3 cyl cruising

[Fedaykin]

the new malibu v8 can aparently shut down 4 of its cylinders or something for better fuel economy... whats the possibility of doing that in an iron head v6, and have only 3 cylinders for cruising?

you would have to have a toggle switch to cut the signal to 3 of the fuel injectors, disable spark to them... i'm not sure what the ecu would do.. but if running a standalone such as megasquirt there should be some way to do it electronically as well... cause i'm sure just switching off those items would not be enough.

[DEI37]

Yeah, there is more to it than that. The PCM alternates which cylinders get cut. It's not like it's always the same four cylinders that are cut out.

[prophiseer]

yeah, it's much more mega-complicated than that. The new Displacement On Demand (DOD) motors use a ton of electronics and special mechanical parts to accomplish this.

From what I understand thus far, each cyinder uses 'telescoping' pushrods that are controlled by hydraulic pressure, through the means of a solenoid. The computer cuts the solenoid, and the pushrod collapses, therefore colsing the valves to the cylinder, also spark and fuel to that cylinder is also cut, and the PCM starts following a different fuel trim map. The cylinders cut are also cycled to keep wear even and uniform, and they're divided equally from one side of the block to the other (v6's 1/5L-4R, 3L-2/6R; v8's 1/5L-4/8R, 3/7L-2/6R) to help keep the power band equal and to reduce secondary imbalance.

That's kinda just the start of the theory behind it, there's a lot more to it than just this.

[bszopi]

And the engine collapse the lifters in the cylinders that they are "turning off". Lemme see if I can find the GM article about it...

Well crap... I found a link about it on Gm Media, but it wasn't a valid link. I'll have to see if I can find it on my computer somewhere.

[grandprixgtp_91]

Yeah i had to learn about DoD for my Gm testing, it shuts off certain designated cylinders by cutting fuel, spark and the lifters are a 2 piece assembly that "unlock" and stop the valves from opening, its pretty cool and complicated. i have the Si breakdown of it, its a long read.

Jake

[bszopi]

http://60degreev6.com/backup/PDF/3900V-6.pdf

I knew I had it somewhere...

[prophiseer]

Some in depth stuff, ain't it?!

Good lord I'm not looking forward to seeing these motors come into the shop when an owner has neglected an oil change for 10k+ miles.

[billy wood]

Seems to me you would have to have a compression release on each cylinder...

[grandprixgtp_91]

i dont believe there is one, from what i can remeber its not good to run an engine without compression in the cylinders,cant remember why, but it only goes into v4 mode on the highway, and only for 10 min max if i can recall.

Jake

[IsaacHayes]

only 10mins max on highway? hmm that seems kind of weak. V8 malibu? Must be making them a lot bigger now...

Yeah I'd like to know why they keep the valves closed, seems to me it'd be sucking pure vacuum or compressing and slowing down the motor as drag. Unless they close the valves when the cylinder has just partialy drawn in air so it's pull and compression is reduced and not a full cycle.

[sharkey]

had it explained a while ago. what it does is shuts the fuel off, and for 2 cycles it fires the plug to clear out any fuel. it then closes the intake valve, the piston goes to the top of the travel and the exaust valve shuts as normal, then stays shut. there is nothing in the cylinder, its a complete vacume. vacume is needed in the cylinder to keep rings sealed.

technology has come a long way. i guess in years to come we will see how reliable the new systems are on the gm vehicles and the new "hemi". remember the caddillac 8-6-4??? that had to be one of the worst disaster motors gm built. the lifters would stick shut and the car didnt have enough power to get the car moving on 4 or even 6.

[FastGT31]

i found it weird sharkey that you mentioned the caddy v8-6-4. there is an older guy here that has one, the ONLY one i have ever seen but read about many times. and the thing is it still runs. i heard that caddy only made the motor in 1982 and discontinued it because of warranty claims

[Jacque8080]

only 10mins max on highway? hmm that seems kind of weak. V8 malibu? Must be making them a lot bigger now...

Yeah I'd like to know why they keep the valves closed, seems to me it'd be sucking pure vacuum or compressing and slowing down the motor as drag. Unless they close the valves when the cylinder has just partialy drawn in air so it's pull and compression is reduced and not a full cycle.

if you didn't keep the valves closed, the cylinder would waste energy compressing air. keeping the valves closed should also keep those cylinders hot.

[Fedaykin]

wow, wayyy more complicated than i thought. I guess thats why we havent seen it yet, haha.

[grandprixgtp_91]

its 10 min, max and then a break(not long), then goes for another 10 min., there supposed to get great fuel milage, we have a few grand prix gxp's here with the 5.3L DoD and its pretty cool.

Jake