Mongo

I received the most recent Panorama magazine for September as part of PCA Membership. There is a very interesting article about Porsche's new design of the 4.0L Twin Turbo V8 (turbos are mounted in the hotside vee of the engine like the C190 Mercedes AMG GTS), but also provides an overview about cylinder shutdown and engine-stops while the car is not in motion.

The article mentions that the Porsche 928 was the pioneer of both cylinder deactivation while cruising, and start-stop features while the car was not in motion. Apparently, Helmuth Bott, head of R&D for the car had developed the concept in the late-70s.

This seems like news to me since I don't believe I have ever read this about the 928. It sounds like these cars were SERIOUSLY underestimated not only by pro-911 engineers in Porsche, but enthusiasts as well who consider the 928 the 'sideshow bob' of Porsche.

Anyone else hear about this or who is an SME on the 928 prior to this article being published?


For your reference, it's in the Panorama Magazine for September 2016, on page 32.

Crumpler

Have not gotten this month's Panorama yet, but yea, this is actually discussed in the Engineer's Talk Shop book, there's a link to Rob's scan in the Dead Sea Scrolls thread.

polecat702

Andy, when did you receive you're September issue? I haven't gotten mine yet.

Rob Edwards

No production 928 ever had cylinder deactivation or stop-start. There is reference to the these subjects in the PETS (Porsche Engineers Talk Shop) book, here's an excerpt on that discussion:

https://webfiles.uci.edu/redwards/pu...%209-22-16.pdf

Mongo

Just got mine in the mail today. There's high winds in Marin county here and not only was I greeted with my new issue, but a tree branch on the roof of my 2003 ML350. I now have a good sized dent in the roof of my 'truck'.

BC

I have a autostop car now. I don't see how it works very well when there is not an electric motor to deal with the low speeds where this happens TOO frequently. The hybrids do the stop start very well. A random X5 with start stop is stupid and abrupt.

polecat702

It's been furnace hot here in Vegas for months. Windy as all get out now. The pool is a mess, so I'll be closing it this weekend, and putting the cover on it till next spring.

Sorry bout you're truck!

V2Rocket

Not saying Porsche didn't experiment with it, but they weren't the first/only ones doing it.

Ford experimented with deactivating 3 cylinders on their venerable 300ci inline-6 truck motor in the 1970s, IIRC it was by depressurizing the hydraulic cam followers somehow to stop those valves from opening. They had reliability problems and the MPG gain wasn't as hoped.

Then there is the notorious Cadillac V8-6-4 of 1981...

Vilhuer

Ludvigsen Excellence Was Expected book has most info about it I have seen.

DeWolf

Mine has this already. It's only running on 7 cylinders.

docmirror

The problem with ALL of the cyl cut designs is they didn't bother to start with a clean sheet. They were variations of kludges glommed on to an existing V8 engine. If an engineer team were given the project to design and build a V8/4 engine from the start, it could be done right. The way to do it is to stop the crank throws and the rods and pistons associated with the cut cylinders. Put a clutching mechanism between the two, and the throttling of both. At least Porsche got the throttling part figured out well.

Tom in Austin

isn't the accepted solution now to open the valves and shut off the injectors and spark for the least pumping loss? That requires that all are controllable by cylinder which are relatively recent features in production vehicles ...

Imo000

This ever made in into mass production?

dr bob

My DD Honda Pilot has Variable Cylinder Management, which selectively deactivates valves and fuel to one, two, or all three of the rear cylinders. The actual deactivation part works pretty well. There are computer-adjusted motor mounts to deal with the extra engine vibration. Challenges come with when exactly to re-engage the cylinders. Honda does an OK job on this, but the times when it should deliver the most benefit (fairly steady-state highway cruising) is the time when it seems to have most noticeable problems. As the cylinders come in and out, the computer-guided auto gearbox hunts for the "correct" gear as you go up and down even gentle slopes. Changes in wind and surrounding traffic seem to bother the system. I've mostly learned to live with those "features", in trade for the improved fuel economy. Then Honda was class-action-convinced to extend the warranty on the engines because of problems with oil ingestion, broken rings, damaged pistons, etc, supposedly associated with how the system engaged and disengaged.

I've defeated the VCM system on that car in the interests of engine life. Like that nagging now-ex girlfriend, the symptoms weren't that apparent until they weren't there anymore. It seems that even with a well-integrated system of deactivating valves, there are still some core mechanical issues around cylinder lubrication and combustion management that need to be addressed before any system of this type is ready for prime time.

Someone mentioned the Cadillac 4-6-8 project that was a knee-jerk reaction to 1970's gas shortages and price spikes. Standard starter motors were used for restarts, which made things noisy and imprecise. Caddy purists were used to not hearing the engine, and having things better than the rest when it came to power and luxury. Not to surging and bucking trying to move off from a stop in traffic.

Meanwhile, keep an eye on the new Panamera plugable hybrid. That should take care of 90+ percent of trips I take, without even starting the IC engine. It won't be long before we start seeing more pure electric "sports cars" with significant performance on the market. As much as I love my 928 as an object d' art, it's a dinosaur compared with current technology.

Will new drivers coming on line now be qualified to drive ancient buckboards like our beloved rides, without all the safety and warning systems? Folks in obsolete non-safety-equipped cars (that would be ours...) would actually have to pay attention and -drive-.(!!!)

Cylinder deactivation isn't quite there yet, IMHO.

BC

Wow. Damning and realistic picture of driving life today Bob. Scary real.

Just had to quickly drive just 40 miles in the mid afternoon, in San Diego. Not less than 5 times did I have to look and find out what the person that couldn't keep a lane/speed/direction/alert driving status was actually doing instead of driving.