High compression spark plug question...

[nickpohlaandp]

So I finally gave my buddy back his 68 Camaro after what seemed like an eternity of fixing the electrical issues and eventually rewiring the entire car. Last night he calls me and is asking me about spark plug heat ranges, saying his friend told him he needs to be running a hotter plug.

Very brief overview of the engine. It's a 13.5:1 383 that he runs on C12, not sure about the cam, but it doesn't come alive until 4000-4500. It's running rich right now because as soon as he got it back from me he installed a tunnel ram and two Edelbrock 600's. That's too much carb... I know, but I'm more curious about the plug heat range.

I've never built anything with that much static CR before so I've never investigated this before. My answer to him was "I don't know, lemme ask some people (you guys!)". My thought would be on a high compression engine you'd want a slightly colder plug to aid in detonation prevention, like in a nitrous application. Can anyone shine some light on this for me? Thanks.

[RaptorLou]

I would guess his buddy thinks the hotter plug will help the rich condition. Needs to jet it better and I would stay towards cooler side of plug.

[mag2555]

Do a search for spark plug reading 101.

[statsystems]

First...it's not too much carb.
Second...heat range won't help a carb tuning issue.

[mag2555]

The two 600s are now splitting the vacuum that one Carb would see, so a lower rated power valve would likely help out atleast on the primary sides.

[Walter R. Malik]

First...it's not too much carb.
Second...heat range won't help a carb tuning issue.

Totally agree ...
Also, C12 is not a good fuel choice for any continuous running below about 5,000 RPM. VP110 would be my choice and is a lot less expensive to boot.

[nickpohlaandp]

I guess I went on too much about the setup to bring focus to my main question, which was the spark plug heat range. I'm aware that a hotter plug will not help with an overly rich combination... and to the best of my knowledge Edelbrock carbs don't have powervalves, so that's not an issue. I know the carbs need to be tuned for proper AFR. I've got a wideband setup to help out with that. I am more curious as to whether or not his buddy's claim of using a hotter plug due to it being a high CR engine has any merit. My first instinct would be the exact opposite. Seems a hotter plug would lead to the greater possibility of detonation.

[nickpohlaandp]

Can anyone suggest a good plug for a 13.5:1 383 on C12?

[GARY C]

I don't know what kind you run but we ran the NGK-8 on motor and the cooler -9 on nitrous this was a 13+.1 377 on C-12 with separate C-16 tank for N2o.
You can probably find a heat range cross reference and plug temps by googeling.

[mag2555]

Sorry those do not have power valves , but power piston springs.

[nickpohlaandp]

Sorry those do not have power valves , but power piston springs.

No biggie. I do not claim to know anything about anything I don't know, lol! That's why I come here to ask questions. I haven't messed with Edlebrock carbs other than one time I took a new one out of the box and put it on my K5... worked awesome, never messed with it.

[nickpohlaandp]

I don't know what kind you run but we ran the NGK-8 on motor and the cooler -9 on nitrous this was a 13+.1 377 on C-12 with separate C-16 tank for N2o.
You can probably find a heat range cross reference and plug temps by googeling.

Thanks for the info. I'll steer him that direction. I don't know what kind of plugs he's got in there now. I think I recall him saying something about Autolite?

[RCJ]

AR 3932 , Is what I run with brodix heads in an Autolite, 112 fuel, 14.0 c/r

[nickpohlaandp]

I just found something interesting while Googling for heat range comparisons between manufacturers in regard to Autolite plugs.

"The last digit in an Autolite part number represents the Heat Range within a plug family.

For example, take the 254x plug series. Autolite has 2544, 2545 and 2546 available. 2544 is the coldest plug in that plug family, and 2546 is the hottest.

However, according to an Autolite reference chart, Autolite 86 has the same heat range as 2244 and Autolite 303 is a hotter plug than 2974.

Therefore, it is impossible to chart an Autolite Heat Range hierarchy, let alone a standardized comparison to other spark plug brands."

Seems like you could easily get screwed up trying to change over from one brand to Autolite, or vice versa.

[statsystems]

I just found something interesting while Googling for heat range comparisons between manufacturers in regard to Autolite plugs.

"The last digit in an Autolite part number represents the Heat Range within a plug family.

For example, take the 254x plug series. Autolite has 2544, 2545 and 2546 available. 2544 is the coldest plug in that plug family, and 2546 is the hottest.

However, according to an Autolite reference chart, Autolite 86 has the same heat range as 2244 and Autolite 303 is a hotter plug than 2974.

Therefore, it is impossible to chart an Autolite Heat Range hierarchy, let alone a standardized comparison to other spark plug brands."

Seems like you could easily get screwed up trying to change over from one brand to Autolite, or vice versa.

This is exactly correct. Pick a brand of plug and go from there. Cross referencing is a crap shoot at best. For your application I'd start with a Champion C63CX and tune from there.