© 2008 by Hib Halverson
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CAC: That sixth generation supercharger...this and the Cadillac (556-hp LSA) are the first two uses of it?
SW: On Corvette, we're the first user of the 2.3-liter rotor set.
CAC: The reason why you would use a Roots blower rather than turbos?
SW: Bottom end torque. The ability to use that on some other applications, particularly, trucks. From an emissions perspective, not having any extra heat sink in the exhaust made it easier for us to get the initial emissions package done.
CAC: Where did the idea to put the blower underneath the intercooler come from?
SW: Having said how nice the supercharger packages in a V, packaging anything underneath the hood of a Vette is a challenge. Dave Hill and I spent more than one afternoon at design staff because I wanted a bump on the hood to get the blower and the intercooler in there. Dave wasn't going to give me anything and we compromised on the little bit of a bump you see on the ZR1 hood, today.
Getting both the intercooler and the blower packaged in the valley and still make that power number was probably our most significant challenge on the program. We had some others, which we can talk about later, but at the beginning of the program, that one kept us up most at night. It took a while to get it laid out so we could move the air efficiently because we are turning it one more time than you'd like to, but the guys got it done.
CAC: You mentioned one challenge of the LS9 development was packaging the blower. What others?
SW: The first one was getting the blower packaged underneath the hood of the Vette and making the power number at the same time. Number two was the program timing. We were pretty tight getting through the development and validation because it did take us a while to get the design right from a packaging, airflow and combustion perspective. Those two caused us to burn a lot of overtime.
CAC: So, the packaging problem took a lot of time and once you solved that, you had a date...
SW: ...that the Corvette guys really wanted us to hit at the end of the program.
CAC: So the third challenge was?
SW: We took a couple of iterations to get the head gasket sealing right. With the combustion pressure we run on this thing to hit that 620+ number, we had to do a couple spins on the head gasket design and that's one reason why you see the 12 mm bolts.
CAC: A few motors gave up the ghost on the dyno, huh.
SW: Actually, no, however, we burned up an awful lot of computer time.
CAC: I guess I should have said, "the virtual dyno".
SW: Yes. A lot of computer time.
CAC: When you do these simulations, do they have, like...a graphic of the engine running?
SW: (laughs) You won't actually see coolant spew out from the head gasket. What you do see, though, is the model run though the thermal test. You can actually watch the cylinder head lift-see it, as it moves and you can watch what's going on as you go through the cycles. When you see that, you go, "Now, I understand why I need an extra layer in the head gasket."
SW: There are five microns of lift per layer of gasket. We ended up with enough lift at these combustion pressures that we had to go to the bigger bolts and put an extra layer in that MLS head gasket in order to keep the thing together.
Now, that analysis, because it is so complex, takes several days on the computer because the finite element is so detailed and the model so complex.
CAC: Those supercomputers were churning.
SW: We dimmed the lights here for a couple of nights getting through all that.
CAC: When you started at GM, there were no computers, to speak of.
SW: Yeah. Head gasket work used to be pretty much, well...I won't say, "totally art", but it was a lot of: run it in the lab and see what you got and make the changes from there. Today, we've developed computer analysis to where we can often nail it the first time, right of the chute. We did 12-mm bolts and a four-layer (four active layers, seven layers total) gasket for this one and it's run just fine.
CAC: All you need do is run it a few times on the dyno and find out it works the first time? That must be a little bit weird feeling vs. the way it was 30 years ago.
SW: Yeah. It's a completely different approach-the way we're going in the future and, frankly, I think one of our sustainable competitive advantages is the ability to learn faster than our competitors. I think it's one of the secrets to why we deliver the world's best powertrains.
Another business reality is this stuff gets so expensive that, quite honestly, we couldn't afford to do all the development work if I had to do all of it by "test it, then fix it".