Hi All,

This was inspired by a comment that I seem to remember reading elsewhere on this board (sorry, struggled to find it again). I’m keen to see additional thoughts on the subject. My apologies if this is a pie in the sky non starter, but I haven’t seen the flogged remains of a dead horse to find out why that may be so.

The idea is to split a slant (or any engine) into two halves, and running/firing only the front or back cylinders at light load. This would be a primitive form of cylinder deactivation. The original post I think referred to dual throttle bodies or maybe six ITB with fuel injection, but I’ve got a set up in my head that would employ a dual carb arrangement, each feeding three cylinders independently. By closing the throttle fully on one group of cylinders, they could be effectively deactivated. When you want the power, lock both throttles together and drive it as a dual carb/TB six cylinder engine.

Advantages are eliminating (nearly) pumping losses in the deactivated cylinders (the dual TB/Carb arrangement would probably allow flow between cylinders in the manifold, so not as efficient as ITBs).

Also, throttle would be much more open in the active cylinders. This would allow higher volumetric efficiency and greater pressure ratios for more efficient operation. Effectively we’d have a 112.5cu slant 3 engine (or 85cu slant 3 if you are feeling especially frugal).

Any reason this wouldn’t work with carbs? Having driven a slant with pushrods missing I can attest to the rough running at low speeds and this is an obvious disadvantage. Like I said, I’m keen to see something of a discussion on this, even if it is a host of reasons why it wouldn’t work (The Cadillac V-8-6-4 being a reasonable argument ‘against’ for starters).

Your thoughts?

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1960 Plymouth Belvedere 4 door sedan
Stock 60 225
Push button 3 speed Torqueflite
Right Hooker

I think you will want the throttle full open on the deactivated cylinders--otherwise the engine has to work to put the air across the closed throttle valve. Not sure if one can deactivate just the cylinders on the end, and have smooth power, from an even firing order. Not sure how you'd lock the throttle open *and* kill fuel to the deactivated carb at the same time.

I think OEM's do cylinder deactivation by killing the oil flow to the hydraulic lifters--no valve actuation, so, whatever air is in the cylinder acts like a spring. Not sure if that approach can be duplicated here. Even if you did do that, I'd think the dual carb approach would still have to be used, due to the difference in vacuum signals to the carb. And then I'd wonder what secondary effects would pop up (fuel puddling? smooth stop/start on the deactivated cylinders) with a carb approach.

Personally, I'd think more compression, EFI, electric cooling fan, etc--long before attempting this. Especially with a carb. Well, cost effective, time and effort effective, and in the end, actually effective in actually getting more mpg's.

But it could be really cool, I guess, in the same way that watching old flatheads racing about is still cool. If you could get cylinder deactivation, with a carb (or carbs), and no computer...

I am looking at building an IR EFI setup in the next year or two based on a Weber 3X2 manifold. I suppose it wouldn't be too hard to do a drive-by-wire and shove open 2 or 4 of the barrels while deactivating those injectors. Yes, the valve deactivation is a better way, but this might not be much worse. Hmmm.

I was thinking a bit about this also because I blew the head gasket on the turbo Dart on 9/2/11 and drove on 4cyl back from Bristol (130 mi) the next day.

Lou

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Home of Slant6-powered fun machines

Hi guys, thanks for the reply.

Yes, I completely agree that there are many other ways of improving the fuel mileage before anything like this be attempted. I'm interested to see what kind of discussion it brings up though, it's not somthing I have seen talked about here.

Interesting idea on locking the throttles open rather than closed. I thought eliminating air flow past the throttles was the objective to remove pumping losses (kind of like closing the valves). Ignoring the air bleed, there would be the fixed mass of air in the cylinder/manifold acting as an air spring. If ITBs were used, holding them closed would be similar to the OEM set up, except for incurring additional losses as a small amount of air flows back and forth past the valve and in the intake runner.

With the throttle open, you would have air flow into and out of the manifold, past both the throttle and a far greater amount past the inlet valve, surely this would have greater losses due to pumping?

With either method, I guess there'd be problems with there being high vacuum in the cylinder around BDC just as the exhaust valve opens. There'd be flow into and out of the exhaust, leading to additional pumping losses.

Lou - Interesting you drove back to Bristol a few cylinders down, I lost my pushrods on the way to Bristol, albeit in the UK. I reckon on the intake side at least, the difference between ITB deactivating and valve deactivating might not be too much.

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1960 Plymouth Belvedere 4 door sedan

Stock 60 225

Push button 3 speed Torqueflite

Right Hooker

Problem with locking the throttle closed is this: on the exhaust stroke, the cylinder is evacuated in a positive fashion--unless if there is an obstruction (or the pressure in the exhaust system is higher than the cylinder), then whatever air is in the cylinder is pushed out. Then, on the intake stroke, the falling piston will try to pull air across the throttle valve.

Now, let's say that the cylinder was evacuated, and the piston drops, and the throttle plate is closed and sealed. The falling piston will generate a vacuum--and it takes energy to make that. Then, on the exhaust stroke, when the exhaust valve opens, exhaust will dump into the cylinder, and then be pushed out. And the process repeats.

Even assuming that if the above didn't happen, that sealing the throttle could be made to work, I'd be worried about deactivated intake manifold runner might fill up with exhaust from the other cylinders. And then those cylinders having issues reactivating. [But I don't think this is a possible scenario.]

With the throttle locked open, yes, there is still drag on the pumped air. How much, I don't know. 'tis probably the reason why the OEM's disable the lifters instead. I do know what my diesel, when it is coasting, has about nil for so-called compression braking.

Your going to want to disable the pump shot and fuel on a carbureted system. The 1/2 of the engine that is shut off, should gasoline be introduced into the disabled cylinders, will wash down oil and cause high wear rates.
Think about reactivation if using a carb held wide open. Your going to want to be absolutely sure it has returned to normal operation. If it's based on load, your climbing a hill, for instance. and something comes up where you have to lift suddenly to slow down, that might not happen if the carb is still locked at WOT.

CJ

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Part of Tyrde-Browne Racing

I think that adapting cylinder deactivation on a carbureted Slant would be next to imposable. GM’s engineers couldn’t get it right in the late seventies with their 8-6-4 V8 for whatever reason. Most likely slow analog computers were a big part of the problem, along with their not quite ready for primetime technology roll-out bent in those days.

So if you want to have cylinder deactivation that works well, drop in one of the new V6’s or Hemi’s that Chrysler is using across the board these days. It would be so much easer, and these engines give one twice the slant... LOl

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I think you're thinking about it wrong. Instead of making it automatically deactivate, make it manual. Most (many?) gearheads like manual transmissions, for the extra control over the vehicle. Get rid of the computer, and use the most highly evolved computer of them all for controlling the mess. What's another switch (or three) on the dash?

Without a doubt this is near-impossible. But it's not my engine. I say, go for it. Little risk to me if it fails... And wicked cool photos if it works!

I've had this as a thought experiment every once in awhile.....

Cylinder deactivation works on the spring principle with the shut down cylinders. The energy used to compress the air is regained when it expands again. Probably very close to even.


The WOT on the rear 3 (or front 3) will almost be as good and not as complicated as valve deactivation.

If you had drive by wire throttle bodies, you could open one TB all the way, and then double the opening of the other TB as a quick approximation of the extra air needed for the other half of the engine.

Or rely on the driver to give to do everything if you add a hand throttle to one of two manual TBs (to get WOT).

Any balance tube between the front and rear manifolds would have to be closed off when only running 3 cylinders.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

For normal engines, pumping losses are highest with the throttle closed (high vacuum reading) and lowest with throttle open. Valves closed and air-as-spring is best way, but hardest. Next best would be to allow the air to freely pass in-out of the TB, I believe.

Lou

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Home of Slant6-powered fun machines

Hi All,

Interesting responses - seems holding the throttle wide open is more favourable than shutting it altogether. The WOT deactivation approach rules carbs out altogether.

Wjajr - I'm mostly interested in the discussion, this is not somthing I intend to do (for experimental purposes, I'd pick an engine I can actually get hold of fairly easily - this would not be a slant here in the UK, I reckon I'd have to drop to four cylinders to make experiments worth while.) Besides, the most economical way to save fuel would be to buy 1.0l geo metro/suzuki swift for £500, but that's not what this board is about!

Supton - I only ever envisaged it being a manual operation - a lever would allow front and rear throttle banks (?!) to be operated synchronously or independently. When independent, the slave throttle(s) would be in deactivation mode, and all driving done on the master (and its cylinders). When synchronous, the throttles would operate as normal. From my point of view I'd only use the deactivation in 'cruise', I'd rather have all six on tap in town driving, might never join a roundabout if I didnt.

Emsvitil - I'm glad I'm not the only one who has thought of deactivation in a Slant. My initial thoughts on the deactivation were to hold the throttle shut and hopfully exploit the air spring principle. The throttle would seal (in a perfect world) completely shut instead of the intake valve. This would allow the compression/expansion, but using the cylinder and the manifold, rather than just the cylinder. I would expect a small loss across the inlet valve since there is a small amount of flow back and forth past it.

As Supton said earlier, the sealed throttle approach doesn't work well since the air spring effect is lost on the exhaust stroke since (reckon this could be modelled as a damping effect?). I suppose you could put slide valves in the exhaust/headers to seal it off if you really wanted to make Rube Goldberg and Heath Robinson proud.

It should be possible to approximate the potential benefits of cylinder deactivation using either method, I'll have a go at it when I feel a bit clevererer.

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1960 Plymouth Belvedere 4 door sedan

Stock 60 225

Push button 3 speed Torqueflite

Right Hooker

A long disjointed light hearted ramble of miscellaneous thoughts on reinventing the wheel before fire came along. Or, I’m pissing away a few minutes while drinking coffee before applying the third coat of joint compound to some drywall in the garage before winter sets in forever; can’t tell from here, and I’m sitting writing this:

I realize this is a theoretical exorcise, so understand that I’m coming from this having already driven a car equipped with this technology for almost five years. To say that one can just pull a leaver to activate & deactivate cylinders seams beyond primitive in anything but an engine bolted to a stand with manually applied loads at the will of a white coated lab assistant…

My car bounces between 4 & 8 cylinder operation hundreds of times in a fifty mile trip, it is almost unrespectable to most folks, but with the aid of the ‘cylinder deactivation read out’ one can train his seat of the pants to copy the readout’s results most of the time.

For deactivation to work smoothly, and unobtrusively, it must be able to switch between rather divergent power outputs under a light throttle. For example, as long as the slightest progressive throttle opening continues, all eight remain engaged, but after throttle opening has been constant or is ever so slightly closed and engine management deems car is in a ‘cruse- no load’ condition by some unknown algorithm, four cylinders are deactivated leaving almost no seat of the pants sensation of that event. That algorithm, and several others in symphony control timing, transmission shift points, injector fuel flow, the wipers speed based on density of rain drops hitting the windshield at one given moment, and perhaps, I’m not sure on this; the volume of the sound system based on anticipated road and engine noise for a given speed. What I’m saying is; that the car puts in a lot more thought and effort controlling its self, than it’s fatherless biped sitting in the driver’s seat humming along to Sixties on six beamed down 22,000 miles from space… if you get my drift here.
As one ever so slightly slowly applies more throttle opening, at some point ‘Engine Management’ decides more ponies & torque are needed, and the missing four reactivate leaving almost no seat of the pants recognition of the event. This will happen if road transitions from slight downhill grade or level travel to slight uphill grade under constant throttle opening.

When a severe elevation change is in countered, or anything other than constant throttle position is increased the missing four instantly reappear, and depending on the situation anything from a nearly imperceptible transition to one’s seat of the pants feeling a second engine was suddenly installed in the blink of an eye. This is a seamless transitioning between activate and deactivation cuts the driver completely out of the control loop other than his choosing of throttle position. It is completely mindless, takes place regardless, and there is no way to deactivate its deeds without rewiring or programing the car, however it is accomplished.

I sometimes try to see how long I can drive in four cylinder mode, and if the road were dead level flat, and thirty second small speed increases were all the was needed, such as changing from 40 mph to 43 mph the cylinders stay deactivated, but don’t reach out to tune to Seventies on seven as the slightest unintended throttle opening will activate the missing four.

I couldn’t imagine trying to synchronize this interaction between load & no load, throttle position, and grade change while driving with one hand on your girl’s knee, and the other on the deactivation lever, steering with a knee, and still having any semblance of smooth driving.
Like I said previously; perhaps Dr. Honeydew & his trained assistant Beaker could manually manipulate a laboratory stand mounted converted slant to perform deactivation, and it would be fun for a moment, but unusable without any black boxes and fuel injection once mounted in a rolling chassis.

So will this deactivation save fuel? Perhaps some savings in a controlled EPA loop, but in real world I can’t believe it saves any to a great degree except for the most patient fuel economy minded with an egg duck taped to the accelerator kind of a person. I can say this; having driven the same lightly traveled 100 miles of road to get to civilization from our old home in the boondocks for years, cruse controlled free driving always yielded better fuel economy by several mpg’s than when that device was utilized in spite of its interaction with engine management.

Disclaimer: cruse control dose keep ones Hemi powered ride generally within a speeding ticket free velocity, so a few mpg’s lost is cheap compared to fines and never ending insurance surcharges. Combusting dead dinosaurs to starve the State, and insurance biz of undeserved cash is a way of life with me.

Coffee pot is drained, now where did I leave the pole sander?

Bill

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67' Dart GT Convertible; the old Chrysler Corp.

82' LeBaron Convertible; the new Chrysler Corp

07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

That was a delightful ramble, Bill. I have no illusions that anything I would build would be undetectable or smooth.

I daily drive 60s cars/engines, one car with a 290 degree camshaft (that BTW gets 26MPG hwy and runs the quarter in 14.5) , so smoothness and niose are not the primary motive. Manual operation also seems futile to me.

Likely, I will spend my time on aerodynamics and EFI tuning, which will probably bury any effects of cylinder deact by any method, but this is fun to consider.

Lou

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Home of Slant6-powered fun machines

Much easier than deactivating cylinders is to run a high overdrive ratio to slow the engine. This increases throttle opening and decreases pumping losses.

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Joshua

Adding EGR also reduces pumping losses by reducing the engine's volumetric efficiency. EGR is disabled when manifold vacuum is low so it has minimal effect on full throttle power.