67 L79 spark plugs - difference between R45s and R45TS

[Ara G.]

Hey fellas,
Am getting my silver L79 out and about. Been too long. She started right up, but started backfiring through the side pipes. Hasn't had plugs in moons. I must have bought a set to have, as I have a set of AC Delco R45TS so I am thinking they were for the L79 but I am reading R45s would be better. I am in a hot climate (South Florida). What's the difference between the TS's I have and 45s? I want the best plug in the car for driving, so any assistance is appreciated. God Bless America.
Thanks so much!
ARA

[Leif A.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Ara,
Hope all is well. The R45S is a resistor (R) type plug with an extended tip (S). Some use this plug with no issues but if your L79 is stock, the extended tip may hit the top of your piston. The R45TS is a resistor (R) type plug with a tapered seat (T) and extended tip (S)...not suitable for your application. If you're dead set on staying with AC Delco plugs, I would simply use the AC Delco 45.
With that being said, you asked for the "best plug" for driving. I'm a huge fan of the Denso W14-U. I currently have a set in my '67 L79 with just over 31000 miles on them...still going strong.
Be well, my friend.

[Ara G.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Leif,
Thanks for the reply. I found these. Are these the ones you're talking about? We are good, busy but good. Hope you are doing fantastic my friend. Regards.
ARA

https://www.amazon.com/Denso-W14-U-T...000VYIHQO?th=1

[Owen L.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

The tapered seat plugs are designed for the cylinder heads that began appearing ~1970. Prior to that the plugs used an aluminum(?) washer that sealed against a flat seat on the head surface. If you have the original heads they should be flat seated for the washer-style plug but if you have later replacement heads they could require the tapered seat plug. Look at your current plugs or the head's seating surface to determine which to use - they aren't interchangeable.

[Leif A.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Yes, Sir...those are they.

[Duke W.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Assuming you have original type heads that require a gasket seat spark plug, taper seat spark plugs are NOT appropriate.

The OE AC 44 non-resistor plug is too cold for normal driving, and owners like myself and the late John Hinckley found back in the sixties that the one heat range hotter AC 45 would not foul like the 44 in normal driving including long highway trips. If you're not in the process of having your car judged there is no reason to use AC plugs.

As shown above, the Denso W14-U is the equivalent of the long out-of-production AC 45, and I have been recommending them for decades for all pre-'71 small blocks with OE type heads that require a gasket seat spark plug and are not being judged.

Duke

[Mark F.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Assuming you have original type heads that require a gasket seat spark plug, taper seat spark plugs are NOT appropriate.

The OE AC 44 non-resistor plug is too cold for normal driving, and owners like myself and the late John Hinckley found back in the sixties that the one heat range hotter AC 45 would not foul like the 44 in normal driving including long highway trips. If you're not in the process of having your car judged there is no reason to use AC plugs.

As shown above, the Denso W14-U is the equivalent of the long out-of-production AC 45, and I have been recommending them for decades for all pre-'71 small blocks with OE type heads that require a gasket seat spark plug and are not being judged.

Duke

Duke,

What is the equivalent you'd recommend for a '67 400HP...?
Normal old fart driving for enjoyment - no hole shots; popin' the clutch; layin' tire; etc.
~57,000 miles - engine never rebuilt as far as I can tell...

Judging is not an issue for me now...I have many "driver-related mods" I have made (translate non-TFP for judging)...
All reversible if I ever want it judged again.

[Leif A.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Mark,
Not answering on Duke's behalf but with the type of driving you're doing with your L68 I would recommend a 45 heat range. The AC Delco plug would be the 45XLS. The Denso would be W14EX-U. The 45 heat range will burn much cleaner than the stock 43 plugs and won't harm your engine in any way.

[Ara G.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Thanks to ALL for the replies. I ordered a set of the Denso's

[Duke W.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

I doubt if the the AC 45XLS is available anymore because I don't think AC offers non resistor plugs and has not for many years, but if they offered non-resistor plugs, that's the one I would recommend.

According to my 2001 Denso catalog the 45XLS crosses to both the W14EX-U and the W14EP-U (both non-resistor type). Suffix P is a "projected insulator nose" and suffix X is "extra projected insulator nose". I'm not sure which is the closest tip geometry to the OE 43N. Maybe you could order both from a parts outlet and choose whatever you think is closest, but I think either is okay to use.

These are what I used to call "standard two dollar" copper core plugs, but make that about three bucks nowadays to account for bidenflation.

As Leif said the OE AC heat range 3 is too cold (the 4 means 14mm thread), and Denso heat range 14 is equivalent to AC heat range 5 that I recommend for both small and big blocks for normal road use including extended highway driving.

BTW the stock numbers (box of 4) for the above are 6010 for the P version and 3011 for the X version.

When you go to a parts store and ask for the Denso plug number you'll probably get the "what's the make and model" response. Just tell them it's a custom application, and you want two boxes of the stock number for whichever plug you choose or order one of each and exchange the box of the type you don't want to use for the type you do want to use.

As a point of interest the Denso heat range convention is opposite most other manufacturers where the hotter the plug the higher the number. The Denso convention is hotter the plug the lower the heat range number. For example my '91 MR2 OE plug is the Denso K16PR-11 (projected tip ISO standard design), one heat range colder than the 14 range I recommend for vintage Corvette V-8s because the MR2 is powered by a hard working, torquey little 2.2L 4-cylinder tractor engine rather than a big V-8, so it operates at higher average load.

For track events that I used to run at Willow Springs and the Streets of Willow Springs I installed a set of K22PR-11, two heat ranges colder since the little tractor engine was working even harder on the track than on the street. I also used Denso heat range 22 in my Cosworth Vega for track events at Riverside and Willow Springs.

I've always been pleased with Denso spark plugs in my cars, and I've never heard a bad word from anyone who installed the W14-U in a vintage small block for road use.

Duke

[Ara G.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

As always, thorough posts and on point. Thanks fellas.

[Mark F.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

Thanks so much, Leif and Duke...

My goodness, I checked out the 2022 Denso Catalog and there must be thousands of spark plugs there !

I'll have to study up on their front-end info; FAKE plugs; differences among TT; Iridium Power; and Iridium Tough Plus - although I'm bettin' you guys are recommending the basics...

thanks, again...

https://www.denso.com/global/en/prod...og_generic.pdf

Mark, Not answering on Duke's behalf but with the type of driving you're doing with your L68 I would recommend a 45 heat range. The AC Delco plug would be the 45XLS. The Denso would be W14EX-U. The 45 heat range will burn much cleaner than the stock 43 plugs and won't harm your engine in any way.

I doubt if the the AC 45XLS is available anymore because I don't think AC offers non resistor plugs and has not for many years, but if they offered non-resistor plugs, that's the one I would recommend...According to my 2001 Denso catalog the 45XLS crosses to both the W14EX-U and the W14EP-U (both non-resistor type). Suffix P is a "projected insulator nose" and suffix X is "extra projected insulator nose". I'm not sure which is the closest tip geometry to the OE 43N. Maybe you could order both from a parts outlet and choose whatever you think is closest, but I think either is okay to use.

These are what I used to call "standard two dollar" copper core plugs, but make that about three bucks nowadays to account for bidenflation.

As Leif said the OE AC heat range 3 is too cold (the 4 means 14mm thread), and Denso heat range 14 is equivalent to AC heat range 5 that I recommend for both small and big blocks for normal road use including extended highway driving.

BTW the stock numbers (box of 4) for the above are 6010 for the P version and 3011 for the X version.

When you go to a parts store and ask for the Denso plug number you'll probably get the "what's the make and model" response. Just tell them it's a custom application, and you want two boxes of the stock number for whichever plug you choose or order one of each and exchange the box of the type you don't want to use for the type you do want to use.

As a point of interest the Denso heat range convention is opposite most other manufacturers where the hotter the plug the higher the number. The Denso convention is hotter the plug the lower the heat range number. For example my '91 MR2 OE plug is the Denso K16PR-11 (projected tip ISO standard design), one heat range colder than the 14 range I recommend for vintage Corvette V-8s because the MR2 is powered by a hard working, torquey little 2.2L 4-cylinder tractor engine rather than a big V-8, so it operates at higher average load.

For track events that I used to run at Willow Springs and the Streets of Willow Springs I installed a set of K22PR-11, two heat ranges colder since the little tractor engine was working even harder on the track than on the street. I also used Denso heat range 22 in my Cosworth Vega for track events at Riverside and Willow Springs.

I've always been pleased with Denso spark plugs in my cars, and I've never heard a bad word from anyone who installed the W14-U in a vintage small block for road use. Duke

[Duke W.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

I don't see a need for a 10-20 dollar "high-tech" spark plug that is designed to last 100K miles on a vintage corvette.

Use of unleaded fuel about doubles the life of a common, inexpensive copper core spark plugs compared to leaded fuels back in the day to say, 30K miles, assuming the carburetor/FI and ignition system are performing properly.

So one has to ask the question: How many miles do I expect to drive my vintage Corvette before I decide to sell it or die.

Of course, it's up to every owner to chose. Expensive long life plugs will not improve performance or fuel economy. They just last longer and use in modern cars is driven by EPA demands for longer emission warranties.

If you do decide on an expensive "high tech" plug, get the heat range right. If too cold they will foul just like a basic inexpensive spark plug.

My concern with vintage car plugs is seizing, especially on engines with aluminum heads, so I try to remember to remove them every few years for inspection, and I also clean the threads and apply a very thin film of anti-seize compound on the thread - a THIN strip along the length of the thread then run the plug in and out of the head three times to spread it out. (I do the same with wheels studs and it lasts for decades).

And I have more than a lifetime supply of new plugs for my cars that I probably bought decades ago in case any of them go out of production.

Duke

[Ara G.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

The tapered seat plugs are designed for the cylinder heads that began appearing ~1970. Prior to that the plugs used an aluminum(?) washer that sealed against a flat seat on the head surface. If you have the original heads they should be flat seated for the washer-style plug but if you have later replacement heads they could require the tapered seat plug. Look at your current plugs or the head's seating surface to determine which to use - they aren't interchangeable.

Thanks for this. So if I found an original set of AC 45 plugs I SHOULD use the aluminum washer? My heads are ORIGINAL. Thanks

[Duke W.]

Re: 67 L79 spark plugs - difference between R45s and R45TS

A gasket should be used with this type of spark plug, but I recall decades ago reading that not using a gasket would raise the CR a bit for more power. I recall trying it once, but found no SOTP difference, and didn't detect any significant leakage either.

Back in the day I bought a box of 100 AC copper gaskets and used a fresh gasket with each plug change. This was when I was still using the OE AC 44 type and bought a spare set to swap back and forth because they would foul out in a few hundred miles of urban driving causing ignition breakup as low at 4000 RPM. Once I switched to the 45 cleaning was much less frequent, and I found that reusing the gaskets at least once was okay.

I learned about spark plug heat range from an article in Corvette News, and the '63 Corvette Owner's Manual has heat range recommendations for various types of service including racing so I bought a set of AC 43 spark plugs for Kent hot lap days.

Duke