Twin plug /4, ROI? Options

[r_towle]

Has anyone done testing to understand the Net difference between single and twin plug on a /4?

[mepstein]

A twin plug doesn't make power in it's self. It's mostly done on sixes to run higher compression. So it would be hard to compare apples to apples if the engines don't have the same compression ratio.

[ablesnead]

I had one of the first ones years ago ....used a datsun pickup distributor..the engine idled a lot smoother..sounded a lot different ....could not tell any power increase

[Mueller]

Good question, i know on aircraft engines you can hear the difference when disabling one set when testing the magnetos while the motor is rumning.

There is a thread place where Jake made some comments about timing and such.

[Elliot Cannon]

These guys rebuilt my heads for me. They can convert to twin plug if you want. I think they told me you can use a Nissan or Datsun distributor. Not sure which one. I'm also not sure if the expense would be worth it. (IMG:style_emoticons/default/biggrin.gif) http://www.europeanmotorworks.com/

[buz914]

And aircraft engines are low compression, air cooled engines.

Good question, i know on aircraft engines you can hear the difference when disabling one set when testing the magnetos while the motor is rumning.

There is a thread place where Jake made some comments about timing and such.

[Mueller]

Microsquirt seems the easiest for twin plugging now that we csn run the low amp drivers.

[Mueller]

And aircraft engines are low compression, air cooled engines.

Good question, i know on aircraft engines you can hear the difference when disabling one set when testing the magnetos while the motor is rumning.

There is a thread place where Jake made some comments about timing and such.

More of a safety feature from what I remember, nice to have some redundancy way up there.

[gms]

The 914/4 combustion chamber is a modified wedge style design which compressions (squashes) the air-fuel mixture toward the spark plug. Adding a second plug may have some advantage but not as much as the 911s hemispheric combustion chamber which benefits from 2 points of ignition.

There was a local guy who did the twin plug 914/4 heads back in the ‘90s his name was Morrison and he was in Aurora IL.

[peteyd]

Here is a build thread of a 2.8L twin plug

http://www.shoptalkforums.com/viewtopic.ph...n+plug#p1200260

[Krieger]

Sounds like one more place for the heads to crack for not much gain.

[gereed75]

Agree with Glenn. The 911 benefits because of combustion chamber shape and typical high domes in higher compression builds. Allows for better timing with a more efficient burn on both “sides” of the chamber.

Not sure the same benefits will happen in a 4 cylinder.

Used in aircraft engines for redundancy and also because the combustion chamber is large (360 cubic inch four banger). The second plug yields a faster and more complete fuel burn by starting two flame fronts.

Again not sure that will benefit a smaller four in the same way.

No testing, just anecdotal, but with dubious benefit probably the reason no testing (and relatively few applications) have been done.

[peteyd]

I have always been interested in a twin plugged engine. I have done quite a bit of research and it seems that the consensus is that only "big engines" like 2.3L or greater benefit from twin plug. At least this is what one engine builder says. But sometimes I feel like he may say things just to dissuade us from doing them.

I was also interested in roller lifters, and he was very discouraging for people to head down that road as well.

Pete

[914work]

The 914/4 combustion chamber is a modified wedge style design which compresses (squashes) the air-fuel mixture toward the [existing] spark plug. Adding a second plug may have some advantage but not as much as the 911's hemispheric combustion chamber which benefits from 2 points of ignition.

This is where a skilled welder/machinist a flow bench, a mule motor & significant time would prove beneficial.
The ROI...well Im sure that is purely subjective.
The old joke/riddle: "How do you make a small fortune?" comes to mind.

The vendor to which Peteyd refers claims to have "built" multiple permutations until finding the best combination of mods.
I think that Len's contributions cant be understated here. (IMG:style_emoticons/default/sunglasses.gif)

[horizontally-opposed]

European Car (RIP), maybe when it was still VW&Porsche, magazine did a story on a black 914 with chrome five-lug Fuchs, the "PORSCHE" side valances, and...a twin-plug Type IV engine—noting it ran noticeably smoother and sounded better with dual ignition. Same car may have been supercharged at some point?

I believe it popped up for sale recently, now with six cylinders. Not sure what to take from that, if anything.

[914work]

European Car (RIP), maybe when it was still VW&Porsche, magazine did a story on a black 914 with chrome five-lug Fuchs, the "PORSCHE" side valances, and...a twin-plug Type IV engine—noting it ran noticeably smoother and sounded better with dual ignition. Same car may have been supercharged at some point?

I have that issue somewhere. (IMG:style_emoticons/default/smile.gif)

You gotta go back to the motivations for modding the base motor to begin with.
Goals: more performance, smother running, alternate exhaust dynamic... retention of *quasi* stock configuration
How much is that worth~ ?
Sure you can yank it & Six it.
Some folks just like to do it the ..unconventional way

[r_towle]

So, lots of cool responses.
I am curious if twin plug, large displacement enables slightly more HP, and a better more efficient motor. I think these motors were something like 35% efficient.
Certainly a less costly road to travel versus a /6

[ablesnead]

..My car was in Volkswagen Porsche way back in the eighties ...one of first twin plug type 4's RPM in Daytona did it...

[Chris914n6]

The dizzy cap is from an 80s Datsun 720 pickup with the z24 engine.

I don't think it's worth the expense with the fuel/spark options we have today.

[jd74914]

So, lots of cool responses.
I am curious if twin plug, large displacement enables slightly more HP, and a better more efficient motor. I think these motors were something like 35% efficient.
Certainly a less costly road to travel versus a /6

Not sure how much you would gain (perhaps a percentage or two max I bet). I think you might end up using the second plug to compensate for the decrease in efficiency with a much larger chamber? They definitely aren't 35% efficient. That's F1 efficiency territory (no KERS), and higher end than pretty much any production cars.