273-4 spark plug question

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mvh

mvh

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Looking to replace the ancient plugs in my Commando, and I realized that none of the replacement charts show a unique plug for the Commando. They just show the same plug for every small block. The FSM shows N10Y for the 273-4, N9Y for the 340, and N14Y for everything else — this makes me think that there was something about either the dual point distributors or the high static compression ratios that mandated different spark plugs (probably the latter). What's frustrating is that I can't find any crossover charts that list the N10Y so I can find a replacement (and I know that Champion recalibrated their numbers sometime in the interval). And manufacturers today don't even tell you what the heat ranges of their plugs are, to enable you to choose a hotter or cooler plug. The engine had N12Y in it (at least 12 years old), but they were fouling up pretty bad. Any suggestions? I am thinking the plugs from a 340 would actually be a better match than those for a 2 barrel, low compression engine.
 
mvh said:
Looking to replace the ancient plugs in my Commando, and I realized that none of the replacement charts show a unique plug for the Commando. They just show the same plug for every small block. The FSM shows N10Y for the 273-4, N9Y for the 340, and N14Y for everything else — this makes me think that there was something about either the dual point distributors or the high static compression ratios that mandated different spark plugs (probably the latter). What's frustrating is that I can't find any crossover charts that list the N10Y so I can find a replacement (and I know that Champion recalibrated their numbers sometime in the interval). And manufacturers today don't even tell you what the heat ranges of their plugs are, to enable you to choose a hotter or cooler plug. The engine had N12Y in it (at least 12 years old), but they were fouling up pretty bad. Any suggestions? I am thinking the plugs from a 340 would actually be a better match than those for a 2 barrel, low compression engine.
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I put in 12's and they have been in for 8 years now? Those cold plugs will cause a idle roughness you will not be able to tune out.(trust me).
 
I worked in a parts store in the late 70's and early 80's. IIRC we sold Champion RN12Y plugs to anyone with a sbm.
 
I messed around with plugs with my 340 back in the day, ran like **** with anything but the 9’s. I would say you need to follow manufacturer recommendations. I would call jegs or summit and tell them you need a plug the same heat range as a champ 10 for your commando 273. When I had my hot rod dart, 318 w/x heads and a wild crower cam they sold me accel plugs and it immediately ran better.
 
Plug applications are just a starting guide, anyhow. The differences in "the same engine" AKA hi vs lo compression/ bigger/ smaller cam, etc would be generally colder for higher performance engines. And it "might be likely" that if the catalog say, say N10Y that up here in the N colder climates you might want to go 11, and in San Diego/ LA/ Tucson, etc, you might want to go with 9 "What came out" and do they look OK?
 
From 67 FSM

N14Y = 273 2bbl
N10Y = 273 4bbl

I'm guessing you got the heat range based on compression correct.

Interestingly the 426 hemi used the same N10Y as 273 4bbl.


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As suggested above, you want the Champion 12 heat range. I have read that NGKs have a broader crossover [ heat ] range than other brands, & I would use NGKs.
My NGK catalog shows the N10Y converting to NGK BP6ES.
For street use, you should use the BP5ES.
 
"Our part number?" Never heard of such a thing. They were always just the plug number...............
 
If you can't find a N10Y or equivalent, I would run 340 plugs (N9Y) but in a platinum tip. Whatever they cross to.

Thanks to 67Dart273 for catching my mistake.
 
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used E3 .46 noticed better idle and throttle response in a stock 69 340
 
66fs said:
If you can't find a J10Y or equivalent, I would run 340 plugs (9Y) but in a platinum tip. Whatever they cross to.
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Too cold. I chased a rough idle issue for a couple summers on my 273-4 and fixed it with a set of 12y's although after a rebuild my actual compression was 9.68-1 and not 10.5-1 like it originally was. I need to pull the plugs next spring and take a look. They have been in there for many years but not many miles.
 
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"J" is 3/8 reach AKA B/RB engines. "N" is "long" 3/4" reach AKA all small block except some of the heavy duty AB truck/ motorhome "dash 3" which used tapered seat Ford type plugs.
 
67Dart273 said:
"J" is 3/8 reach AKA B/RB engines. "N" is "long" 3/4" reach AKA all small block except some of the heavy duty AB truck/ motorhome "dash 3" which used tapered seat Ford type plugs.
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You are so right. Brain fog. This getting old is hard.
 
That makes sense. 405 is what I was finding in a look-up for a 273. But it was lumped with the 318.

Funny that Bewy recommended NGK BP6ES.... I actually have a bunch of those.... use 'em in my 1966 MG.

Thanks, everyone, for the background and recommendations. The car has been parked for 9 years, so it has been a while since I have gone through a tune-up.

Dana67Dart said:
Found this.
Car Part Number Results for Champion Auto Parts

You can search for other old plug numbers
N14Y comes out to 405 with a 14 heat range

N10Y comes out to 302 with a heat range of 11
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Here's what I found out by calling the parts stores...

NGK BP6ES is usually listed as part # NGK 7333. but now that has been "superseded" by NGK 7131, which is actually NGK BPR6ES — in other words, the resistor version. Waddaheck? I figure that makes no difference.
 
mvh said:
Here's what I found out by calling the parts stores...

NGK BP6ES is usually listed as part # NGK 7333. but now that has been "superseded" by NGK 7131, which is actually NGK BPR6ES — in other words, the resistor version. Waddaheck? I figure that makes no difference.
Click to expand...

You do have to be careful as there (has been) some glitches along the way. Champion used to make a "booster gap" plug--had a gap inside the ceramic. This was 'back when' and at that time both GM and Chrysler had "long and short" rotors. GM started leaning towards "short" rotors on everything, and that sort of negated the Champion booster gap.

BOOSTER GAP PLUG

Found this evidently NGK as well

Spark Plug Booster gap ??

I guess what I'm saying is, there are little tricks and glitches along the way..............
 
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