Amazing, Chevy builds a 330 HP engine with 28mpg Options

[Hawktel]

So the new Impalla that chevy has released has a option for a 330 HP V8 with 28 highway fuel consumption.

Thats amazing. Just amazing. I wonder how far fuel efficency can be pushed?

[jniemeier]

I'm new to the group, but you're on a topic I know something about.
Warning: long boring post to follow: Read only if you want to know more than absoutely necessary about cylinder deactivation.

(I was the Engineering Supervisor for the Delphi Valve Train group when we developed the cylinder deactivation system used by GM.)
The old Cadillac system used an electric rotary actuator on top of the rocker arms. We found a '82 Seville with a V8-6-4 when we started working on the new system in '99, and it was still working fine. Must have been the only one left. Putting electrical connections under the valve covers is generally a bad idea. Someone mentioned the Mercedes. Their V8 and V12 were the first of the 'modern' systems (I think in '99), and was very complicated. Big surprise. It's very tough to switch off the valves in an overhead cam engine. It has a very expensive, high pressure valve asm. You've only got the rockers to do it in, and it's hard to get the right oil circuits to your hydraulic actuators (inside the rockers!). Honda have also done it this way. You need a pivot shaft running down the length of the head so the rockers stay in perfect alignment and for the oil to run in. ($)
The new systems from GM (Displacement on Demand) and Chrysler (Multiple Displacement System) are almost identical. They (we) are doing the switching in the Roller Hydraulic Valve Lifters of pushrod engines. Much cheaper. There's enough space there to add locking pins and when hydraulically unlocked to absorb the cam lift without moving the pushrod. Ford would be doing the same, but they seem to have forgotten how to make pushrod engines, so they are out of the party for now. Chrysler's are made by INA (Germany); GM's by Delphi and Eaton. (Yes, legal wrangling has ensued, but let's not talk about that)
Operationally, it switches off the exhaust first, then the intake of every other cylinder as you go throught the firing order. The lifter has to be on the cam's "base circle" to allow the locking pins to move. That means inside cylinders on one bank and outsides on the other. Hence, the motor stays even firing. The engine mounts are bi-state (!), and are electrically switched to a different natural frequency in sync with the motor switching. It is all done within two engine cycles, and no, you can't feel it. GM's calibrators can't even feel it. They wire up an LED on the dash for reference. There is an electrically actuated hydraulic control valve for each cylinder that fire in sequence driven by the ECM and the cam position sensor. Think high speed: elec signal, solenoid movement, oil pressure buildup, locking pin movement... all in 10 milliseconds, and repeatable over the full range of oil temps. Hint: changing your oil regularly is a good idea.
As to economy, as always, it depends. I'm talking full size trucks and TrailBlazers here. The overall real world average they figure to be 8%. Might not sound too huge, but to a car company, that's a big number. In suburban driving, ~45ish and lot's of light loads, it could be over 20%. On the other hand, I heard the calibration guys say once that about 75mph is where the "road load" power required prevents it from going into deac. So, I doubt the heavier versions of the trucks are deac'g much on the highway. I guess running a 6 or 7 thousand pound truck on 4 cylinders isn't too easy. Our job was to just get them turned off and on, not make it more powerful in 4cyl mode. As mentioned, not it's also in the Impala SS. I didn't think they were doing the Corvette, but maybe so. It's also possible to do a V6, although the useable range of loads is a bit narrower. To even-fire a V6 in 3 cylinder mode, you need to deac one whole bank. And, yes, it's been done on a 4 cylinder by a research firm, but... well, let's see how the V8's are accepted.
Concerns? Oil puddling on top of the valve guides, and then getting sucked in when the cylinder suddenly "re-acts". GM's trucks periodically switch back to 8 cyl even if not required to prevent this. The fuel injectors are off of course, but the spark is still on. No need to add the complexity of switching it on and off.
Sorry for the long post, but engineers never know when to shut up.
(IMG:http://www.914world.com/bbs2/html/emoticons/driving.gif) Jim N.
'73 2.0