Chrysler Engineer Burke Brown on the Hemi and Multiple Displacement V8s

5.7 liter Hemi V8 engine cutawayWe had planned on MDS [multiple displacement system or cylinder shutoff] as a company, it had been there from the beginning of the Hemi. But as we were putting together all our plans and all the goals and objectives, I wanted the LX cars to have MDS. The guy I worked for at the time was Larry Achram; he agreed and said, “We really want to make that part of the LX.”

Larry’s a NVH [noise/vibration/harshness] kind of guy, and he said, “Boy, it’s going to be really tough to make it really smooth and quiet on four and eight cylinder mode, and you’re doing it on a top-end luxury car.” The worst possible, most demanding scenario.

I remember distinctly that Wolfgang Bernhard said, when we introduced this car in the auto show — which would be January 2004, because it was a super-early ’05 model — “We ought to hold back a couple of things so we really surprise everyone,” because the media had seen the car. They knew what it was going to look like or had a good idea.

The two things that got held back were the selling price and the fact that it had MDS on a Hemi. And it wowed them with its bargain price, because they had done some clinics and people would look at the car and look inside. They were estimating… [laughs] That was good. But it became very painful for me to not talk about MDS because General Motors had been inviting the press out to the GM proving grounds and letting them drive development cars with what they called displacement on demand, DOD. Same technology just like they’d done on the Cadillacs years before. Not very well, but they’d done it, 4-6-8.

The truck guys were supposed to do it [use MDS] too, but they were saying, “Well, the customers aren’t really that interested in fuel economy.”

I was remember a preview at CTC, and Motor Trend specifically asked, “How are you guys handling fuel economy, are you going to do what GM had done?” Well, we had to say no, we’ve got other things we’re doing. We couldn’t say what they were. That turned into an article that said, “I don’t think Chrysler is going to have very good fuel economy because they’re not doing DOD.” I was really upset about that. But the PR guy said just cool off. Just wait until January at the auto show…

We made it so you really couldn’t tell that it was on four-cylinder versus eight-cylinder. The day of the press event I went up to the Motor Trend guy and said, “Now you know why I gave you such an evasive answer back four months ago or whatever that was?”

The fun part was when we were out in Palm Springs which was right after that, later in January, we were driving cars on public roads, and some of the press guys said, “I drove that car all day long and I can’t tell it’s going in and out of four-cylinder mode. Are you sure it’s working?”

Burke Brown and Bernie Robertson

We had made the decision not to put anything on the instrument panel, at least not in the beginning, because it would go in and out of four-cylinder mode a lot, depending on what you were doing to the throttle. There was some concern that people would see if you put a green light flashing on and off and they’d think, “That’s not what it’s supposed to be in, it’s not right,” and take it back to the dealer and say “I was driving down Main Street and the green light wasn’t on. Something’s wrong.”

So we didn’t put any public display on it. But I had the instrumentation with me in the hotel room. After I heard a couple of those comments I made an announcement after dinner. I said anybody that would like to go out and drive it with instrumentation on it, I’m here all night.

After 2007 or 2008, we put MDS status in the display.

Not that many hands went up, because it was an open bar. But the EPA and ARB [California Air Resources Board] were all over it. They were out driving them all the time. In fact, I had one of the early cars as my assigned car and one of the guys said EPA wants to drive another car, not just the test car but the official car. I gave the guys the key to my car; I forget exactly the story but it didn’t come back for a few days. I think one of them took it to Washington because they wanted to show some of the senators or something.

I got myself another car, and I honestly can’t even remember what happened to that car. We got it back, but I didn’t. I switched to a different one. But if I had to think of all the stuff we did, I think having MDS and being able to pull it off a year and a half before GM ever did by the way and have it that flawless…

I kept watching the warranty and all the customer stuff and it was like nothing. Nobody was having any trouble with it or complaints about it should’ve worked and it didn’t or whatever. It just was such a big boost in fuel economy for no customer implications.

Closeup of Chrysler MDS systemThe customer can notice some of the stuff you do for fuel economy. For example, if you put on real skinny little tires or something to get better rolling resistance, the customer’s going to notice that. Maybe it’s the right thing to do for a given car, but MDS is totally transparent, the customer doesn’t know it’s there working for them that every day, while it’s shutting down four injectors and saving fuel. I think that’s really cool.

Dave: They did add that light. There seems to be a natural lag since that thing works in milliseconds, but how does the light relate to the actual MDS operation?

I think it’s pretty much what’s going on. It may have a little bit of delay so the light doesn’t just flash on and back off. … I remember our ’08 Magnum, that had the reconfigurable display where it had the little bar that went back and forth, and I guess the trucks now they just bring the word ECO up I think. That’s probably what you’re thinking of. I’m pretty sure it’s exactly when it’s in four.

There’s plenty involved. The signals are there. You change the solenoids and the lifters respond instantly. That was the neat part of seeing that thing all come together, all that stuff’s all got to be perfectly timed. The fuel’s got to go down at exactly the right time.

The first development car was not running on an engine controller, but running on PCs. The trunk was literally full of stuff to run the MDS because they had a ton of programmable stuff in there, as they were starting to develop their way through it. Then we developed the exhaust system stuff and made the system work.

That was a big fear. I think that might have been why GM had some trouble, they were having trouble getting it quiet enough, because the things you want to do for an exhaust system in four-cylinder mode is not what you want to do in V8 mode. Then you still want it to be kind of throaty sounding a little bit. You don’t want it to sound like a vacuum cleaner when it’s in wide-open throttle either.

Dave: How did you deal with the exhaust? It couldn’t have been a baffle, it works too quickly.

No, it isn’t. In fact, we had some advice from the Mercedes guys, don’t try that, because they did try that and they couldn’t make them live. They would rust up and the corrosion and exhaust if you let them set and so forth.

I was pretty quick to agree with that because I lived through the variable-nozzle turbo, and that was an issue there too. But what we would do with that is every time you start it up, we’d swipe them back. You’d flip the nozzles back and forth a few times to kind of clean off any deposits that were built up.

chrysler hemi engine

Well, it all happened one night in Arizona. We were out at the Arizona proving ground when it was cold back here where we could do more. But we used a combination of modeling, looking at tuning lengths and so forth. We’d have something that would sound good and we’d want to know what the back pressure was.

If I can call it the magic or whatever in the system is in those rear resonators – the length of tubes and so forth in there. In fact, we had a little demonstration car setup that we had the resonators were in their location but we had a pipe coming out of them past the back bumper maybe 15” and we drove that car one night about midnight and said holy cow. This is it. That was in the model. That was the tuning length that we needed. So we just needed to get that length all stuffed inside the can.

Marc: Yes, you always want to have the least amount of back pressure and yet still keep the car quiet in a fly-by test, and that was always a battle between the engine guys and the vehicle guys. We want the power but we want the quietness too, how can we achieve both?

You’ve got the regulatory pass-by noise too, and Europe is different, so you’ve got to do it all over again.

Marc: You always start with no exhaust at all, and add as you went along, but for dyno testing, we always had a restrictor to simulate the back pressure of an exhaust, but never the actual muffler. It would emulate the full exhaust for our calibration purposes. It’s not overlooked, that’s for sure.

Well, there was some engine mount work and some induction; it all played in to make it nice and quiet and transparent so you couldn’t tell it.

My retirement at the end of ’07 was not driven so much by what was going on here, but things my wife and I wanted to do and had never done. In fact, the very first thing we did right after my party in January which was here was drove a Hemi Magnum about 6,700 miles. We went out to our daughter’s on the west coast and pretty much ran everywhere on the west coast with a total trip average of 26.4 mpg. One caveat is that, being retired, I took advantage of not having to go 85 mph to get there. If the speed limit was 75, I went 80 — I ran the “five over” thing, I didn’t push it.

Marc: At 70, you’d be surprised, even two miles an hour over…

One of the goals we set for the system, for the MDS system, was that I wanted to be able to cruise at 80 mph on four-cylinder mode, at least on level ground. I figured if we put a system out there that only works at say 60 or 65, everybody going 70 or 75 would complain, “I’m not getting good fuel economy! What the hell’s going on here?” The EPA test never goes over 70 — in fact, it barely gets there.

I remember being at the Arizona proving grounds on the oval, and driving carefully, but I edged it up to 92 one night in four-cylinder mode. No major winds, all the right conditions. I think in general most cars on level ground will do great around 80 to 85.

Marc: You don’t realize it either, if you do tip into it at all, it’s in eight-cylinder mode. It’s there, you don’t feel it.

No, you don’t know it, and usually if you go up a little bit of a grade or whatever then that’s over… still, one guy went out to like Pennsylvania, which is pretty hilly. He still came back with like 90-something percent of the trip having run in four-cylinder mode, because once you get over the hill, you go down or it levels out. So you really do get a lot of four-cylinder time.

Note: some parts of this interview have been re-ordered for easier reading.

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