Rosco
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| posted on 16/11/08 at 09:00 PM |
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Spark plug choice.
I went into Halfords today to buy some plugs for my 4AGE and was a little surprised to see that the ones recomended by RAW are not the same as those
by Halfords for this engine. I have a high regard for RAW and since I have a Ford coil and different plug leads from RAW I went with their
suggestion, but it got me thinking about what dictates plug choice.
Obviously thread size and length are key but why is there such a choice and what dictates which plug for which engine; is it just coil and lead
impedance or is there more to it? And if it's that simple then what's the idea with different grades; double copper, v-grove, tripple
electrode.....etc. Do they really make a difference.
Also how much does the mechanics, geometry.... of the engine matter, if at all?
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MikeRJ
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| posted on 16/11/08 at 09:09 PM |
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Apart from physical size, the most important parameter is the heat rating. Use a plug which runs too hot and you risk pre-ignition and potentially
holes in pistons. A plug that runs too cold will tend to foul up quickly and cause misfires.
The Halfords book will give the standard manufacturers recommended grade of plug. RAW have had plenty of experience with this engine, it's
quite possible they have found a slightly different grade provides better results, but I'm sure they'd explain this if you asked.
[Edited on 16/11/08 by MikeRJ]
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mookaloid
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| posted on 16/11/08 at 09:55 PM |
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I agree with the above I'd go with Raw's choice 
"That thing you're thinking - it wont be that."
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BenB
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| posted on 17/11/08 at 11:10 AM |
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Yup. Ditto. If they've gone "off-piste" there's likely a reason. As much as I'm wary of people saying "ooh, you
want to use XYZ for this engine- much better", in this case I believe them!!!
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nick205
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| posted on 17/11/08 at 11:34 AM |
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Aside from temperature rating, the plug gap may also be different. Plug gap is related (IIRC) to compression ratio and ignition system type/energy
amongst other things.
Gaps can of course be changed manually though.
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