Monday, January 19, 2009

Casting Call!

Hello to all, including those of you who have mentioned my blog is difficult for them to read due to the small size of the print. Of course, in their next breath they admit there's nothing I can do about it because it is just as difficult for them to read everyone else's blog as well, meaning the problem is in the font and if I used a larger font, my articles would probably become too large to manage... or something.

But I appreciate the problem and while going to a LARGER FONT, as I have done here, is not much of a solution, it should serve to show you that I really do read all that mail... and that I really do try to do something about it.


This article happens to be about casting parts. That's right; melting some metal (Aluminum in this case) and using the pot of molten Alumin
um to CAST some NEW parts (cylinder heads, in this case). Which I can probably do. But I am such a klutz when it comes to this BLOG, you will be lucky if you can read the thing at ALL, regardless of the size of the print.

So here come some DRAWINGS that have been converted to ILLUSTRATIONS, which means they are virtually useless for doing anything more than giving you a very rough idea of what's involved.

Later on, as I progress through the process, you MAY get some idea of HOW it is done but right now the best I can do is to offer you some illustrations.

The first illustration is a collection of lines and circles that represent (to ME ) the head of a Volkswagen engine. This particular head was introduced about 1965 and the KEY DIMENSIONS of this head have remained the same right up to the last head Volkswagen produced... ANYWHERE and for any size of engine. That should offer you a hint with regard to the problems faced by the engine-builder when trying to produce more POWER from a VW engine.

The fact is, the HEADS are the critical factor with ANY air-cooled engine, in that so long as the heads remain unchanged with regard to certain critical dimensions, the maximum OUTPUT of an engine fitted with those heads will ALSO remain unchanged.

So what are those critical dimensions? They are the dimensions of the FINS. It is the FINS, especially those in close conjunction with the EXHAUST VALVE which dictate the maximum amount of HEAT that can be coupled to the ATMOSPHERE. It is this coupling or transfer that determines how HOT the heads can get. If you have too LITTLE fin AREA, the cast aluminum will literally start to crumble. Yes, CRUMBLE rather than MELT. That's because aluminum is what's know as a 'white-short' metal (as are most other non-ferrous metals ). With ferrous metals, such as iron or steel, as the metal gets hot, glowing red and then yellow and finally an incandescent WHITE... it still retains a good bit of its strength.

But Aluminum doesn't do that. When it enters it's 'plastic' range -- where the farrier would commence to shape the bar into a horseshoe by pounding upon the thing with a hammer -- if it is subjected to any amount of stress... such as HAMMERING, 'white-short' metals will literally CRUMBLE like a cube of sugar. This is what limits our maximum Cylinder Head Temperature to relatively low values... about 450 degrees F. for a casting and about 550 for a forging.

So where does this heat come from? It is a product of COMBUSTION. If you want the engine to produce any POWER it's going to have to produce one hell of a lot of HEAT. In fact, for every horsepower's-worth of TORQUE you'll see at the crankshaft, you will also see about THREE HORSEPOWER'S-WORTH of WASTE HEAT in the exhaust, and in the jugs, and in the oil and so on and on and on until you go a little crazy trying to deal with the waste heat.

The most elegant way to deal with WASTE-HEAT is to simply pass it on to the ATMOSPHERE -- to let your forward velocity force the AIR through the FINS on our heads and simply blow the heat away!

Which is what I'm trying to do here.

But it turns out to be a difficult task. There is a finite limit to your fins. Pump too much heat into them and they will crack or bend or do any of a dozen other things. Those are the problems I must overcome. So wish me luck, if you've got any to spare.



dennis gwynn said...

Bob, Font size [on my linux/firefox system] is enlargable by pressing control + after you get to a blog. Reading glasses also help but a larger monitor is the most convenient solution...I use a 42" lcd tv for a computer monitor. I used to run two 19" monitors side-by-side with the "desktop" spread across both but the gap between them could be irritating.

Anonymous said...

Good luck !

Anonymous said...

I've just read about your cylinder head redesign for the VW head. What I've come up with is to redo the crank case as well and have two cam shafts one above the crank and one below. This will allow for vertically stacked angle valves. And lost of cooling fin area.

As far as cooling on a stock VW push rod engine, what I was thinking about was using oil to help with the cooling of the bridge of the exhaust/intake valves. If you were to run an oil passage through the bridge then you would have much lower local metal temperatures. Just a thought.