I was considering doing this on a 1987 volvo 760 GLE (so it has the PRV V6), and has been getting the same or worse fuel economy than the 7.

The firing order is 1-6-3-5-2-4, so it alternates banks of the V6 for firing order. What I was thinking of doing was just putting a switch on the 12V wire for the injectors in each bank, so when on the highway I could shut one side off to save fuel. Although I would have to give it more throttle, this should bring the engine closer to it's BSFC "sweet spot", which is typically at higher throttle openings since there are less pumping losses and higher intake velocities.

I can imagine a couple reasons why this wouldn't work or would be harmful, but there are still a bunch of unknowns. First, The car only has 1 AFR sensor after the exhaust from both banks come together, so that would see very lean conditions since the deactivated cylinders would still be pumping air straight through. I don't know the authority that the old LH-Jetronic systems give to the AFR sensor to adjust mixture, but I doubt it'd be more than 10%. Unplugging the AFR sensor may default the mixture to the maps, so that might be a work-around, but I'm not sure on that point either.

There will be thermal differences between the banks, and worst-case-scenario they would be great enough to cause cracking... but I'm pretty positive that the coolant and oil will keep the temperature difference small enough.

The cat. converter will be seeing much leaner mixtures and may not work as effectively. I dont know whether the cat's effectiveness is based on the relative ratio of the species that it is reducing (NO, NO2, HC's, CO), in which case the relative ratios should still be OK since the firing cylinders would be close to stoich, or whether the effectiveness also depends on the amount of fresh O2 there (and an excess would cause a reduction of effectiveness).

Vibrations... the cylinders to be shut off would be evenly spaced, so instead of 6 evenly spaced firing pulses, it would only be 3 evenly spaced firing pulses. However, since its only one bank firing at a time, i dont know what sort of resonances or vibrations this may cause that wouldnt be present otherwise.

Can anyone explain any other reasons why this could be bad for the engine, or just flat out not work?

There must be some hidden issue with what you're trying to do or the auto guys would have jumped on it long ago. I would think pumping all that air into the exhaust system would really heat up your catalytic converter. The O2 sensor would measure a lean condition and may even cause the injectors that are still running to squirt more gas defeating your efforts.

Cadillac tried this in 1981 and it was so bad they recalled them and converted them back to run on 8 cylinders all the time. On the current Chrysler Hemis (and possibly others) they have made it work but it requires considerable computer power to do so. This is largely because cylinders that have not been in use for a while cool off somewhat, and don't want to run smoothly (and cleanly) until they have reached operating temperature again. The Hemi gets around this problem by alternating the cylinders that are not in use, so they all stay fully warmed up. There are also sensors to monitor the operating conditions and an ECU that determines when to drop the unneeded cylinders. Seems like all this would be hard to duplicate in a home workshop.

For DIY maximum Volvo fuel efficiency, you would want to start with a 90+ 740 wagon, install a manual transmission, 3.31 rear axle, or better yet the very rare 3.15 found only in early 760s with AW55 3 speed automatics. Install a free-flow exhaust, remove as much weight as possible from the car, clean up the aerodynamics, possibly lower the car an inch or two, have it aligned with minimum toe, get some narrow steel wheels and run 165-15 tires pumped up to the maximum allowed on the sidewall. All this should get you close to 40 MPG, which is better than a Smart. If you can find one, install a smaller engine---there were 1.8 and 2 litre versions of the B230 sold in markets outside the United States.

I just wanted to try this since I had already pulled the wiring harness to repair all the rotted out wires, and noticed that the firing order for it would work well. Basically, I'm trying to squeeze as much out of this car as I can for next to nothing moneywise (college student). Swapping engines, transmissions and rear ends would definitely help (hell, even just a manual transmission instead of the auto it has now would be a step up, as well as the stock B230 instead of the B280), but all of those require considerably more time and money.

The only thing i'm worried about is possibly thermal expansion or cracking, since one bank will be running at almost full load, while the other is just motoring and is pretty cold. The coolant and oil should equalize it a bit, but im not sure.

On it's maiden voyage earlier this afternoon, it was much smoother than I thought it'd be with 3 cyls, and could maintain 70 mph in OD on flat ground in undisturbed air (barely though). I kept switching between the banks every 3 or 4 min, just to try to avoid any possible thermal problems, but I didnt notice any. I need to figure out how to properly test the difference in fuel economy though... I have a nice long trip coming up (600 miles, all highway), so i could try the flat section one way with all 6 cyls and the other using 3 where necessary, attempting to keep the same speeds.

If you could automate the switching between banks (with some kind of basic electronic timing circuit and a relay) so that it happens at frequent intervals, and it runs smoothly while doing so, you might have something workable. I have no idea what that interval should be, you will have to experiment. My guess is something in the range of 5 to 15 seconds on each side, which would keep everything warmed up fairly well.

First, though, you should do a long enough highway run, (switching it manually) to get an idea of what the mileage will be, and if it's a worthwhile improvement.

Well, I have a breadboard and probably everything i'd need to make that circuit from a digital logic class besides the relays, so it prob wouldnt be that much more effort (not nearly as much as getting the alternator out to re-wire it when everything is caked with 20 years of road grime).

The trick to this conversion, is getting a Rex-Regina M47 flywheel (impulse trigger spacing is supposedly different between EZK and Rex). The other option is converting to LH 2.4/EZK.

The other trick for me would be getting my sweetie to let me do it! :-)

I've got my 5-spd 245, so I won't complain...

-Ryan
--

Athens, Ohio
1987 245 DL 314k, Dog-mobile
1990 245 DL 134k M47, E-codes, GT Sway Bars
1991 745 GL 300k, Regina, 23/21mm Turbo Sway Bars

Just some quick thoughts.

I think that you should try it!

Wouldn't it be relatively easy to split the exhaust system and only monitor the running side. Dual exhaust would give you better mileage as well.

Using two cats gets around cat problems.

Don't most systems shut off valves to shut down cylinders? Closed valves convert cylinders to air "springs" using little energy during a complete revolution.

Wouldn't there be considerable pumping losses, kinda like a Jake brake in the un-fueled cylinders?
--
'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 435,000 miles put on 9 bricks

I'm definitely planning on trying it, I already have it wired up since I had the harness out to repair some badly rotted wires.

The exhaust system would be relatively easy to do, and may be a next step.

I think the way the cat works is just based on the ratios between species to be reduced, as long as there is "excess" oxygen, and if that's correct, then one cat will be enough. Either way, there will never be a situation where there are too many unburned HC's and the cat overheats, so it may just work more ineffectively since approx half the flow thru it will be at ambient temperature instead of exhaust temperature.

Being able to keep valves shut and make the deactivated cyl's work as air springs would be part of the "proper" way to do it, but the amount of work required to retrofit a system that will raise and lower the pivots of the lifters to accomplish this just... seems very substantial with the budget I'm on.

There will be pumping losses, but those would be there regardless of whether those cylinders were firing or not, since most of the losses (in an ideal situation anyway) are due to the differences in intake and exhaust pressures in throttled applications. A smaller effect is due to the momentum of the inlet air and the sudden pressure drop of the exhaust (after the cylinder fires) that evacuates a lot of the exhaust mass when EVO is before BDC. These smaller effects should be more than made up for with the reduced difference in intake and exhaust pressure when running on 3 cyls, since to make the same amount of power the throttle would need to be much further open.

If I understand how a jake brake works correctly, it compresses the air in-cylinder until TDC, then opens a valve briefly to allow the compressed air to escape, then closes. Then the cyl expands whats left in the cylinder to BDC, another valve is opened and the cyl fills up, and then it starts over again. This way work needs to be done on the engine for each half-turn, which should be quite a bit different than just motoring half the cylinders.

Hello,


Be careful, one fouled plug will limit top speed to 50 mph. Don't get stranded over an experiment.


Goatman

only 3 firing cyls still maintained 70 mph, so thats not too bad.

I know it was done to a V8, mechanics illustrated magazine, during the gas crunch around 1980?

they used solenoids on the lifters to shut down 4 cylinders.
Its not commercially viable.

Yea, GM did it to a caddy V8 in the 80's, and the technology just wasnt robust enough then. They've been doing it again for a few years now, and honda (and a few others IIRC) have joined the game too. Probably the most durable way of doing it would be hydraulicly, lifting the pivot of the lifter up to deactivate (on a pushrod setup anyway) and down to activate the valves.

If I end up stranded, I have enough tools in the car to get it to run far enough to get home, so i'm not too worried about that one.

Yea, a friend of mine has a '08 Avalanche with this gas saving feature and he raves about how economical his new rig is on gas. Power when you need it and economy the rest of the time.




Dan


hope your idea works out... sounds like an interesting project