temp sensing

[gstallons]

differences in interpretations of words? Or a lack of interest in hearing what the other person is actually saying.

[Dan M]

differences in interpretations of words? Or a lack of interest in hearing what the other person is actually saying.

 

I think you're close to the mark Gene. Factor in the need to split hairs and argue about the width of the split until the crux of the original post has been long forgotton and you'll have a bullseye.

[Guest ratchethack]

The thermal inertia of a material is defined as the square root of the product of the material's bulk thermal conductivity and volumetric heat capacity, where the latter is the product of density and specific heat capacity:

 

 

SI units of thermal inertia are J m − 2 K − 1 s − 1 / 2 also occasionally referred to as Kieffers[2], or more rarely, tiu.[3]

Dave, since Wikipedia has provided you with such a full, complete, and accurate understanding of the term, could you explain in your own words, in one short sentence, using the Wikipedia definition, why it would make more sense to have a head temp sensor with low thermal inertia vs. one with high thermal inertia? See if you can work in Kieffers or tiu, as used in the everyday vernacular of the Pro Guzzi mechanic/engine builder.

 

Many TIA.

[Greg Field]

Now for all those who posted earlier who are unable/unwilling to look things up, and/or for whom the concept of “study” is as loathsome and as habitually avoided as a root canal, (you know who you are, and by now, so does everyone reading this thread) here’s a nice word picture for you:

 

Take your 1.4 oz brass body OE sensor, along with a 1 g. GM plastic body sensor, and heat both up to a normal hot day, hard Guzzi riding sensor temp of 100°C. A little swim up to a nice rolling boil in a pot of H2O will do nicely. Fish ‘em out and wait exactly one minute for both to cool. Now suck in your gut, yank open your trousers, and drop both of ‘em down the front of your gauchies. Now which one of the two d’you figure will have you screaming like a schoolgirl and doin’ the Lambada at ludicrous speed until you manage to drop your drawers? HINT: It won’t be the GM sensor. That’s thermal inertia, Binky. Capice?

 

Hope this helps.

 

OK, in response, I will say that your example above may impress those who are unable to think but is absolutely meaningless in comparing what is really going on here. Here's what would be meaningful: Hook the sensor and holder to the head. Heat the head to 100 C. Let all heat be applied to the chamber side of the head and flow through to the sensor. Measure the temperature the sensor reads vs. actual temp of the bulk of the mass of the head (i.e. not the tip of a fin). Now, letthe head cool, and as it does, compare the readings. Does the head cool faster than the sensor? If the sensor reads hotter than the head, you will be proven right. If not, all of this thermal diffusivity and inertia will stuff'll be proven to be inconsequential in comparison to the relative masses involved (i.e mass of head vs. mass of sensor holder). You cannot look at the sensor isolated from what it reads.

[mike wilson]

Sadly, nor can you look at the head in isolation.

[Guest ratchethack]

OK, in response, I will say that your example above may impress those who are unable to think but is absolutely meaningless in comparing what is really going on here. Here's what would be meaningful: Hook the sensor and holder to the head. Heat the head to 100 C. Let all heat be applied to the chamber side of the head and flow through to the sensor. Measure the temperature the sensor reads vs. actual temp of the bulk of the mass of the head (i.e. not the tip of a fin). Now, letthe head cool, and as it does, compare the readings. Does the head cool faster than the sensor? If the sensor reads hotter than the head, you will be proven right. If not, all of this thermal diffusivity and inertia will stuff'll be proven to be inconsequential in comparison to the relative masses involved (i.e mass of head vs. mass of sensor holder). You cannot look at the sensor isolated from what it reads.

Hm. The example I gave above was to demonstrate the principle of thermal inertia to those who were obviously unable or unwilling to comprehend it, nothing more. Do you really believe the property of thermal inertia is "absolutely meaningless" to the consideration of head temp sensors? It looks like that's exactly what you've said above. If so, I don't know how you could be more incorrect. I speak from the direct experience of having proved how important it is beyond any shadow of a doubt in my real-world testing on the road, as well documented and discussed at length previously.

 

As far as how "meaningful" your suggestion might be, as Mike points out, stepping over the more obvious concerns of duplicating heat flow through the head when it has been separated from not only the cylinder, but from anything remotely resembling the actual heat source and gas flow dynamics, absent the cooling effect of the intake, without exhaust gas dynamics, and without proper external cooling air flow to match that on the road -- if someone wants to dismantle their heads to take temperature readings on them on a bench, or hopefully, experiment in a more reasonable way with head temp sensors, I'm all for it, and more power to 'em.

 

But I don't see anyone taking heads off to experiment with head temp sensors here, nor would I be willing to as much as attempt it myself. Not by a long shot. As I'd mentioned multiple times previously, running a multi-channel data logger on the motor with a brake dyno in a wind tunnel would without much question be infinitely more informative and valuable in a practical sense in terms of tracking pertinent, usable data on an all-important TIMELINE than dismantling a head to take static temp readings on a head sitting on a work bench, but not too many of us here have access to anything close to that capability at our disposal. Lacking that, actual testing on the road is a "real world" testing environment that has served myself, Dan, and Velf, among others, quite well, not to mention being considerably more convenient and far less invasive than dismantling heads.

 

Do you honestly believe that dismantling the head to take temperature readings on a bench would allow someone to achieve something beyond what several of us have already accomplished? To what advantage, exactly?

 

As a matter of fact, why haven't you already done what you've suggested yourself and posted about it here, rather than repeatedly ridiculing what I've done, and suggesting that other people do what you apparently aren't willing to do yourself? I reckon your resources to do what you've proposed are infinitely beyond those of most of the rest of us, myself included.

 

It looks like ALL of us who have actually done what you haven't done have SOMEHOW been able to achieve the same kinds of positive results WITHOUT taking heads off the motor, WITHOUT buying expensive temperature monitoring gear -- and WITHOUT any downside. I reckon our thinking differs quite a bit from yours and others, and as far as I can tell, that's a good thing. Otherwise, like yourself, we wouldn't have accomplished anything a-tall.

 

Fortunately, those of us capable of LEARNING here have been able to achieve results that we consider well worth the effort, regardless of available resources.

[Greg Field]

Apparently I need to connect the dots. I'm not gonna bother, though. Those with the wits to see the obvious implication probably already have.

[Guest ratchethack]

Apparently I need to connect the dots. I'm not gonna bother, though. Those with the wits to see the obvious implication probably already have.

Hm.

 

Not having wits enough to see obvious implications has gotta be a terrible personal tragedy and a real cryin' shame.

 

Though I sure have seen it happen more'n a time or 2 hereabouts -- despite having performed a public service by connecting all the dots myself. . . Repeatedly. . . Recently, too. . .

 

 

. . .Other 'n that, waddayagonna do?

[Dan M]

OK, in response, I will say that your example above may impress those who are unable to think but is absolutely meaningless in comparing what is really going on here. Here's what would be meaningful: Hook the sensor and holder to the head. Heat the head to 100 C. Let all heat be applied to the chamber side of the head and flow through to the sensor. Measure the temperature the sensor reads vs. actual temp of the bulk of the mass of the head (i.e. not the tip of a fin). Now, letthe head cool, and as it does, compare the readings. Does the head cool faster than the sensor? If the sensor reads hotter than the head, you will be proven right. If not, all of this thermal diffusivity and inertia will stuff'll be proven to be inconsequential in comparison to the relative masses involved (i.e mass of head vs. mass of sensor holder). You cannot look at the sensor isolated from what it reads.

 

I'm thinking the sensor will lag way behind especially if it is in a brass holder packed with paste and the head is cooled with fast moving air as in actual use. The moving air against the fins will cool the aluminum much faster than the thermistor that is encased in brass and paste.

The idea of using a plastic sensor with an exposed thermistor is all about reduced lag time.

[Greg Field]

I believe the opposite. The mass of the head is so much greater, and it is hooked directly to the source of heat. The brass holder is finned, too, and positioned up in the breeze, though I have insulated mine to prevent it from cooling faster than the head. The plastic one is well insulated, and it has lower mass, which helps it heat up faster.

 

One of us is wrong. Absent a test to prove which of us is right, it remains a matter of opinion, not scientific fact. When it's couched as opinion, I have no issue, but when it all gets couched in scientific mumbo jumbo and trotted out as truth, then I have issue.

[Dan M]

One of us is wrong. Absent a test to prove which of us is right, it remains a matter of opinion, not scientific fact. When it's couched as opinion, I have no issue, but when it all gets couched in scientific mumbo jumbo and trotted out as truth, then I have issue.

 

You are correct, it is a matter of opinion. I have just presented the facts from my experience and have not called anything scientific. I do think sensor being near the back of the head, under the gas tank is not really up in the breeze though, it is practially mounted in the worst spot on the head for air movement. The fact that the actual thermistor is exposed in one rather than being encased in brass, then paste, then more brass will allow it to respond to head temp faster. My approach works for me and yours for you. It may be proper to extrapolate from that if your bike has typical lean issues at hot temps, then the air temp sensor is the way to go; if it runs rich, the brass & goo is the way. I tried the paste first, had it that way all last season and my bike developed lean issues in hot weather, now that I've switched it runs great. One thing I know for sure, there is quite a wide variance in how these bikes fuel from the factory so no one fix covers all.

[Greg Field]

Are we not civil?

[Dan M]

Are we not civil?

 

true gentlemen

[dlaing]

Dave, since Wikipedia has provided you with such a full, complete, and accurate understanding of the term, could you explain in your own words, in one short sentence, using the Wikipedia definition, why it would make more sense to have a head temp sensor with low thermal inertia vs. one with high thermal inertia? See if you can work in Kieffers or tiu, as used in the everyday vernacular of the Pro Guzzi mechanic/engine builder.

 

Many TIA.

No John, I can't explain it, because it is not true.

Low or high thermal inertia is not what would make sense.

This fact is exactly why your theory is wrong.

You allege that your design works well because of low thermal inertia. Your design has low conductivity and low heat capacity.

Low thermal inertia is the product of low conductivity and low heat capacity.

In one short sentence:

We want high conductivity and low heat capacity because it allows the sensor to accurately follow the cylinder head temperature.

But one short sentence is not enough. Not all Guzzis tune the same. Some run rich. Some run lean. As Dan suggested, going with Greg's high conductivity, high heat capacity design will work for rich bikes, and Dan and your low conductivity, low heat capacity design will work for lean bikes. But neither follow the theoretically ideal high conductivity and low heat capacity, which is not necessary, because either Greg's or yours and Dan's solution can be great improvements on the OEM configuration.

Also simply following the axiom, We want high conductivity and low heat capacity because it allows the sensor to accurately follow the cylinder head temperature, does not guarantee better results because we still need to match up the ECU's fuel output with the needs of the engine. If we are getting more conductivity, the ECU MAY overly lean the mixture. AAYMMV As Dan suggested, "if your bike has typical lean issues at hot temps, then the air temp sensor is the way to go; if it runs rich, the brass & goo is the way."

There is a third way to go, and that is to combine high conductivity and low heat capacity with ECU reprogramming.

[Dan M]

In one short sentence:

We want high conductivity and low heat capacity because it allows the sensor to accurately follow the cylinder head temperature.

 

 

Dave, remember the part about temp spikes of an air cooled motor. Again, it is only theory but smoothing them out with a small air gap seems to lead to better fueling in hot weather.