97 454 L29 Vortec into a 80 K25

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Those are the double platinum OEM plugs for the L21 engine... which is the CNP version of the L29. Those are the plugs I'll be using since I've converted to the LS CNP setup on mine. You keep the .060 gap and you get a smoother idle and still have good power up top because the individual coil packs have plenty of power to light that spark way above where the 454 tops out at.

Ac Delco 41933 are double platinum

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Ac Delco 41993 are iridium, platinum plated

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Ac Delco 41933 are double platinum

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Ac Delco 41993 are iridium, platinum plated

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Ah, yep... the 933 are the correct plug, although rockauto wants a stupid amount of money for each one so I would probably use the OEM 41979 instead. I'm not sure what the application is for the 993... but they appear to have a vastly different heat range and also a different resistor value than the L21 plugs. The 993 appears to be a Heat range 4, while the 979 is a heat range 14? Maybe a typo, but I found heat range 14 in multiple places for that plug. Also the 993 says it is a gasket style plug, while the L29/L21 head uses a taper seat plug.

When I searched on the ACDelco website, the 993 plug comes back as the OEM plug for the L31 5.7L from 96-2009... so probably not a good plug to run in a BBC.

 

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Ah, yep... the 933 are the correct plug, although rockauto wants a stupid amount of money for each one so I would probably use the OEM 41979 instead. I'm not sure what the application is for the 993... but they appear to have a vastly different heat range and also a different resistor value than the L21 plugs. The 993 appears to be a Heat range 4, while the 979 is a heat range 14? Maybe a typo, but I found heat range 14 in multiple places for that plug. Also the 993 says it is a gasket style plug, while the L29/L21 head uses a taper seat plug.

When I searched on the ACDelco website, the 993 plug comes back as the OEM plug for the L31 5.7L from 96-2009... so probably not a good plug to run in a BBC.

Yup, you are correct. I've read a few sites where the guys run the 41993 plugs in the vortec 454. They do mention they are from an L31 also but they never mention the seat type and I didn't realize that. Thanks for checking. I'll have to buy different plugs now lol

 

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Yup, you are correct. I've read a few sites where the guys run the 41993 plugs in the vortec 454. They do mention they are from an L31 also but they never mention the seat type and I didn't realize that. Thanks for checking. I'll have to buy different plugs now lol

Story of my life right there... "buy cool thing for truck, figure out it wont work, get different cool thing for truck".. lol

The odd thing with ACDelco plugs after 1995 or so is that they changed the part numbering. You used to be able to tell heat range and specs of a plug just from the part number. Now all you can tell is that it is a spark plug(41), and that it is a platinum(900 series). The last two digits of the part number only specify the application and have nothing to do with heat range or specs. By part number, the 993, 933, and 979 should all be platinum plugs with different applications. A "100" series number indicates iridium, like the 41-162 that is used on most Gen III/IV LS motors. I think the 993 is numbered that way because it is a platinum electrode with just an iridium pad on it, but frankly I'm just guessing. The 162 is an iridium electrode with a platinum pad on the ground strap... so it isn't even full iridium.

 

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I'm not sure what the application is for the 993... but they appear to have a vastly different heat range and also a different resistor value than the L21 plugs. The 993 appears to be a Heat range 4, while the 979 is a heat range 14? Maybe a typo, but I found heat range 14 in multiple places for that plug. Also the 993 says it is a gasket style plug, while the L29/L21 head uses a taper seat plug.

When I searched on the ACDelco website, the 993 plug comes back as the OEM plug for the L31 5.7L from 96-2009... so probably not a good plug to run in a BBC.

So I got my plugs yesterday. They are tapered seat. Also read they they are a better heat range for colder climates. I'll probably run them and see what happens

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So I got my plugs yesterday. They are tapered seat. Also read they they are a better heat range for colder climates. I'll probably run them and see what happens

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Interesting... and those are NGK iridium plugs too, based on the part number on the plug base.

 

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Interesting... and those are NGK iridium plugs too, based on the part number on the plug base.

They are Delco #19256067 or 41-993.
Or are you saying NGK uses the same #?

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They are Delco #19256067 or 41-993.
Or are you saying NGK uses the same #?

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The first picture you posted showing the tapered seat has "ITR4A15" stamped into the plug base... which is an NGK Laser iridium spark plug part number. I'm guessing AC Delco just has NGK make them those plugs and brands them as ACDelco instead of NGK iridium.