Hi guys!
I used the search function, and saw that NGK #ZFR5N is recommended.
I read to remove the washer for a 63-74 motor, what about a 1975? Also,
I am having a hard time finding the #ZFR5N, but how about #UR5?
Thanks!

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Harry
1975 Plymouth Scamp 225/904/8.75
1968 Plymouth Road Runner 383/727/8.75

I believe RU5 Fits 1976 on up, the exact year when Chrysler changed from the larger plug used in drool tube head to the smaller plug found in peanut head, rather the head without drool tubes.

NGK RU5 is what I am using in a 1977 head. There may be hotter and cooler plugs in this series available, however NGK’s numbering system escapes me at the moment. I suspect that a quick search on NGK’s web site will fill in the heat ranges for you.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

From NGK's website:
For NGK, the higher the number, the colder the plug

http://www.ngk.com/charglossary.asp?kw=Heat+range

For your 76+ head, NGK UR4 or Autolite 25 are stock replacements. If you want a colder plug get a UR5 or Autolite 24.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

So do I need to remove the washer for installation on a '75 head?

Here's the numbers from NGK site

1975 PLYMOUTH SCAMP 3.7 L6 C 1 bbl

V-Power UR4 6630 .035
G-Power UR4GP 2869 .035
Iridium IX UR4IX 7401 .035

No #ZFR5N or #UR5 mentioned for my car. Are those part numbers still available? If not, which one would you recommend?

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Harry
1975 Plymouth Scamp 225/904/8.75
1968 Plymouth Road Runner 383/727/8.75

There is no washer for the UR4 or Autolite 25. They are taper seat plugs.

http://www.autolitecatalog.com/PartDeta ... ?b=A&pn=25

I've had good luck with autolite plugs. They are readily available and cheap. If you want a colder plug get an Autolite 24 or NGK UR5

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

1975 was the first year for the taper-seat spark plugs on the slant-6.
Higher number = colder plug.

Autolite plugs used to be decent. Now they are Chinese-made garbage. The first time I had an Autolite ground electrode break off during ordinary careful use of an appropriate plug gapping tool was the last time I touched an Autolite plug. The difference in quality between an NGK or Denso plug and an Autolite or Champion is readily visible using just one's senses of eyesight and touch, before even installing them in an engine.

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