8 - Plug Head advice

[Pigford]

Whats the best way of arranging the coils

Is it: 1 x coil per cylinder or do you split HT lead from each coil to different cylinders?

I'd have thought the first option is best, so if a coil goes down you'd have more chance of detecting it

Also, how about wiring them in - do you just double up from the low tension supply to each pair Diagrams would be good

[kev edwards]

Only way i have seen it is one coil per cylinder, the 1100 zephyrs are the same.

[Pigford]

Cheers Kev, sounds logical to me

[zed1015]

You need two pair of 1.5ohm coils ( the orangey/brown ones if using DYNAS).
Wire each pair in series, you only need to add a link wire between each pair so no alteration to existing harness.

It is preferable to share each coil to each pair of cylinders.

See diagram below (do the same for cyl's 2 'n' 3)

[Pigford]

OK Rob, cheers

Best put out the feelers for some 1.5 ohm Dyna coils

[Robw]

The 1.5v coil method is the one I used. I linked the coils using the wiring diagram and everything works a treat. Also I got the coils from Joe Hooper as they were by far the cheapest even with import tax etc.

Cheers Rob

[j.wilson]

If a plug gets fouled then the other plug on that coil will fail to spark too.
Its a question of whether you want this to cause a problem or not- ie easily "detectable".
My problem was that the 4 plug set up did not provide very good sparks till i changed the EFI settings.

Use one of these to check spark power.

[neilbarrett]

got 6v coils on mine,

[Pigford]

got 6v coils on mine,

Ahhhhhhhhhhh - can wire in series then - errr, or parallel even

[alan bauly]

Hi Mark, The way that Rob (zed1015) has described and shown wiring diagrams for is exactly the same as mine, ie; the way Debbens do it.

And yes, if a plug does foul it's instantly noticable. but i'd rather have that than not knowing so that you can investigate the cause.

Good luck

[garyd]

Remind me please...it's been bothering me all day...was it Minstral Eng who used to do the 8 plug conversion.?

ta

[KWACKERZ1]

I think Mistral did but its not exclusive,

Jim wells race motors had 8 plugs,

P+M Did some and numerous drag racers.

It was a fairly common way of getting a good spark, my question would be it it really useful and noticeable, unless you run AVGAS, RACE fuel or similiar.

Surely these days with crap fuel, and we have better ignitions dyna+coils an 8-plug head is for pose value only?

Be interested in peoples views and any proven dyno figures to understand if its worth the investment?

[zed1015]

Lots of advantages depending on application.
Easier starting.
lower cylinder temp's.
Reduces or eliminates detonation on high comp or forced induction motors and helps combat the same on any engine as a result of todays low octane piss poor fuel (common mod on BMW'S and Hardleys)
High domed pistons mask the flame front on single plug motors and as a result a full burn is not achieved and unburnt fuel goes out the pipe, this equals loss of potential power, lower mpg, etc,
twin plug will ignite the fuel on both sides of the piston dome for a full burn = more potential power achieved, more mpg,
Same with big bore motors, flame front can't travel the distance fast enough on single spark (especially at higher rpm's) for a full burn before exhaust cycle starts so again fuel goes out the pipe, lower mpg, loss of potential power etc etc.
List goes on.

Oh! and it looks good too

[KWACKERZ1]

1015 Ok I am convinced! I could always see the advantage on blown and race motors just not for the road.

But your argument has convinced me!

Now then where's my drill and sparkplug tap!!

[j.wilson]

In my experience road bikes are much more difficult to set up than a race bike with a sole purpose, for example my bike pinked when it was 1170 and 1395.

Always the same issue, 4000 rpm or so, when the ignition advances.

To get the best performance from the motor requires an adequate ignition system- strong sparks, more than one, and good control over advance curve.

Fixed stuff (things you do once) like compression ratio, squish clearance, sharp edges on piston crowns and cam type/timing will have an effect on detonation, as will number of plugs.

Lastly there's the adjustable stuff ....fuel and spark.

Clearly there is a trade-off between pinking and making the bike perform well. As volumetric efficiency goes up and bmep (Brake Mean Effective Pressure) peaks the engine will be susceptible to pinking- this happens at around 4000rpm- there is time for the cylinders to fill their best.

Everything you can do to help the situation is important- personally I go for twin plug head, FI, and programmable ignition timing, after all you spend a lot of time at 4000rpm.

My bike does not pink now and is very crisp through 4000rpm.

I junked my original set-up (fixed timing and a cdi box) and fitted the mechanical advance and dyna ignition, this gave a better spark and I fiddled with the mechanical advance to slow its rate to full advance by 500 rpm- it worked to a degree but it was a crude solution (not very controllable, nor was it throttle dependent).
I think making a good road bike is more difficult than a satisfactory race bike- it’s the transients that are difficult to get perfect.

Everything to make the bike run nice helps.