No biggie, we all read over stuff sometimes

 

How about you yank the spark plugs on the cylinders you cut off? then make something that has spark plug thread with a check valve on it to let compression stroke blow out and not suck air in on the inhale stroke.

 

you cant yank the wires off they are still being used just skipping every other fire.

 

In theory, all energy lost during the compression stroke should be gained during the power stroke due to the expansion of the air in the cylinder. Obviously it won't be 100% efficient, but not all energy will be lost. I think the big factor is the frictional loss.

 

Thats a good point. My next point would be your fuel corrections. Your o2s will go crazy seeing all that extra air pumped through the engine. Have to keep the valves closed.

 

He said he was going to run in open loop I believe. So fuel corrections won't be an issue.

 

wrong. Exact opposite.

 

DOD deactivates the lifters and seals the intake and exhaust valves to change the cylinders into "air springs" like you mentioned. This wasn't done with the Caddy 2-4-8 V8 in the past due to technology/cost limitations... and was one reason it really sucked for efficiently.

The other problem these "on demand" systems had in the past was the noticable loss in power or "on/off switch" feel they had when activating. This is apparently not an issue anymore as the dead cylinders aren't "dead weight" or engine braking the whole time, and the EFI allows for instant fueling adjustments to the other cyclinders during the transistion... the live cylinders get a hp boost as the other's shut off to prevent the on/off clunk feeling.

I'm sure there's other features to the GM and Dodge V8 DOD engines, but those are the two that stand out from what I've read about them.

If you could removed the rockers on the dead cylinders you'd be way ahead of the game... but then you wouldn't be DOD, it'd just be a handicapped V8.

 

The new v8 impala should be interesting

 

Sorry I haven't replied, I've been a busy dude

This is certainly not as good as having the valves closed but I think it'd still work. Those frictional losses are present no matter what. Keeping the valves closed would help with all those pumping losses though.

The cats will likely burn up in open loop because the open loop table runs richer than stoich under many conditions and stoich at best. It would only take a little bit of fuel to drastically raise the temps of the cats with all that available O2. WOT would be a big no-no as well because of the extra fuel.

It does work and it runs smoothly. I would think that 4 cylinders would see more load, increasing their thermal efficiency and reducing waste heat.

I suppose I could remove the pushrods on those deactivated cylinders but I wouldn't expect my rev kit to completely control lifter motion with any decent RPM and what about WOT power?

I did this out of curiosity more than any hopes of practicality. It certainly does work and I think it might be possible to see some gains. Too busy to tune WOT much less play around with this

 

You can tune the open loop tables to elliminate this issue (Open Loop Temp vs. Load). As you can tell, the MAP really drives any real open loop fueling... but you could tune for a warmed-up engine, prevent closed loop by programing the closed loop temp table at 255*F, and then control start-up temps with a) using the air pump for the cats, and b) advancing the timing.

Again, proper tuning is no problem for this one... PE mode has it's own tables, you could zero-out any changes if you want.

Interesting idea though. A hydra rev kit may be enough to keep them planted, but I agree it wouldn't be ideal... and you'd definitely want to limit engine speed to "valet mode" (say 3500? ).

 

I know I could tune it open loop with the help of my wideband (already have done some actually). At cruise it is fine to run a bit lean but you wouldn't want to run lean at any significant load.

Again, I know all about WOT tuning. I'm tuning for around 13.1:1, which is rich, which WILL cook the cats with all the extra O2 present. Why do you think the factory uses a fuel cutoff for a rev limiter and not an ignition cutoff? If you dump a cylinder full of fuel and O2 into a hot catalytic converter, you generate massive amounts of heat. In this case some cylinder are dumping fuel while the others are dumping O2. Running rich normally cools the catalytic converter down because of lack of oxygen, having four cylinders pumping air through the system changes everything.

This simply isn't something that will work well with catalytic converters, period.

 

Please humor me... why do you think you'd be dumping so much excess fuel into the cat if:
a) the dead cylinders' injectors are unplugged
b) the open loop fuel vs. temp table is corrected to remove the "start up fueling" enrichment bias
c) the PCM is forced to stay in open loop (so excess O2 won't trigger BLM corrections)
d) only half the cylinders are actually exhaling HC.

Maybe if we were talking about running a open loop tune 24x7 with a full V8, but even then there are reports of guys do so for turbo use.

Maybe I don't quite understand your problem... is it that you don't want to mess with tuning the Open Loop Fuel table?

There's more reasons that that.

1) it's safer than iginition cut-offs. A lack of fuel mandates engine/compression braking... a lack of spark just hopes there isn't a hot ember or other source of ignition in the chamber.

2) it prevents fuel-fouling of spark plugs, combustion chambers, ring washout, and O2 sensors as well as the cats.



I agree it's a pretty pointless project from an economy standpoint, the friction losses are pretty significant from a 2.9L 4-cylinder engine rotating without power generation... but it is an interesting project in LT1 PCM tuning.

 

Instead of unplugging the dead cylinder's injectors, you could try 0'ing out the cylinder balance table. That may be interesting to see if it reacts as advertised.

 

I have done tuning work to the open loop tables. It runs richer than stoich at any significant load and certainly at WOT. Not a lot, but it does run richer than 14.7:1 and that is what the engine wants under those conditions. Under normal circumstances this isn't a problem because the little bit of extra fuel just cools the catalytic converters because there isn't any O2 in the exhaust. In fact, catalytic converter protection mode means the engine runs rich. If you have 4 cylinders pumping nothing but air, ANY fuel from the other 4 cylinders will oxidize in the cats, creating lots of heat. Think of a giant air pump always running. The AIR pump normally shuts off after a short period of time because its purpose is to raise the temp of the cats. Granted it gets help through added enrichment in the open loop table (which I've removed since I don't run AIR).

This is also a problem with running large cams with lots of overlap and cats. The overlap from the cam dumps fuel and oxygen into the exhaust and it makes for some very hot cats. I've got mine tuned to keep the cats as cool as possible but they still get very hot at idle. Luckily not hot enough to cook 'em. In fact, this is why I shut the car down after not much time in 4 cylinder mode, the cats were starting to glow red.

The fuel cutoff rev limiter is probably also for emissions

It also doesn't make sense to run cats if you run open loop anyway. The biggest purpose of closed loop is to ensure proper operation of the cats. The PCM dumps a little extra fuel than a little extra air constantly. It keep the cats running perfectly and a good balance of clean emissions. If you're running open loop you're negating much of this so why even have the backpressure or weight?

I can't say the cats would immediately fail or even how long it would take. I can assure you though that this would have a very negative affect on them. It was fun just to hear the car run smoothly on 4 cylinders