427 Sparks
Thread Starter
Intermediate
Joined: Sep 2018
Posts: 36
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From: Venice - Italy
427 Sparks
Good morning! I'm sorry if I go back to this topic, I know there are a lot on this but I didn't find what I look for.
I drive a '69 427 L36.
So: originally for my car was indicated the acdelco R43N spark, no longer existing and replaced by the R43XLS. According to the Delco scale, it would therefore be spark that tend to be cold (the AC DELCO heat scale goes from 0 - COLD to 9 - HOT) ; using the NGK scale that is more widespread should correspond to an 8 at least (the NGK scale is inverse, goes from 10 for the coldest to 5 for the hottest). Well, looking on the sites I find that the differentes brands recommend for my engine sparks that tend to be hot (6 on the NGK scale, more or less 7 for the ac delco scale). The same watching the cross references tables, the acdelco R43XLS is compared with hot sparks (6 of the NGK scale).
Without going to extremes, I have not yet figured out if I need a spark tending to cold or hot...
Now I mount an NGK with grade 6 (warm tendency), the car is fine but I would still like to understand this.
Sorry, another stuff: what can you tell me about thin electrode sparks? I found a recommend for a Denso IW20TT in the tables ... Thank you all!
I drive a '69 427 L36.
So: originally for my car was indicated the acdelco R43N spark, no longer existing and replaced by the R43XLS. According to the Delco scale, it would therefore be spark that tend to be cold (the AC DELCO heat scale goes from 0 - COLD to 9 - HOT) ; using the NGK scale that is more widespread should correspond to an 8 at least (the NGK scale is inverse, goes from 10 for the coldest to 5 for the hottest). Well, looking on the sites I find that the differentes brands recommend for my engine sparks that tend to be hot (6 on the NGK scale, more or less 7 for the ac delco scale). The same watching the cross references tables, the acdelco R43XLS is compared with hot sparks (6 of the NGK scale).
Without going to extremes, I have not yet figured out if I need a spark tending to cold or hot...
Now I mount an NGK with grade 6 (warm tendency), the car is fine but I would still like to understand this.
Sorry, another stuff: what can you tell me about thin electrode sparks? I found a recommend for a Denso IW20TT in the tables ... Thank you all!
Thread Starter
Intermediate
Joined: Sep 2018
Posts: 36
Likes: 0
From: Venice - Italy
Thank you very much fo your answer but I really can't understand the cross reference between AC Delco and other sparks.
For example AC Delco vs NGK:
AC Delco range is: 0 (cold) to 9 (hot)
NGK range is: 12 (cold) to 2 (hot)
The second number of AC delco code should be th heat reference so a R44 could be a little bit cold BUT is given like a little bit hot NGK (5)...
The R43XLS recommended for my car should be a 3 heat reference so quite cold and is compared at 6 in NGK range, so middle way...
For example AC Delco vs NGK:
AC Delco range is: 0 (cold) to 9 (hot)
NGK range is: 12 (cold) to 2 (hot)
The second number of AC delco code should be th heat reference so a R44 could be a little bit cold BUT is given like a little bit hot NGK (5)...
The R43XLS recommended for my car should be a 3 heat reference so quite cold and is compared at 6 in NGK range, so middle way...
Race Director
Joined: May 2006
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I did not use cross reference because it can list too many interchangeable spark plugs. I went to the AC-Delco site and looked up a 69 427 for the R44XL and the NGK site and looked up a 69 427 for the BPR5ES. You are correct that the companies have their sequence of numbers reversed and I can not tell you why they do this to confuse people. On the other hand Champion spark plugs do the same heat range numbering as AC-Delco, 10 is colder than 11, both companies originated in the US while the others are foreign.
Le Mans Master
Joined: Apr 2001
Posts: 5,941
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From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
This is what NGK specs for a 69 427.
BPR5ES for Iron heads NGK (4006) is their standard plug.
They list a V Power plug as a GR5 NGK(2851) for iron heads. This would be my plug choice as I like the V power plugs.
BPR5ES for Iron heads NGK (4006) is their standard plug.
They list a V Power plug as a GR5 NGK(2851) for iron heads. This would be my plug choice as I like the V power plugs.
Last edited by Sigforty; Oct 3, 2018 at 11:02 AM.
Le Mans Master
Joined: Apr 2001
Posts: 5,941
Likes: 281
From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Thread Starter
Intermediate
Joined: Sep 2018
Posts: 36
Likes: 0
From: Venice - Italy
I had some fun doing a bit of testing, changing heat grade and type of electrode. In the end, the solution that seems the best is a NGK with heat degree 7 (a little bit colder than the previous ones, but theoretically closer to the original R43 ac delco) and with 3 mass electrodes. I have found that with this spark plug the engine runs turns very much smothness, starts well and has a good power supply increasing rmp. It's less rough at low rpm (I liked it...) but it's so smooth that I like the compromise ...
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