Spark plug grade

D

Dochie

Member
I am going through the car during its winter hibernation and today I removed a couple of spark plugs. I found they were NGK BP5HS but I thought the standard plug should have been BP6HS, so my question is what difference will these plugs make to the running of the engine?
In the past the car used to run a bit hot (now resolved) , would that be a reason for fitting the BP5HS plugs ?
Also the plugs were light grey in colour, so is this down to weak mixture or does the grade of plug have anything to do with it ?

Any comments welcomed
 
Hello Dochie,

Unleaded fuel does not colour plugs in the way that leaded fuel used to. There is nothing wrong with light grey, but heading towards white would certainly indicate a lean mixture.

What is the compression ratio of your engine? Reason I ask is that the 10.5:1 engines run better with Champion plugs L92YC, whereas the 9.25:1 engines tend to run better with NGK plugs. I have never used the latter plugs, so I am not in a position to shed any light.

Have you posted some photos of your Rover as yet? We all love to have a good look!

Ron
 
SydneyRoverP6B said:
Hello Dochie,

Unleaded fuel does not colour plugs in the way that leaded fuel used to. There is nothing wrong with light grey, but heading towards white would certainly indicate a lean mixture.

What is the compression ratio of your engine? Reason I ask is that the 10.5:1 engines run better with Champion plugs L92YC, whereas the 9.25:1 engines tend to run better with NGK plugs. I have never used the latter plugs, so I am not in a position to shed any light.

Have you posted some photos of your Rover as yet? We all love to have a good look!

Ron
Click to expand...


Thanks for taking the time to answer my queries.
I dont really know what my compression is but I think it will be 10.5:1 as the car is a 1972 auto. I have ordered a set of BP6HS plugs and will fit them and see how it goes.

I have probably been a bit rude jumping on to this forum and asking questions without introducing myself properly, but I will do when I can figure out how to transfer photos from my phone to my laptop.

Happy new year to all the members

Dochie
 
Dochie said:
I dont really know what my compression is but I think it will be 10.5:1 as the car is a 1972 auto.
Click to expand...
The CR is above the engine number on the left rear of the block, adjacent the cylinder head flange, assuming it is original and unmolested, internally.
 
unstable load said:
The CR is above the engine number on the left rear of the block, adjacent the cylinder head flange, assuming it is original and unmolested, internally.
Click to expand...

I had a look a while back and didn't find it but I will have a closer look tomorrow

Thanks

Dochie
 
Didnt the early v8s have their no and CR on the bellhousing flange at the left rear? Back to the point, my 9.25CR is running NGK plugs - starts VERY easily, runs well.
 
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