All You CHT Gauge Drivers Report Here

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Bleyseng
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Re: All You CHT Gauge Drivers Report Here

Post by Bleyseng » Sun Jan 27, 2019 11:01 am

I am going to have my stepson look into this (going for his PHD in Physics) and do a computer simulation if it's not beneath him.
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hippiewannabe
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Re: All You CHT Gauge Drivers Report Here

Post by hippiewannabe » Mon Jan 28, 2019 2:42 pm

Amskeptic wrote:
Fri Jan 25, 2019 12:12 pm
hippiewannabe wrote:
Thu Jan 24, 2019 11:20 pm
Amskeptic wrote:
Fri Jan 25, 2019 12:12 pm
Please define "effects of a breeze"
---just means moving air. Newton didn't know about centrifugal fans, otherwise he would have said "forced convection".
Exactly. Newton did NOT address dynamic like air flow. I am wondering about high speed airflow being limited in its ability to pick up heat via the conduction/convection interface.
I thought it was quaint to quote Newton in his own words, sorry for the confusion. Dynamic means moving. The law addresses dynamic air flow. It is the equation that applies here.
Amskeptic wrote:
Fri Jan 25, 2019 12:12 pm
hippiewannabe wrote:
Thu Jan 24, 2019 11:20 pm
Amskeptic wrote:
Fri Jan 25, 2019 12:12 pm


Absolutely no such implication was offered. My entire thesis had to do with the limitations of "the breeze" to pick up heat.
---That is precisely and exclusively what you are saying. The heat transfer is the coefficient times delta-T, period, full stop. delta-T is what it is, the coefficient is the only variable. Newton has been dead for 300 years, but his law hasn't changed.
Settle down. I believe you are misapprehending the kernel of my inquiry, young man. The coefficent is not the only variable. We "size" HVAC systems based on heat-carrying volume and rate. I am stuck currently at the "rate" variable, NOT OF THE AIRFLOW, but the rate of heat conduction from the aluminum. I wonder if the aluminum has a "constant" of heat conduction that makes the temperature of the cooling air much less important than the volume of that air (see: house fire)
Is it sad that I am passionate about Thermodynamics? :geek:
Let me try to explain better. All of the brainstorming we are engaging in to figure out what is going on with the heat transfer from the heads are all components of the coefficient. The coefficient is the number, when multiplied by the temperature difference, which gives you the amount of heat transfer. It is impacted by the velocity and properties of the air, the surface properties of the fin, etc.

hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
Amskeptic wrote:
Fri Jan 25, 2019 12:12 pm
---You're pointing out something interesting here. At a given fan speed, the volume of air is going to be pretty much the same. But colder air is denser, so you are moving more mass. That denser air may or may not be better at removing heat, but it definitely takes more horsepower to move the same volume of colder, denser air.
Now move the variable. At a given temperature of cooling air and a given temperature of the engine, does air speed through the fins change the "heat load" carried by that air?
Absolutely. The coefficient is not fixed, it is dependent on many factors, air speed being a crucial one.
Amskeptic wrote:
Fri Jan 25, 2019 12:12 pm
Then add an unusually hot engine with a big delta-T on a cold cold day, and does the aluminum bottle up the heat because it cannot conduct fast enough to the fin area?? THEN you have a hot engine on a cold day.
The aluminum has its own thermal properties. In its case we are talking about conduction between the combustion chamber and the outside air. The rate of heat transfer is the temperature difference times the conductivity of the material. Analogous to the coefficient for convection, but it is a known constant for each material, not dependent on myriad factors. The equation is for steady-state heat flow. There is thermal inertia in metals, so things can be different until they settle in to equilibrium. Once equilibrium is reached, there is no “bottling up”, it is a continuous flow.
The aluminum only knows what’s on each side of it. So if it is hotter in one situation vs another, the only choices are:
1) More heat is being produced on the hot side
2) Less heat is being carried away on the cool side.

In our situation, the only choices that explain the same temperature with a higher Delta-T are:
1) more heat is being produced because the engine is working harder or something else is different with the combustion
2) the same amount of heat is being carried away, even though Delta-T is higher (and this must mean the coefficient is lower, whatever the reason)

I'm willing to entertain reasons for (2), but I think (1) is more likely.
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Amskeptic
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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Tue Jan 29, 2019 11:06 am

hippiewannabe wrote:
Mon Jan 28, 2019 2:42 pm
Is it sad that I am passionate about Thermodynamics? :geek:
It is a joy. I have re-arranged your points for my mental thought-flow, which has a very low coefficient in the best of circumstances . . .

hippiewannabe wrote:
Mon Jan 28, 2019 2:42 pm
A) There is thermal inertia in metals, so things can be different until they settle in to equilibrium. Once equilibrium is reached, there is no “bottling up”, it is a continuous flow.

My question (why does a hot vs cold day not correspondingly increase/reduce CHT readings?) is mostly apparent at full throttle. That would be the bottling up thermal inertia as the combustion chambers are treated to a transitory (up to ten or fifteen minutes on a long hill) blast of 2,000*F combustion temperatures.
That would correspond with E 1 below, yes?

hippiewannabe wrote:
Mon Jan 28, 2019 2:42 pm
B) The coefficient, multiplied by the temperature difference, gives you the amount of heat transfer.
C) The coefficient is not fixed, it is dependent on many factors, air speed being a crucial one.
D) combustion chamber / outside air rate of heat transfer is:
temperature difference X the conductivity of the material. it is a known constant for each material, not dependent on myriad factors. The equation is for steady-state heat flow.



Per C above, is there a formula that determines the heat carrying capacity of air Lets declare temperature and humidity as constants) at different speeds? I need to know if the efficiency of heat pick-up is linear or if it curves.

Per D, does your stated coefficient number include both conduction and convection in our inquiry?

hippiewannabe wrote:
Mon Jan 28, 2019 2:42 pm
E) The aluminum only knows what’s on each side of it. So if it is hotter in one situation vs another, the only choices are:
1) More heat is being produced on the hot side
2) Less heat is being carried away on the cool side.

So my questions here would be:
E 1 a transient hill climb where combustion gas temperatures are 2,000*F at mid-stroke, 1,500* at the moment of exhaust valve opening where gas flow is "damn quick", then about 1,200* steel valve seat temperature at the moment that the exhaust valve re-contacts, (note: very low mass in the valve and seat) which then floods through the heat-sink of the entire cylinder head, dispersing the temperature to about 400* at the top of the combustion chamber and about 600* at the exhaust pipes (which have intermittent hot gas flow pumping heat into them.

MEANWHILE, E 2 our cooling air, way at the outside of this metallurgical hell, is let's say 28* cold day! and 121* hot day! We'll claim exactly the same RPMs at full load.
WHYWHYWHY is my CHT gauge showing 400* on the 28* day, and only 425* on the hot day?
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BobD - 1978 Bus . . . . . . . . . . . 112,660 miles
Chloe - 1970 bus . . . . . . . . . . . 206,845 miles
Naranja - 1977 Westfalia . . . . . 112,885 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,899 miles

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hippiewannabe
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Re: All You CHT Gauge Drivers Report Here

Post by hippiewannabe » Fri Feb 08, 2019 10:52 pm

Amskeptic wrote:
Tue Jan 29, 2019 11:06 am

MEANWHILE, E 2 our cooling air, way at the outside of this metallurgical hell, is let's say 28* cold day! and 121* hot day! We'll claim exactly the same RPMs at full load.
WHYWHYWHY is my CHT gauge showing 400* on the 28* day, and only 425* on the hot day?
Well gosh, I was struggling to explain how head temps could be the same. If you spot me 25*, I think we can easily do it.

400-28 = 372* Delta T
425-121= 304* Delta T
(372-304) / 372 = 18% difference, to be explained by more heat produced at colder temperatures and/or more efficient heat transfer by hot air than cold air.

We know that:
- cold air is denser than hot air, making the engine work harder to push the car through the air and the air through the fan
- denser air hangs on to laminar flow longer before turning turbulent, meaning it will be less efficient at removing heat

I'm satisfied the above can adequately explain the mystery.
When thousands of people believe a made-up story for a month, we call it fake news. When a billion people believe a made-up story for a thousand years, we call it a religion.

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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Sat Feb 09, 2019 1:23 pm

hippiewannabe wrote:
Fri Feb 08, 2019 10:52 pm
Amskeptic wrote:
Tue Jan 29, 2019 11:06 am

MEANWHILE, E 2 our cooling air, way at the outside of this metallurgical hell, is let's say 28* cold day! and 121* hot day! We'll claim exactly the same RPMs at full load.
WHYWHYWHY is my CHT gauge showing 400* on the 28* day, and only 425* on the hot day?
Well gosh, I was struggling to explain how head temps could be the same. If you spot me 25*, I think we can easily do it.

400-28 = 372* Delta T
425-121= 304* Delta T
(372-304) / 372 = 18% difference, to be explained by more heat produced at colder temperatures and/or more efficient heat transfer by hot air than cold air.

We know that:
- cold air is denser than hot air, making the engine work harder to push the car through the air and the air through the fan
- denser air hangs on to laminar flow longer before turning turbulent, meaning it will be less efficient at removing heat

I'm satisfied the above can adequately explain the mystery.

I live with an airline pilot. I will discuss it with him. His thrust settings and EGTs and fuel burn in cold vs hot conditions may offer insights . . . stay tuned.
Colin
BobD - 1978 Bus . . . . . . . . . . . 112,660 miles
Chloe - 1970 bus . . . . . . . . . . . 206,845 miles
Naranja - 1977 Westfalia . . . . . 112,885 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,899 miles

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hippiewannabe
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Re: All You CHT Gauge Drivers Report Here

Post by hippiewannabe » Mon Feb 11, 2019 8:24 am

When thousands of people believe a made-up story for a month, we call it fake news. When a billion people believe a made-up story for a thousand years, we call it a religion.

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Re: All You CHT Gauge Drivers Report Here

Post by 71whitewesty » Tue Mar 19, 2019 11:14 am

Where is that thread on Colin’s test of running with and without the foam seal? I’ve searched and can’t seem to find it.

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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Thu Mar 21, 2019 3:18 pm

71whitewesty wrote:
Tue Mar 19, 2019 11:14 am
Where is that thread on Colin’s test of running with and without the foam seal? I’ve searched and can’t seem to find it.
It is not in the technical Forums because I have a bunch of technical nuggets stuck all in my stories of avoiding police and trains. I believe it was 2011. Found this passing reference using asterisks in the body of the thing to conclude at the end. I have not found the "technical report" of all of those pieces I was taking off:

viewtopic.php?f=65&t=9995&p=179211#p178990
BobD - 1978 Bus . . . . . . . . . . . 112,660 miles
Chloe - 1970 bus . . . . . . . . . . . 206,845 miles
Naranja - 1977 Westfalia . . . . . 112,885 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,899 miles

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Re: All You CHT Gauge Drivers Report Here

Post by 71whitewesty » Fri Mar 22, 2019 7:32 am

Ok. I know there was another part of this and I have actually looked hard for it. But no big deal. It was only to show some non believers that taking the foam seal out actually won’t melt the engine. I would never have guessed it but your report I found quite interesting.

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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Sat Mar 23, 2019 1:46 pm

71whitewesty wrote:
Fri Mar 22, 2019 7:32 am
Ok. I know there was another part of this and I have actually looked hard for it. But no big deal. It was only to show some non believers that taking the foam seal out actually won’t melt the engine. I would never have guessed it but your report I found quite interesting.

I posted a correction on theSamba regarding my testing on the BobD.

The foam seal and the engine compartment seal, and the oil fill pipe grommet, and the fresh air hose grommets, caulked alternator and rear tins, and whatnot, all have little to do with engine cooling. It has been verified through the countless VWs I have driven with missing this's, thats, and the others, yet they ran cool. Why did they run cool? Because they felt like it. Only the spark plug boots and a couple of little plastic caps (for the Porsche TS 2) on the actual cooling tins downstream of the fan mattered, and they mattered big.

However, there is a very real reason that VW went nuts with the sealing, the grommets, the engine hatch seal, the caulking, and that is that Volkswagen HAD to ensure that the heater intake air was exhaust-free! Consumer Reports busted them in 1971 and it was almost a death blow to the family wagon crowd.

Makes perfect sense.
Colin
BobD - 1978 Bus . . . . . . . . . . . 112,660 miles
Chloe - 1970 bus . . . . . . . . . . . 206,845 miles
Naranja - 1977 Westfalia . . . . . 112,885 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,899 miles

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Johnooot
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Re: All You CHT Gauge Drivers Report Here

Post by Johnooot » Mon Aug 12, 2019 6:27 am

Amskeptic wrote:
Sat Mar 23, 2019 1:46 pm
Only the spark plug boots and a couple of little plastic caps (for the Porsche TS 2) on the actual cooling tins downstream of the fan mattered, and they mattered big.
Can you elaborate on the impact the spark plug boots had on cooling?

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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Mon Aug 12, 2019 9:46 pm

Johnooot wrote:
Mon Aug 12, 2019 6:27 am
Amskeptic wrote:
Sat Mar 23, 2019 1:46 pm
Only the spark plug boots and a couple of little plastic caps (for the Porsche TS 2) on the actual cooling tins downstream of the fan mattered, and they mattered big.
Can you elaborate on the impact the spark plug boots had on cooling?

Spark plug boots are downstream of the fan. They count for cooling (I had a 20* uptick @ 107* ambient without them).
Colin
BobD - 1978 Bus . . . . . . . . . . . 112,660 miles
Chloe - 1970 bus . . . . . . . . . . . 206,845 miles
Naranja - 1977 Westfalia . . . . . 112,885 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,899 miles

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Re: All You CHT Gauge Drivers Report Here

Post by airkooledchris » Tue Aug 13, 2019 12:56 pm

Here's a trick I have been meaning to try out that is supposed to help get rid of heat faster than stock:
(this isn't my idea, and these aren't my pictures)

Image
Image


(reportedly) Jake discovered that this can lower head temps by 10 degrees.
1979 California Transporter

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Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Tue Aug 13, 2019 5:36 pm

Interesting pictures. Someone on the Shop Talk Forums (years ago) mentioned running without the sled tins showed a noticeable drop in head temps. These seem to bridge the gap between cooler temps and protected pushrod tubes!

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Re: All You CHT Gauge Drivers Report Here

Post by airkooledchris » Wed Aug 14, 2019 9:22 am

exactly, retain the rock guard feature but allow more heat to escape. very slowly ive begun to understand Jake's approach of 'all in the combo' with things like this or leaving off the fan guard for another 5* of cooling. Add in the plug boots like Colin mentioned above and all of the *little* things and you are talking about taking 410* head temps at highway speed down to 360* - and that takes a LOT of weight off your shoulders when pushing it down the highway all day long.

It would be worth compiling a list of all of the 'little' things that add up to better cooling.
Dump tubes
Fan guard (though not without monitoring head temps, because god forbid you suck in a bag or something and fail to realize)
pushrod tube guards
plug boots
body to tinware foam seal
underpants
profits
1979 California Transporter

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