Hello Thirdgener’s,

Looking to change out the plugs but not sure which one to go with. I purchased the car already modified. It’s a 1990 G92 IROC. Couple owners ago put a lot of nice parts on it and supposedly stroked the 350 to 383. From a visual overlook it has Arizona TPI specialists throttle body, AS&M runners, 880 casting on block, 8mm taylor pro wires, Omni magnum ignition, shorty ceramic coated headers, 3” exhaust that Y’s after the dual cats. The current plugs are champion rs12yc. I was wanting to go with some NGK or equivalent replacements but want to make sure I get the proper heat range and fitment.

Thanks for your time,
Ted

 

Champion wouldn’t be my first choice, or second. I like NGKs or ACDelco. I don’t subscribe to all the platinums and gimmicks.

 

I agree on both accounts. Those triple and quadruple platinum plugs are designed for modern cars...

 

Just be aware that whatever plug you choose, you don't want it any longer than what you currently have because the plug boot will get burned by the header tubes.

Did you notice the copper indexing washer? The headers look like they are SLP.

 

What heads are on it? Aftermarket could be different than stock L98 heads for plugs

if its a mild build with lower compression a ngk in a 5 heat range should be fine. If higher compression and smallish cam maybe run a 6 heat

 

Okay, I was considering the Rapidfire but they are 1/4” longer than factory plug so I think I will look for another option. Yes I saw the copper washer, I honestly didn’t know what it was until I just looked it up. Do I just re use the washer on each plug?

 

Thats the problem, I don’t know what heads/cam/compression or anything like that. Just based on driving it I would say has a mild cam.

 

Any markings on the heads? Pull a valve cover to see any casting marks? Iron or alum?

need to know proper reach length for a plug. Probably gasketed seat. Still would run a 5 or 6 ngk heat range

 

A magnet stuck to the heads so they are cast iron. I was able to take this picture by removing the oil fill cap. Does this help to identify at all or do I need to completely remove the valve cover?

 

I was able to lift the valve cover up and get this pic. Looks like it corresponds to a iron Vortec head.

 

Yup. Iron Vortec head. One of the better ones. Bonus points for it being really clean.

Oh, and NO, you can't re-use the indexing washer. Every plug is threaded differently in relation to the ground strap.
Different thickness indexing washers allow you to position the strap so that it does not block the spark from the air/fuel mixture.

 

I honestly dont believe you’ll find anything by indexing plugs on street applications

Ngk tr5 or tr55 might be best for you

 

Here are the (4) choices for the tr5 and the (4) for tr55. The vehicle is equipped with a Jacobs Omni Magnum ignition. They all seem to be heat range 5. Is the only difference the material of the electrode tip and the reach? Which should I get? Also on a side note I am trying to identify which intake manifold it has, I can see “firing order” stamped on the manifold under the throttle body with the firing order sequence but that’s it. Thanks for all your help, I really appreciate the learning experience.



Ted

 

Tr55 part 3951 is what i would try in 5.5 heat lol inbetween heat good for mild performance higher compression.
tr5 part 2238 is what i would try in 5 heat
a 4 is typically stock rating

the rest of them are slightly different designs. Looks to be a typo on reach tho, ones saying.807 should be .708.

 

I went with the Tr55 3951 gapped at .040, seems like its running real well. Bought the go-through sockets set from Harbor Freight, worked excellent. Thanks for all your help.

Ted