The Ford Barn

Joe/Ct · 06-09-2023, 03:58 PM

I have older style Offy heads on my '39 coupe and I have been using 437 plugs, based on an earlier (15+ years ago) recommendation. Is this still a good recommendation?

drolston · 06-09-2023, 04:06 PM

Thread length is deeper on Offy versus stock heads. I use 7/16 thread length on my Offy 425 heads. That brings the plug to about one thread from being flush with the combustion chamber. Not sure what the right answer is, but that has worked very well for me for over five years in all kinds of driving conditions. Determining the right heat range plug is another matter. That difference is how far the center electrode and insulator extend.

Ronnieroadster · 06-09-2023, 05:09 PM

To answer your question I think your reference to 437 is the plug reach .A very good choice for your early Offy heads would be NGK-B4L or NGK-B6L which offer the 437 reach.
Note the lower the NGK plug number the hotter the plug which is opposite from Champions. I have found the NGK plugs to superior to all other brands for a Ford flathead.
Ronnieroadster

tubman · 06-09-2023, 05:26 PM

Depending on when your Offenhhauser heads were made, they can be problematic. The spark plug holes can be an odd depth, and no standard plugs fit exactly right. Here is a link to a discussion that has a link to an even earlier discussion : https://www.fordbarn.com/forum/showt...ht=offenhauser.

The bottom line is that you have to find out what you have and perhaps use spacers.

I have spent a lot of time on aftermarket heads and spark plugs, and it is not a simple "Use XXX".

Ronnieroadster · 06-09-2023, 08:11 PM

Older Offy heads which the poster is referring to use the shorter plug. New era Offys and Edelbrocks as well require a longer reach plug.
Ronnieroadster

tubman · 06-09-2023, 08:34 PM

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Quote:

Originally Posted by Ronnieroadster

Older Offy heads which the poster is referring to use the shorter plug. New era Offys and Edelbrocks as well require a longer reach plug.
Ronnieroadster

It's really not that simple. I have a set of new "in the box" Offenhauser heads I purchased from Speedway Motors in the late '90's. I/2" reach plugs are too short; 3/4" are too long. As was stated in the previous posts listed, no one makes 5/8" reach plugs in 14 mm. (They are available in 12 mm).
I never used these heads because of the plug fitment problem and also that I was able to find two good used sets of Edmunds heads, which I consider superior because of the placement of the spark plugs in the transfer area.

Admittedly, I am a little fussy about spark plug fitmant (as well as piston clearance) with all of these heads, but that's just me. I want things to be the best they can be.

As I said, the bottom line is to check the plug fitment and perhaps use the proper spacer under the plug. Either that, or run a less than optimum setup (which will probably work OK in most instances) and live with it.

Ronnieroadster · 06-09-2023, 09:42 PM

Quote:

Originally Posted by tubman

It's really not that simple. I have a set of new "in the box" Offenhauser heads I purchased from Speedway Motors in the late '90's. I/2" reach plugs are too short; 3/4" are too long. As was stated in the previous posts listed, no one makes 5/8" reach plugs in 14 mm. (They are available in 12 mm).
I never used these heads because of the plug fitment problem and also that I was able to find two good used sets of Edmunds heads, which I consider superior because of the placement of the spark plugs in the transfer area.

Admittedly, I am a little fussy about spark plug fitmant (as well as piston clearance) with all of these heads, but that's just me. I want things to be the best they can be.

As I said, the bottom line is to check the plug fitment and perhaps use the proper spacer under the plug. Either that, or run a less than optimum setup (which will probably work OK in most instances) and live with it.

Wonder what you mean by less than optimum set up?
From my extensive experience there's no performance loss if the plug electrode is not at the end of the threads or protruding into the combustion chamber on a Ford flathead.
The electrode can be above the combustion surface a number of threads and you will have no ill effects. Yes its true.

Ronnieroadster

tubman · 06-09-2023, 10:13 PM

Quote:

Originally Posted by Ronnieroadster

Wonder what you mean by less than optimum set up?
From my extensive experience there's no performance loss if the plug electrode is not at the end of the threads or protruding into the combustion chamber on a Ford flathead.
The electrode can be above the combustion surface a number of threads and you will have no ill effects. Yes its true.

Ronnieroadster

I have a hard time believing this, but I don't think there is a practical way to prove or disprove it.

I'll still do it my way; it just feels "right".

Joe/Ct · 06-12-2023, 08:23 AM

Wow!!! Lots of great discussion and food for thought. The subject is a bit more complicated than I thought...but that is the newbie in me.

Looks like I have a job to measure the depth of the threads on my heads. Could be interesting, given that they are installed.

tubman · 06-12-2023, 08:28 AM

I think my "perfectionism" might be getting in the way here. If "Ronnieroadster" says that "The electrode can be above the combustion surface a number of threads and you will have no ill effects.", you can count on it. If it runs good, I wouldn't tear into it.

Krylon32 · 06-12-2023, 09:04 AM

I've used several sets of Offy heads and I always use a little anti seize on each plug. Is that right or wrong?

tubman · 06-12-2023, 10:07 AM

I think Anti-Sieze is always a good idea with dissimilar metals (aluminum/steel).

sshep · 06-12-2023, 07:41 PM

Quote:

Originally Posted by Joe/Ct

Wow!!! Lots of great discussion and food for thought. The subject is a bit more complicated than I thought...but that is the newbie in me.

Looks like I have a job to measure the depth of the threads on my heads. Could be interesting, given that they are installed.

You absolutely do not have to do that!

Do not confuse post counts with experience.

Members such as Ronnieroadster and Bored&Stroked have recommended the same NGK plugs time and time again for use in Offy heads. These two men have built a lot of flathead engines over the years and have seen a thing or two.

Don't take my advice either though. Do yourself a huge favor and spend some time searching this topic on the fordbarn and you can draw your own conclusions.

Bored&Stroked · 06-13-2023, 07:42 AM

If it was mine, I'd pick up a set of NGK B6L's and run them . . . you'll be happy with this plug. I switched over from Champion H-10's about 30 years ago - and will never go back to them (for 7/16's reach plugs). On modern Edelbrock heads, they are using 3/4" reach plugs - which give you a TON of options.

I always use a bit of anti-seize on the plug threads . . . might save you from ruining a plug thread and having to pull a head to fix it.

06-09-2023, 03:58 PM	#1
Joe/Ct Senior Member Join Date: May 2010 Location: Waterford, CT Posts: 250	Spark Plugs and Offenhauser Heads I have older style Offy heads on my '39 coupe and I have been using 437 plugs, based on an earlier (15+ years ago) recommendation. Is this still a good recommendation? __________________ Joe/Ct "The older I get, the better I was"

06-09-2023, 04:06 PM	#2
drolston Senior Member Join Date: Jun 2014 Location: Williamsburg, VA Posts: 1,627	Re: Spark Plugs and Offenhauser Heads Thread length is deeper on Offy versus stock heads. I use 7/16 thread length on my Offy 425 heads. That brings the plug to about one thread from being flush with the combustion chamber. Not sure what the right answer is, but that has worked very well for me for over five years in all kinds of driving conditions. Determining the right heat range plug is another matter. That difference is how far the center electrode and insulator extend.

06-09-2023, 05:09 PM	#3
Ronnieroadster Senior Member Join Date: Dec 2010 Location: East Coast in CT Posts: 1,530	Re: Spark Plugs and Offenhauser Heads To answer your question I think your reference to 437 is the plug reach .A very good choice for your early Offy heads would be NGK-B4L or NGK-B6L which offer the 437 reach. Note the lower the NGK plug number the hotter the plug which is opposite from Champions. I have found the NGK plugs to superior to all other brands for a Ford flathead. Ronnieroadster __________________ I use the F word a lot no not that word these words Flathead , Focus and Finish. "Life Member of the Bonneville 200 MPH Club using a Ford Flathead block" Owner , Builder, Driver of the First Ford Flathead bodied roadster to run 200 MPH Record July 13, 2018 LTA timing association 200.921 in one and a half miles burning gasoline. First ever gas burning Ford flathead powered roadster to run 200 MPH at Bonneville Salt Flats setting the record August 7th 2021 at 205.744 MPH Last edited by Ronnieroadster; 06-09-2023 at 08:15 PM.

06-09-2023, 05:26 PM	#4
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,320	Re: Spark Plugs and Offenhauser Heads Depending on when your Offenhhauser heads were made, they can be problematic. The spark plug holes can be an odd depth, and no standard plugs fit exactly right. Here is a link to a discussion that has a link to an even earlier discussion : https://www.fordbarn.com/forum/showt...ht=offenhauser. The bottom line is that you have to find out what you have and perhaps use spacers. I have spent a lot of time on aftermarket heads and spark plugs, and it is not a simple "Use XXX". Last edited by tubman; 06-09-2023 at 07:06 PM.

06-09-2023, 08:11 PM	#5
Ronnieroadster Senior Member Join Date: Dec 2010 Location: East Coast in CT Posts: 1,530	Re: Spark Plugs and Offenhauser Heads Older Offy heads which the poster is referring to use the shorter plug. New era Offys and Edelbrocks as well require a longer reach plug. Ronnieroadster __________________ I use the F word a lot no not that word these words Flathead , Focus and Finish. "Life Member of the Bonneville 200 MPH Club using a Ford Flathead block" Owner , Builder, Driver of the First Ford Flathead bodied roadster to run 200 MPH Record July 13, 2018 LTA timing association 200.921 in one and a half miles burning gasoline. First ever gas burning Ford flathead powered roadster to run 200 MPH at Bonneville Salt Flats setting the record August 7th 2021 at 205.744 MPH

06-12-2023, 08:23 AM	#9
Joe/Ct Senior Member Join Date: May 2010 Location: Waterford, CT Posts: 250	Re: Spark Plugs and Offenhauser Heads Wow!!! Lots of great discussion and food for thought. The subject is a bit more complicated than I thought...but that is the newbie in me. Looks like I have a job to measure the depth of the threads on my heads. Could be interesting, given that they are installed. __________________ Joe/Ct "The older I get, the better I was"

06-12-2023, 08:28 AM	#10
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,320	Re: Spark Plugs and Offenhauser Heads I think my "perfectionism" might be getting in the way here. If "Ronnieroadster" says that "The electrode can be above the combustion surface a number of threads and you will have no ill effects.", you can count on it. If it runs good, I wouldn't tear into it.

06-12-2023, 09:04 AM	#11
Krylon32 Senior Member Join Date: May 2010 Posts: 4,489	Re: Spark Plugs and Offenhauser Heads I've used several sets of Offy heads and I always use a little anti seize on each plug. Is that right or wrong?

06-12-2023, 10:07 AM	#12
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,320	Re: Spark Plugs and Offenhauser Heads I think Anti-Sieze is always a good idea with dissimilar metals (aluminum/steel).

06-13-2023, 07:42 AM	#14
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,073	Re: Spark Plugs and Offenhauser Heads If it was mine, I'd pick up a set of NGK B6L's and run them . . . you'll be happy with this plug. I switched over from Champion H-10's about 30 years ago - and will never go back to them (for 7/16's reach plugs). On modern Edelbrock heads, they are using 3/4" reach plugs - which give you a TON of options. I always use a bit of anti-seize on the plug threads . . . might save you from ruining a plug thread and having to pull a head to fix it.