What are the benefits and problems(in any) of the two spark plugs per cyclinder in the M8 engine? Does dual plugs make everything more complicated and thus likely to cause problems over the long run? Does it create more heat or less heat? Are the two plugs fired at the same time or does each plug have its own timing table? Any more thoughts on this would be helpful.

 

I wouldnt over think it. The M8 is a great engine, lots of low end torque without the need for a stage 1. Your car has even more spark plugs, I hope you're not worrying about that.

 

I think you need to remove the fuel tank on a M8 to replace all four plugs.

 

Ok, thats it. I'm selling mine.

 

You have to at least raise it a good way. Dual plugging been around for decades, used to be a popular mod for pumped up harleys. Been running duals on my 88" and bigger shovels 25 plus years. Lot of conversations both sides of the are they worth it debate. My personal experience is while not a noticeable performance enhancer, my bike starts easier and with a kicker this is a biggy, plugs last longer and stay cleaner and throttle response is a bit crisper, doesn't care what gas you feed it and since you now have some wiggle room you can play with retarding the timing a bit which kills detonation knock, bear in mind this has been my shovelheads.

Plugs in each cylinder fire at the same time but you can set it up for single fire per hole , meaning front & rear will fire separately. On the M8's I'm not sure how they have the ignition setup, haven't looked yet. I can't see a downside to it aside from costs if anything goes bad and the hassle changing them.

 

dual plugs especially on a big cylinder can reduce detonation as you have better combustion and less unburned fuel pockets. small airplane engines have 2 magnetos and 2 plugs per cyl. when you cut off 1 of the mags, rpm will drop off anywhere from 30 to 50 rpm.

 

 

when they went to 4 valves per cylinder in the M8, they had to reduce the "squish" area of the combustion chamber. the squish zone is the flat part of the cylinder head surface which comes very close to the piston crown as it approaches top dead center (TDC):



when the piston approaches TDC, it "squishes" out the air:fuel mixture from that zone creating a ton of turbulence in the chamber which improves mixing, prevents detonation, and promotes uniform burn of the air:fuel mixture. the less squish you have, the less turbulence you have and your ignition reliability and detonation resistance goes down. Here's a Twin Cam "bathtub" chamber:



those flats at the top and bottom are the squish areas of the chamber. here's an M8 "pentroof" chamber:



see how much smaller the squish area is?

and this is nothing new, Harleys used to be hemi chambered, which are absolutely the worst for ignition reliability and detonation resistance because they have no squish whatsoever. The modern (5.7/6.1/6.4) Chrysler Hemi is not a true hemi yet it still needs two plugs per cylinder.

 

2 spark plugs to a cylinder means more efficient fuel usage.