Help picking spark plugs.

[Dutch Rutter]

A very stupid question and one I don't ask easily but heres the deal.

I have a set of aluminum pro comp heads on my 350. They recommend a longer reach.

Their website recommends:
ngk r5671a-7
Autolite ar3924
Champion rc12yc

Normally, I'd run a ngk yr5gp or ur4gp.
I had ngk ur45 (just what the in town shop had) but after <3500 miles they look like crap (see pictures of #1 and #5)

Whats everyone's thoughts?

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[MikeB]

The bottom plug doesn't look too bad. Not sure what's going on with the top one. Besides selecting the proper heat range, which should give you a light tan color after some extended driving, make sure you do have the right reach for your heads. You definitely want the plug in the center in the chart below.

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Yours look like tapered seat plugs, but this chart shows the NGK R5671A-7 as having a "flat" seat. I assume that means with a steel gasket.

• Details about NGK R5671A-7:
• Thread diameter: 14mm
• Thread reach: 19mm
• Seat type: flat
• Hex size: 16mm
• Tip configuration: non projected

Cross references here:
https://www.sparkplug-crossreference.com/convert/NGK_PN/R5671A-7

 

[Dutch Rutter]

The bottom plug doesn't look too bad. Not sure what's going on with the top one. Besides selecting the proper heat range, which should give you a light tan color after some extended driving, make sure you do have the right reach for your heads. You definitely want the plug in the center in the chart below.

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Yours look like tapered seat plugs, but this chart shows the NGK R5671A-7 as having a "flat" seat. I assume that means with a steel gasket.

• Details about NGK R5671A-7:
• Thread diameter: 14mm
• Thread reach: 19mm
• Seat type: flat
• Hex size: 16mm
• Tip configuration: non projected

Cross references here:
https://www.sparkplug-crossreference.com/convert/NGK_PN/R5671A-7

You are dead on Mike. The heads do call for a gasketed plug. Which the ones I had in them were not, they also were not the correct reach so I'm thinking getting the correct plug should help everything run quite a bit better. Not that it's been running poorly just not 100% perfect.

I'll start with those r5671a-7s and keeping checking them for the right temp range and adjust fire as needed.

Thanks!

 

[MikeB]

Cool. That should help a lot.

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[Rusty Nail]

I enjoyed this thread, thanks to all who contributed.
I have yet to choose spark plugs for my aluminum #113s , but I realllly wanted Delco though cuz I sure as hell ain't runnin any of the options you listed..

Please advise.

 

[bucket]

When I put the Edelbrock heads on my Camaro, the instructions called for a longer reach plug and gave a Champion number. I just went to my local NAPA with the Champion # and asked for the AC Delco equivalent.

 

[Dutch Rutter]

I enjoyed this thread, thanks to all who contributed.
I have yet to choose spark plugs for my aluminum #113s , but I realllly wanted Delco though cuz I sure as hell ain't runnin any of the options you listed..

Please advise.

Delcos are always a good choice but they were pretty proud of them. I guess NGKs are normal for me from running them in my dirtbikes and quads. Never had any problem with NGKs. That being said, I've also never had a problem with any spark plug.

So far it's been running fine. I'll be pulling and inspecting them this coming weekend when I do my first official oil change on this new engine. I'm thinking if anything these will be on the colder side being a 7 on NGKs 1-11 heat scale. 11 being the coldest. I did end up gaping them to .045 instead of the .035 or whatever they came in.

From what I understand the more performance and higher compression your engine has you should run a colder plug rather then a hotter.

Bucket is right, they can cross reference plugs and give you something comparable in any brand and that would be a good way to go about it.

Quick side note the damn iridium plugs were freaking 8.99 a piece! Platinum were only 3.99 and mine being nothing fancy "racing" plugs were 2.99 each.

 

[Rusty Nail]

my thought was:

Ngk is for Honda
Autolite is for Ford
Champion is for Chrysler

I'm not talking ****, i'm very interested in this topic... Please continue.
Got my first car for my 15 years Birthday, and have owned at least two since I was 19 but never owned a SBC with aluminum heads... Just bought my first pair and i've got about $700 invested after valves and springs.

No spark plugs.

 

[Frankenchevy]

I ohmed a full set of delco mr43lts plugs for my vortec and they were all over the place and out of spec. All 8 of my NGK tr55 plugs were dead on.

The old guy at the speed shop down the hill from me that seemingly builds most of the classic cars I talk to owners about—he swears by NGK.

 

[Dutch Rutter]

I was also wondering about resistor vs non-resistor spark plugs. My new ones are non-resistor types. I really have no idea if there is a benefit between the two.

I also had no idea that spark plug reach was a thing until last night there is probably alot more to spark plugs then I'll ever know. Do all aluminum heads take a longer reaching plug?

Edit: I know I'm probably now a commie for putting Chinese plugs in my SBC's Chinese made aluminum heads

 

[Rusty Nail]

Yup. Lmao dude... Good one.

 

[WFO]

my thought was:

Ngk is for Honda
Autolite is for Ford
Champion is for Chrysler

I'm not talking ****, i'm very interested in this topic... Please continue.
Got my first car for my 15 years Birthday, and have owned at least two since I was 19 but never owned a SBC with aluminum heads... Just bought my first pair and i've got about $700 invested after valves and springs.

No spark plugs.

NGKs are good for everything. I first learned about them from riding 2 stroke Motocross bikes. They would outlast every other brand by a longshot.

In the 70s, me and pretty much every gearhead I knew ran Autolites. They were the only ones at the time to use a one piece insulator, instead of a top and a bottom made from two pieces glued together.

Champions ain't worth a **** for anything, including Chrysler. They were only made popular by their large advertising campaign, including contingency money for racing. Kind of like these new fangled snakeoil plugs their pushin nowdays.

 

[QBuff02]

My Engine guy swears by NGK's, I have a set of V-Power's in my big block (cast iron heads) and pulled a few a couple times since the engine went back in and they always look good. I did play around with plug gap a few times as well. I know generally for aluminum heads you don't want to run a tapered seat plug (not a deal breaker) but some form of a gasketed or sealing washer style plug. Like I said, not critical and some if not all at this point aftermarket heads it doesn't matter because they're machined for both styles. How you drive it also comes into play, a hotter plug for creeping around town might not be a bad thing, but if you consistently "thrash" on it, you might consider a colder plug by a step or two. A heat range of 4 seems a little hot, i'd probably try a 6 or 7 heat range. But I also don't know all of your engine's specs. Also, depending on your ignition system could have some determination in the gap of the plugs. I started with mine gapped at .035 but ended up through a couple of times of trial and error gapping them out to .060. I also run a full MSD Ignition. The wider gap made a huge difference in idle quality and how "clean" the engine runs with my Ignition set up.

 

[Dutch Rutter]

Update on this. Still have 600 miles until oil change time but I went ahead and checked the spark plugs anyway. Here is number 2, 4 and 6. All of the others looked the same. I'm not sure about the white soot look so I'm thinking I need more miles on them before making a decision. The new plugs cleaned up the down low pull and all but removed an annoying off idle stumble I was chasing.

As for the engine itself it's pretty mild. 355, with stock like pistons, a mild torquey cam, and 64cc chamber pro comp heads with 190cc intake runners that have been fully gone over with new studs, valve seats, valves etc. An performer RPM intake and an edelbrock 1405 performer carb more details here if needed.
Https://www.gmsquarebody.com/threads/working-over-a-motor.25526/

For the big picture people the last two photos are why I started looking at my plugs. Only saw this on #6 and #7 I did a compression test, fearing the worst, and found all cylinders to be 168-171 without any leaking down quickly. So I chalked it up to misfiring or maybe my rings gaping got lined up? I really have no idea. Probably nothing to worry about since it's running great.

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[Rusty Nail]

Looks wicked lean to me but i'm just a schlub on the innerwebs.

I forward the motion that you are also wicked under-carbed. 1405 is a 500. That's not enough
Maybe for a stock 305...


Think 670 Street Avenger and be like word up.