Quote:
Originally Posted by SVOboy
Have any of the large engines started using two plugs? I know honda has started doing it but I don't know about anyone else...
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The only multiple plug engines I know of are Porsche 964 (911) 3.6L - 2 per cyl, Ford 2.3 Lima or Pinto - 2 per cyl, Honda experimental lean burn - 5 per cyl. What large Honda motor are you referring to? Haven't heard of this one yet.
With 2+ plugs per cylinder it apparently helps complete the burn with increased NOx reducing EGR. The added complexity and cost of a redundant ignition system along with the use of faster, more complete burning 4 valve heads along with squishing everything into the head and the extra energy required to run the extra plugs just isn't worth it for most OEMs.
The new cats deal with NOx so maybe a large amounts of EGR is no longer necessary further reducing the requirement, not to mention more refined burning characteristics in the 2 and 3 valve heads of the newer larger engines (Ford, GM).
The Ford 2.3 netted something like 12 hp and a couple of mpg with a less efficeint flowing head (due to the second plug on the intake side). On the Porsche 911, pre 964 dual plug engine, a rule of thumb for converting to dual plug is you can raise compression one point ie 9.5:1 to 10.5:1 with the same fuel requirement. Driveability is also much improved, especially when cold, hp is up from 180 to 205 or so. They have a really disorganized swirl if you could call it that, and a highly domed piston with a large half domed shape combustion chamber, no squish area, so dual plugs are a big help to get everything lit. Modern designs with squish, small flat or sphere-like combustion chambers burn much better with a single plug right in the center of it all, good recipies for a fast burn. Fast burn means less ignition advance and less ignition advance means less pressure on the piston as it comes up during compression before pressure spikes at peak pressure. This all means more power for the fuel used.
Ok I'm done. Sorry for the disorganized ramble. Back to work...
Is Honda yet again improving the burn efficiency of thier engines, this time with dual plugs? If this nets a tangible gain, maybe other mfrs will follow?