here is one for you on heat

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sgkent
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here is one for you on heat

Post by sgkent » Tue May 23, 2017 3:44 pm

Why is it that the T1 motor fixed up and running right produces lower head temps than the T4 engine does at the same speeds? The fan is bigger on a T1 engine but its speed is reduced by the pulleys vs the T4 engine. The T4 has a larger oil cooler than the T1. Yet - compared to my 1971, my 1977 runs hotter. It just occurred to me that rarely do I hear someone complaining that their T1 runs too hot, while many complain the T4 runs hot even when the bus speeds are similar. Engine RPM?
TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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Bleyseng
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Re: here is one for you on heat

Post by Bleyseng » Tue May 23, 2017 6:58 pm

I'd say exhaust design as T4 exhaust ports have a sharp bend right off the bat. The heads were designed for a Type Four car which is a different animal. 914's run hot but its the problem of the cooling intake behind the rear window and long exhaust runners .
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
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Ronin10
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Re: here is one for you on heat

Post by Ronin10 » Wed May 24, 2017 11:00 am

To get the same CHTs for two different engines, your (Heat Generated - Heat Dissipated) would need to be constant.

From the Heat Generated aspect, an engine will create heat from the combustion chamber, friction of the moving parts, and reheating from heat dissipating sources on the engine (i.e. the heat exchangers when sitting at idle, although you could treat this as a diminished Heat Dissipation).

On the Heat Dissipated side of things, the engine dissipates heat through the cooling airflow over the cylinder heads, via the oil cooler, through the exhuast, and via thermal conduction through the engine block into the vehicle body and other components.

There may be other heat sources or sinks that I overlooked, but these are the heavy hitters, I think.

So with the table set there, here are some random Type 4 vs. Type 1 comparisons that hit my mind before I need to get back to work that would affect the Heat Generated and Heat Dissipated for the two engines:
  • The cooling flow generated by the Type 4 flows over the top of the cylinders then has to make a 180 deg turn to flow out underneath the cylinder heads. That 180 deg turn is not a smooth, free flowing turn and will slow down the air substantially, create substantial eddies, allowing it soak up more heat than on a Type 1 where the cooling air is ejected right out the bottom of the fan along a contoured engine tin, making only one 90 deg turn.
  • As I recall, both engines have similar compression ratios, thus should have near similar combustion chamber pressures at the time of spark, so the larger displacement of the Type 4 engine will have a greater heat release per combustion event.
  • As Geoff said, the 75-78 buses have a much more tortuous exhaust path, leading to elevated exhaust temperatures leading to elevated heat exchanger temps and thus, everything they contact and re-radiate heat to being at slightly higher temps.
  • The aluminum Type 4 block is a much bigger heat sink, but that only benefits when the engine is getting up to full operating temperatures. Once stable, the thinner, magnesium case of the Type 1 (and everything it touches) is better cooled by a given airflow.
  • Given the robustness of the aluminum case, the VW engineers, may simply have concluded that they can tolerate a operating temperature since there will be much less thermal expansion relative to a magnesium case.
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Re: here is one for you on heat

Post by airkooledchris » Wed May 24, 2017 1:16 pm

sgkent wrote:
Tue May 23, 2017 3:44 pm
Why is it that the T1 motor fixed up and running right produces lower head temps than the T4 engine does at the same speeds? The fan is bigger on a T1 engine but its speed is reduced by the pulleys vs the T4 engine. The T4 has a larger oil cooler than the T1. Yet - compared to my 1971, my 1977 runs hotter. It just occurred to me that rarely do I hear someone complaining that their T1 runs too hot, while many complain the T4 runs hot even when the bus speeds are similar. Engine RPM?
I agree on the engine RMP portion of that, but can't say it's the difference between the two engines. I just know that while we've always been told not to lug these engines, rather hit that max cooling RMP of 3600 while climbing, I can usually keep my head temps much cooler by lugging the motor up a hill rather than downshifting and giving it more cooling fan. I DO notice however that this tends to drive the oil temps up much higher/faster, so you have to pick your poison. Running slightly larger diameter tires also drops the RPM's down at faster highway speeds, albeit while increasing the load on the engine. Ive seen higher head temps on my setup after switching to the BFG's in their 195 size Vs the 27x8.5R14's that I used to run before (though I can ramp UP to speed faster with the BFG's.)
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sgkent
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Re: here is one for you on heat

Post by sgkent » Wed May 24, 2017 2:44 pm

I wonder if the thicker air vanes in the T4 fan flow less air than the scooped metal ones on a T1. T4 ones are more air foil shaped so one would expect them to pull more efficiently for the surface area however, I suspect that the observation made by Ronin10 is a good one. The air comes into the T4 shroud and is forced out to the edges where it is ejected under pressure. It turns 90 degrees down in a short space with little guidance, and then makes another 90 degree to exit out the back. While it may allow each molecule of air to pick up more heat as it passes thru, I suspect that the volume of air suffers somewhat due to all the turns. I will say this to support that theory - in racing in years past I found that simply adding an air horn (Venturi stack) to a carb did more to increase engine RPM and air flow than any type of air cleaner or open carb.

example from online photo:

Image
TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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Re: here is one for you on heat

Post by Amskeptic » Fri May 26, 2017 7:05 am

sgkent wrote:
Wed May 24, 2017 2:44 pm
I wonder if the thicker air vanes in the T4 fan flow less air than the scooped metal ones on a T1.


The Type 1 engine has a fan that runs at 1.6 times that of the crankshaft. That means a downshift really does help.

The Type 4 engine's fan is 1:1 at all times.

In my experience, the Type 1 engine runs cooler generally because it has less output. If you ran a Type 4 exactly to mimic the output of a Type 1 instead of availing yourself of all of its power, you'd see less of a difference in temperatures.

Perhaps more importantly, the bus Type 1 engines get to enjoy richer mixture specifications straight from the factory. 1-3 % Co is more relaxed than the later Type 4's .7%

In the engineering, Type 4 heads allegedly flow 22% greater cooling air. I believe it. But while the Type 1 sensibly exits the exhaust ports out the sides, the Type 4 torturously routes the exhaust in a hoped-for "cross flow" that never actually worked to its intended effect, the Type 1s have always breathed better.

Both cooling systems are fine. The stock fan shrouds and fans are well designed in both instances, there is more available air than the engine "consumes". We all get to enjoy the excess capacity of these cooling systems as we build performance engines that manage to cool themselves with stock cooling system parts.

The greatest problem with cooling seems to me to be the inadvertent errors we make with compression ratios/effective compression, variable tin fitment/color issues, mixtures, timing curves, and filth. Add to that those rebuilders who love to bump compression ratios and stick in performance cams and exhaust systems all over the place, and the factory engineering can't overcome some of the unleashed variables.

My 1700 and 1800 Type 4 engine experiences have been that they cool themselves just fine. The 2.0 engines have just a little too much low down torque, too much mass in the pistons, crowded cylinder barrels, and lean mixtures. VW had one moment where their engineering tripped up and that was the 2.0 engines that scuffed 94mm pistons. They decided that 2.0 was pretty much it for engine size.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Bleyseng
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Re: here is one for you on heat

Post by Bleyseng » Fri May 26, 2017 7:24 am

The exhaust heat problem is why Raby kept the exhaust valve open for a little more duration in his cams. With the early heat exchangers ( shorter length and separate runners) combined with a 4 into 1 tuned exhaust muffler they run cooler than stock. Mine does in addition to the additional HP. Raby has always said "Its in the combo" which means heads, cam, exhaust, CR and AFR all have to be right for more HP and cooler temps. If not you overwhelm the cooling system. VW kept having to run leaner mixtures and restrictive exhaust to pass the emissions regs which made everything even hotter so they had to go to engines with water cooling just to control the heat.
Type 1's had a single carb that dumped a rich fuel mix down into the heads to cool them in addition to being being small HP engines.
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
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Re: here is one for you on heat

Post by asiab3 » Fri May 26, 2017 9:07 am

I've been interested in replying to this thread for a few days, but I couldn't figure out how to say what I wanted to say.

Doesn't the Type 4 head have more aluminum mass and surface area for cooling? If so, why should we even bother comparing numbers between the two? Or what if the difference really is just the vertical T1 fan blowing straight on the CHT thermocouple?

I think the almost unrelated topics of oil temperature and head temperature are fun to examine, but I also disconnect my gauges for beautiful drives. No sense in ruining the scenery.

When the Type 1 sucks a rag or a bag into the fan, no gauge in hell will get your attention faster than the pure chaos that is your newfound chassis vibration. (Try it; have a helper throw an anti-Californian grocery bag into your fan while you hold the engine at 3,000 rpm in the driveway!) I haven't put a bag in a Type 4 without the fan guard yet. Any volunteers?

Robbie
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sgkent
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Re: here is one for you on heat

Post by sgkent » Fri May 26, 2017 6:02 pm

because aluminum softens whether it is a T1 or T2 head. I've been told Adrian uses wider valves and seats on T4 heads to get the seat into metal that has less damage to it from the heat. I have never seen T1 head damage like T4 buses get.

And yes - it may have to do with the T1 plug area faces the direction the fan air hits first (straight down), where as the T4 plugs being cooled by air thar turns 90 degrees (air from front then forced down by shroud). I don't know for sure but I was thinking about how much hotter a T4 engine gets even at the same speed as a T1 engine and it just seemed like VW missed something on that. Maybe the bottom of a T1 head gets hotter than a T4 head.

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TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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Re: here is one for you on heat

Post by Amskeptic » Fri May 26, 2017 6:39 pm

sgkent wrote:
Fri May 26, 2017 6:02 pm
Maybe the bottom of a T1 head gets hotter than a T4 head.

I just drive'm.

We need to paint that horrid coil of yours in factory black with my patented "sort of looks like phenolic" brown on the end then slap a blue Bosch sticker on it. It really does run cooler.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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sgkent
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Re: here is one for you on heat

Post by sgkent » Fri May 26, 2017 7:30 pm

Sorry - the black one is on the bus now. The blue one I used until I found the right black one then guess what - the manufacturers part number on the bottom is the same on both. How could that be? They ran out of blue paint? Or the other way around?

Decided on a crank yet?
TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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asiab3
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Re: here is one for you on heat

Post by asiab3 » Sun May 28, 2017 10:52 am

Amskeptic wrote:
Fri May 26, 2017 6:39 pm
I just drive'm.
Aye.

Perhaps the T4 higher power output translates to more heat generated; I don't know of anyone running a 2-liter Type 1 engine with a CHT gauge installed. Anybody?

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: here is one for you on heat

Post by Jivermo » Sun May 28, 2017 12:22 pm

Ya know...I just like looking at these engines. They are pure works of art.

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Amskeptic
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Re: here is one for you on heat

Post by Amskeptic » Mon May 29, 2017 8:25 am

sgkent wrote:
Fri May 26, 2017 7:30 pm
Decided on a crank yet?



I will stop at BugHaus in Connecticut and see if there is an actual genuine NOS forged 1600 crank.
ColinDamnRainWon'tStop
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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