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Author Topic: Trying Alternate Spark Plugs  (Read 722 times)
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Don Johnston
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« on: July 14, 2017, 02:21:13 PM »

I am currently running Autolite AR32 plugs on the rebuilt HIPO and find the engine running a bit smother in the lower range RPM than using BF42.  Right now the engine is in a mild break in period so no hard running yet.  Any comments or experience with these plugs?  The 66 will only get street use and is using a 650 Holley DP with Paxton.

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stickshift
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« Reply #1 on: August 07, 2017, 06:17:53 PM »

I'm getting confused by the Autolite plug numbers.

IF we were speaking of Morotcraft an A plug is the small diameter and the B is the large diameter plug. The big plug would not be on any engines until somewhere in the mid 70s production.

The heat range on any Ford with over a 10:1 compression ratio should be the 32 which is the cooler plug. The 42 was typically what would be installed on a lower compression 2v carbed engine.

Motorcraft has dropped the 32 heat range and revised the listing to state erroneously that the 42 is the same as the 32.

Lots of people have used the 42 heat range plug but not in any kind of a performance application. Certainly a Paxton that works and is not just for show for safety should require the cooler 32 heat range plug.

The 42 will tend to act as an rpm limiter on any engine in the Ford line up and would start to show problems of misfiring somewhere in the 5,000 to 5,500 rpm range.

The varying factor now is going to be what fuel you are using and what additives you are using if any, but the 32 should be hot enough to give you good street performance with your set up. The 42 is going to probably be marginally too hot if you are going to turn this engine over 5,000 rpm.

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sg66
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« Reply #2 on: August 07, 2017, 07:47:08 PM »

Here is a good read on plugs and factors that lead to using a hotter or colder plug. http://www.enginebuildermag.com/2011/05/understanding-spark-plug-heat-range/




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GT350Lad
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« Reply #3 on: August 07, 2017, 11:08:44 PM »

What about the 45's? I am using and have found them ok.

Cheers

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6S273
jk66gt350
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« Reply #4 on: August 08, 2017, 04:01:56 AM »

I have also run 45's for many years and find they work very well in my car - normal street use with no sustained over 5,000 rpm runs. 

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stickshift
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« Reply #5 on: August 08, 2017, 05:20:55 AM »

If you are running the 65-6-7 715cfm Holley carb, the hotter plug will definitely help you. Those carbs run so heavy, the hotter plug helps.

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zray
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« Reply #6 on: September 06, 2017, 08:20:43 AM »

What about the 45's? I am using and have found them ok.

Cheers

I have also run 45's for many years and find they work very well in my car - normal street use with no sustained over 5,000 rpm runs. 


I too have been using the Autolite 45 spark plugs for at least 30 years.  They are a wide range plug, that will work VERY WELL. I've used them in all my vintage Paxton GT350's, and my Weber equipped  K codes as well.   They have proved to be  a great plug even during extended high speed endurance runs of 100+ miles.  And they are low cost as well.

Of equal importance is your spark plug wires.  Unless you are tied to a concours correct looking wires, upgrading the wires will keep the spark where it belongs…..

Z

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rkm
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« Reply #7 on: September 06, 2017, 08:59:57 AM »

I'm using AR 33s in 427 up to 6300 rpm, single Holley with good success. 9.5:1 cr. I spoke with an Autolite racing factory guy and that is what was recommended. No problems for 10 years at least.

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