Twin plug, Question Options

[r_towle]

I have read a bunch of threads and a few valid studies, but few demonstrate results with a focus on better gas mileage when moving from a single spark plug to dual plugs.

In this application, on an otherwise stock 3.0 liter 6, wouldn’t a more efficient burn and combustion result in better fuel economy?

I keep seeing more CR, better torque, less advance, all great things.

But…what if the goal is better mpg?
Is twin plug and modern EFI the path forward?
Assume modern ignition also.

Rich

[technicalninja]

The "goal" has ONLY been mileage and decreased emissions for my entire life!

The fact that making engines convert fuel more economically with fewer emissions WAS the path to higher power was just a handy byproduct...

In fact, it was handy enough that it's being put to further fuel economy today.

Engine sizes are dropping faster than they ever have before...

Smaller displacement means less fuel consumption.

Many cars are available now with 1200 CC turbo 3 cylinders (which I HATE) and they have MORE power than an early 21st century 2.0l NA engine.

When they are in cruise mode this engine probably doubles the economy of the 2004 2L.

It's always been about CAFE and EPA...

Dual plugs help most on a bore size nearing 4" as keeping the flame travel distance under 2" seems to be a limit.
Halving the distance the flame front needs to travel (on any bore size) allows for reduced timing (this is GOOD) and provides further resistance to detonation.
This can lead to increasing compression ratio and improving efficiencies...

An ignition "scenario" that has been on the forefront is what they call "surface discharge" and has no plugs. I'm not well versed enough in this (hasn't come out on anything I'm aware of yet) to be "technical" enough to properly describe it.

I know it exists and it may be a far better way to ignite the charge.

[mepstein]

Production cars - fuel economy like was said above
Hot rod Porsche engine built in the shop or your garage - more power due to high compression, timing, etc.

Fuel economy is all about getting from A to B for less money. That not usually the top concern when driving an air cooled Porsche.

Same with adding a turbo to an air cooled engine.

[East coaster]

Apples to cantaloupes, but on my aircraft I see a 300 rpm drop when switching from dual ign to single. This is with the same throttle setting and load, so I would assume I’m losing a 300 rpm efficiency (and power) with single ign. And a 300 rpm drop is expected result (spec).

[VaccaRabite]

Apples to cantaloupes, but on my aircraft I see a 300 rpm drop when switching from dual ign to single. This is with the same throttle setting and load, so I would assume I’m losing a 300 rpm efficiency (and power) with single ign. And a 300 rpm drop is expected result (spec).

Perhaps off topic, but why would you want to go from dual ignition to single ignition on an aircraft? Especially if it reduces your efficiency while doing so? Is the added electric load running 2 plugs instead of one an issue? Or an air density issue?

Zach

[toolguy]

I was always amazed when doing the pre-flight check of the Mags before takeoff. . turning the mag off and running on just one. . beside the explicit drop in RPM, there was the exaggerated roughness of the motor. . . sort of on the level of pulling off a plug wire on a car engine in comparison. . .

[914Toy]

(IMG:style_emoticons/default/popcorn[1].gif) (IMG:style_emoticons/default/popcorn[1].gif)

[Mikey914]

I was always amazed when doing the pre-flight check of the Mags before takeoff. . turning the mag off and running on just one. . beside the explicit drop in RPM, there was the exaggerated roughness of the motor. . . sort of on the level of pulling off a plug wire on a car engine in comparison. . .

yes a 10-15% drop in RPM immediately. Loose a system in midair and that will wake you up, even if it's only one plug!

[Arkady]

Thirty + years ago, I bought a 1961 Chevy Bel Air with a 283 cu. in. V8 and a cast iron Power Glide automatic transmission for $200. I found it in a barn in Brookneal, Virginia. Its transmission had 'Drive', but no 'Low' or 'Reverse', so I couldn't make any mistakes on the way home. I bought a transmission rebuild kit, (bands, clutches & seals) for about $50, a reprinted '61 Chevy shop manual for $19 from a company in Blairsville, PA (Crank 'n Hope) and a modulator for under $20. This was my first transmission rebuild, but with the help of a really well-written manual, it went smoothly. (Manual writers could learn a lot from looking at the 'old' shop manuals...)

Now, to get more on-topic. This Bel Air got about 14 miles per gallon once I had it road worthy. Even back then, this fuel efficiency was unacceptable. So, I rebuilt the Rochester 2-barrel carburetor and installed an MSD (multiple spark discharge) ignition box. (https://www.holley.com/brands/msd/) These units provide several sparks for each power stroke. At the time, these were used mainly on race & hot rod engines. Between the carburetor rebuild and the MSD box, the Bel Air mileage went up to 22 MPG. At the time, I recall the MSD box cost me about $30. They are still available today (see the web site), and likely are an economical way to boost MPG. I confess, I've never tried one on an air-cooled engine, but I suspect it would perform well here too. On air-cooled engines though, I defer to those here with much more experience than me...

I like the dual spark plug option for the reasons mentioned, but have no idea what that modification would cost. Though I too question why, if you already have the dual-plug stuff, why you'd change it out.

Oh, I forgot that I had a custom dual exhaust system installed by a muffler shop guy that owed me a favor. Man, did that make it sound sweet with its low rumble. My Dad loved that car...

[ctc911ctc]

I thought you only fly Kerosene burners!

(IMG:style_emoticons/default/smile.gif)

I was always amazed when doing the pre-flight check of the Mags before takeoff. . turning the mag off and running on just one. . beside the explicit drop in RPM, there was the exaggerated roughness of the motor. . . sort of on the level of pulling off a plug wire on a car engine in comparison. . .

yes a 10-15% drop in RPM immediately. Loose a system in midair and that will wake you up, even if it's only one plug!