I have done some EFI Conversions in the past but I have been thinking. Has anyone come up with a conversion that runs on 8-6-4 concept. I am thinking it should be based on load and anytime there isn't a 20% or better throttle request from the TPS than the ECM uses logrithms to determine if it needs 8-6-4 cylinders to acheive the proper power. It would also rotate the cylinder it powers like the Northstar limp home mode they used when the coolant leaked out. I had a buddy who blew a hose on his and it worked AWESOME he said it didn't ruin the engine and he drove 100 miles home with NO coolant. I just think this technology could be used to keep our cars from getting hot when cruising and that we could drastically improve MPG if we did it. I have a C3 I would like to upgrade but thought you guys might have a source?
Some newer cars have a similar technology which got me to thinking.
-Thanks,
Charlie

 

GM has several engines that have displacement on demand (DOD) that drop out cylinders based on load. I know Honda and Dodge use similar ideas as well. Why not just swap one of those in? It would probably be easier than trying to program a custom ECM to do it smootly.

In the 80's Cadillac tried to do it with there 4-6-8 engine and it was a disaster. The algorithms are probably much more complicated than you would think. At a minimum you would need a sequential EFI that would allow you to turn off individual injectors. I think the GM engines also partially open both intake and exhaust valves on the dead cylinders to prevent any compression on the stroke.

The LS1's have a limp home mode like the Cadillac you mentioned. They fire every other cylinder every other time.

 

I too have been wondering the same thing recently....I have a DPFI setup on my 355 roller engine for some years now, and it's the old speed density 1227730 reliable GM computer with aftermarket chip/calpac....

some time ago, I had a loose wire, because I was doing some modification or so, think it was the hydroboost mod....anyway it was the ground side of the driver's FI bank...so the engine ran like total crap of course.....but it DID RUN....and it got me home through the hood, I was not on the freeway or anything higher speed.....

at any rate, it got me thinking about all this stuff, and even with sequential firing I can't see how to kill some cylinders on the banks that have O2 sensors in there, which is just the pass bank in MY case....IF I had a more sophisticated computer in there, and had a O2 sensor on each bank, and sequential firing, I still can't see how to keep the O2 sensor from sensing WAY too much oxygen in the exhaust, which of course there would be....UNLESS like we somehow stopped the intake valves from opening....too much like tooo much to type work for me.....

the electronics I can handle, with programing help, but not that major a mechanical......

but the thing is....the stupid engine ran fairly decent with enough power to pull the local 'hills' and get me home, the thing I worry over is eventually snapping the crank from just using the pass bank and say putting a switch in the driver's bank to kill the injectors ....

I look at the firing order.....7218, 4365 4 corners, 4 middles.... and compare to just the pass bank running....I get

x2x8, 4x6x humm.....2 corners two middles...BUT if I express it another way....it's 2x84x6xx which gotta be ragged as hell on crank harmonics....at SOME engine speed I bet it would tear hell out of the bottom end at BEST, and snap the crank at worst.....so I left the idea alone.....

IF I could get around the O2 sensor being messed up AND/OR program around it, but if subjected to extended excess oxygen at speeds what would that DO to the O2 sensor.....

which comes back to the General killing the compression and all that mechanical crap.....

 

Sounds like a good idea in theory, but in practice I would think it would be very difficult to make it work properly. It took the OEMs this long to get it right, so I can't imagine it was easy. Why not just swap in an LS motor with this system already, using the original harness and computer to run it? Still wouldn't be easy, but there is no reason it wouldn't be doable.

 

exactly what is the "drastic" mpg improvement u r looking for?

 

Go from 22-24 mpg to maybe 30?? like the new vettes with a 350 engine.....but my old 355 roller engine is in decent shape with L98 heads and a modded up LT1 intake on it, using L98 dizzy....so the question is why can't I just take the later computer and hook IT up to the existing engine??? not that I wouldn't WANT a LS engine, sure enough, but I rejected one next door for a GRAND even off Craigslist...as it was just a bare engine, no induction, no exhaust, no assessory brackets, no nuttin....getting all that crap together would be another grand....at best...especially with fresh enough injectors and fuel rails....lovely.....so no go...

so the thought, well what ELSE does the General DO to the late engines to not upset the O2 sensors....do they release the valves from functioning?? anyone???

 

Try the megasquirt forum, I don't see why a modern efi computer can't handle dropping a cylinder almost a random.
If you're doing this to have something different, or just "because I can", have fun. If you're doing this for economy, I'd seriously rethink the project. Either way good luck with it and don't listen to the other people who will put you down. It's nice to see people who think "Outside the box"

 

I tried the MegS. route a bit over a year ago, and the programing and problems with computers and .commm never got the system running, so it was forget about it....went back to the stockish system on there now....

took my 150 buck loss on the project and moved ON....

I sold the computers and MS off at a loss, cost me about a month's worth of effort just on the futility of programing....what a mess....

 

Sorry to hear about your grief, MRVETTE, did you buy a "ready made" MS system or did you build it yourself from scratch?

 

You will not gain any fuel mileage by simply removing the fuel and ignition from a cylinder. The engine would still be fighting the pumping losses of the piston moving downward during the intake stroke and you would still be compressing the air, instead of saving fuel you would be burning more fuel because the cylinders that are producing power would have to produce more to overcome the "drag" of the engine.

The late model "modulated displacement" engines have solenoids that apply oil to passages in the lifters that deactivate the lifters during the cylinder off phase of the engine. The valves remain closed therefore the pumping losses are reduced and there is very little energy expended to compress the slight amount of gas that remains in the cylinder.

Stormin

 

Now I understand what my buddy was trying to say about "Closing the Valves" in the economy mode. I just thought it would be cool and would be a way to keep the car from running HOT since it is a 400 and as well as save some fuel.
Between the O2 issue mentioned and the compression parasitic draw if one can't figure out how to shut down a cylinder the whole thing is a bust......
OH well...
Thanks for all your help and advise, I knew you guys would have the answers. Now I know what I am up against!
-Thanks again

 

YUP, right there above, it's what I figgered needed doing, the old 4-6-8 Caddy 425 engine did that, with solenoids on top of the engine to deactivate the valves.....I figger it had to be done that way, and so the old 350 like I have will be well close to impossible to do for a guy in a home shop.....

oh well....

but not ALL LS series engines had that feature, did they??, talking of the mechanicals involved with the valves there....