Quote from 1997 Haynes Engine Management book:
?A weak (fuel) mixture with a high level of O2 is good for the efficient oxidation of CO and HC. On the other hand, a relatively rich mixture with some CO aids the reduction of Nox. A compromise is reached by adjusting the air-fuel ratio of the catalyst-equipment engine to the stoichiometric ratio of 14:1. This means that the engine is perhaps adjusted slightly richer than desirable??. ?A catalyst needs to reach a minimum temperature of 300?C before it begins to work efficiently, and a working temperature of 400-800?C is more desirable. As the temperature rises over 800-1000, the precious metals will begin to break down. Above 1000?C, the catalyst will melt.??. ?Excess fuel due to misfires causes overheating. Leaded petrol and excessive oil residue also destroys the catalyst.?
So. more oxygen in the exhaust dosen't lead to CAT destruction.
Bit for the critics:
This my be a bit hair-brained but if anything else it is interesting to study about...I'm learning heaps about engine managment.
At best if it works it works, at worst I've leant something and given it a go in the process.

I've looked at all the threads I can find here about this kind of thing and all I see is the same kind of FUD you get about putting more air in the tires, and dismal failures with 4 cylinder vehicles that were marginally powered in the first place. GM through abject incompetence appears to have "proved" it impractical, much as they "proved" diesel engines aren't for cars, EVs are baaaaad, and as they seem to be "proving" that hybrids are impractical and unsellable due to offering a system in the same class as the conventionally powered Elantra that gets less mpg....

So, all the nay-sayers that say it's been proved not to work, are you gonna point out a particular example of a 6 or 8 cylinder motor that someone has gone to all lengths to get this working on, and failed??? It's a given you've got to fight or fool the engine computer, failures in that regard will not be regarded as proof.

I'd admit I might be skeptical, if I hadn't known of a guy who was getting 40mpg highway in a '89 voyager with an injector kill switch. He tried to tell people how to do it, but got much the same closed minded reaction as seen here.

Actually, I think their latest attempt with "AFM" is working fine. I hang out on a GM forum where many users have AFM and they don't seem to be having any problems with it. There is some FUD but I don't recall any reports of actual problems.

They did do a bad job with diesel cars, but AFAIK the only problem their hybrids is the price. They proved that EVs are good, not bad; just ask anyone who had the GM EV1, all the reports I've read say that people were sorely disappointed to give them up.

I was meaning more the spin they put on the whole thing. It appears to be inconvenient that the people who had them liked them.

Pumping and frictional losses together consume about 20% of rated output at peak output, i.e. high rpm, it's a square law thing so round about 3000 rpm cruise, they'll be a grand total of about 5%..... OMG IT'S LIKE A BRICK WALL!!!!!

Roadwarrior, do you have any more info on the guy getting 40mpg out of his Voyager...I'd be interested in the details of his setup...thats pretty impresive.
Good point on the pumping losses...would be good to get rid of them as much as posible by closing off valves but if it's only 5% or so then why bother with that extra complication...

Check the difference between coast down times in a FI manual trans car w/ the engine off during WOT and closed throttle. More to the point, trapping exhaust gases in the cylinder keeps things pretty hot. Just how cold would the block, pistons, mostly importantly IMO, rings get w/ this system if there was new air at whatever the ambient temp is being cycled in and out? Drop temps enough and we'll see accelerated wear IMO. Granted, manufacturers could somehow cycle exhaust gas back into the deactivated bank (maybe not if they deactivated two cylinders on an I4), but even then, w/ all that energy via hot air, I think that the closed pistons would be better "springs" than those filled w/ air at ambient temps. Just my opinion of course. :thumbup:

omgwtfbyobby: I seem to remember an engine safety feature on my mom's old GMC Yukon. It had the 4.3L V8, and if it overheated, it'd alternate firing cylinders. Maybe this is a better option here? Of course, with a v6, you'd have to figure out a better way of 'alternating' cylinders, maybe cycle is a better word.

It twinning the O2 sensors together doesn't work you could at least trigger open mode my removing or setting the coolant temp sensor low (depends on vehicle). This should be better than limp home mode.

As for the rest of it, definately I3 should be ok because most V engines share opposite banks on the same spot of the crank (I say most because I don't think the VR6 engines do), but definately stay away from I4. Lateral force (that is unbalanced perpendicular to rotation) would be very bad and potentially bend the crank.

For the rest of the idea, my friend thought once of somehow installing a valve in the spark plug hole so you could decide when to remove compression. I think the best way would be to add another valve in the head that wouldn't interfere with the piston that you could open either with cable or electromagnets or whatever. I think best would be to hook this to a central plenum between all 'dead' cylinders and then as one went up another would come down and all pressure forces should cancel and wouldn't pull fresh air or pull on exhaust flow but would eventually cool down and may cause the other issues mentioned by others.

The other thought would be to somehow drop out the compression and power strokes and just always intake-exhaust-intake-exhaust. This provides no compression, but causes issues with fresh air in the exhaust and it would be pretty hard to do, you'd need two cam profiles.

I am really curious if it's even worth it though. It just doesn't make sense to me that compression without ignition would cause much of a loss. As said before it's basically a spring, any time spent compressing is returned on the power stroke. I feel like the biggest loss (at least the biggest drag when turning by hand) is the valve train. Next would be friction and last would be compression.

If I fully seal my valves and install the head I can still spin the crank on my CRX very easily but it's a real pain to spin the camshaft.

I've always wanted to explore a rotary or electric valve system but that's a whole nother discussion.