Spark Plug Confusion

[SlantedMark4]

I am sorry to create another thread about the spark plug thing but the more I read about it the more I get confused.
I own a '74 built 225 Slant Six (2806830-7 block if that helps) built in Newark.
I recently got told I have to remove the spark plug washers, thats not the problem, but my problem is the spark plug itself.
I had ordered two sets on rockauto.com like 2 years ago which seemed to be the ones I needed. Those were some NGK6630 UR4 // NGK7401 UR4IX Iridium. These were listed for the /6 on rockauto.com
In this forum I got recommended ZFR5N or B7ES without the washers, but none of them are listed for the '74 Valiant on summitracing.com, not even the ones I ordered earlier.
Currently installed are W16EXR-U but with the washers but it leaks oil there.

 

[MidnightSwinger]

That’s because they are Jeep plugs I believe, just search for ZFR5N. If you have the tubes in the head, remove the washers. Get some new tube seals while you are at it to help with the oil leak.

 

[Scody21]

Here is the NGK chart. Can also Google search it. Not to hard to figure out what plugs to run. Iridium plugs were made for new cars.

 

[slantsixdan]

People who actually know what Slant-6 engines are will tend to give more reliable advice than catalog listings on websites. The ZFR5N is a better pick, even though not in the catalog. Whichever plugs you use, remove the washers before installing them.

 

[chryslercruiser]

If you are leaking oil at the spark plug, then the spark plug tubes need new oil seals..

And the washer gets removed because the spark plug tube acts as the washer...

 

[volaredon]

I just run champions like I've done for years

 

[RustyRatRod]

People who actually know what Slant-6 engines are will tend to give more reliable advice than catalog listings on websites. The ZFR5N is a better pick, even though not in the catalog. Whichever plugs you use, remove the washers before installing them.

Dan, the center electrode on that sure has a long reach. No problems with interference?

 

[slantsixdan]

Dan, the center electrode on that sure has a long reach. No problems with interference?

Well, there are two possibilities:

1. I've been recommending them for close to three decades just to try and make people break their stuff, and somehow all their reports of broken stuff have been suppressed and erased from the internet

or…

2. I've been recommending them for close to three decades because they fit and work and make a worthwhile improvement and there's no interference

»Final Jeopardy music plays«

 

[RustyRatRod]

Well, there are two possibilities:

1. I've been recommending them for close to three decades just to try and make people break their stuff, and somehow all their reports of broken stuff have been suppressed and erased from the internet

or…

2. I've been recommending them for close to three decades because they fit and work and make a worthwhile improvement and there's no interference

»Final Jeopardy music plays«

You know, there ARE times when you don't always have to be a smart aleck. lol I ask mainly because the cylinder head on Vixen's engine has been heavily milled.

 

[Scody21]

You know, there ARE times when you don't always have to be a smart aleck. lol I ask mainly because the cylinder head on Vixen's engine has been heavily milled.

Well the best time to check the reach is when that head is back from the machine shop…

 

[RustyRatRod]

Well the best time to check the reach is when that head is back from the machine shop…

I didn't do that, because I'm running stock length plugs and I knew even though the head had a heavy cut, with the pistons .180" in the hole, they'd still fit. This head was cut so the chambers are 34cc from 58cc. I feel certain there'll still be room, but that's a really long center electrode.

 

[slantsixdan]

You know, there ARE times when you don't always have to be a smart aleck.

Yeah, right, I'm so sure.

I ask mainly because the cylinder head on Vixen's engine has been heavily

So you'd want to do a physical check, accounting for your piston deck height and the head mill, but it's kind of academic because if your compression is way higher than stock, you will probably want a colder-than-stock spark plug, which would eliminate the ZFR5N from consideration.

But they work great in stock and nearish-stock motors, which is kind of the kind this here thread is about.