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Hotter plugs or OEM plugs?

blacknight

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BPR6EF-13 is the OEM plug for the S/C version. I read that it is the plug recommended for highway driving and the city center. I've now transferred to the city with lots of stop and go traffic within 20sq.km (house / shopping / work / hobbies). should I change to a hotter plug like the BPR6EF-11? Reason i'm asking is because my mileage has gone down the drain. Car is well maintained, tire pressure, empty boot and my driving is rather conservative in the city. I've read where owners had melted the tops of piston heads and the engine will run hotter if i change to a hotter plug. Will this happen? The plug gap for the 11 is 1.3mm while the OEM plug is 1.5mm. Is a smaller plug more economical and easier on the coils?
 

Brett_jjj

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Usually you would put colder plugs in an engine that gets used/driven hard in hot conditions. Youd go with hotter plugs if the engine is just basically idling around etc as hotter plugs will help stop an engine from getting carboned up if its not reved much or worked hard. With NGK plugs, the first number- BPR (6) EFS-15, represents how hot or cold a plug is. For example, a BPR6EFS-15 is one step hotter than a BPR7EFS-15, a BPR8EFS-15 would be one step colder than a BPR7EFS-15. Basically the lower the first number is, the hotter the plug, and the higher the first number, the colder the plug. The number on the end, after the dash, shows what the gap should be set to. A plug that has a 15 on the end should have its gap set to 1.5mm. A plug that has 13 on the end, should be set to 1.3 mm and so on. Check out the link below.

http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp

The workshop manual says
The V6 ecotec (non supercharged) should be set to 1.5mm. NGK BPR6EFS-15.
The supercharged ecotec should be set to 1.3mm. NGK BPR6EFS-13.
The 5 litre V8 should be set to 1mm. NGK BPR6EF.
The 3.6 litre V6 should be set 1.1 to 1.2mm. NGK LTR6AP-11.
The 5.7 and 6.0 litre engines should be set to 1.5mm. NGK PZTR5A-15.
 
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blacknight

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would there be a huge performance difference in using spark plugs with a smaller gap? or less fuel economy? i'm under the impression that smaller spark=less power and bigger spark=more power. and on cold starts would a smaller gap in the plugs make it easier for the coils to start the car?
 

Brett_jjj

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On a standard engine with an ignition system thats in good condition, the plug gap wont make much difference to engine power etc. A bigger, or smaller plug gap, may make the car idle or run slightly different though..
 

blacknight

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Thats where my curiouslty begins. What does a few +-.02mm of a gap in a spark plug makes a difference in the stock supercharged engine? MY VX is due for its routine general service, but this time in a completely different city
 
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