BlueEyes

While shopping for pickups, looking at 5L+ V8's, I can't help but wonder this. Yeah, a 5L V8 would be awesome when I am towing a car, or boat, or whatever behind me. But, the rest of the time I could do without it. SUV/Truck's in my mind would best suit the cylinder deactivation technology like in the 300C. Anyways, why do you think they don't offer this? I would think at least Toyota would do something like this.

As well, does the 300C shut down a bank of cylinders or the 4 front/rear cylinders?

guy321

I had all the cylinders in my 8 deactivated!!

BlueEyes

haha, I knew someone was going to say something like that!

babylou

It is significantly cheaper to offer cylinder deactivation systems in pushrod engines.

expo1

Because it's taken this long to recover from GM attempt at it in the early 80's
Google "Cadillac V-8-6-4"

globi

Have they entirely solved the vibration problems that come with it?

The Honda Accord Hybrid shuts off one cylinder bank as well (including the camshafts), but it uses the electric motor to take care of the vibration that would normally arise. http://www.hondanews.com/CatID1000?m...48444&mime=asc

Ike

In my dad's Magnum RT there is no noticeable vibration. In fact you can't even really tell when the cylinders are deavtivated.

babylou

I'm not finding any mention in that article of the electric motor reducing vibration.

BlueEyes

It's good to know the vibration isn't noticible in the magnum. That was one of the things I was concerned about.

babylou

All 8 pistons are still moving so all balance forces should be the same. The only difference will be the torsional acceleration frequency will be cut in half. I'm confused as to the earlier post mentioning the Honda hybrid electric motor reducing vibration during cylinder deactivation.

globi

You're right it doesn't but I read it somewhere. The electric motor accelerates the flywheel when one of the 3 deactivated cylinders doesn't provide any torque (and/or brakes it when the 3 others provide torque).

globi

Here's a link:
http://www.insightcentral.net/encycl...vibration.html

The Accord V6 Hybrid uses the same trick.

truemagellen

DAMN...I was just about to post a thread on Cylinder deactivation

the simplest tech to save boatloads of Gas on any vehicle

reach cruising speed in that V8...turn off 4 and you have a 4banger sipping away

how did it take so long for such a simple technology change to be realized?????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ??//

globi

There have been threads about rotor deactivation as well.
https://www.rx8club.com/showthread.p...ighlight=rotor

RG actually tried it, but I think you'd need 2 throttle bodies in order to cut off the air supply to the deactivated rotor. (Otherwise the unused rotor has to compress and pump air for nothing).

LycosV

I think the problem is that you can't just turn off the other cylinders.
*Now I'm just going on what I remember here, so if I'm totally off on something, meh*
I think the new ones turn off fuel injection to some of the cylinders and seal them off so they just compress air. I think gasoline helps lubricate/clean the cylinders slightly when the car is running, so with no gas entering the chamber for combustion you're just spinning empty cylinders. Remember, cylinder engines don't inject oil into the combustion chamber like rotaries (at least not on purpose, my parents have a truck that does. )
Anyway, bottom line is I think it increases wear on the unused cylinders. I'm sure my mechanical engineer brother knows more but I'm too lazy to ask him.

rx8wannahave

SUV/Truck's in my mind would best suit the cylinder deactivation technology like in the 300C.

What’s sad…is that even with it the 300C get’s nasty fuel economy. When looking for great fuel economy in a V8, go no place but to the good old Chevy V8. I wonder what cylinder deactivation on the Chevy's V8 could do. A V8 with 30+ mpg city....no way!!!!

I’ve thought about this before also, I’ll have to PM RG about it I would love to hear the details on his attempt.

jefferrari

the fuel consumption and emission jumps up when reactivate those cylinder.

KYLiquid

The following is spoken from my understanding of the system, and may or may not be correct.

The current american push-rod motors that have cyl deactivation simpy have a 'colapsable' push rod, so that when you turn those 4 cyl off, the motor stops dumping in fuel and camshaft is still turning but it doesnt move the valves since the pushrod had 'colapsed' so that it isnt moving up and down.....

now in the motor you have 4 sealed chambers, the air that was in there acts like a spring to push the piston back down....you dont turn on one side of the motor (also called a bank of cyl) you turn off one on each side, so you turn a v8 into a v4.....turning off one side would lead to major vibration problems, There is still some 'wasted' energy moving the pistons up and down when only half of them are making power...so its not a cure all, but it does help use less fuel and boost economy.

The reason the 'sealed' chambers the 4 unused pistons have air in them rather than no air :

If there was no air, there would be a vacume as the piston moved down...this would rob power from the engine, as its haveing to work to pull the piston down, they chose to have air traped in there, while it takes force to compress the air on the upstroke, the compressed air pushes the piston back down like a spring....so you get a little bit of tq added to the crank....

The C6 corvette was supposed to offer 'displacement on demand' but they ran into problems with vibration and trying to get a smooth transition from 8 to 4 cyl.....in the end they ran out of time...so it wasnt included as a feature on the car, but they are still working on it.

Honda will be able to corner the market on SOHC and DOHC (non-pushrod) motors with the ability to shut off cyl. The reason is becuase they are the pro's at cams, their VTEC system already switches the cam to a 2nd profile....while most of its cars with VTEC and iVTEC use the system for more power....you could easily tune the 2nd cam for less power/cruising and make it load dependant vs rpm dependant....letting less air in, means you can also let less fuel in without running too lean.

You could also easily make the 2nd profile on the cam have no lift at all....so that you seal the chamber off, then also turn the fuel injector off and youve got the same thing as chrysler.....

it is a system that you will see on more cars in the future....

The I motor (inline) is a better platform from a vibration stand point.

Mikelikes2drive

i know the new m5 has it and i think the maseratis have this feature as well
in the m5 you can use 400hp when cruising and 500hp when you're racing... thats just chump change i guess though

rx8wannahave

Nice post KY

babylou

Here is a nice article on GM's DOD: http://www.popularhotrodding.com/eng.../0405sc_gmdod/