Spark Plug experts needed
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Colder=less likely to detonate due to high combustion temps.
Hotter=more likely to detonate under high performance operations but self clean better under low performance operations.
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
well most of my driving will be in city, not much highway use at all. That being said the motor is fairly high performance with brodix aluminum heads, rpm air gap, Holley 770, 1.6 roller rockers , xe274h cam. Would I be better off with a hotter or colder plug
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
I would start with a 5 heat level plug. That is a pretty good all around heat range. You know your gonna get on it sometimes. If your plugs get all dirty and your jetting is good then you might try a hotter plug.
Higher compression may want a cooler plug as well. Say 11.0:1 or more.
I run 10.6:1 and use the FR5 NGK without problems.
Higher compression may want a cooler plug as well. Say 11.0:1 or more.
I run 10.6:1 and use the FR5 NGK without problems.
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
I would start with a 5 heat level plug. That is a pretty good all around heat range. You know your gonna get on it sometimes. If your plugs get all dirty and your jetting is good then you might try a hotter plug.
Higher compression may want a cooler plug as well. Say 11.0:1 or more.
I run 10.6:1 and use the FR5 NGK without problems.
Higher compression may want a cooler plug as well. Say 11.0:1 or more.
I run 10.6:1 and use the FR5 NGK without problems.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Burning Brakes
Joined: Jul 2013
Posts: 963
Likes: 57
From: Vancouver, BC
So I took a look and the plugs I have now are accel 576s which are heat range 6. Based on my build would you go with the al3924 or fr4 which are heat range 4 or the fr5 which is heat range 5?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Ok like said before, the heat range numbers are not the same from manufacturer to manufacturer.
Look at this chart and note that the 3924 and the FR5 are the same heat range.
If you read the rest of the article it'll give you a good explanation of heat ranges and their use as well.
https://www.autolite.com/docs/defaul...heat-range.pdf
Look at this chart and note that the 3924 and the FR5 are the same heat range.
If you read the rest of the article it'll give you a good explanation of heat ranges and their use as well.
https://www.autolite.com/docs/defaul...heat-range.pdf
Last edited by REELAV8R; Oct 5, 2019 at 05:25 PM.
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Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Cross references for both FR4 and FR5 if you choose to go autolite or any other manufacturer.
Also note that the Accel 576 is equivalent to the heat range 4 NGK.
https://www.sparkplug-crossreference...vert/ACCEL/576
https://www.sparkplug-crossreference...ert/NGK_PN/FR4
https://www.sparkplug-crossreference...ert/NGK_PN/FR5
Also note that the Accel 576 is equivalent to the heat range 4 NGK.
https://www.sparkplug-crossreference...vert/ACCEL/576
https://www.sparkplug-crossreference...ert/NGK_PN/FR4
https://www.sparkplug-crossreference...ert/NGK_PN/FR5
Last edited by REELAV8R; Oct 5, 2019 at 05:33 PM.
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
I run the champions in y 383 with RHS PRo-Action heads and have no problems with them. They fire fine and burn clean...in fact I'm still running the same set from when the motor was built in 2015.
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
My theory is that for a given heat range the Champion plugs err on the cold side so In my experience tended to foul easier if you were putting around at low revs. A lot has to do with the fuel air ratio you are running, if your engine mixture is set up on the rich side I found Champions would foul and misfire before an equivalent NGK. Your risk though should you decide to fit a hotter heat range plug than say the car manufacturer or cylinder head manufacturer recommends. When I was setting up my new carb, it came out of the box stinky rich and during the process of getting things right the plugs would foul NGK FR5 or Champion RC12YC (Dart heads) and once fouled it was game over, they just wouldn't clear. I'm thinking our poor fuel quality here doesn't help either.