Drilling lightening holes in cylinder barrels

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ntst8 said:
Before the fins can release heat first it needs to get into them. I suspect that the drilling would reduce the ability of the fins to conduct heat away from the source, and reduce the quantity of heat which the fins could remove/hold, so that whether they then are better worse at releasing it would be irrelevent. Just my seat of the pants 5c worth.
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Holes like parallel fins can't radiate well so conduction at the source and convection at the ends. Welding extensions on would help best.
Hold the end of a foot long bar of 1 inch metal and heat the other end with a torch till you can't touch it. By the time heat gets to the end your holding the other end may by cool enough to grab. Drill a couple holes in it and it stops the flow or conduction.
The holes may work well with a lot of air flow like a ducted shroud karts use. I'm sure its been done.

I did drill 5/32" or 4mm all the holes between bores and I'm certain it had to help somewhat.
 
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The crux of the matter is that stated by TomU and ntst8 (and edgefinder who has chimed in as I write this)..... the purpose of the fins is to conduct heat away from the core (cylinders). Heat conduction is done via solid material; holes are an impediment to conduction.

Airflow wise, virtually no air will move thru any holes perpendicular to the fin surface, so the holes do nothing for convective heat transfer.

Convective heat transfer is enhanced if the horizontal fin surface is rough. Roughness breaks up the laminar boundary layer on the fin surface, changing the boundary layer from laminar to turbulent, which greatly increases convection.

Fin temperature drops quickly so the ends, or edges, of the fins do very little heat transfer. If they did do a significant amount of heat transfer, they should have been designed longer.

Black cylinders radiate more heat than other colors .... 3 times more than silver or white, unless we are talking about modern paints which are especially formulated to have high emissivity, nearing that of black.

Slick

EDIT: Polish the vertical edges of the fins if you like. Since the fin ends do little heat transfer, removing the surface roughness on the vertical edges, does not reduce convective heat transfer.
 
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Some great replies gents. It certainly looking like a thumbs down for the drill addicts !

It was actually Dave Degens who told me, some years ago, not to do it as holes would disturb the air flow and reduce cooling. He may not have been 100% up to speed with the exact science behind it, but it sounds like he was basically right.
 
TomU said:
That's kind of my point. And aluminum transfers heat significantly better than steel (but not as good as copper)

www.metalsupermarkets.com

Which Metals Conduct Heat Best? - Metal Supermarkets

Metals conduct heat, called thermal conductivity. It is important to consider in applications with high temperatures. But which metals conduct heat best?
www.metalsupermarkets.com www.metalsupermarkets.com
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It seems, by the above, copper wins the day, so assuming you can successfully block off the bores,push rod tunnels cam lifters, you should take said barrel to a chrome platers and get it dipped in a copper vat !
 
Bernhard said:
It seems, by the above, copper wins the day, so assuming you can successfully block off the bores,push rod tunnels cam lifters, you should take said barrel to a chrome platers and get it dipped in a copper vat !
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Nope, silver wins the day.

Metals, Metallic Elements and Alloys - Thermal Conductivities

Thermal conductivities of common metals, metallic elements and alloys.
www.engineeringtoolbox.com www.engineeringtoolbox.com

Bronze was used as a cylinder head material, I believe silver was as well.

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My rear sprocket is made of steel, but I painted it with aluminium paint. It is drilled and lightened like an aluminium Yamaha TZ sprocket. Everyone who sees it, thinks it is made from aluminium - really racy ? That is probably the reason some Commando barrels were painted silver. Makes everyone think you are riding a sports bike ?
Doesn't copper plating alone on steel, corrode badly ? It is usually used as the first coat when doing decorative chrome or nickel.
 
I have seen historic race bikes which have had aluminium brake stays which have been drilled for lightness. If they were made skinnier between the fastening holes, it might make more sense
But I'm just being picky.
 
Fast Eddie said:
Some great replies gents. It certainly looking like a thumbs down for the drill addicts !

It was actually Dave Degens who told me, some years ago, not to do it as holes would disturb the air flow and reduce cooling. He may not have been 100% up to speed with the exact science behind it, but it sounds like he was basically right.
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In the "old days" people determined if something worked/didn't work by trying it. It worked or it didn't. Nowadays we have scientific studies that cost millions of dollars to tell us things like "This study proves that if you touch a hot stove it will burn your hand." ;)
 
Air is an insulator and holes contain air, but holes increase surface area and hot air carries heat. To me it is like the ring and ball experiment, where you heat a ball and ring together and the ball falls through the ring, where it would not fit without the whole lot being heated.
 
Does a hole in a cooling fin increase surface area? Seems to me that it reduces surface area... Oh well, I'm no topologist!
 
I've been around lots of aircraft cylinders and have never seen any fins drilled. I have seen up-horsepower engines of the same displacement go from straight to angle valves with more and larger fins added, especially around the exhaust valves. If there was any advantage to drilled fins the aircraft engine manufactures would have been all over it long ago.
 
JimNH said:
I've been around lots of aircraft cylinders and have never seen any fins drilled. I have seen up-horsepower engines of the same displacement go from straight to angle valves with more and larger fins added, especially around the exhaust valves. If there was any advantage to drilled fins the aircraft engine manufactures would have been all over it long ago.
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I have known cast iron fins to just fall of the cylinder of old motorcycles, through vibration. What does a hole do to the strength of a fin ? 'Because I can' is never a good reason for doing anything. To me bobbers are shit. Many a good motorcycle has been turned into crap by idiots.
 
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