In a message dated 3/20/2004 4:09:21 AM Pacific Standard Time, da...@alltel.net writes:
> I hope > that Bob Hoover will chime in here, because he is the expert. ------------------------------------------------------------------------------ ------------------- Dear Dan (and the Group), I don't consider myself qualified on the Type IV. When I happened to have one in the shop I'd drive up to Mark Stephens place for parts & advice (they had some valve seat problems.) I think it's the best aircooled Volkswagen ever built but I simply haven't worked on enough of them to speak with any authority. ----------------------------------------- As for the cam question in general, over on the AirVW Group (Yahoo) I've posted the specs for the A-series Continental, VW (1300 thru 1600; all the same), Ford 9N tractor (nearly identical to the Model A) and a few others for comparison purposes, along with some computerized dynamometer pulls. For anyone interested in a whiff of reality, the data is there. Alas, it does not agree with the horsepower-oriented Conventional Wisdoms on the nose of some many VW powered aircraft :-) As a point of interest, the power output of flying Volkswagens built by myself and two other fellows, at different times and locations, unaware of each other until the advent of the Intenet, formed a neat cluster on the power curve despite different methods of measurement (although all were some form of torque meter). ----------------------------------------------------------------- For the type of flying I do, I've found the basic chugger to be the most reliable VW conversion. (A 'chugger' is an engine that in which peak power and torque occur at an rpm most suitable for swinging a prop typically 69 to 72 inches in diameter.) Since peak torque always coencides with peak volumetric efficiency, I focused on displacement and deep-breathing exercises :-) Although there are a few chugger cams out there for VW's they are wildly unpopular unless the engine is attached to an orchard blower or water pump. In fact, my most successful configuration simply borrows a page from the Volkswagen Industrial Engine Division and uses the stock cam, retarded four degrees. This works fine for a grain auger or motor-generator set but when you open the engine up to anything over 120cid or so I found it necessary to use the 1.25:1 lifters from the alcohol-burning engines built by VW du Brasil. I know VW offered a complete line of industrial engines based on the Type IV and if I were to do it all over again I would probably devote some time to winkling out their cam data, largely because of the expense in starting from scratch. I think you have to put at least a hundred hours on an engine before you can define it with any degree of confidence. I've done that many times with Type I's, back when when gas was cheap(*) and my nearest neighbors weren't all that close. Now the yuppies have me walled in and rarely a week goes by when some blue-haired lady chuggs up the hill desperately eager to sell my 'house'. (Don't they know the difference between a 'house' and a home?) Build an engine nowadays, I have to sneak it out to the airport to run it in. Sorry I can't be of more help. -R.S.Hoover (*) Most of the price of gasoline reflects transportation-related taxes. If you live in the country, use gasoline for your tractor or other non-transportation applications, a drum of gas was about $17, delivered. I built a test cell out behind one of the sheds, ran-in my engines there using two or three drums of gas per month. (mid-70's thru early 80's). Big problem was getting rid of the drums :-)
