Time-sert and plugheat range
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Joined: Dec 1997
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From: Windsor,Ontario,Canada
Time-sert and plugheat range
Mike,
After Doing a time-sert repair I have a question about the correct selection of the spark plug heat range. As you know there are only 4 factory threads in some cylinder heads. When a time-sert repair is done the whole plug thread is used making for complete contact on the spark plug thread. That will lead to better heat transfer away from the plug. Does that mean we should switch to a hotter plug to compensate, or will using the same heat range still be ok?
Regards
JMC
After Doing a time-sert repair I have a question about the correct selection of the spark plug heat range. As you know there are only 4 factory threads in some cylinder heads. When a time-sert repair is done the whole plug thread is used making for complete contact on the spark plug thread. That will lead to better heat transfer away from the plug. Does that mean we should switch to a hotter plug to compensate, or will using the same heat range still be ok?
Regards
JMC
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Joined: Mar 1998
Posts: 13,385
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From: Virginia
Hi JMC,
Good to see you again - and I haven't had a chance to properly thank you (and Neal) for giving consideration to potentially flying down for that last event - much appreciated, I'll try to get you a call soon, too.
In short, that is not a concern - but it is an excellent question. What we find with the various inserts we've seen s that changing from the "half thread" design, where they are 4 threads to grip the plug, to a "full thread" design that grips anywhere from 8 to as many as all 12 of the threads (depending on plug & insert design), the heat range is not affected enough to make a difference. Just as it was not changed from 2002 to 2003 when Ford went from a half thread to a full thread design on their modular motor cylinder heads, at least, in the F-150's.
It's primarily the amount of the spark plug's insulator "nose" that extends into the combustion chamber that determines a plug's heat range, as opposed to whether it's a half thread or full thread design.
I do agree with you, that a full thread design would seem to be a bit more efficient at drawing the heat thru that area - but in practice it's apparently not enough to effect spark plug heat range in a street-driven vehicle, in our experience, as roughly only about 20% of the heat generated by the combustion process is dissipated via the spark plug. So adding 4 or even 8 more threads just doesn't seem to make enough difference with as much "tolerance" as there is in heat ranges for street driven vehicles. It's more about the power level & the cylinder head design - we generally say to drop a heat range for every 75 HP you add in the 2-valve mod motor V8, as a loose guideline, and like to fine-tune that according to the EGT's & detonation threshold.
Only *you* would think of that, Jean-Marc - only you. It's all in the details, & you don't miss a trick.
Good to see you again - and I haven't had a chance to properly thank you (and Neal) for giving consideration to potentially flying down for that last event - much appreciated, I'll try to get you a call soon, too.
In short, that is not a concern - but it is an excellent question. What we find with the various inserts we've seen s that changing from the "half thread" design, where they are 4 threads to grip the plug, to a "full thread" design that grips anywhere from 8 to as many as all 12 of the threads (depending on plug & insert design), the heat range is not affected enough to make a difference. Just as it was not changed from 2002 to 2003 when Ford went from a half thread to a full thread design on their modular motor cylinder heads, at least, in the F-150's.
It's primarily the amount of the spark plug's insulator "nose" that extends into the combustion chamber that determines a plug's heat range, as opposed to whether it's a half thread or full thread design.
I do agree with you, that a full thread design would seem to be a bit more efficient at drawing the heat thru that area - but in practice it's apparently not enough to effect spark plug heat range in a street-driven vehicle, in our experience, as roughly only about 20% of the heat generated by the combustion process is dissipated via the spark plug. So adding 4 or even 8 more threads just doesn't seem to make enough difference with as much "tolerance" as there is in heat ranges for street driven vehicles. It's more about the power level & the cylinder head design - we generally say to drop a heat range for every 75 HP you add in the 2-valve mod motor V8, as a loose guideline, and like to fine-tune that according to the EGT's & detonation threshold.
Only *you* would think of that, Jean-Marc - only you. It's all in the details, & you don't miss a trick.