Has anyone done testing to understand the Net difference between single and twin plug on a /4?
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.
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
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.
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. http://www.europeanmotorworks.com/
And aircraft engines are low compression, air cooled engines.
Microsquirt seems the easiest for twin plugging now that we csn run the low amp drivers.
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.
Here is a build thread of a 2.8L twin plug
http://www.shoptalkforums.com/viewtopic.php?f=1&t=145699&p=1200260&hilit=twin+plug#p1200260
Sounds like one more place for the heads to crack for not much gain.
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.
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
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.
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
..My car was in Volkswagen Porsche way back in the eighties ...one of first twin plug type 4's RPM in Daytona did it...
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.
So perhaps Im incorrect, but I get the sense that many think this mod is a waste of time? OR is it that what might be gained doesn't justify the cost?
So anyone who has BTDT willing to offer what EMW, Len (when he was willing to do this work) or FAT charged to twin plug a set of heads ?
A related but important question is, along with simply drilling for the plugs, was that the extent of the service? Or is there always a degree of unshrouding /porting that makes the application viable?
Not worth it IMHO, only good place to put the plugs will need modified exhaust stubs.
Spent the coin on good 2.0 head work, stroker crank, rods and/or nickies. 2270 iron jug makes a nice street engine.
But then if it's a pro built engine you're quickly getting into /6 conversion cost territory.
I've done it on a few /6 engines now, different chamber, 4/6 chain box even has the cast rough-in to seal the plug. Lets you run a full point higher compression. Only worth doing with higher CR pistons, cams and carbs, MFI or PEFI.
Bring money.
Aero-VW airplane engines use the second plug as a redundant back up fail safe. Not for performance. They use a magneto for ignition.
Attached image(s)
That chamber shape looks somewhat different than ours, too...
--DD
Hello, I've been running a twinplug 2.8-4 for a few years now, it was a process to
put together , I went from 48 dell carbs & unilite distributor @ 9-1 c.r. & smaller cam, to
MS2extra (megasquirt2extra) with sequential injection & ignition 11-1 c.r. & bigger cam
(320* dur. ) with twinplugs , I've never dyno'ed this motor so I don't know if it makes
more HP , I kinda doubt it , it does give me more torque , which really helps my bottomend with the cam I run,
it runs COOLER , uses less timing ,no more pinging, single plug version I used to run as much as 32* timing =
heat & pinging, I even tried W.I.
(water injection) to much hassle not worth the return, so next option was twinplug ,
Bill D.
sorry I never finished this thread,
Bill's 2.8 -4 Twin Plug Thread, 48x38 twin plug conversion
http://www.914world.com/bbs2/index.php?showtopic=225696&st=0
comment by jake ;
What you'll find with twin plugs isn't so much more WOT power on the dyno and bigger numbers, but
mostly insane throttle response and unreal torque gains below 4K RPM, especially with the larger bore size
that needs all the help with flame propagation that it can get.
Aha, great to hear from some one that’s been there done that. Thanks Bill.
The comments are right in line with what you see in the aircraft world where your engine is fairly well instrumented - a CHT and an EGT on each cylinder and the ability to turn one set of plugs on or off. Twin plugging enables less advanced timing while still getting complete burn, less advance means lower combustion peak pressures, lower peak pressures mean lower CHT’s and more torque ( the piston is not fighting an early combustion event while still traveling up towards TDC) and there is better combustion even in the shorter time available because of the two flame fronts.
How much better will certainly depend on lots of variables, but the more compression and the bigger the chamber the more advantage to be gained.
Worth it on a small, low compression four?? Dunno but More worth it on a bigger high compression motor, just as Bill found out.
BTW, awesome build thread linked and very informative info from Jake, that guy knows his shit! Miss him around here
Twin plugs allows the mixture to burn quicker which must be accompanied by timing retard (closer to TDC). Twin plug also permits higher compression ratio. Higher compression can equal more HP.
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