Spark Plug Heat Range

[JohnnyPopper]

Hi guys & gals,

This has probably been discussed, but here's the question:

Is the compression ratio the only factor in selecting the Spark Plug heat range for your engine?

On my 5.7 there are 4 different plugs available.

If there are different factors, can someone please link to the answers or elucidate the pro's and con's of using different plugs in the same engine?

Thanks in advance!



Thanks!

[VileZambonie]

Compression ratio, timing advance, fuel enrichment, emissions controls, cooling system, engine design, fuel type/octane rating, engine wear, usage, ambient temp, altitude, etc. so yeah, CFR is not the only consideration.

[JohnnyPopper]

That made my head hurt VZ!   Maybe the better question is when would you use, say, the hottest range?

For your entertainment I offer the following:

Fresh 5.7 V8
Unverified 8:1 CR (crate motor, bought circa 2010)
1978 K-10, no active emissions control, only vac operated crap
4BBL Quadrajet
Four row stock radiator
Timed by Ear at 2500-3500 RPM
Sea level
Mean temp 74 degrees
Current octane 87

[VileZambonie]

I think the better question is why are you asking? What is motivating you to want to go hotter?

[JohnnyPopper]

I dunno, Guy thing?

Seriously, the question could be asked in the other direction: When would you use a 'cold' plug?

I mean, I have 4 choices after all.

[VileZambonie]

Running a different plug heat range from the norm would be due to a specific setup or configuration i.e. modifications or to help remedy a symptom like preignition, oil fouling etc. If you have no issues then leave well enough alone.

[JohnnyPopper]

I can't... it's another guy thing! 

When I was a lad in '78, I bought a '69 Chevy with a 396 (queue the Boss) sans fuelly, headers, and the Hurst thing. TH400, Big Base 2 BBL

Some fellow knucklehead said he used hotter plugs and it made a difference.

So I tried it in my new ride and BOOM, turned her into a 'hotter' beast. (see what I did there?) I had no idea why and since then have always stuck with stock recommendations.

Until I put Iridium XP plugs in my wife's Benz. Again, hotter and zippier!

So I'm due to change my plugs in the K-10, ergo my question(s).

[bd]

Watch the short segment of this video discussing Spark Plug Heat Range and then learn to read what the plugs are telling you - purring with a smile, screaming for some needed relief (Please sir, could you bring me an iced tea?), or sleeping on the job and dead to the world.

[JohnnyPopper]

Thanks BD! (as usual  )

So my take is that in spite of all the variable cited earlier, pay attention to what the plugs tell you.

[bd]

Your catching on!  Move to the head of the class.  You need to take in the entire picture and consider all of the symptoms and variables within the context of what you are attempting to accomplish.  Each situation will make some spark plug parameters more relevant than others to your particular circumstances.  With regard to heat range, as stated in the video, unless you have introduced new variables by significant straying from the factory configuration, it is generally best to stick with the factory recommendations.  If symptoms develop that degrade ignition effectiveness, learn to read the spark plugs as part of your diagnosis.  After all, it's their toes in the fire.  They can provide invaluable feedback.

[JohnnyPopper]

LOL "toes in the Fire"!

So, I think instead of changing out 8 at a time and looking for clues, (read=expensive) I'll do a sampling of  the current 'toes' and determine if there is room to move up or down in the temp range.

Then I'll do the unthinkable by installing one (1) hotter or colder plug in a hole that looks average.

I'll run it for a bit and take a look at it, and go from there.

Thanks again! I'll post what I find...

[jeremy.farlow]

Figured this was as good a place as any to leave this tidbit...:
Iridium and other high-dollar plugs are great in newer vehicles. They do definitely work better and cleaner for higher compression motors. That being said, like synthetic oil, the benefits are a lot harder to find with older engines of unknown provenance. I definitely don’t think you’ll find any value in a high-dollar spark plug in ANY stock GM V8. Additionally, iridium plugs generally won’t “self-clean”. Leave the choke on too long, let the coil get a little weak, burn a little bit too much oil and the expensive plugs become worthless. Old school copper plugs don’t foul nearly as easily, can be cleaned and will often “come back to life” with a little more juice through the coil, etc.
Again, the OEMs are spec’ing synthetic oils and fancy plugs, mostly to extend as far as possible their maintenance intervals. I think most of the German makes are at or above 10k miles before they want to see that car back at the dealership. Synthetic oil and iridium spark plugs definitely help that concern. Meanwhile, we’re working on older, low-compression trucks. There’s not a dealership in the world that even wants to know they still exist... We’ve got a football field under the hood and the plugs are easy to access. Most of us are here because we either DO or want to work on our older trucks. We can change spark plugs. We DO...
Save that money and put it towards literally anything else you want on your truck.



Jeremy

[bd]

Agreed.

[JohnnyPopper]

Well, that was a good summary.

The Benz is a '96 and the IR plugs made her much more peppy, better mileage. (wife even noticed) 

No. 6 hole in the K10 would foul due to a lackluster seal on the EGR using standard range plugs. IR equivalent fixed that issue, so I don't know... 

[bd]

No. 6 hole in the K10 would foul due to a lackluster seal on the EGR using standard range plugs. IR equivalent fixed that issue, so I don't know... 

This caught my attention.  Post pics of the #6 and #8 spark plugs if you have any.  How is the #6 plug fouling?  Oil?  Did you notice significant crud encasing the electrodes?