Topic: Need sparkplug info cb550 NGK R DPR8EA-9

[ajracer]

I'm in the process of putting my 1974 cb550 back together with Dyna S coils and ignition that came with the bike. The guy I bought it from was running the standard plugs with resistor caps and the dyna setup. The last plug I was running before I took it apart and is back in it now is a NGK R DPR8EA-9. I assembled with new Dyna wires and left the resistor caps out. Is this right? Can anyone tell me if these are resistor plugs or how I would find out and also if this is the right plug for my bike. It seemed to run ok before i tore it down but had less power then the standard plug.

[Sam Green Racing]

AJ, this should be in the tech forum, I'll leave it here for a while to see if any of the guys can help before moving it.

Sam.

[Bill/BentON Racing]

Let's see,it is a resistor plug,D-12mm,P-projected nose,R-resistor,8-heat range,EA-3/4 reach,9-gap,it's good to have some resistance.Check the forum articles Sam mentioned.Good Luck,Bill,CB500/550's called for D7ES,78K D7EA.

[ajracer]

thanks for the reply. so is it the higher the number in the heat range the colder the plug? and also is there a way to find out how much resistance a plug has? I looked on the ngk web site and it looks like the resistor caps that came with the orional bike were 50 ohms. Is there a certain resistance the Dyna system likes to run at?

[mlinder]

d7ea's or dr7ea's should prolly be used. I would just go with d7ea's.

And yes, the higher the number, the colder the plug.

I ran dyna s with no resistor caps, copper wires, with stock d8ea's (750).
Worked great.


Moving topic now.

/edit: er, sam moved it while I was typing this.

[TwoTired]

Colder plugs are really only needed if flogging the engine long and hard in hot weather.  D8's will make the bike so cold blooded you can hardly ride it until completely warmed up.  There is no need for colder heat range on the stock motor.  I would think extended nose plugs might run some risk of hitting the piston crown.

You do want some resistance in the spark plug circuit.  Resistance wire, plug caps or plugs.  The stock plug caps for the 74 CB550 were 10K ohms, with 5k showing up sometimes.  The 750 used 5K plug caps, slightly different coils.

You can measure the plugs for resistance with an ohm meter.  Measure from center electrode tip to where the wire attaches.

I thought the Dyna wires were suppression wires with internal resistance.  The last ones I saw were, anyway.  If so, you don't want resistor plug caps or resistor plugs using those.  If your wires have metal core, you want either resistor plugs or plug caps, not both.  Some resistance in circuit will improve the spark and extend spark plug life.  It will spark if there is resistance or not, though.

You didn't mention much about your coils.  If they have 3 ohm primaries, you will probably have battery charging issues, as they draw more power than the stock 5 ohm coils do.  At idle, the battery will discharge faster.  When above 2500 or so, the battery will recharge slower.  When the battery voltage goes low enough, no more spark!
It helps if you don't run any lighting.  The 550 charging system is only 150 watts and then only at around 5000 RPM.

[ajracer]

wow, good info. I haven't had any problems with piston contacting the plug though maybe if I had the head decked. They are about 1mm longer. I have the green 3 ohm coils. Now that I think about it there was a little bit of a battery issue and I just had my crank and rotor lightened too. Hope it still charges enough.

[mlinder]

If there are issues, going back to 5ohm coils is an easy fix
Or, get hondamans resistor pack for dyna coils.

[ajracer]

what is a resistor pack and how do I get one?

[mlinder]

Contact Mark Paris (forum name is hondaman).

It's jsut a little box that brings your coils up to 4ohm so that there is less drain on the battery.

[ajracer]

so is it the lower the ohms the more the coil draws? does a lower ohm coil make a hotter spark? also is there a way to boost the charging system?

[TwoTired]

A direct short draws infinite power from a fixed power source.  This is the lowest resistance attainable.  Raise the resistance and less power is drawn.  I=ExR , P=IxR ; These are the standard electrical equations that define DC circuits.

The coils make an output voltage based on a turns ratio for multiplying the input voltage.  Primary turns of wire vs secondary turns wire.  The more turns of wire in either of the windings, the more resistance.  Reducing the primary turns, makes for a higher turns ratio.  But, the resistance gets lower, too, drawing more power.
You don't get something for nothing.

Yes, there is a way to boost the charging system.  Replace the stator, rotor, and field coil with a different design.  How much would you like to invest in that research and development?  How much do you want to spend on replacement parts?

[ajracer]

yah nothings free. I was looking at a stator and rotor on ebay for a newer cbr600 and I was thinking it could be adapted. but yes more time and money. If there turns out to be a problem I will probably just get the resistor pack. Thanks for all the great info. I don't know to much about electrical but I like learning about it.