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Spark Plug Heat Range Comparison
Posted by: JimBrandberg ()
Date: January 05, 2018 07:03AM

It seems like spark plug comparison charts I've found don't really agree. Most seem to have a vested interest in getting you to their brand.
I would like to get opinions on the relative heat range of other brands comparing them to baseline AC.
We had AC 44FF and 46FF to begin with. That changed to 44F and 46F with the loss of one thread. The 44F is for higher performance engines like 102, 110, 140 and 180. The slightly hotter 46F is for the lower compression engines like 80 and 95.

Would a Bosch 7502 or 7902 W8AC compare more to a AC 44F or 46F?

Would a NGK B6HS compare to a AC 44F and would a B5HS compare to a AC 46F?

What AC plug would the Autolite 425 compare to?
Is the Autolite 275 a naughty extended tip? Local auto parts didn't have one.
What AC plug might the Autolite 2656 compare to?

Does the Champion L87YC compare to AC 44F?
Does the Champion L92YC commpare to AC 46F?

I used Bosch W8AC and W8AC+ for several years in all Corvairs. I've been looking around for something else since they are no longer in stock at O'Reillys or NAPA. I know I could just get them elsewhere.
Folks seem to like the NGKs.
Larry Claypool seemed to like the Autolite 425 in everything.
My older brother asked me what ever happened to Champion, they used to have something for everyone? I just don't see Corvair folks recommending Champions. Did they just get a bad rap because of the old extended tip, what were they UL15Y or something like that?

I was hoping to make up our own little comparison chart regarding heat ranges. Thanks in advance for input. I did some searching here but didn't find much, mainly testimonials regarding one experience with a particular engine.

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Spark Plug Heat Range Comparison
Posted by: Brizo ()
Date: January 05, 2018 08:48AM

Asking people what spark plug works best is a lot like asking what motor oil is best... get ready for a hundred different answers!

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: Spark Plug Heat Range Comparison
Posted by: joelsplace ()
Date: January 05, 2018 10:43AM

I don't think he's asking about what is best just what heat ranges are equivalent.

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Re: Spark Plug Heat Range Comparison
Posted by: dryenko ()
Date: January 05, 2018 10:47AM

Would a NGK B6HS compare to a AC 44F and would a B5HS compare to a AC 46F?

YES

Bob C aka Dryenko
Dobson, NC 27017

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Re: Spark Plug Heat Range Comparison
Posted by: 66vairman ()
Date: January 05, 2018 06:13PM

Jim - you can find cross reference charts with heat ranges on-line, BUT they don't all agree!

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Re: Spark Plug Heat Range Comparison
Posted by: American Mel ()
Date: January 05, 2018 08:06PM

66vairman Wrote:
-------------------------------------------------------
> Jim - you can find cross reference charts with
> heat ranges on-line, BUT they don't all agree!


EXACTLY, that is why he wants to create one based on real world experience from those who actually have used them in Corvairs.thumbs up

.
-----------------------------------------------
WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
'66 Monza Coupe - 4spd, 140 Daily driver beater
'67 Monza Vert. - PG, 140 Daily driver beater

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Re: Spark Plug Heat Range Comparison
Posted by: JimBrandberg ()
Date: January 06, 2018 05:19AM

So far we have NGK advice.

Anyone know how Bosch W8AC compares to AC?

Anyone know how Autolite 425 compares to AC? How about 2656?

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Spark Plug Heat Range Comparison
Posted by: Brizo ()
Date: January 06, 2018 10:03AM

Brizo Wrote:
-------------------------------------------------------
> Asking people what spark plug works best is a lot
> like asking what motor oil is best... get ready
> for a hundred different answers!


What I should've said was, comparing spark plug performance is like comparing oil performance - its a moving target. A B6HS that works great in your 110 might not in another guys. Carb jetting, oil consumption rate, cam, tuning, C/R, etc. all effect how the plugs burn. The original heat range charts were developed under controlled conditions.

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: Spark Plug Heat Range Comparison
Posted by: 63turbo ()
Date: January 06, 2018 11:02AM

Brizo Wrote:
-------------------------------------------------------
> Brizo Wrote:
> --------------------------------------------------
> -----
> > Asking people what spark plug works best is a
> lot
> > like asking what motor oil is best... get ready
> > for a hundred different answers!
>
>
> What I should've said was, comparing spark plug
> performance is like comparing oil performance -
> its a moving target. A B6HS that works great in
> your 110 might not in another guys. Carb jetting,
> oil consumption rate, cam, tuning, C/R, etc. all
> effect how the plugs burn. The original heat range
> charts were developed under controlled conditions.

You nailed it!! the factory plugs were developed knowing that most cars were not going to the track and not going to be driven hard. The best possible heat range for a car that is intended to be driven hard is way too cold to be used on a grocery getter, as they will foul quick. The reverse is also true. A plug that is hot enough to never foul on a car that is never warmed up and never driven hard is also too hot for a car that is going to be driven hard all the time. For what it is worth, I've experimented with both ngk 5's and 6's on my
turbo over the years, and with other brands of plugs that would cross to colder heat ranges than I could get with an ngk ranges, just to see what would happen. I found that with a carb and mostly easy driving (boosting for short periods) the 5 heat range was the one that would NEVER foul, and the 6 was border line too cold, as too much light cruising would cause partial plug fouling leading to engine roughness. Going to a plug one step colder (approximately an ngk 7) and then it would take about six or seven days for it to run rough vs about 1 month on the ngk 6... going another step colder, (about the same as an ngk 8), now it only took 2 days and all of 30 or 40 miles for the engine to run rough.
Your plug mileage may vary!smiling smiley

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: Spark Plug Heat Range Comparison
Posted by: RobertC ()
Date: January 06, 2018 11:44AM

JimBrandberg Wrote:
-------------------------------------------------------
> So far we have NGK advice.
>
> Anyone know how Bosch W8AC compares to AC?
>
> Anyone know how Autolite 425 compares to AC? How
> about 2656?
>
> Jim Brandberg
> Isanti, MN
> CorvairRepair.com

One spark plug cross reference site states that W8AC and Autolite 425 crosses to 44F, 45F and 46F.

The various spark plug x ref results do not appear to be consistent.

Probably best to use a manufacturer's spark plug x-ref.

As stated above, you run the spark plug that makes your engine run the best.

Though, you do not want to err on the side of "too hot".

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Re: Spark Plug Heat Range Comparison
Posted by: SteveInMarietta ()
Date: January 08, 2018 02:56PM

An extensive comparison of spark plug equivalents was published in the December 1996 issue of the Corsa Communique.

Steve

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