Aluminum heads and spark plugs

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Dohc Rocks

Dohc Rocks

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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?

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Newbomb Turk said:
Absolutely not. You are skating on thin ice.

A 3/4 reach plug is not shrouded.
Click to expand...

Care to elaborate?

For such a blunt reply accompanied by a cryptic threat, you've provided no substantiation or details.

- the bottom photo shows the projection of the hemi plug vs the RC12YC, and there is clearly shrouding with the latter;
- The hemi plug threads right in without issue;
- Gasket style is identical to that found on the RC12YC;
- There is about .250" clearance from the ground strap to the deck surface so there's no chance of mechanical interference on zero deck, flat top piston setups; and
- The plug is not in the opening path of the intake valve, so no concerns there.

The only concern I see is the possibility of carbon buildup on the exposed plug threads making plug removal difficult, but the exposed threads would be getting washed continuously by the incoming fuel charge.
 
Exposed threads in the combustion chamber are several different kinds of a bad idea.

Go get an NGK ZFR5N (stock № 3459), which has projected electrodes along with physical specs (thread, etc) that match the RC12YC, with a similar heat range. Thread it in and see if you like what you see.
 
What heads are those? To me, neither one looks right. I run NGK BK6RE (stock#6962) in my Edelbrocks and they fit perfectly.
 
@318willrun has a video which illustrates the plug hole issue and how he addressed it.






Newbomb Turk said:
What cryptic threat.
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VV
Newbomb Turk said:
You are skating on thin ice.
Click to expand...

slantsixdan said:
Exposed threads in the combustion chamber are several different kinds of a bad idea.
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I fully agree, however I am not in a position to redesign the existing combustion chamber. This was just an idea I had while
inspecting my old plugs from my truck and was looking for feedback on. Ideally the spark plug entry to the combustion chamber should have been spot faced to eliminate the plug being sunk/shrouded.

slantsixdan said:
Go get an NGK ZFR5N (stock № 3459), which has projected electrodes along with physical specs (thread, etc) that match the RC12YC, with a similar heat range. Thread it in and see if you like what you see.
Click to expand...
That plug will certainly help to better place the spark event into the chamber and would be an improvement.

Ironmike said:
What heads are those? To me, neither one looks right. I run NGK BK6RE (stock#6962) in my Edelbrocks and they fit perfectly.
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The heads shown in the photos are from Promaxx. You might have the Edelbrock heads for the Magnum engines which do not have this issue...
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mygasser said:
try fine tuning the 'projection' by stacking gaskets/washers on the longer hemi plug. you can get it where you like it then.
neil.
Click to expand...
I was thinking the same thing.
 
After you run that plug for a while, you’ll play hell getting it out. And you’ll be damn lucky not to pull the threads out of your aluminum heads when you try. The exposed threads themselves are nice little sharp hot spots that will heat up and glow red, helping detonation, and very likely deforming their own shape just enough to make you throw a spark plug socket through your garage wall. Please don’t do it.
 
TT5.9mag said:
After you run that plug for a while, you’ll play hell getting it out. And you’ll be damn lucky not to pull the threads out of your aluminum heads when you try. The exposed threads themselves are nice little sharp hot spots that will heat up and glow red, helping detonation, and very likely deforming their own shape just enough to make you throw a spark plug socket through your garage wall. Please don’t do it.
Click to expand...
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.

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Dohc Rocks said:
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
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What, if anything, do you expect to gain by dialing in the length of your spark plug? Do you think there is a bunch of efficiency there? Or power? Or what?
 
TT5.9mag said:
What, if anything, do you expect to gain by dialing in the length of your spark plug? Do you think there is a bunch of efficiency there? Or power? Or what?
Click to expand...

Just looking for a nicer fit and finish and if it improves efficiency, so be it. I've gathered all the pieces for my engine build and am just throwing around ideas.
 
Dohc Rocks said:
@318willrun has a video which illustrates the plug hole issue and how he addressed it.







VV



I fully agree, however I am not in a position to redesign the existing combustion chamber. This was just an idea I had while
inspecting my old plugs from my truck and was looking for feedback on. Ideally the spark plug entry to the combustion chamber should have been spot faced to eliminate the plug being sunk/shrouded.


That plug will certainly help to better place the spark event into the chamber and would be an improvement.


The heads shown in the photos are from Promaxx. You might have the Edelbrock heads for the Magnum engines which do not have this issue...
View attachment 1716314438


I was thinking the same thing.
Click to expand...


Just so you know, the skating on thin ice statement was related to you doing something I consider just dumb.

What you want to do is inviting disaster.

If that’s a threat to you and not a warning to not do something stupid so be it.

So screw those long plugs in there and go beat the **** out of it.

I’m out.
 
Newbomb Turk said:
Just so you know, the sharing on thin ice statement was related to you doing something I consider just dumb.

What you want to do is inviting disaster.

If that’s a threat to you and not a warning to not do something stupid so be it.

So screw those long plugs in there and go beat the **** out of it.

I’m out.
Click to expand...

I didn't feel threatened but I found your choice of words dismissive and foreboding which was surprising considering I was just brainstorming an idea and looking for constructive feedback.

Disparaging remarks and insults are a big part of what's alienating people from this hobby and the industries whose success depend upon generations of new enthusiasts. Food for though the next time you hear about yet another track/venue being shut down, specialty vendor closing up shop or project car being abandoned / parted out.
 
Dohc Rocks said:
I didn't feel threatened but I found your choice of words dismissive and foreboding which was surprising considering I was just brainstorming an idea and looking for constructive feedback.

Disparaging remarks and insults are a big part of what's alienating people from this hobby and the industries whose success depend upon generations of new enthusiasts. Food for though the next time you hear about yet another track/venue being shut down, specialty vendor closing up shop or project car being abandoned / parted out.
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And for the record I keep people in the hobby by helping them not do stupid ****.

Grow up.
 
Dohc Rocks said:
Just looking for a nicer fit and finish and if it improves efficiency, so be it. I've gathered all the pieces for my engine build and am just throwing around ideas.
Click to expand...
Got it. Keep it in your head as a passing idea and don’t think about it again. There isn’t much of anything to be gained at the spark plug if you can’t change its location. Make sure the tune up is clean and the ignition system is as good as it can be and you’ll be 99.99% of the way there. Everything else you might gain is minimal and should be left to the 1%ers like pro stock, NASCAR, top fuel. Let them worry about stuff like that.
 
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.
 
Oldmanmopar said:
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.
Click to expand...

Lol, I'm well aware of the dumpster fire that is the Ford 3V Triton. I have the plug extractor tool in the bottom of my tool box.

The reactions of some folks in this thread make it seem like I am promoting the use of the 5.7 Hemi spark plug, which I'm not. I just shared the photos and idea for feedback and group discussion. I just find the spark plug set up on some of these LA aluminum heads to be half arsed and sloppy. The Edelbrock Victor and Magnum heads and Trick Flows are notable exceptions and show that the spark plug's presence in the combustion chamber was properly considered.
 
Dohc Rocks said:
Lol, I'm well aware of the dumpster fire that is the Ford 3V Triton. I have the plug extractor tool in the bottom of my tool box.

The reactions of some folks in this thread make it seem like I am promoting the use of the 5.7 Hemi spark plug, which I'm not. I just shared the photos and idea for feedback and group discussion. I just find the spark plug set up on some of these LA aluminum heads to be half arsed and sloppy. The Edelbrock Victor and Magnum heads and Trick Flows are notable exceptions and show that the spark plug's presence in the combustion chamber was properly considered.
Click to expand...
I never payed much attention to that ' Most heads come here with no plugs in them . Now you convinced my brain to start looking.
 
If ya want the plug that far in your better find some surface gap plugs…. They also have spark plug king certs to fix the treads once you use an impact to get them out…
 
Exposed threads will carbon up. Carbon is HARD & the SOFT alum will not be amused when somebody tries to remove the plugs. I had this problem of exposed threads with another brand of engine & even with the recommended 3/4" reach plugs, several threads were exposed. Very bad design.
I machined about 3/16" off the end of the plugs so that there was no thread for carbon to clog up....
 
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