape the piston, the bowl and the chamber, so it varies.
CAC: You have to be proud of what your guys have done not only with LS9 but other engines...the LS7, LS3, LS2 and so forth.
SW: I go home smiling most nights. When you look at this job, globally, I smile even bigger. The four-cylinder team in Europe--almost as big as the Small-Block in terms of volume--do just as well as the Small-Block guys. Look at that LNF turbo, the L850 guys (Ecotec engine team) did? That little monster is a four-cylinder, turbo, direct injected (used in Chevy Cobalt SS and HHR SS along with the Saturn Sky Redline and the Pontiac Solstice GXP) and makes 130 horse per liter. Look at the direct injection on the high-feature V6...won Wards 10 Best Engines this year.
I'll stack my guys up against anybody and I'll win. I feel pretty good.
Click image for larger view
This is the direct injection hardware for the LNF. V8 hardware would look similar but with a fuel rail typical of V8s rather than an I-4.
Image: GM Powertrain
Click image for larger view
The twin-cam, 2.0-liter Ecotec, LNF, used in the Cobalt SS and the HHR SS. At 260-hp, this engine makes an astonishing 130-horsepower-per-liter. Part of that comes from direct injection. Will the 2013 Corvette have a 4.8-liter, 500-hp supercharged DI "LS10" base engine? Wadaya think?
Image: GM Powertrain
CAC: Let's go back in time a little bit. The first time you drove Blue Devil and stepped on it...almost 640 horsepower...How'd it feel?
SW: What do you want to know? The size of the grin on my face?
CAC: Who was riding with you?
SW: The first time I drove it was with Tom Stephens (GM's V.P., Global Powertrain).
CAC: Out at Milford?
SW: Yeah. Tom had a grin on his face about as wide as that building over there.
CAC: Did you turn the traction control off and smoke the tires?
SW: Uh...I will say this: you want to pay attention when you launch this one because most of the 600 pound-feet is right there, right now.
One of the things I tell the guys, "If you have a bad day at work? Just call up the guys at Milford and ask 'em to let you go for a ride in a ZR1."