More Thoughts.

I have wanted to get to the local Vw shop since I saw the article in Hot Vws magazine about the different heads on the market. I needed to buy a carburetor for my sawmill so I figured I wouldn't put it off any longer. While I was there I took the time to look at some heads on the shelf, unfortunately he didn't have exactly what I wanted in stock ( they will be in next week) but what was available will do for today's thoughts.

 Bob Hoover always told me to use stock head castings, they would cool better than the aftermarket types. I wouldn't listen and bought the dune buggy heads the first go around. After I saw the magazine article I knew where Bob was coming from and so I wanted to get my hands on a few different examples for the blog. Here is what I found.    

The head casting that I originally started with and flew for the first 60 hours. I later modified these heads with the fat fin extensions.







The picture above is a well known 042 casting with 40 mm intake and 35.5 mm exhaust valves. I tried to open up the passages where possible but the thickness and shape of the casting prevented much improvement. The fins on the end of the head were nearly completely blocked due to mold shift and I did take the time to open those passages. As I said earlier, I tried unsuccessfully to add fin extensions to this head and just gave up because I was in a hurry and everyone told me it was not needed. Big mistake. I flew these heads for 60 something hours when the issue with the bottom plugs came up. See the earlier text. I went back to them later adding the fins and putting them back in service, that is where the fun began, literally. 



Here is a different casting that is like the original Vw, the difference between the two heads is clearly visible. 



When the two heads are compared you can see the wide open passages in the photo above that are filled in on most heads. How much better would this head cool ? I don't know, I would expect some improvement and in a aero application you need all the help you can get. I'm thinking that there is not a great amount of surface area added but the most important issue is the exhaust valve. Just above and to the right of the screw boss you can see the exhaust valve guide between the two port castings. More accurately I should say the valve guide is in the casting under the fin. Now look again at the top picture. Which guide is going to be cooler? The guide that is buried in the casting and getting heat soaked from the exhaust gasses passing through the head or the one that has air flowing all around it. The only way a exhaust valve is cooled is by heat transfer through the seat when the valve is closed and also up the stem into the guide where the heat is then transferred to the head. A little cooling is accomplished with oil bathing the stem. I have had folks argue that the stem will in effect be cooled better in a solid head because of more mass to absorb the heat. I  just don't buy it and neither did Bob, or Hot Vws.    



Here is what I'm talking about. How much air will get through this head?

Looking at the head above you can see how the two halves of the casting mold were not in alignment. There isn't alot of room for air to get through if this is perfect so with this kind of issue you can imagine how restrictive it will be. This MUST be corrected even if you do the fin extensions. I used a slitting saw in my mill but you can use anything that works, grinder, file etc. This head is the one with better passages down around the valve guide in the middle picture but they blew it on the ends. No free lunch. I would love to have the resources to buy a set of these and try them naked and then try the fat fin mod for comparison to my other data. I have been  tooling with the idea of building a test stand to measure engine performance and start trying different things to see what works best, but money is an issue..... maybe I could just build a MONSTER size motor and use these heads with the fat fin extensions, hmmmmmmmm.


I had to add this for inspiration, I hate winter and needed a pick me up. I flew over 4 hours this weekend on a cross country and doing a photo shoot for Kitplanes magazine. The work, effort and expense of the fat fin engine has paid off. I now just get in and go with much less worry than before.  

 I'd have to come up with a better redrive though. Maybe that will be my next project, I'm getting pretty bored this winter.