Twin plug /4, ROI? Options

[914work]

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?

[Mark Henry]

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.

[pete000]

Aero-VW airplane engines use the second plug as a redundant back up fail safe. Not for performance. They use a magneto for ignition.

[Dave_Darling]

That chamber shape looks somewhat different than ours, too...

--DD

[Mark Henry]

That chamber shape looks somewhat different than ours, too...

--DD

Stock chamber...Type 1 heads (IMG:style_emoticons/default/wink.gif)
That method you run the plug through the valve cover.

[Bills914-4]

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 (IMG:style_emoticons/default/smile.gif) , 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 (IMG:style_emoticons/default/smile.gif) ,
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?sho...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.

[gereed75]

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

[gothspeed]

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.