The plugs recommended by my head supplier are NGK R5671A-7.
Summit lists them at $6.99 ea.

I'd like to find a less expensive plug for engine break in and tuning.
Is there any reason I can't select a less expensive pug that has the same thread, reach, seat style and heat range?

I've found a few that match the specs for less.
I never knew manufacturers made so many of the seemingly same type of spark plug.

 

Why wouldn't you use that plug during break in and timing and continue using the same plugs afterwards if that's what is recommended

 

Different manufacturers' plugs, though similar specs, will tune differently with your engine. Choose one, tune with it, and keep it if it works well for you. For instance, on my engine NGK's perform better and last longer than AC Delco.

 

They're 7 bucks each, vs. 3 for standard, I don't know if they're the correct heat range and they may get fouled while I'm tuning the carb.
NGK lists them as "racing" plugs, I have no idea what that means but I can't see them making enough difference to spend over twice the price.

If this were a top shelf build looking for every ounce of HP I may spring for "racing" plugs.
This is a budget build, only intended to get a better engine in the car while I work on a better one.

Plugs are consumables, I may go through three sets while tuning.

 

With a price difference of $32 a set, I’m not even worried about $96 difference all in for 3 sets. Why be cheap about it now? I’m sure you have a bunch of money in the rebuild. Help me understand so that I may be understood.

 

I'm cheap.

If I weren't cheap I'd have bought the chrome bumpered 4 speed equipped C3 I really wanted.

Maybe I began by asking the wrong questions, I tend to ask for the information I want, rather then explain where I'm coming from.

What am I getting for an additional $32 per set for spark plugs? Why do I need "race" plugs for a mild street engine with aftermarket heads?
This is my first performance build, I don't mind spending money if I see a difference in parts.
When I see plugs for half the price, paying $7 per plug, only to chuck it in the trash can if it's the wrong heat range bugs me a bit.

 

If I can't find an alternative it would make sense to use the recommended plug for the initial start while I break in the cam.

 

Why aren't you asking the head manufacturer as to why they recommend this plug?
Maybe if you provided some details about the heads and overall build it would help.

 

It's a 9.1:1 327 with 65cc Flowtek heads.
Cam is a 269/279 dur. w. .303"/.310" lift.

I'm not looking for a plug recommendation, I want to learn how to select a plug.
I emailed Flowtek asking about their plug recommendation.

I doubt they will tell me how to select a plug.

 

Use AC-DELCO R44XL the reasoning is the NGK cross references to R43XL which is too cold for typical street usage.

 

Thank you, how did you find those?
They didn't come up when I did my search on Summit, I see they are .044" longer so they wouldn't have.

 

Found it here
Cross Reference

 

If you are certain those are the correct plugs, buy them for $5- each at Rock Auto.

 

your question should be "How Do I select a Heat range for my Spark Plugs"... THe depth and seat are determined by the head ans arent changeable,
here is a few of answers to that.

https://www.onallcylinders.com/2018/...ug-heat-range/

https://www.championautoparts.com/Te...eat-range.html

https://www.e3sparkplugs.com/blogs/n...ur-spark-plugs

https://carsbibles.com/how-to-determ...ug-heat-range/

https://www.jalopnik.com/2085134/wha...hy-it-matters/




for your Cam and compression you wouldnt heed a hotter heat range, you have a low compressiona and small cam by performance standards

 

I bought mine at rock auto mainly because there is a huge counterfeit plug issue with online plugs and even a decent amount of fake garbage plugs on amazon the last time I looked with NGK being the most faked plug. there are a few videos on this going into detail of the issues on youtube like exploding electrodes.

 

I was wondering the same thing that MelWff mentioned. Why change the plugs?

Money is a concern, which I can appreciate.

I have tried a few plugs. Accel yellow jacket plugs, Champions (the worst), AC plugs, Bosch+4 plugs and NGK. The car ran OK on the street. But if I took the car to a Time Trial, the only one to run good afterwards was NGK.

My point is running the NGK may save you money with a longer life.

 

I'm unclear on why you'd need 3 sets of plugs for break-in/tuning. (Maybe I've just not done it right all these years) 😉

For a regular street driven engine, just go with standard spark plugs and don't waste money on "racing" or fancy-metal electrodes. NGK is a widely preferred brand, in a "5" heat range for pump gas. I'd try the BPR5ES - it's a dependable, old-school copper plug and is equivalent to the AC Delco R45XL. Way back when gas contained lead and all the other good vitamins, cooler plugs were the norm; today's ethanol-laced gas burns better with a slightly hotter plug, especially if you do much idling and town driving.

BPR5ES
vs.
R5671A7

(I like that the BPR plug has a more exposed electrode.)

 

The head supplier says the R5671A-7 is the recommended starting range.
That tells me I may need a hotter or colder plug after I inspect them after the cam break in run.
I'm suspecting colder after seeing @Rescue Rogers post, thank you for the links and note on heat range.
That's why I don't want to buy the expensive plugs right out of the gate.

So maybe I need a second set in a different heat range, if I get the heat range right with the second set I may still need another set if I need to tune the carb, depending on how dirty they get and if I feel like cleaning them.

I've been searching plugs on Summit, because they list all the specs.
As I mentioned in my first post, I'm comparing all plugs with the same thread, reach, gasket style and heat range.

I wasn't aware that there were spark plug counterfeiters, if I'm shopping Summit or a local parts store is there any risk of counterfeit plugs, or is that mostly on Amazon and eBay?

 

I think you're over-thinking some of this: the head design dictates thread length and gasket vs. tapered design and 14mm is the standard thread pitch. The only choices you have are electrode material, how much projection of the electrode, and the plug's heat specs. (FYI, in case you're unfamiliar, the plug's heat spec is not how hot it fires but how easily it dissipates and transfers combustion heat to the heads. A "hot" plug holds heat to better burn off deposits. The spark energy is the same.)

I'd buy just one set of 5-heat plugs and use them to do all of your initial tuning and driving for a few hundred miles. After that amount of use, determine if the engine needs something different. 5-heat is pretty universal these days and, unless you're doing extended high-speed highway driving, will likely be just fine. Be aware NGK uses a heating range opposite of Delco; the lower the NGK number, the hotter the plug. Both brands cross over at 5-heat and are roughly equivalent.

The R5671A-7 plug the head manufacturer recommends is pretty darned "cold" for today's street gas (NGK 7-heat). Being a "racing" plug, it's intended for extended high rpm driving where engine combustion heat is extreme. The Delco equivalent must be about a 3 or 2 (43 or 42). That's incredibly "cold" for a street engine and will likely become quite loaded with deposits.

Counterfeiting was more of an Amazon/eBay thing, but as I recall it did get into chain stores. That was quite a few years ago and, I believe, isn't much of an ongoing concern if you're buying from local auto chains, Rock Auto, or Summit.

 

Back in post 10 I told the OP the NGK is equivalent to an R43XL which is too cold and recommended the R44XL for his tests.