Pops, I must have missed Bob Hoover's blog post about that head design. I can understand that having the exhaust connect underneath makes the plumbing easier, but it would seem that his design also allows the exhaust to dump more heat into the head (a longer run inside the well conducting AL head rather than a short trip to a steel flange and pipe). I'm sure I'm missing something simple and important.
Valve Problem
- Thread starter Marc W
- Start date
Help Support HomeBuiltAirplanes.com:
I don't know his reasoning on the down exhaust outlets. VW did run the exhaust out the bottom on the Type 4 engines. But from a market point of view, in making a new designed head, for the max market the exhaust should come out the ends as in the stock VW heads. Auto's VW muffler and headers will fit.
I don't think he every said why. Look at January 19, 2009.
The old aviation engines had open valve guides for direct air cooling.
The way he explained his thinking to me was that by turning the exhaust port down it frees up area above the exhaust valve guide allowing more direct air flow. The Tp IV and Corvair heads go one step further and move the exhaust port straight down. Unfortunately that isn't practical due to other architecture of the Tp 1. The other limiting factor is the pushrod tubes. We can only tuck the ports in a certain amount before they run into the tubes.
The pic Pops posted was his way of trying to modify/weld an existing head rather than start with a new casting. This was all back before the days of 3D printing. Big game changer for a project like this....
Edit: Added a quick view of how moving the exhaust port opens up the exhaust guide. It's the best I can do right now without opening SW. Notice that there is 360 degrees of air around the exhaust guide boss. The flange is at stock VW height, and patern, but rotated 45 degrees.
Last edited:
Thanks much for the diagram, that makes things more clear. Those fins look very generous--if that kind of depth and spacing is practical, it won't matter which way the exhaust exits!
The way normal VW heads are cast, for high volume, and with my abilities at sand casting - it isn't. Back when Hoover was still alive, and Saturn had just introduced lost foam casting, I was thinking lost foam would work. It could but the tooling to make the foam cores would be expensive and there is no real advantage over plain multi century old technology - lost wax.
Using 3D printing one can even use, for lack of a better term, 'lost print'. But that is still so time consuming it's probably only practical for very intricate one of a kind projects.
Also, that head shown is full of ideas that just aren't practical or even needed. It weighs too much and the combustion chamber shape is little more than 'monkey see monkey do' guess at good squish and fast burn. Lots of work left to do..........
