Colder plug for a renix

[8Mud]

My old-school learnin' has me not understanding how a spark plug's ability to burn off deposits, can change the combustion temperatures.

I'm not going to pretend I know everything about it, but the colder plug ignites the fuel air mixture a tiny bit further from the center. The plug doesn't ignite in exactly the middle anyway, but a colder plug ignites a little higher in the combustion chamber. Colder and hotter plugs aren't a name somebody just thought up, they actually change temperatures at the piston top (one spot). I've seen motors running too hot of a plug burn a pit in a piston top.

On a practical level, colder plugs tend to carbon foul a little quicker, hotter plugs less so.

A lot of variables on how the fuel air mixture ignites. I used to run what I called freeway fliers, high gears around 290 to 1, first gear was almost like second gear. The object was top end. They'd tend to ping under certain vacuum conditions. You can increase octane, you can run a colder plug, richen the mixture, lower the compression ratio or you can retard timing to reduce ping, detonation or temperatures. The object is to keep them from detonating and destroying the motor, the motors aren't designed to run like a diesel. No speed limits on the autobahn here, I used to dig coming up behind a Mercedes at around 120+ MPH in my Dodge P.U. and signaling for him to get out of the way, I'm coming through. The limiting factor on my top end wasn't horsepower, it was the windshield and tires.

A colder plug makes sense to lower combustion temperatures a little and reduce nitrous oxide. As long as the PCM doesn't compensate too much and cancel the benefits. I used a fuel additive to increase octane, before my smog tests.

 

[blondejoncherokee]

ya my rig runs hot on 100* plus days driving 3+ hours uphill, has 220K+, long tube headers, bored out TB, and 37" tires, 5.13 gears, and its very very very heavy over stock with tons of metal glued to it. I think it weighs over 5K these days...I would not recommend colder plugs for a stocker or mild build , I think in my situation just to smog it ill take what I can get to bring the NOX down.

 

[Hypoid]

I had to do some reading to tie it all together. I recommend this page for anybody who is changing plugs to alleviate a high NOX condition: http://www.ngksparkplugs.com/tech_support/spark_plugs/index.asp?mode=nml

To answer my own question, a plug that is too hot can help set up pre-ignition, which raises cylinder temperatures. There is more than one variable to the condition, and not wanting to change the other variables makes switching to colder plugs attractive.

8Mud described the effects of detonation, I'll go one step further:

I like this picture because they include the plug, which shows material transfer caused by detonation.

The crux of my post is, WHAT DO YOUR PLUGS LOOK LIKE?

ya my rig runs hot on 100* plus days driving 3+ hours uphill, has 220K+, long tube headers, bored out TB, and 37" tires, 5.13 gears, and its very very very heavy over stock with tons of metal glued to it. I think it weighs over 5K these days..

That usage alone would have me reading the plugs. If the ECU is seeing detonation, it should be pulling the spark advance to compensate. A colder plug just might help the fuel economy. :idea:

Have you ever checked the run-time stats to see if the fuel system can keep up?

BTW, your build sounds like a monster. :thumbup:

 

[blondejoncherokee]

No but I like the idea of checking the run time stats. I have been watching eBay for snap on mt2500s to go cheap for a long time.

 

[blondejoncherokee]

From what I understand messing with plug heat ranges is an iterative thing. you want to only go down one heat range at time and see what it does.

 

[blondejoncherokee]

Failed smog again with high NOX at 25 mph. dammit. fixed 4 exhaust leaks, replaced 02, cat, colder plugs, FPR, and EGR. ugh.

still pretty damn high too. like 1100 ppm at 25 mph.

I am wondering if some higher flowing injectors would help richen it up and cool it down?