Maximum safe cylinder head temperature (CHT)

[HeadSmess]

yesh, i does, i predict a slightly cooler head with the hotter plug

my apologies for saying anything that may have caused offence. i get excited.

civility again

this subject has me almost...only almost...contemplating. yes, only contemplating, about going and digging out the couple for my multimeter. last time i checked it was dead on from 0 to the curie point of mild steel... about 954C or summink i recall...

and then, conclusive results really rely on a bench test, with a cooling fan a fixed distance away, fixed load etc.

but yeah. test temperatures in several places.

my frowny face with the stud location is that its also the area in contact with the cylinder itself... really need a few very small 1/8 holes filled with transfer goop at various points. meh


and there you go.... full circle...these engines are too cheap to bother with

 

[Fabian]

apparently ive been offensive, yet i havent out right called anyone anything.... im waiting for my infraction notice still

If you want an infraction notice, just pretend that you are "me" and the infractions will come thick and fast, especially if doing so on the other website where they really seem to appreciate my presence

 

[KCvale]

This topic is titled ' Maximum safe cylinder head temperature (CHT)'.

That 'max safe' would of course depend of the heads materiel and size but this has gotten pretty silly and though I really didn't want to chime in again I just can't help it when it comes to a spark pugs direct effect on it and what I 'feel' first hand.

IF I was inclined to take the time and energy which I am NOT unless I got really bored I would just do it this way:

My wife picked up this digital cooking thermometer recently for $20 at Wallyworld and it is pretty handy and should handle the job.

http://www.acurite.com/digital-cooking-thermometer-00994w.html

- Instant readout of inner food temperature during cooking cycle
- 3 ft. 450ºF high heat resistant cord reaches outside of oven or grill so you don't let heat escape while checking food internal temperature
- For use in: ovens, deep fryers, barbeque grills and smokers
- Commercial quality stainless steel thermometer probe
- Wide temperature range from 32ºF to 392ºF (0ºC to 200ºC)

The test vehicle wouldl have to be a known good running broken in vehicle and tested on a day with unchanging weather conditions for constitutive testing.

Then order all 4 BPR(5-8)HIX plugs as you don't gap them so no change there.

Then I'd just crimp an eyelet to the end of the probe and attach that to a head bolt and put the display on the handlebars so I can watch it's instant readout and go through the plugs with multiple exact same rides.

Simple, cheap, you have extra plugs for changing season weather, and a spiffy thermometer for other uses, I love it for the BBQ ;-}

One other note is the cylinder exhaust temps but really, lets not go there other than running cheap gas can make the tailpipe hotter, enough to burn the paint off if you run too cold a plug.

 

[Deleted member 12676]

time to eat dirt

drum roll please....
...
who is right?

...
who is mr. know it all?

...
ha! I'll bet you think I'm gloating because I'm right.

OK I did two really good tests and have the results in. Ya'll be easy on me now, nowhere have I ever read (from a spark plug manufacturer) that hotter spark plugs increase cylinder head temp. If I was right in my first assumption about the ceramic then my opponents would be eating their shoes right about now. But I was wrong. The ceramic conducts a lot of the heat to the body of the plug and to the head. Here are the tests:

55cc ported for 8300 rpm. 18mm Mikuni with reed valve. non-squish-band slant head with cranking pressure of 140psi and spark plug screwing in at the rearward intake side of the combustion dome. torque pipe. Jaguar CDI. Fiber head gasket insulating the head from the cylinder. Fiber washer insulating the thermocouple from the cooler cylinder studs/nut. Thermocouple connected under a forward head stud/nut leading to digital readout at handlebars.

NGK max temp
B5HS 299F
B6HS 268F
---------------
Second test:
Same engine but with squish band head with 165psi. Metal head gasket. Champion plugs tested which spanned 3 NGK heat ranges. The #87 had an extended tip (protruding more into the combustion area).

from http://www.clubplug.net/champ_ngk.html
Champion L82C = NGK BP7HS
Champion L87YC = NGK BR4HS

Thermocouple at spark plug base:
Champ max temp
L87YC 448F
L82C 418F

Thermocouple at front head nut/stud:
Champ max temp
L87YC 399F
L82C 333F

So basically there was a 10 degree change per heat rating at the spark plug, and a 20 degree change per heat range at a forward stud.

I may be eating dirt but I am proud as hell to be able to present test results to put an end to this dispute (both here and at other forums) once and for all. And now I know that once I move back to Paraguay, where it is as hot as Arizona in the summer, to use a colder plug and just clean it more often.

 

[Fabian]

A point to note in this discussion is the significantly improved thermal convection between a water cooled cylinder head and an air cooled cylinder head.

When an air cooled cylinder head experiences virtually no cooling air flow (hauling heavy loads at low speed with the engine working it's guts out), the efficiency of the spark plug heat range drops away as the cylinder head becomes ever hotter.

I have experienced cylinder head temperatures (using a standard cylinder head) that have sent a KOSO cylinder head temperature gauge off the scale and it stops at 275 degrees Celsius so i'm suspecting that it exceeded 300 degrees Celsius which works out to be 572+ degrees Fahrenheit.

With the CR Machine Manufacturing billet cylinder head, i haven't experienced cylinder head temperatures over 230 degrees Celsius (446 degrees Fahrenheit).

For this reason i use colder heat ranges than most would use; typically being an NGK BP8HS whereas most people use the No 6 heat range.

The hotter the cylinder head, the greater the difficulty for the spark plug to get rid of heat and the less reliable is the heat range number on affecting spark plug tip temperature, so i always default to a cold plug in an air cooled situation.

 

[HeadSmess]

wait. im trying to work this out...i was right?

wow. . hotter runs cooler. brag brag brag logic, baby, logic!

i can see a pretty big temp change. of course it wont be the same exactly on each step, but 10F as an average will do.

test results are conclusive enough for me. no whinging this time. results are obvious enough to not be picky

this time i shall apologise properly.

sorry to have a go at you but it really gets up my goat to see something heralded as "the truth" when its only half the truth. im sure youll understand. its all about understanding and the increase of knowledge. always be open to new facets on any subject im glad now that this subject is basically over. we all learnt something that temp difference is a lot more than i even thought possible!

i know i tend to ramble a bit on what may seem to be completely unrelated topics but to me, everythings related, and everything must be considered.


you did well


though it is sort of irrelevant?

 

[Deleted member 12676]

HS, so sorry to break the bad news to you but the results were the opposite of your prediction. You thought a hotter plug would allow lower head temps, but the hotter plug delivered more heat to the head and raised its temperature. Between the intake side plug and the exhaust side stud, the temperature increase was 15 degrees for every higher heat range of spark plug.

 

[KCvale]

If I was right in my first assumption about the ceramic then my opponents would be eating their shoes right about now. But I was wrong. The ceramic conducts a lot of the heat to the body of the plug and to the head.

I may be eating dirt but I am proud as hell to be able to present test results to put an end to this dispute (both here and at other forums) once and for all. And now I know that once I move back to Paraguay, where it is as hot as Arizona in the summer, to use a colder plug and just clean it more often.

You are a fine man with integrity Jag and I applaud and respect you both for doing the actual tests and admitting the results with humility.

Take it from a guy that has been wrong many a time learned long ago, a little humbling is good for the soul, it builds character, and you gain a little more wisdom along the way ;-}

One last tip as we stick a fork in the plug controversy, the temp to burn off any deposits on the plug is pretty low and with an Iridium plug here in Arizona never had to even do it even running 7's in the winter.

Again well done Jag and you are 'Da Man' today ;-}

 

[Deleted member 12676]

thanks KC I appreciate it.
yeah that iridium plug is great.
One thing I didn't mention, probably because it sounds unbelievable, is that with both the NGKs and the Champions the top speed was more with the hotter plugs. (5% difference with the Champions, probably because they spanned 3 heat ranges). So either that is because sparks jump easier from a hotter electrode, or the tip heat helps to ignite the mixture. I don't know for sure. It's another puzzle waiting to be solved. So for me, I will continue to select the hottest plug I can run and still maintain head temps below 450 when streaking down the highway.

 

[Fabian]

Take it from a guy that has been wrong many a time learned long ago, a little humbling is good for the soul, it builds character, and you gain a little more wisdom along the way ;-}

I completely understand the feeling. I have been told i was wrong many a time by moderators on the other site and banned over and over and over again Apparently this was the method they used to humble me and then humble me (i.e. shutting my trap) for good with a lifetime ban,

so,

i do understand the concept of humblement by a higher power, even if it has been a character building exercise