Hey guys i am looking at changing my spark plugs, and i have been reading about a bunch of people talking about bring there KR down. What is KR. What kind of plugs would give me the best lap time. I heard the autolite 103's work the best but i cant find them anywhere, any suggestions?
Spark Plug question
- Thread starter Kenny75k
- Start date
Poil336
New member
KR is knock retard. it's explanation is a physics lesson:
a gas's pressure, volume, and temperature are all related. what causes KR is as the piston compresses the gas, the volume decreases, causing the temperature and pressure to increase. now, gases have a certain temperature that cause them to ignite and combust without a spark. this temperature is reached easily if the car is not properly tuned, i.e. too much air/fuel mixture, which is why dropping a pulley size with no other mods will blow your motor. this isn't supposed to be the case, which is why a spark plug is necessary. the spark plug is set up to ignite the compressed air/fuel mixture at precisely the right time for max performance, which is right at (or fractions of a second after) top dead center. if the gas combusts prior to TDC, the explosion will force the piston downward while the crankshaft is still pushing the piston up. if severe enough, you will chip pistons, etc...
the reason guys change out their plugs is because some plugs run at a cooler heat range, not letting the motor get to a high enough temperature for KR to happen. they're often used with a cooler thermostat and intake/exhaust mods to help drop a pulley size and get into other modding. if you're not modded, you won't see improvements from a cooler plug, and might actually see a decrease in performance. it's really the same concept as intercooling or methanol/water injection, just on a much smaller scale.
this thread also helps:
http://www.grandprixforums.net/f81/safely-modding-your-3800-powered-car-17482.html
a gas's pressure, volume, and temperature are all related. what causes KR is as the piston compresses the gas, the volume decreases, causing the temperature and pressure to increase. now, gases have a certain temperature that cause them to ignite and combust without a spark. this temperature is reached easily if the car is not properly tuned, i.e. too much air/fuel mixture, which is why dropping a pulley size with no other mods will blow your motor. this isn't supposed to be the case, which is why a spark plug is necessary. the spark plug is set up to ignite the compressed air/fuel mixture at precisely the right time for max performance, which is right at (or fractions of a second after) top dead center. if the gas combusts prior to TDC, the explosion will force the piston downward while the crankshaft is still pushing the piston up. if severe enough, you will chip pistons, etc...
the reason guys change out their plugs is because some plugs run at a cooler heat range, not letting the motor get to a high enough temperature for KR to happen. they're often used with a cooler thermostat and intake/exhaust mods to help drop a pulley size and get into other modding. if you're not modded, you won't see improvements from a cooler plug, and might actually see a decrease in performance. it's really the same concept as intercooling or methanol/water injection, just on a much smaller scale.
this thread also helps:
http://www.grandprixforums.net/f81/safely-modding-your-3800-powered-car-17482.html
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Poil336
New member
sh!t, beat me to it lol
CTKGP09
New member
this might help too, just to add to poil's nice explanation...
http://www.grandprixforums.net/f18/what-is-octane-kr-explained-here-1507.html
http://www.grandprixforums.net/f18/what-is-octane-kr-explained-here-1507.html
Poil336
New member
unless your exhaust is smaller than stock, you won't be generating more heat, so the stock heat range is what you want. Autolite 606's are what i replaced mine with. not sure about anything else, but you don't need to go find anything special.
I'm gonna learn where that one is too lol. i honestly thought it would be easier to type an explanation that to find that one. really good write-up though.
I'm gonna learn where that one is too lol. i honestly thought it would be easier to type an explanation that to find that one. really good write-up though.
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