Need some info about spark plugs for a 440. I have a 76 440 from a motorhome with the 452 heads. The spark plugs are the 5/8 hex plugs. All the listing I find for 440's have the 13/16 hex. QUESTION NUMBER 1: Are the plugs interchangable? Can I use the 13/16 hex plugs or do I need the 5/8 hex?

This 440 is going into a truck and I have a set of headerss to fit it. It has been recommended that I use shorty header plugs with these headers so I don't burn up the plug wires. I asked the person I bought the headers from and he said his 440 had the standard size plugs in it and the boots were close to the headers, but I guess they weren't burned up So I may be fine. The only listings I can find for short plugs are Accel plugs with a 13/16 hex.

QUESTION NUMBER 2: Can anybody please provide me with part numbers I need for spark plugs to fit these 452 heads, either standard size or short.

Thanks

yes the plugs are interchangable.
Champ RJ12YC is a good plug. i think
Accel has the only shorty plugs.

Ok, Thanks.

So you're saying I can use the 13/16 hex plugs in place of the current 5/8 hex? Why would they use two different plugs like that?

Also, are the Accel plugs any good? I've always strictly used Champions or Autolites before and Don't want to use something that is going to run like carp. I appreciate the help.

Merry Christmas

NO, the motor home heads one year only take a different plug.

If you look at the head it is cut different where the plug threads in. The plug has a tapered seat , not the normal flat with washer seat.

Those heads even though they have same 452 casting have extra cooling around the spark plugs as in steam holes . Used only in the motor homes and police applications.

If you look in a spark plug catalog it shows the different listing.

It's hit and miss on the plugs for motor homes. I have three here, one has tapered, the other two have the normal plugs with the washer. Not to mention someone could have swapped heads in the last 30 years!

I be needing the same plug also

452 head with tapperd seats and autolight 23 in it right now

my buddys 73 MH 440 not sure what heads and has tapered seats with AL 666 plugs

is that it? dont they have some for different heat ranges?

I would like to run a champion in mine also,but have run plenty of the ALs

Is there a Champion Plug that will fit? Scratchnfotraction says he has Autolite 23's in his 440 with the same heads. That could be a viable alternative if Champions aren't available, but I would really like the Champions.

Thanks

I have ran these 452 "MH" heads on my race car (10.8x @ 122 mph, 3270 lbs) for years (1994). The champion pn# RV12YC. I know someone will come on here and poo poo Bosch, but thats what I have run forever in my engine (pn# HR9BPX Bosch Platinum, Advance Auto has them in stock).
Funny story, I was at Indy at Mopar nationals 1995 and blew center porslin out on my last time trial sat. It was so hot that I just put the car in the trailer and went to motel. Went to track sun morning and could not find anyone who had ONE plug to fit it. I had to go back into town & found K-Mart open and bought the only thing they had to fit it, Bosch Plat. Hurry back to track, changed plugs, just made the end of first round and got down to 16 cars, lost on double brake out. Never had a problem with Bosch, but had 2 champions come apart.

Another good thing about these heads/plugs is you have quite a bit more room around headers. I run Hooker Super Comps w/ 2'' tubes in a E body and was always burning plug boots. After changing to these heads, I never have burned a plug boot.
Brian Dunnigan

Thanks 72CudaRacer. That has been most helpful.

Armed with some part numbers now, I was checking out cross references on AutoZones website and found some interesting stuff. By entering the Delco number R42TS, that crosses to a Champion number 406, and also an Autolite 23 as Scratchn has. If I enter your Champion number, I also get the Champion No 406 and the Delco R42TS, but I get an Autolite 25. Hhhhmmm. Strange. At least now I know what I am looking for. Thank you.

I found something else interesting about the Delco plug on O'Reilly's website. They have a compatibility chart for what this plug fits. Along with the various Gm products that is obvious for a GM plug, the only Mopar products it shows to fit is the 225 /6 available in the Plymouth Traildusters. Didn't list any other Mopars but that. Among the Ford engines it fits is the 5.0 and 5.8 v-8 used in mid 80's-mid 90's Ford trucks and also the Boss 429 Mustangs.

As far as header clearance, truck headers are different than car headers in that all my tubes come pretty much straight down. Plugs number 2 and 8 are going to be VERY close, and 1 and 7 are pretty close as well. See the pics posted in my other thread about this:

https://board.moparts.org/ubbthreads/show...e=3#Post5670451

Thanks again for the help!

Merry Christmas all!

you need Autolite 23s 5/8 hex, taper seat...

Thanks for all the help with the spark plugs!

I have one more question for all you experts.

Will the distributor cap from a magnum small block fit an older model distributor, like a big block? I want to use wires that fit a magnum style cap, with the male type terminal.

Thanks again for all the help!

It will fit but dosent have the hold downs.A member here was making adapters for them but I believe he stopped.Unless you can find them you need to use the stock type cap.I wonder why no one has made a cap that does that yet.Rocky

Well, that sucks! I thought the magnum caps clamped on the same way the old caps did. It's been a while since I did a tune up on a magnum.

I suppose an MSD cap wouldn't fit either? I can't afford a whole MSD distributor. Any other options?

Thanks

I run AUTOLITE R73's.But for a mostly stock eng the AUTOLITE 75's will work if you can still find them. Ron