All You CHT Gauge Drivers Report Here

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Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Tue Oct 02, 2018 10:06 pm

Latest post of the previous page:

Has anybody who stays in one state for a while noticed a rise or fall in head temps due to fuel formulation? I just realized my DD CHT ADD may just be... that..

Robbie
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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Wed Oct 03, 2018 10:00 am

asiab3 wrote:
Tue Oct 02, 2018 10:06 pm
Has anybody who stays in one state for a while noticed a rise or fall in head temps due to fuel formulation? I just realized my DD CHT ADD may just be... that..

Robbie

I do not believe I am able to discern fuel formulation as a CHT variable.
It is a great mystery to me why ambient temperatures seem not to have as great an effect on CHTs as I might have surmised.

I have done delta-T analyses in my head that suggest that a drop in ambient temperatures from 115* to 43* should improve heat transfer off the heads by a nice ridiculous amount, but when you add to the equation that the engine is a big huge heat sink that has stored up a big pile of excited atoms, the cooling air that only briefly passes by the hot heads is limited in its absorption of heat. That means that 43* air can only absorb "X" calories of heat barely different than 115* air that briefly passes by. Does this make sense?
Colin
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Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Wed Oct 03, 2018 2:43 pm

It makes sense!

I think back to my remote control car racing years and years ago, when changing ambient temperatures would screw with our fuel mixtures enough to warrant leaning out the engine when hot (thinner air = less O2 content) and richening the mixture when cold (more O2 content in cooler/denser air) for optimal performance without smearing pistons on the cylinder walls. My, those 1.2/1.5cc two-cycle engines were remarkably similar to our Volkswagens...

366* tops last night, floored from New Hampshire to Manhattan.
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Re: All You CHT Gauge Drivers Report Here

Post by SlowLane » Wed Oct 03, 2018 3:45 pm

Just want to be clear that I have no special insight into gasoline formulations or how they may or may not affect cylinder combusiton temperatures. I was just throwing that out as an example of a variable which one might normally not consider when deciphering CHT behavior.

Although I could certainly see how the winter gas could be formulated to run hotter in parts of the country where winter actually occurs. I should think that it would help with improving engine warmup times.

Or maybe I'm just blowing gas and simply adding to the conjecture, myth and poorly understood science that drives our internet entertainment.
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Re: All You CHT Gauge Drivers Report Here

Post by hippiewannabe » Wed Jan 23, 2019 11:27 pm

Amskeptic wrote:
Wed Oct 03, 2018 10:00 am
It is a great mystery to me why ambient temperatures seem not to have as great an effect on CHTs as I might have surmised.

I have done delta-T analyses in my head that suggest that a drop in ambient temperatures from 115* to 43* should improve heat transfer off the heads by a nice ridiculous amount, but when you add to the equation that the engine is a big huge heat sink that has stored up a big pile of excited atoms, the cooling air that only briefly passes by the hot heads is limited in its absorption of heat. That means that 43* air can only absorb "X" calories of heat barely different than 115* air that briefly passes by. Does this make sense?
Colin
Hmm.
Newton's Law of Cooling states the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings while under the effects of a breeze. The constant of proportionality is the heat transfer coefficient.
q=h*A*(delta T) where q is the rate of heat transfer, h is the heat transfer coefficient, A is surface area.

You're implying the heat transfer coefficient increases as air temperature increases, such that hot air is so much better at removing heat than cold air that it makes up for the decreased delta-T.

I don't think so.

If we assume the head temp is 400 degrees, let's compare a 115 degree day with a 43 degree day.
400-115=285, 400-43=357. 357/285= 25% greater delta-T on a cold day. If h is the same, that's a 25% increase in heat transfer. In 16 credit hours of Thermodynamics, Heat Transfer and Fluid Mechanics, a change in h with temperature was never mentioned. But I can see hot air has different density, more energetic molecular movement, greater water vapor capacity, etc. So maybe a a few percent greater h. Low enough to be ignored in most cases, but something. Let's give it 5%.

I think another 20% could be explained by:
- cold air is denser, leading to greater air resistance to our rolling billboards, making the engine work harder
- colder temps reduce air pressure in the tires. If we forget to adjust, it makes the engine work harder
- colder temps make the rubber in the tires stiffer, making the engine work harder
- colder temps tell the fuel system to enrichen the mixture, perhaps beyond what stoichiometry would be

whaddya think?
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Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Thu Jan 24, 2019 12:06 am

hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm

I think another 20% could be explained by:
a - cold air is denser, leading to greater air resistance to our rolling billboards, making the engine work harder
b - colder temps reduce air pressure in the tires. If we forget to adjust, it makes the engine work harder
c - colder temps make the rubber in the tires stiffer, making the engine work harder
d - colder temps tell the fuel system to enrichen the mixture, perhaps beyond what stoichiometry would be

whaddya think?
All interesting thoughts. Having taken zero credits in thermodynamics, I can only respond to certain bits…

a) Our buses are not THAT inefficient in the wind tunnel, especially considering most folks seem to drive 55-60mph.

b) I always adjust my tires when the weather shifts, as I have onboard air and it only takes a minute or two for all four. (And those Maxxis tires aren't cheap!)

c) Would stiffer give them less rolling resistance?

d) No way, no how would a stock carb choke richen up a mixture once warmed up. A fuel-injected TS1 in the intake air sensor? Maybe. Someone want to trick their TS1 into "full warmed up" mode and report back? Even then, wouldn't the temps go down more than what the CHT drivers are seeing? (Which is not a significant drop…)

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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Thu Jan 24, 2019 9:25 am

hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
Hmm.
Newton's Law of Cooling states the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings while under the effects of a breeze.
Please define "effects of a breeze"

hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
The constant of proportionality is the heat transfer coefficient.
q=h*A*(delta T) where q is the rate of heat transfer, h is the heat transfer coefficient, A is surface area.

You're implying the heat transfer coefficient increases as air temperature increases, such that hot air is so much better at removing heat than cold air that it makes up for the decreased delta-T.
I don't think so.
Absolutely no such implication was offered. My entire thesis had to do with the limitations of "the breeze" to pick up heat.

hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
If we assume the head temp is 400 degrees, let's compare a 115 degree day with a 43 degree day.
400-115=285, 400-43=357. 357/285= 25% greater delta-T on a cold day.
If h is the same, that's a 25% increase in heat transfer.
The missing variable here is the "breeze". My muse had to do with the absorption of heat in a rapidly moving breeze. We need to address the conduction/convection interface between a hot (conducting) aluminum fin and whatever the speed of the (convection) breeze is going past that aluminum.

hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
In 16 credit hours of Thermodynamics, Heat Transfer and Fluid Mechanics, a change in h with temperature was never mentioned. But I can see hot air has different density, more energetic molecular movement, greater water vapor capacity, etc.
I, and every pilot everywhere, find that hot air is less efficient in every way, lift, combustion, cooling.

hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
whaddya think?
My observation is that an air-cooled engine seems less sensitive to ambient cooling air temperature and more sensitive to the volume of whatever-temperature-the-air. Why do my CHTs seem so relatively impervious to the day's temperatures?

The experiment would be to provide a controlled quantity of air, lets say 100 cubic feet, at 40*, and ram it through an air-cooled engine at a CHT of 400* let's say, and a fan speed of 3,500 rpm, then measure its temperature increase.

Then get another 100 cubic feet of air at 120*. Ram it through an air-cooled engine at same CHT of 400* at fan speed of 3,500 rpm, and measure its temperature increase.

Your assumption would be that the 40* air should pick up more heat because of the deltaT difference. My observations/intuition/experience says something's up, and I would not be surprised to find that the two different temperature air quantities actually pick up a net same quantity of heat.
Colin
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BobD - 1978 Bus . . . . . . . . . . .111,145 miles
Chloe - 1970 bus . . . . . . . . . . . 206,812 miles
Naranja - 1977 Westfalia . . . . . 94,655 miles
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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Thu Jan 24, 2019 9:34 am

asiab3 wrote:
Thu Jan 24, 2019 12:06 am
hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm

I think another 20% could be explained by:
a - cold air is denser, leading to greater air resistance to our rolling billboards, making the engine work harder
b - colder temps reduce air pressure in the tires. If we forget to adjust, it makes the engine work harder
c - colder temps make the rubber in the tires stiffer, making the engine work harder
d - colder temps tell the fuel system to enrichen the mixture, perhaps beyond what stoichiometry would be

whaddya think?
All interesting thoughts. Having taken zero credits in thermodynamics, I can only respond to certain bits…

a) Our buses are not THAT inefficient in the wind tunnel, especially considering most folks seem to drive 55-60mph.

b) I always adjust my tires when the weather shifts, as I have onboard air and it only takes a minute or two for all four. (And those Maxxis tires aren't cheap!)

c) Would stiffer give them less rolling resistance?

d) No way, no how would a stock carb choke richen up a mixture once warmed up. A fuel-injected TS1 in the intake air sensor? Maybe. Someone want to trick their TS1 into "full warmed up" mode and report back? Even then, wouldn't the temps go down more than what the CHT drivers are seeing? (Which is not a significant drop…)

Robbie
Time to corral the fancy speculations, that's what.
Colder tires have less resistance, yes, so do over-inflated tires. Colder air improves the engine output way above the increased drag of denser air. These points are way beyond my inquiry. My inquiry is actually all about the amazing and mysterious interface between a conducting aluminum "radiator" and the convective properties of high speed air going past the radiator.

Keep the speculations coming, it is good mental exercise.
Colin
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BobD - 1978 Bus . . . . . . . . . . .111,145 miles
Chloe - 1970 bus . . . . . . . . . . . 206,812 miles
Naranja - 1977 Westfalia . . . . . 94,655 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 76,560 miles

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Re: All You CHT Gauge Drivers Report Here

Post by hippiewannabe » Thu Jan 24, 2019 10:52 pm

asiab3 wrote:
Thu Jan 24, 2019 12:06 am

a) Our buses are not THAT inefficient in the wind tunnel, especially considering most folks seem to drive 55-60mph.
---mediocre drag coefficient and a large frontal area argues otherwise. But irrespective of the efficiency, wind resistance is the dominant factor in required power to push the beast along, and it is related to air density

b) I always adjust my tires when the weather shifts, as I have onboard air and it only takes a minute or two for all four. (And those Maxxis tires aren't cheap!)
---well done

c) Would stiffer give them less rolling resistance?
---the Google says no

d) No way, no how would a stock carb choke richen up a mixture once warmed up. A fuel-injected TS1 in the intake air sensor? Maybe. Someone want to trick their TS1 into "full warmed up" mode and report back? Even then, wouldn't the temps go down more than what the CHT drivers are seeing? (Which is not a significant drop…)
---I'll punt on this one

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Re: All You CHT Gauge Drivers Report Here

Post by hippiewannabe » Thu Jan 24, 2019 11:20 pm

Amskeptic wrote:
Thu Jan 24, 2019 9:25 am
hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
Hmm.
Newton's Law of Cooling states the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings while under the effects of a breeze.
Please define "effects of a breeze"
---just means moving air. Newton didn't know about centrifugal fans, otherwise he would have said "forced convection".

Amskeptic wrote:
Thu Jan 24, 2019 9:25 am
hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
The constant of proportionality is the heat transfer coefficient.
q=h*A*(delta T) where q is the rate of heat transfer, h is the heat transfer coefficient, A is surface area.

You're implying the heat transfer coefficient increases as air temperature increases, such that hot air is so much better at removing heat than cold air that it makes up for the decreased delta-T.
I don't think so.
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.

Amskeptic wrote:
Thu Jan 24, 2019 9:25 am
hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
If we assume the head temp is 400 degrees, let's compare a 115 degree day with a 43 degree day.
400-115=285, 400-43=357. 357/285= 25% greater delta-T on a cold day.
If h is the same, that's a 25% increase in heat transfer.
The missing variable here is the "breeze". My muse had to do with the absorption of heat in a rapidly moving breeze. We need to address the conduction/convection interface between a hot (conducting) aluminum fin and whatever the speed of the (convection) breeze is going past that aluminum.
---Right. The absorption of heat is h*delta-T. Either warmer air is better at removing heat than colder air, or more heat is being produced at colder temperatures. Math can't lie.

Amskeptic wrote:
Thu Jan 24, 2019 9:25 am
hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
In 16 credit hours of Thermodynamics, Heat Transfer and Fluid Mechanics, a change in h with temperature was never mentioned. But I can see hot air has different density, more energetic molecular movement, greater water vapor capacity, etc.
I, and every pilot everywhere, find that hot air is less efficient in every way, lift, combustion, cooling.
---I was willing to let that explain some of mystery, but the impact is limited in either direction.

Amskeptic wrote:
Thu Jan 24, 2019 9:25 am
hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
whaddya think?
My observation is that an air-cooled engine seems less sensitive to ambient cooling air temperature and more sensitive to the volume of whatever-temperature-the-air. Why do my CHTs seem so relatively impervious to the day's temperatures?

The experiment would be to provide a controlled quantity of air, lets say 100 cubic feet, at 40*, and ram it through an air-cooled engine at a CHT of 400* let's say, and a fan speed of 3,500 rpm, then measure its temperature increase.

Then get another 100 cubic feet of air at 120*. Ram it through an air-cooled engine at same CHT of 400* at fan speed of 3,500 rpm, and measure its temperature increase.

Your assumption would be that the 40* air should pick up more heat because of the deltaT difference. My observations/intuition/experience says something's up, and I would not be surprised to find that the two different temperature air quantities actually pick up a net same quantity of heat.
---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.
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Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Fri Jan 25, 2019 12:39 am

I will wait and type a more thorough reply when I get off this phone, but I can absolutely attest to the difference in power a Type 1 engine makes when it’s fanbelt snaps on a 98* afternoon.

Robbie
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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Fri Jan 25, 2019 11:47 am

asiab3 wrote:
Fri Jan 25, 2019 12:39 am
I will wait and type a more thorough reply when I get off this phone, but I can absolutely attest to the difference in power a Type 1 engine makes when it’s fanbelt snaps on a 98* afternoon.

Robbie

Be helpful here.
Do you find that your engine runs inexplicably warmer than expected at 44* outside compared to 98* with a functioning fanbelt?

What would be your physics answer based mostly on intuition?
Colin
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BobD - 1978 Bus . . . . . . . . . . .111,145 miles
Chloe - 1970 bus . . . . . . . . . . . 206,812 miles
Naranja - 1977 Westfalia . . . . . 94,655 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 76,560 miles

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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Fri Jan 25, 2019 12:12 pm

hippiewannabe wrote:
Thu Jan 24, 2019 11:20 pm
Amskeptic wrote:
Thu Jan 24, 2019 9:25 am
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.

The only analogy that I can conjure up here, is the house fire.
a) Does a high speed blast of spraying water do a better job of dousing the flames than a contiguous (not broken up) slow stream of water?
b) Does 38* water put out the fire "better" than 118* water?
hippiewannabe wrote:
Thu Jan 24, 2019 11:20 pm
Amskeptic wrote:
Thu Jan 24, 2019 9:25 am
hippiewannabe wrote:
Wed Jan 23, 2019 11:27 pm
You're implying the heat transfer coefficient increases as air temperature increases, such that hot air is so much better at removing heat than cold air that it makes up for the decreased delta-T.
I don't think so.
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)


hippiewannabe wrote:
Wed Jan 23, 2019 11:27 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?

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.
ColinMyHeadHurts
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viewtopic.php?f=41&t=13755

BobD - 1978 Bus . . . . . . . . . . .111,145 miles
Chloe - 1970 bus . . . . . . . . . . . 206,812 miles
Naranja - 1977 Westfalia . . . . . 94,655 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 76,560 miles

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Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Fri Jan 25, 2019 4:09 pm

Amskeptic wrote:
Fri Jan 25, 2019 11:47 am
Be helpful here.
Do you find that your engine runs inexplicably warmer than expected at 44* outside compared to 98* with a functioning fanbelt?

What would be your physics answer based mostly on intuition?
Colin
I notice trends once the engine is fully warmed up, in head temperatures. It is not a 1:1 increase as the weather gets warmer, but maybe for every two or three degrees in ambient rise, the CHTs will go up one degree. I do know that I can not crest 400° unless it's at least 90° outside.

I was thinking that the drag of air could be worse on colder days, but the more I think about it once the engine is floored, it doesn't matter what the load is. Headwind, uphill, dragging generator/fan…

Robbie
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Re: All You CHT Gauge Drivers Report Here

Post by Amskeptic » Sat Jan 26, 2019 7:43 pm

asiab3 wrote:
Fri Jan 25, 2019 4:09 pm
A) It is not a 1:1 increase as the weather gets warmer, but maybe for every two or three degrees in ambient rise, the CHTs will go up one degree. I do know that I can not crest 400° unless it's at least 90° outside.

B) I was thinking that the drag of air could be worse on colder days, but the more I think about it once the engine is floored, it doesn't matter what the load is. Headwind, uphill, dragging generator/fan…

Robbie
a) And this is so utterly fascinating that I must find an answer.

b) and this is armchair physiczing the likes of which I used to get utterly lost in. And like you, I thought about things more and yes, once the accelerator is floored, the engine has no idea what the load is. I also discovered some real answers along the way like the foam seal has jack to do with cooling, and blocking off fan housing outlets actually diminishes cooling and most importantly for me as a Road Warrior, I seriously have to conclude that our driving techniques mean so very little and our set-up and state of tune means so very much. I am embarrassed to read of my exaggerated exit ramp cool-down techniques back in 2005/6/7/8 and ten years later, the new technique is "just drive it".
Colin
2019 Annual Funding Drive!
**********************************
viewtopic.php?f=41&t=13755

BobD - 1978 Bus . . . . . . . . . . .111,145 miles
Chloe - 1970 bus . . . . . . . . . . . 206,812 miles
Naranja - 1977 Westfalia . . . . . 94,655 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 76,560 miles

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Re: All You CHT Gauge Drivers Report Here

Post by asiab3 » Sat Jan 26, 2019 10:49 pm

May I make the following suggestion to the New Technique?
Amskeptic wrote:
Sat Jan 26, 2019 7:43 pm
the new technique is "just tune it and drive it".
In the first summer of owning my bus, (2012) I was too scared to drive over 50mph or 3/4 throttle in the Phoenix late-summer - 80°f-90°f. In traffic I was afraid of idling because I wasn't sure if it revving fast enough to cool itself. I would slow down or panic if my oven thermometer reached a certain point down the dipstick. Over-revved every shift "for better cooling." I got a CHT gauge the next year. Numbers seemed so so nice, (low 300's,) once Colin helped me dial the ring sender in and learn to drive… The engine didn't have proper dual port tin, and ended up releasing an intake valve seat a few months later.

In July of 2018 I was anxious to get home after a three month trip, and I wrapped up lunch with SGKent and floored it from Sacramento to Los Angeles. My phone told me it was 102°f outside most of the way° The cylinder head temps were in the high 420's for a few hours, and only cooled at all during fuel stops. Speeds averaged from 60mph to MmmHmmmDon'tWorryAboutIt until the Grapevine around 4pm. The intent was to replace this Colorado Mishap engine the next week with the pristine long-block I built recently. Life got in the way so I unplugged the CHT gauge drove it around the country again in September…

Valves haven't moved since June.
Robbie
1969 bus, "Buddy."
116k miles with me.
295k miles on Earth.

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