Aluminum heads and spark plugs

[fishmens67]

I use permatex anti-seize on the plug threads.

 

[Bewy]

So do I...

 

[mopar head]

I machined about 3/16" off the end of the plugs so that there was no thread for carbon to clog up..

I was just going to suggest that.

 

[Moparmonster]

While I'm grateful that small block Mopar engines have affordable aluminum cylinder options, I never really liked the way that the spark plug's entry into the combustion chamber was implemented. I looks like a machining process step was skipped resulting in the recommended RC12YC spark plug being sunk and shrouded.

Yesterday I was replacing the plugs in my Ram and looking at the plug I had an idea.

RC12YC have a .750" thread while the 5.7 Hemi plug (NGK LZFR5CI) has a 1" thread.

What's worse, to have a sunk plug with the shrouding and ~0.300" exposed aluminum threads or have a plug that makes full use of the available cylinder head threads (improved plug cooling?), bump in compression with a comparable ~0.300 of exposed plug threads?

View attachment 1716314295

View attachment 1716314296

View attachment 1716314297

View attachment 1716314304

My understanding is, and correct me if I'm wrong, that aluminum's non-ferrous nature means that it naturally lowers compression when used as a cylinder head. Thus, the valves are closer to the pistons to make up for that loss, and to maintain the same compression ratio. Something like that, as I recall.

 

[mygasser]

My understanding is, and correct me if I'm wrong, that aluminum's non-ferrous nature means that it naturally lowers compression when used as a cylinder head. Thus, the valves are closer to the pistons to make up for that loss, and to maintain the same compression ratio. Something like that, as I recall.

only the chamber 'size' can affect the compression ratio, not the material it's made from.
it's not like the chamber if made from aluminum swells up when the mixture's compressed is it?
it seems to be accepted that aluminum heads will work with a higher compression ratio without detonation if that's what you meant? something to do with that material transferring heat better than iron from memory?
neil.

 

[340six]

As mentioned above, I agree that the exposed threads are not ideal. The Edelbrock Magnum chamber is what should have been done across the board.

View attachment 1716314439

That's what i think my Camando Heads have. Magnum casting machined to LA and have pedestals for rocker shafts

I use permatex anti-seize on the plug threads.

Me too.

 

[StreetSleeper]

I belive Ford tried this and then had issues with the plugs breaking off when trying to remove them Due to debris on the threads.

Also they would blow the plug right out of the head from lack of threads. They make a special kit for the fords to repair the head in the truck. I would be leary of doing that to your heads.

But once you mill the threads away it is only a little welding to fix them. Your heads, Do what you believe is money well spent. But as for me I would have left them as they were.

Not just the 3 valve engines, even the 4.6 2 valves did this to me and separately to my uncle on our ford products. You are absolutely correct sir.

 

[slantsixdan]

I use permatex anti-seize on the plug threads.

Might want to read point (1) here.

 

[Moparmonster]

only the chamber 'size' can affect the compression ratio, not the material it's made from.
it's not like the chamber if made from aluminum swells up when the mixture's compressed is it?
it seems to be accepted that aluminum heads will work with a higher compression ratio without detonation if that's what you meant? something to do with that material transferring heat better than iron from memory?
neil.

I have to plead ignorance here. Metallurgy isn't my field and I was repeating something that I clearly didn't remember correctly. I stand corrected.