My brother bought a '06 hemi ram and I noticed it has 16 spark plugs in it was wondering why. THANKS!

helps it pass emission standards, newer 4.7's have them as well

Thanks a lot. Appreciated

They've been doing it for years. Nissan 2.4L had it in the 80s. My impression is they need the burn time of the mixture to be as fast as possible while still being a controlled burn, so they make sure the mixture is squished and moved during hte last few degrees of the compression stroke, then they light it from opposite ends so it takes 1/2 the time with less loss of efficiency.

The way I heard it was one plug was firing to light the mix and the other fires during the exhaust stroke to clean it up for emissions...?

Don't know the science behind it, but it makes a big difference. Light aircraft engines are mostly horzontal opposed "flat" fours and sixes, most designs dating back to the late 30's. They mostly use dual magnetos and dual sparkplugs. A pretakeoff check is to check the ignitions one at a time, looking for excessive RPM drop when going from single igntion to dual igniton, indicating a fouled plug or worse. Once was taking off one morning from a gravel bar alongside a river in Alaska. No good place to do a power runup, so just did a rough mag check while taxiing. Real slow takeoff and acceleration, had to turn upriver and not doing so good. Was running on one mag. Improved considerably when I switched the other mag in. Work swiftly; not hastily! My $0.02

Airplanes require two independantly powered ignition systems for safety reasons, nothing more. If your plane ran better when you switched the other mag in then your first mag setup has problems. Not that mags are all that great an ignition system.

The second is a "wasted spark". It fires 1/2 degree after the primary.

I know in rotary engines, since the combustion chamber is fairly long and flat, it would take too long for the fire from one plug to fill/burn the entire chamber, so they have two plugs to speed up the burn.

Could be something similar with the Hemi's? Either way, there's probably a list of benefits of using two plugs

The Nissan (Datsun back then) called their's the NapZ. It was a DOHC Hemi IIRC.

Thanks everyone

technically,
the dual sparkplugs allow less ignition timing before top dead center,
which reduces the 'wrong direction' pressure on the piston (called 'negative work')
and leads to slightly better torque and less fuel consumption

in one of the Chrysler histories there was an account of how Chrysler and Daimler engineers got together after the merger and shared previously confidential twin sparkplug research... and both sides admitted that they learned some new effects they had not known before

the gains are real but not large, in the 1 to 3% range

by the way,
the Datsun NapZ was inspired by the original Chrysler Hemi,
then in a turn around,
the NapZ good emissions performance as published in a SAE paper was used to argue successfully for the modern 5.7 Hemi V8

My 1971 250cc single cylinder 2 stroke CZ motocross motor cycle had two plugs per cylinder and two coils.

Wow, that's quite a mixed bag of responses.

Anyone want to take a guess what the power difference is between waste spark and firing both plugs in all 8 at the same time, on an otherwise stock 5.7?

6.7 jigawatts?

Hey DZ, you also have 2 plugs/mags a cylinder in ur prop so you dont foul a plug and lose the engine since you are usually taking off and landing with full rich (unless high elevation). I am sure when you've done your run ups before you ran into a semi fouled plug, then had to run up and lean the mixture, let run for a little till it cleaned up, then did your mag checks again. Now if only cars could have that leaning knob to coax a few more miles a gallon.

Mark

3hp advantage for waste spark vs firing both at the same time. This is a real, measured number not theoretical.