Spark plug heat range?
02-22-2007, 01:55 PM
#1
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Spark plug heat range?
I shamefully admit that I have never adjusted the heat range on my spark plugs. 
I've (very) slowly come to the realization that maybe I should be going colder since I have lots of cam and ignition advance. Now that I've been actually reading up on how to examine the plugs, they do look overheated, on both my '81 and '86.
Stock plug for the '86 is WR7DC (although I'm partial to the siblers, WR7DS). I should be using a WR6D C/S, correct?
Oh, and by the way, with the resistor plug ends, are the resistor plugs really necessary? I ask because I found that I have non-resistors installed, and I did have (problems with Hüco ignition amps).
I've (very) slowly come to the realization that maybe I should be going colder since I have lots of cam and ignition advance. Now that I've been actually reading up on how to examine the plugs, they do look overheated, on both my '81 and '86.
Stock plug for the '86 is WR7DC (although I'm partial to the siblers, WR7DS). I should be using a WR6D C/S, correct?
Oh, and by the way, with the resistor plug ends, are the resistor plugs really necessary? I ask because I found that I have non-resistors installed, and I did have (problems with Hüco ignition amps).
02-22-2007, 02:05 PM
#2
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I think if you have resistive ends in your leads, then you should be using none resistor plugs, otherwise you'll be getting too much resistance and a weak spark. This is quite a common topic on the MB forum I frequent, because the only easily available none resistor plugs for the old V8's seem to be Beru.
I have Beru none resistive in both the 928 and my 500 Benz.
I have Beru none resistive in both the 928 and my 500 Benz.
02-22-2007, 02:10 PM
#3
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The lower the number the 'colder' the plug.
Resistor plugs and caps are to reduce/eliminate electrical noise interfeering with electronics such as ignition and radio systems but they can be source of problems. I'd go with a colder set of resistor plugs if it were me.
Resistor plugs and caps are to reduce/eliminate electrical noise interfeering with electronics such as ignition and radio systems but they can be source of problems. I'd go with a colder set of resistor plugs if it were me.
02-22-2007, 03:19 PM
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Originally Posted by the flyin' scotsman
The lower the number the 'colder' the plug.
02-22-2007, 03:26 PM
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Very true Bill but the question was on going from a 7 to a 6 Bosch plug.
Champion follow the same while NGK and perhaps ND do opposite. Perhaps a Euro/ Japanese thing?
Champion follow the same while NGK and perhaps ND do opposite. Perhaps a Euro/ Japanese thing?
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02-22-2007, 03:32 PM
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Basic rule of thumb - run the coldest plug you can without fouling. Im running two ranges cooler on my supercharged 81. I check the plugs at least once per week (at least I did last year). 100% clean every time.
02-22-2007, 05:31 PM
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Malcolm,
Good info at NGK:
I put in some WR6DC+ (plus = fancy V-notch tip), I'll see how they do. I'll also retry the Huco amps with the resistor plugs.
Good info at NGK:
In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber.
Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C
02-22-2007, 07:56 PM
#11
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No worries Ken............it was fresh in the grey matter from another thread that on one boring evening I got into.
I raced 2 stoke m/cycles for many years and became very proficient at reading plugs...........best advice is to get yourself a proper magnifier for spark plugs.
I raced 2 stoke m/cycles for many years and became very proficient at reading plugs...........best advice is to get yourself a proper magnifier for spark plugs.
Last edited by the flyin' scotsman; 02-23-2007 at 11:15 PM.
02-23-2007, 07:03 PM
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Originally Posted by PorKen
Malcolm,
Good info at NGK:
I put in some WR6DC+ (plus = fancy V-notch tip), I'll see how they do. I'll also retry the Huco amps with the resistor plugs.
Good info at NGK:
I put in some WR6DC+ (plus = fancy V-notch tip), I'll see how they do. I'll also retry the Huco amps with the resistor plugs.
Where did you get those Ken?
I was in Autozone today looking for a similar bosch plug. The parts list the guy had said WR6, but when i opend the box and read the actual number on the plug it was WR7 on each box we tried.
Dont trust what the parts computer says in other words.
10-31-2009, 04:07 PM
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The heat range numbers used by spark plug manufacturers are not universal. Some manufacturers numbering systems are opposite the other, for domestic manufacturers (Champion, Autolite, Splitfire), the higher the number, the hotter the plug. For Japanese manufacturers (NGK, Denso), the higher the number, the colder the plug