V-Twin 2 and 4 plugs

[psychocycle]

OK, looking for gear-head feedback. Got into a discussion with a buddy of mine the other day why a V-Twin (Nomad) needs 4 spark plugs. A normal consideration would be one plug per valve, why does our bikes (and some other metric bikes) have 4 plugs, while all new Harley's and some metrics have only the 2 plugs? ??? This has been bugging me and I don't know the answer....do you?

Thanks in advance for your input!

[ringadingh]

We have two plugs per cylinder because of the head design, one plug is not sufficient enough to give the fuel charge a proper burn. This is because of the way the valves are positioned in the head.

[dennis49]

Originally Posted by Ringadingh

We have two plugs per cylinder because of the head design, one plug is not sufficient enough to give the fuel charge a proper burn. This is because of the way the valves are positioned in the head.

shoulda bought a Hemi.

[GIBBY]

A Nomad with a 5.7L Hemi.....now that's and idea.
More Power!!!

[reaper]

Originally Posted by Gibby

A Nomad with a 5.7L Hemi.....now that's and idea.
More Power!!!

No that would "Mopar" :)

[dennis49]

I saw a bike today at the Tommy Frank annual motorcycle rally that had a BIG Block Chevy with pipes no longer than most Harleys sounded loud but good. It looked good except for the large gas tank, it looked to be probably 10 gallons or more, very odd to say the least. Rear tire was a very low profile car tire and the frame was, well the best I can discribe it is Huge. There were no highway pegs on this rig.

[ve3hzz]

Originally Posted by dennis49

I saw a bike today at the Tommy Frank annual motorcycle rally that had a BIG Block Chevy with pipes no longer than most Harleys sounded loud but good. It looked good except for the large gas tank, it looked to be probably 10 gallons or more, very odd to say the least. Rear tire was a very low profile car tire and the frame was, well the best I can discribe it is Huge. There were no highway pegs on this rig.

Sounds like you saw a BOSS HOSS and yes they are a production bike and YES they have a small block 350 that you ride. Apparently they don't ride that bad...well OK for what it is....just don't do any mall parking lot maneuvers with it.

As for the 2 spark plugs per cylinder, Steve has it right that it is for efficiency in many cases due to cylinder head configurations. But not always. Some bikes use it as the wasted spark using 2 coils can be used to burn the fuel mixture more cleanly and therefore reduce emissions as well. also for some the explosions happen at the same time per cylinder and the wave from the outside inward from both sides caused the wave to meet in the middle of the piston (or close to it) which helps with the downward force on the top of the piston on the power stroke. There is also a 2nd spark which occurs on the exhaust I think as well which helps to burn any left over hydrocarbons and this helps with reduction in some pollutants.
This is what was explained to me by a long time bike mechanic, and some of the engineering in these engines. Some of it maybe propaganda and some of it is likely fact....

[dennis49]

Sounds like you saw a BOSS HOSS and yes they are a production bike and YES they have a small block 350 that you ride. Apparently they don't ride that bad...well OK for what it is....just don't do any mall parking lot maneuvers with it.
[/quote]

This bike had a Big block in it not a small block. I wouldn't have posted about a Boss Hoss, everyone has seen one of them, this is the first Big block I have seen on two wheels. The guy riding this had no problems going slow he pulled it up slow turned feet up before putting feet down to back it to the curb. He must have many miles on it.

[MAS Tequila]

BOSS HOSS has been selling 501 versions of their bikes for several years now. The first time I saw one was in 2007. It was a 501 with nitrous on the showroom floor. They had bikes as well as trikes with that set up.

MT

[blowndodge]

twin spark plugs end up being used on engines who's head design and valve angle are poorly designed. Twin plugs allow a more complete burn because of this design...

show me a big bore diameter engine that runs two plugs and it will be a low power engine.

Nomads are over square meaning the bore is larger than the stroke of the motor. Our bore diameters are the same as a 110 cu in Screamin' Eagle.

Technically our Nomads could have easily been set up to run like a M109 Suk.... big bore shorter stroke more RPM's.

After seening all the low RPM strong torquing V-Twins out there I'm at a loss why the Nomad is a big bore V-twin...

[snarleybill08]

Originally Posted by Blowndodge "Darksider"

twin spark plugs end up being used on engines who's head design and valve angle are poorly designed. Twin plugs allow a more complete burn because of this design...

show me a big bore diameter engine that runs two plugs and it will be a low power engine.

Nomads are over square meaning the bore is larger than the stroke of the motor. Our bore diameters are the same as a 110 cu in Screamin' Eagle.

Technically our Nomads could have easily been set up to run like a M109 Suk.... big bore shorter stroke more RPM's.

After seening all the low RPM strong torquing V-Twins out there I'm at a loss why the Nomad is a big bore V-twin...

i have to agree on this dual plugs make up for a design deficiency in the heads. they make up for a very slow burn.

[MAS Tequila]

Look at one of the heads from the bottom and you will see that the ideal place for the plug would be dead center, like a hemi.

How would you change it?

MT

[dennis49]

Originally Posted by MAS Tequila

Look at one of the heads from the bottom and you will see that the ideal place for the plug would be dead center, like a hemi.

How would you change it?

MT

Better question to ask is how would you change the spark plugs.

[blowndodge]

Spark plug placement is not the issue .... It's the piston crown design as it relates to valve angle and the shape of the heads thats at issue. Triump'sh 1600 thunderbird parallel twin has more compression than the Nomad because they have the proper shaped heads, and stroke for the type of power it makes...and runs on regular gas...

[Netnorske]

Originally Posted by dennis49

shoulda bought a Hemi.

I watched a show last week where they were restoring a 1950's single cylinder Matchless Motorcycle for a guy. When they took it apart, they found it had a hemisherical piston that provided a lot of power....ala Mopar! Wonder why today's designs don't incorporate that feature?