I purchased a good running, low mile motorhome 440 with 452 heads for my Dart and it had Autolite 3294 plugs in it.

Ive seen this plug recommended for aluminum heads but they project a fair bit into the chamber with an 452 head.

Is this acceptable? any upsides or downsides to using this plug?

Thanks

the threads do or the insulator/ground electrode does? Cant have threads in there. EDIT I ain't sure of the # but iirc I used those in my mag heads

There are 4-5 threads showing in the chamber.

Is there a 5/8 head plug that would work? They are a lot easier to get in with my TTi headers.

not sure what is avail in a 5/8 plug of the right length

Add another washer?

those are the wrong plugs. they're 3/4" reach and iron heads use 3/8" reach. use an autolite 85.

Late 452 heads in motorhomes, and what are termed POLICE motors, used the peanut plugs because of the extra cooling passages that run around either side of the plug and into the block, they do not use the standard mopar 3/8 reach plug.

Is the "peanut" plug a 3/8 reach with a 5/8 hex? EDIT brand/part #

Yes. It's the same plug that went into my 1972 chevy nova.

To the OP: The 3924 plug IS NOT THE RIGHT PLUG for a bigblock Mopar cast iron head. It will thread into either of the two head configurations but will be sticking way too far into the chamber.

It would be appropriate for most, if not all, of the aftermarket aluminum heads, and also the LA heads.

The 3/8" reach gasketed plug is correct for Poly motors and most of the bigblocks that were ever produced. Some motorhome heads used the 3/8" reach tapered seat plug, which takes a 5/8" socket, but not all of the 213 heads used this plug even though in most books the 213 head is called the motorhome head.

How confusing, right?

R.

OK, after looking again this morning the motorhome 452 head has a tapered seat with 6 threads in the hole. The other 452 heads I have that I swapped on because they already had the springs I needed and a better valve job have a flat seat and 6 threads.

The 906 I checked the 3294s in last night had flat seat with 4 threads in hole and 3 threads showing in the chamber.

So yes, Im still not sure on the plug number I need because a 3/8 reach plug would be short in the hole to me.

There aren't a whole lot of different thread configurations. Gasketed or tapered seat. 3/8" reach or 3/4". That gives you four combinations. Your bigblock Mopar head has tapered seats. The only plug that will work is a 3/8" reach tapered seat plug, it will use a 5/8" wrench.

A-C R43TS or 44 or 45 or 46
Autolite 25 or, I think, 26
Denso 5029
Champion 18 or 25
etc.
Uses the same plug as a 1970 454 chevy or '72 350.

Beyond that you are thinking too hard or worrying too much.

The attached picture shows the plug you need.

R.

I think I got it solved. Thanks for all the help.

and now to throw a wrench into the mix. i know many guys use lawnmower plugs for header clearance. with that said, what are the choices/heat range comparisons for those type of plugs in this head combination ?

OP asked about plugs with a tapered seat. I am not aware of a small gasoline engine that uses a tapered seat. I have only seen gasketed seats.

Many years ago Walmart blew out a whole bunch of single sparkplugs that were bubble packed on a green grassy background. These were full size gasketed short reach plugs and I bought them whenever I ran across them. They had the same numbers on them as the Champions I was buying at the time.

Others will have to help you on the heat range issue.

R.