On Mar 14, 2009, at 6:25 PM, glen wrote:
> I'm always amazed at the mechanical/electrical comparisons. So here > are some random thoughts. Bear with me it gets bak on topic. > > If you bore out an old Ford Flathead cylinders enough to make it a > larger engine the cast iron cylinder walls can get too thin to > conduct the necessary heat from the internal gas combustion to the > water based coolant and the engine will fail. > > Realizing this in my high school days in the 60's; I went to small > block 1955 Chevy engine and bored it out to a reasonable size (265 > to 283 CI) for my 1934 Ford Coupe hot rod and got more horsepower > than the old flathead I orginaly wanted to use. Wish I had that > "rod" today -- it would be worth a lot! Oy, there are MANY more differences between that Chevy small block (possibly the best V8 design ever made) and the Ford flatheads that accounted for the difference in performance. Valve design, better machining, improved coolant channels, better cams, etc. Most importantly, the exhaust manifold comes off the sides of the engine, not down the middle... Anyone who cooks is fully aware that cast iron is, in fact, a rather poor conductor of heat, it's why heavy cast iron pans are used, once they heat up they retain their heat well. A thicker wall would impede heat transfer; the problem with boring them out is not that the walls are too thin to transfer heat, it's that more heat is generated in the first place because you're burning more fuel per cylinder charge. Coupled with the flatheads lackluster cooling in the first place you rapidly overheated. The thinner walls are more susceptible to heat- related warping, and voila: blown engines. > > > Back on topic, the same heat transfer principle applies to computer > processors. Air is not a good medium for heat transfer. Water is > better and metal to metal is the better yet. So, the smoother the > contact between the heat sink and the processor (no air) the better > the heat transfer. Heat sinks are radiant; cool by air. A water > cooling system will transfer heat more efficiently. > > Lapping is a good way to get better a seat between metal objects. Be > it a computer heat sink/processor, auto cylinder/piston or musical > instrument valves. > > Thermal paste/grease or whatever you call it is just an attempt to > eliminate the imperfections in the heat sink/processor contact that > allow air to impede the heat transfer. The conductivity of good quality thermal paste is on par with copper or aluminum, which means thermally, there's no difference; it has to be, because otherwise the components would expand and contract at different rates, messing up the connection. This is where the mechanical analogies break down. We lap trumpet valves and engine cylinders because they are *moving* parts dependent on the properties of very thin hydrocarbon films to work; the performance of these films is highly dependent on the microscopic surface characteristics of the materials. CPUs and heat sinks never move, they simply need a thermally conductive join. And yeah, that '34 would be worth a whole boatload of money today...:-) -- Bruce Johnson U of Az College of Pharmacy Information Technology Group Institutions don't have opinions, merely customs --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed Low End Mac's G3-5 List, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/g3-5-list?hl=en Low End Mac RSS feed at feed://lowendmac.com/feed.xml -~----------~----~----~----~------~----~------~--~---
