Spark Plugs for 383 and Head Compatibility

[BlueManCrew]

Hello Sweepers.

My son and I are rebuilding an old D200 Crew...turned W200 Crew. The 383 came to us fresh from the re-builders wrapped in plastic, along with complete fresh heads. I don't know where it all came from. I'm guessing it is all from a 1969 D200 or the heads could have come from another source. Motor has RV cams. The heads have a machined out recessed spot for the spark plugs to seat. The local car parts store set me up with some plugs. I installed and ran for awhile but then noticed that the plug threads were showing around the base of the plug. They were not the right spec...too long of threads. So in looking for a new set I went to Summit Racing whose catalog shows a narrow shoulder RJ12YC or RJ14YC champion plug. I went down to O'Reilly today and picked up some RJ14YC plugs. Unlike the Summit Racing picture, they actually have standard width shoulders. I tried to install one of them but it seems like the compression washer isn't being engaged and the shoulder appears to be touching the cast head body instead of the compression washer doing its job.

Am I imagining all this, or is there a fitting issue with some mopar heads? Do I need special plugs?

Should a RJ12YC or ....14 fit?

And finally, if I return these plugs, what do you all recommend for a spark plug?

Many thanks.

[712edf]

Do you know the casting number on the heads? You will have to remove a valve cover to find it.

I believe I have the RJ12YC plugs in my big block.

Bucky

[dodgeboykim]

Is it possible it has the motor home heads on motor.

[BlueManCrew]

Yes it is possible that it has motor home heads. How can I tell them apart? What might that mean for spark plugs?

[Roxyflash]

Look into the plug hole see if it has a tapered seat if it does it a later model year set of heads it should have the 906 heads if its the year your saying probably been upgraded to later model year heads for the unleaded fuels rv9yc for tapered plugs

[BlueManCrew]

The head casting number is 4006 452. I counted the threads in the plug holes and they appear to better match the shorter plugs. It is a tapered seat. Auto parts store cross reference to rv9yc brings up both short thread and long thread plugs.

So what is the recommendation for plugs for this 383 motor with a 452 head and RV cams with an Edelbrock 1405 carb?

Seems like I'm getting closer to the answer. Thanks for you help.

[712edf]

Those heads were made much later than the 383. They were offered on 75-later 440/400 engines.

Bucky

[BlueManCrew]

I think the previous owner spec'd out the 440 heads for the 383. They came to me freshly built and wrapped in plastic ready to mount. I looked up the casting number and it came up with 76 to 78 mopar. I looked up spark plugs for a 6.6L and 7.2L motor that was in those trucks during those years. I could use those plugs. It looks like they would fit since they are tapered and short thread.

They list Autolite AR12, AR13 or 23. NGK BPR6FS. I guess I'll try one of these unless someone has a better idea.

Thanks again for all the input.

[Duh]

Hola Blue

Glad that you now have some Spark Plugs to use.

The Heads that you have A Higher Flow Volume than the older #906 heads. They are also spec'd for The After 1972
Fuels Used. The internal "Hot Spots" are addressed.

______________
The is no such thing as 440 -

.. Heads ( and related parts that are under The Valve Tappet Cover )
... Cam Shaft/ Timing Assembly/ Timing Cover
.... Exhaust Manifolds
..... Water Pumps
...... Oil Pumps ( and related parts )
.......Oil Pans
........ Cam Shaft "Lifter's"

All of these items are 383 or 400 Engine Parts that a 440 Also Uses ( check the parts number coding ).



Rodger & Gabby
FltSgt@outlook.com
COS

[asf93555]

I have two different ‘452 head castings

‘452 from a car which uses the typical JY plug
‘452-3 from an RV which uses the tapered, “peanut” style GM plugs

The ‘452-3s have additional water cooling passages around the spark plug which keeps a cooler running engine if they are installed on a matching -3 engine block; does nothing special on a regular block. My machinist said that back in the day, you could get a “jig” that would allow you to drill-out a regular block and turn it into a -3. I’m going to try to have this done to my 383 when I re-install the -3 heads.