spark plugs

#1
Ive got a v8 p6 auto 1974 ( low compression engine) fitted at present with champion plugs, and after reading various threads on here and else where i am thinking of changing no NKG.

question is which ones would be more suited BP6HS or BP5HS i have seen both advertised,

advise would be great

many thanks Steve
 

SydneyRoverP6B

Well-Known Member
Staff member
#5
Thanks, but its the fact that its a low compression engine 9.25 cr that has got me thinking.
Hi Steve,
Your engine is not strictly low compression, but in terms of plugs, I am aware that the NGK plugs are preferred by many over the Champion plugs for that compression ratio.
Ron.
 
#6
Thanks Ron, that is what i have read, but im still not sure as to which are the best BP6HS or the 5, is there much difference?

regards Steve
 

SydneyRoverP6B

Well-Known Member
Staff member
#7
Thanks Ron, that is what i have read, but im still not sure as to which are the best BP6HS or the 5, is there much difference?

regards Steve
Pleasure Steve! The NGK plugs that owners typically use in the 9.25:1 engine are the BPR5HS, not the 6. Personally I have never used NGK plugs, but then I have never owned an engine with that CR. I do know that owners that have used them with your Rover's CR are happy with the results. :)
The BPR5HS is the NGK replacement for Champion L92YC plugs, so this is the type that you need.

Ron.
 

clive P62

Active Member
#8
Been using NGK BP5HS plugs in my P6s for 40 odd years, never had an issue with them unlike Champion which must have had bad runs in production, at the garage I worked at we had cars coming back after a week or so with misfiring after servicing hence we used NGK from then on.
 

cobraboy

Well-Known Member
#9
Please note BPR5HS are a resistor plug, The R is the designation for resistor. If you use a resistor plug in conjunction with a resistor lead, ie a silicon lead then you will compromise spark quality.
likewise, if you use a resistor plug, resistor lead and resistor plug cap then you will all but snuff out the spark.

I was reminded of this only last week at work when we has a misfiring car that had all three, the spark at the plug was miserable, when in the cylinder under compression it would have been non existant. Removing the resistor plug cap visibly improved the spark, swapping the plug for a non R plug again improved the spark.
The answer if you run silicon leads is to use a plain cap, and non R plugs.
 

quattro

Administrator
Staff member
#10
During my recent engine rebuild I noticed that I had resistor plugs and resistor leads o_O

I thought that you shouldn't use both and couldn't remember why I had fitted them, but after a severe googling I discovered that it is advisable for a fuel injected engine as the RF can interfere with the ECU.

Still not 100% certain I have still used both and the engine runs very well. Could be the coil packs and EDIS producing a lot more power I suppose ?
 

cobraboy

Well-Known Member
#11
Our cars that go to Emerald for mapping always come back with R plugs because of the interference issues. But three of us stood around the mis firing car last week and witnessed the improvement in spark quality as resistance was taken away.

As with life - everything is a compromise.
 
#13
During my recent engine rebuild I noticed that I had resistor plugs and resistor leads o_O

I thought that you shouldn't use both and couldn't remember why I had fitted them, but after a severe googling I discovered that it is advisable for a fuel injected engine as the RF can interfere with the ECU.

Still not 100% certain I have still used both and the engine runs very well. Could be the coil packs and EDIS producing a lot more power I suppose ?
EDIS definitely kicks out a lot more power than a regular single coil + distributor setup -its more like a lightning bolt!
 

cobraboy

Well-Known Member
#14
The car we had being worked on was equipped the an HEI system using a Ford coil pack. When fitted with all the resistor elements it knocked the performance for six, somewhat defeating the purpose of fitting a High Energy Ignition.

It is something to watch if you are fitting new plugs and leads to a conventional coil ignition where there is no need to shield the ECU. If you have resistor leads you definitely don't want anything else resistor wise in the line taking away energy from the spark.

Resistor plug caps come in many grades of resistance, so you could be unaware and have a real crimp in ignition performance.

The green spark plug company is a useful point for research.

Ignition Leads - Reels & Lengths | The Green Spark Plug Co

Spark Plug Caps - NGK, Bosch & Champion | The Green Spark Plug Co
 
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