CrazyPhuD

So here's an early concept for better MPG, lower emissions, figured I'd float it here to see if they're are obvious issues. So automotive engineers, mechE's have fun.

So some of you have heard about the Caddy concept car with a V16 1000HP, 1000TQ, really nice engine, and it gets 21 MPG. How, well not all of it's 16 cylinders are active all the time. In fact depending upon the load of the engine, either 4, 8 or 16 cylinders are firing. Kind of a cool approach to power with drivability. How they do it is a bit technical, however it may be possible to do something similar with regular cars. For instance with the high HP available per cylinder on the s2000 it may be possible to run it with only 2-3 cylinders active.

It is possible to design a circuit to prevent the spark plug and the fuel injector from firing in a given cylinder depending on load. High load, i.e floored, would run all cylinders. Low load would only run 2. The question is how bad for the engine would it be to have no combustion in a cylinder. As long as proper oil flow is maintained, is it bad? No misfire since ignition, no detonation, either, there's no fuel or spark. Would the engine be unbalanced? You would lose power but that is a trade off.

I've had this happen involuntarily on my old car(lost 2 of 4 spark plugs), so I wonder how bad it is for the engine.

Part of my motivation for this is just general tweaking and part is to be able to go to CARB and say yes I can install the turbo since my car has lower emissions than a standard s2K. Yeah I like you're intent but FU CARB if I can't mod my car how I want as long as I still meet tailpipe emissions.

Just some thoughts could generate interesting discussion.

RACER

If two out of four cylinders are doing all the work, then I would think that the two cylinders that are doing all the work would wear out before the other two. The two cylinders that are not firing are just causing unwanted resistance in the engine as well as a possible balance problem.

This may be possible with a 16 cylinder engine, but thats 16 cylinders, as our beloved S has only four cylinders. I will go out on a limb to say that this idea would only hurt the performance in all aspects including conservative driving.

The F20C is designed to run on all four cylinders ALL the time. If I wanted to drive conservatively, I would shift at no higher than 4,500 rpm and cruise at a engine speed of no more than 4,000 rpm.

The thing is, I don't want to drive my S conservatively. I bought my S to drive with a type of flair, style and spirited aggressiveness.

Maybe it would work, maybe it wouldn't. I just don't care one way or the other.

jankemi

I believe that Cadillac tried that in the late 70's or early 80's. It was a flop. With today's electronics & computer controls it may be time to re-try the concept.

silvershadow

I don't know exactly how Cadillac does it, but there was quite a bit of discussion about it years ago. One thing that I don't believe you mentioned is that you some ideas actually disable the valves in the cylinders not firing so you don't get the pumping losses on those cylinders.

Gernby

I thought that the 16 cylinder engine actually disengages the cylinders that aren't active, so they don't even get turned. It wouldn't make any since to move pistons, crank, valves, cams, etc if you aren't even using them.

Besides, a 2 cylinder 4 stroke would be extremely rough since there would only be 1 combustion per rotation. Consider cruising at 3K RPMs versus 1500 RPMs. You probably wouldn't even have enough torque to maintain cruising speeds up hill.

Gernby

Another issue is that there really isn't much of a corralation between engine size and fuel economy or emissions. I got better mileage out of my 270 HP Lincoln Mark VIII than I do with my S2000. Fuel economy has to do with efficiency and aerodynamics. If it takes 100 ft-lbs of torque to the wheels to maintain 70 MPH, then it is pretty much going to take a fixed amount of combustion to achieve it whether that is done with a large engine at low RPMs, or a small engine at high RPMs.

vader1

It is easiier to turn off a couple cylinders in a V configured engine, two at a time and keep things balanced. I don't know for sure, but an inline four with just a couple cylinders firing might jump lope along goofily. How's that for scientific lingo?

I think instead or a fairly smooth whirring of all four firing in sequence, you would just get an oddball whump whump whump of two or three firing. If the four were in a V configuration rather than inline, it might be easier to turn off two cylinders, but I am an accountant and have never designed a car. Well, never one that ran anyway.

vader1

Oh yeah, in my reading of the articles on the technology, I think the cylinders that are shut down just get no gas and spark. Valves and cylinders operate normally.

ButtonBoy

I remember the last time Caddy tried to peddle that engine concept. Mid 80's I think... highly undesirable, and never delivered on any of it's promises of reliability, economy or performance.

jeffbrig

Doesn't Mercedes currently have "displacement on demand" available on their big V8's? I remember reading out these systems in Autoweek a few years ago when the new S class came out. As I recall, they had no gas going into the de-activated cylinders, but did keep the spark plug firing so that it was 'hot' and ready to come to life when needed.

Chevy also played with this during development for the C6 vette, but couldn't get it to run smoothly, so they dropped the idea.