[Dragncar]

I have 3 different plugs for my High Ports, different manufacturers.
Trying to figure out which is the hottest to coldest.
Plugs are-
Autolight AR3911
Champion Race 794 C61YC
NGK (7173) R5672A-8

Thanks for any help.

[steve25]

Well first off do they all have the same projection length?
Shorter ones right off the bat are cooler.

[Jay S]

Those three plugs look relatively close in there heat ranges. I don’t think you would find one much different than another?

[Formulas]

there is heat charts on the interwebs

[steve25]

Plugs have a 600 degree range where they will work as intended.
If after a full throttle hard run you color change over line is centered pretty much then you can safely assume that running in the center of that 600 degree range.
So for a example let’s say your motor was making a known 350 Hp and as stated above your color change over point was centered then to need to go to a one step colder plug your motor would be modified to produce 700 Hp.

If your tune is lean at full throttle then color change line might be seen as getting too close to the plugs body.

[Dragncar]

The Champions looks to have 1-2 more threads than the others. Plugs are dark, not tan at all.
But I have not been able to get a true reading, shutting it off at WOT and checking. Tough to do during actual racing.
I have not tried to lean it out either with jets or air bleeds.
Only one more race weekend for me and I will try the 1050 I had built for the engine.
I had a 1.39 sixty foot one run. Pretty good for not even playing around with launch RPM. Been setting it at 3400 and leaving it.
That 1.39 gave me a 6.08 but at this time I consider it a blip, I did not get a MPH that run. Have not been able to reproduce it in my 2 other passes.
The engine is not making 750+ HP to run that ET. I know its making more than the last engine.
But if there is a 1.39 in her just starting out there has got to be a 1.37 or better once I get it figured out.

[Cliff R]

I've always had the best success with NGK and the worst with Champion. V-Power 7's worked the best in my last 3 engines and matter of fact I never change them, just hit them with the bead blaster and put them right into the next build.

Even with that said these days many things that we used for decades that made the grade may currently being outsourced overseas. I've been finding this out with a lot of the parts I've used over they years so have to search and find alternative sources to still get high quality USA parts instead.

As a disclaimer I know that there are some decent offshore parts out there. Even so I make it a "mission" to keep my money in the USA with most things. It's a loosing battle but I'm trying to keep the Chinese from overtaking our Country by funnelling all our money over there so they can just come over hear and buy up all the businesses and real estate they can.

Sorry for the rant. As far as spark plugs go I've not been able to find measureable differences over the years tuning with spark plugs, provided they all were in good working order and close in length and heat range. I even played with plug gaps and found nothing there either, so settled on setting them at .035" no matter what was firing them.......

[PAUL K]

Originally Posted by Dragncar

The Champions looks to have 1-2 more threads than the others. Plugs are dark, not tan at all.
But I have not been able to get a true reading, shutting it off at WOT and checking. Tough to do during actual racing.
I have not tried to lean it out either with jets or air bleeds.
Only one more race weekend for me and I will try the 1050 I had built for the engine.
I had a 1.39 sixty foot one run. Pretty good for not even playing around with launch RPM. Been setting it at 3400 and leaving it.
That 1.39 gave me a 6.08 but at this time I consider it a blip, I did not get a MPH that run. Have not been able to reproduce it in my 2 other passes.
The engine is not making 750+ HP to run that ET. I know its making more than the last engine.
But if there is a 1.39 in her just starting out there has got to be a 1.37 or better once I get it figured out.

Did you look at the chamber with the plugged screwed in? A lot of the high ports it's common to have several threads sticking into the chamber.

[Dragncar]

Originally Posted by PAUL K

Did you look at the chamber with the plugged screwed in? A lot of the high ports it's common to have several threads sticking into the chamber.

No I did not. How negative a thing is a couple threads showing ?
I was thinking about running the Champion Race plugs the last race just because they look to be a tad hotter than the others.
Maybe I will try the NGK plugs.
They are the most expensive by far, 5$ each. Autolights are the best deal, 3.25 $ each, Champions in the middle.

[PAUL K]

Originally Posted by Dragncar

No I did not. How negative a thing is a couple threads showing ?
I was thinking about running the Champion Race plugs the last race just because they look to be a tad hotter than the others.
Maybe I will try the NGK plugs.
They are the most expensive by far, 5$ each. Autolights are the best deal, 3.25 $ each, Champions in the middle.

The exposed threads can act as a glow plug. It usually doesn't cause a problem but I'd be cautious with a pump gas deal.

NGK used to be cheap. Then one day someone at NGK realized they could increase profits by raising the price. For some unknown reason they gave their wharehouse distributors a month notice they were going to triple prices. This caused a massive shortage that took more than a year to fix.... I'd stick with the Autolites.

[Dragncar]

Originally Posted by PAUL K

The exposed threads can act as a glow plug. It usually doesn't cause a problem but I'd be cautious with a pump gas deal.

NGK used to be cheap. Then one day someone at NGK realized they could increase profits by raising the price. For some unknown reason they gave their wharehouse distributors a month notice they were going to triple prices. This caused a massive shortage that took more than a year to fix.... I'd stick with the Autolites.

Still mixing my gas right now. Running 96 octane at the moment. Started out with 100, then 98.
I just want the plugs to come out looking like they are supposed to. The HO engine, plugs looked great, all the time.
Maybe its has something to do with the iron heads.What want to do is get the engine warm. put in a new set of Autolights except have a NGK and Champion in cylinders 1 and 2.
Make a run with no burnout or tree lights and shut her off just past the stripe at full power, coast down to the turnaround and change 3 plugs. Come back to the pits and inspect them.
See if I can talk the track boss into it.

Maybe I can talk the track boss into

[steve25]

It will take 2 passes to get a real good color change over point to judge your heat range by.

Plugs that are off in their intended heat range can cost a ton of power it seems!

DV relates a story from a dyno test where a supercharged 4 cylinder motor was down 90 Hp from what the motor should make.
The motor had no problem making the intended rpm.

After hours of checking things and more runs proving no cure they changed out the plugs and Bam the 90 Hp showed up.

[steve25]

It can take 2 passes on a new plug for it to show a definitive color change over point, especially if the plug is on the cold side of what you need.

[Dragncar]

Is the Autolight 3910 Hotter or colder than the 3911 ?

[Dragncar]

The NGK plugs showed the "# 2 pencil" line after one pass. About 2/3-3/4 down the insulator. I like them. I had a Champion in one hole and it looked pretty good, then put a NGK in that hole.
The Autolights have not had a good color yet, very dark. And have 3 sets of them.
Not sure why the Autolights are not working out.