Temperature management questions for a turbo engine

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Re: Temperature management questions for a turbo engine

Post by ptuomov »

Atom wrote: Thu Jul 19, 2018 5:09 pm
ptuomov wrote: Tue Jul 17, 2018 11:05 am - Additional vents in the hood to cool down the area around the exhaust manifolds
Here is Aston's solution on the 90's Vanquish.
See the 4 rectangular chimneys.
What’s the intended direction of air flow thru those chimneys? Up from the exhaust manifolds and out thru the hood, I’m guessing.
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Re: Temperature management questions for a turbo engine

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That part of a hood is usually low pressure, reinforcing convection flow.
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Re: Temperature management questions for a turbo engine

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In the 928 (and other transaxle Porsches of the era), the air is designed to flow first thru the radiator and then cooling the exhaust. I don’t want to vent it up thru the hood in this particular make and model.

To the extent that the factory has flown something out the hood, it’s been the separate intercoolers ducting in 968 Turbo.

For engine cooling, if I do something, I need to flow more air in thru the hood with NACA ducts and route the extra air down towards the exhaust manifolds. 968 Turbo has that sort of air inlet in the hood:

Image

The 928 stock belly pan already has NACA ducts from the factory flowing air up from under the car towards the motor mounts and exhaust manifolds.
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Re: Temperature management questions for a turbo engine

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ptuomov wrote: Thu Jul 19, 2018 1:06 pm David, those numbers are for the top piston ring groove temps, right? Not the whole engine temps (which would be ambiguous anyway, as it depends so much on the cooling system).
These numbers are also from Mahle, twenty years ago. Don't know which engine they used.
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Re: Temperature management questions for a turbo engine

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David Redszus wrote: Fri Jul 20, 2018 12:09 am
ptuomov wrote: Thu Jul 19, 2018 1:06 pm David, those numbers are for the top piston ring groove temps, right? Not the whole engine temps (which would be ambiguous anyway, as it depends so much on the cooling system).
These numbers are also from Mahle, twenty years ago. Don't know which engine they used.
You mentioned that piston to bore clearance has a big impact on temperatures. Did you mean piston temperatures or the temperature or rather cooling heat flow of the whole engine?
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Re: Temperature management questions for a turbo engine

Post by David Redszus »

ptuomov wrote: Fri Jul 20, 2018 6:59 am
David Redszus wrote: Fri Jul 20, 2018 12:09 am
ptuomov wrote: Thu Jul 19, 2018 1:06 pm David, those numbers are for the top piston ring groove temps, right? Not the whole engine temps (which would be ambiguous anyway, as it depends so much on the cooling system).
These numbers are also from Mahle, twenty years ago. Don't know which engine they used.
You mentioned that piston to bore clearance has a big impact on temperatures. Did you mean piston temperatures or the temperature or rather cooling heat flow of the whole engine?
Thermal flux or heat transfer flow rate, is a function of surface area, distance, and specific heat of the oil film.
The tighter the clearance, the better the heat transfer up to a point....of metal asperities touching each other.
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Re: Temperature management questions for a turbo engine

Post by ptuomov »

Ok since loose piston clearances (within reason) lead to less friction and more power but less heat transfer from piston to bore, looser clearances should therefore tax the engine cooling system less (but make pistons run hotter and create risk there).
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Re: Temperature management questions for a turbo engine

Post by ptuomov »

bentvalves wrote: Tue Jul 17, 2018 11:33 am care to share some under hood pics of this love affair?
Here's something:
https://www.youtube.com/watch?v=16XiHPpvuzk
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Re: Temperature management questions for a turbo engine

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MadBill wrote: Tue Jul 17, 2018 10:14 pmAt a glance, more oil capacity would seem logical, but in reality it just takes a little longer to peak.
Better to live to fight another second, in my opinion. It's a car engine with highly variable duty cycle, so thermal inertia of more oil will help.
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Re: Temperature management questions for a turbo engine

Post by ptuomov »

gruntguru wrote: Wed Jul 18, 2018 12:07 am
peejay wrote: Tue Jul 17, 2018 10:20 pmAdd more fuel as temps rise. Period.
Better still - add water.

Beyond about 14:1 the extra fuel is doing nothing except evaporative cooling. A litre of water provides 10 times the cooling of a litre of gasoline.
Water injection is a possibility to suppress knock, but not being implemented at this round. From the convenience perspective, it would have to be windshield wiper fluid. How much water (or wiper fluid) would you have to inject per minute to "move the needle" in terms of the heat flow requirements on the cooling system?
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Re: Temperature management questions for a turbo engine

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gruntguru wrote: Wed Jul 18, 2018 8:30 pm
ptuomov wrote: Wed Jul 18, 2018 7:51 am Interestingly, you mention piston temperatures. I was just studying Mahle’s piston temperature results in their knock detection study. This is a chapter in the piston book.

What they found is that holding ignition timing constant, richer mixture lowered the piston temperature. If they however then advanced the ignition timing back to the knock limit, the piston temperature actually went up while the engine didn’t make any more power. Their conclusion from this test was that fuel cooling doesn’t help pistons run cooler, holding the power produced constant. So running rich and advancing ignition doesn’t make pistons any safer.
Doesn't make sense. If advancing the timing didn't increase the power, they have advanced past MBT. Why would you do that?
I think that almost all well-designed pump gas motors are knock limited and making most wot power at the knock limit. If this weren't the case, in my opinion one should add compression (or, better, boost).
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Re: Temperature management questions for a turbo engine

Post by Caprimaniac »

One other thing you can consider is - if you still have inner fenders- is to make vents in the inner fenders to make the air, especially near the headers, move. Vents out the low pressure area in the Hood is a must, agree to that.
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Re: Temperature management questions for a turbo engine

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Caprimaniac wrote: Fri Jul 20, 2018 4:07 pm One other thing you can consider is - if you still have inner fenders- is to make vents in the inner fenders to make the air, especially near the headers, move. Vents out the low pressure area in the Hood is a must, agree to that.
The engine bay is designed to flow air from the radiator into the exhaust manifold and out under the car. I feel that venting out from the hood would improve radiator cooling but hurt the air cooling of the exhaust components. The belly pan bleeds some of the air under the car, but then picks up even more with NACA duct under the car to cool the exhaust manifold and motor mounts:
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Re: Temperature management questions for a turbo engine

Post by Kevin Johnson »

Herr Kuhn's next project; graft it on there somehow. Use it for cooling something -- MORE. :wink:

https://www.ebay.com/i/222820036425?chn=ps
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Re: Temperature management questions for a turbo engine

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Kevin Johnson wrote: Sat Jul 21, 2018 9:39 pm Herr Kuhn's next project; graft it on there somehow. Use it for cooling something -- MORE. :wink:

https://www.ebay.com/i/222820036425?chn=ps

s-l1600.jpg
If I put that on a 928, it'll look like me in my 30th birthday party. It was a costume party. I was dressed up as a German man who was dressed up as a woman. True story.
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