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
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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.
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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..........
Bumping this thread to get a little quick feed back. The recent thread about Great plains apparent slide into obscurity has me thinking about the VW "problem" again.
The whole thing ends up pretty wide. A stock VW is about 29 inches wide at the valve cover and my version of heads ends up about an inch wider, primarily due to moving the valves to a vertical position and trying to retain a good amount of 'squish' in the combustion chamber - which leads to a deeper chamber to keep the compression low with large displacements.
So my question for the day is:
How about following the lead of the D-motor and going back in time to a flat head design?
Works for either a 4 cylinder VW or a half VW and there is plenty of cooling around the exhaust valve guide.
*The pic is little more than my CAD scratch pad
I've been working on this project off an on for the better part of a decade and fully expect to do some casting this summer - one way or another. I'd been working along a path based on pretty conventional thinking and have a a design in CAD that is essentially ready for 3D printing to verify but.........................
The whole thing ends up pretty wide. A stock VW is about 29 inches wide at the valve cover and my version of heads ends up about an inch wider, primarily due to moving the valves to a vertical position and trying to retain a good amount of 'squish' in the combustion chamber - which leads to a deeper chamber to keep the compression low with large displacements.
So my question for the day is:
How about following the lead of the D-motor and going back in time to a flat head design?
Works for either a 4 cylinder VW or a half VW and there is plenty of cooling around the exhaust valve guide.
*The pic is little more than my CAD scratch pad
I like your idea of a flathead. Would solve a lot of problems. With the rpm's a straight drive VW's is turning, maybe the intake flow of the flathead design wouldn't make a lot of difference.
I'm old enough to have had some good running street flathead Fords V-8's.
I'm old enough to have had some good running street flathead Fords V-8's.
I remember my father's 1951 Plymouth Cambridge with a flat head six. Great car and neat engine although I was quite young and I just marveled at it.
As to the bottom exhaust exit idea ... yes the Corvair heads use a "crossflow" design with canted valves.
As to the bottom exhaust exit idea ... yes the Corvair heads use a "crossflow" design with canted valves.
Mosler used special heads made by Scat, individual heads for each cylinder with the intake on the bottom and the exhaust on the front for the front jugs and the back for the rear. It required a RH and LH head, or rather a right-front/left -rear and a left-front and right-rear version. Some people said they didn't cool well but I never had that problem on mine. A dual plug version with more fins and it could be a winner.
Bill-Higdon
Well-Known Member
You mean like the HCI Radial uses?
I'm thinking very similar. The HCI has the advantage of having the lifter bore collinear with the valve stem. No way to do that with a stock VW cam location but there is a workaround ..... and we get hydraulic valves in the deal too.
The whole idea of a purpose built head is to improve the heat tolerance of higher Hp engines, specifically the exhaust valve area. Moving to a flathead configuration makes cooling the exhaust valve pretty easy but I've not yet convinced myself it is the right direction to go.
After all the goal is longevity with increased Hp. The conventional wisdom is that the flathead/sidevalve engines give up power compared to OHV engines - especially at higher PRMs due to poor flame propagation, low compression ratios* and the obviously restricted induction and exhaust.
For direct drive aircraft RPM is not a real problem. 4000ish RPM for a fast plane is probably as high as is practical. The low compression ratio lets us use cheap fuel. Ricardo managed to improve the efficiency of the flathead at about the time everyone was going to the OHV configuration. His work seems to have been mostly forgotten.
Plusses for the flathead VW head:
Narrower engine. For the same stroke and deck height about 6 inches for the VW based engine
Simpler casting and machining.
Lighter weight
Hydraulic valve adjustment without modifying the case.
Pushrod tubes that are less likely to leak.
Minuses:
Power per displacement is lower than an OHC*
Lower fuel efficiency due to larger combustion quench area and higher HC emissions
For the VW configuration one more sealing surface - somewhat offset by not having any valve cover gaskets to leak.
*If the cooling parts works out as hoped, the naturally low compression ratio opens the possibility of turbocharging to regain the power/displacement and maybe still keep the same power to weight ratio.
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Wow, interesting. There haven't been many air cooled flathead models in airplanes, but the Continental A40 was popular.
Your sketch makes it look like it could be pretty compact, doing away with all the rockers, etc. The fins on top of the head would need to be generous, and there would be a lot less heat in the oil. Do away with the oil cooler entirely?
This is actually one of my concerns - too little oil on top to lube the valve stems. Spent a small portion of the time allotted to slumber last night trying to envision a way to let some of the hydraulic lifter bleed take care of that function.
I have to correct one of the 'advantages' from an earlier post. We are stuck with the same leak pron pushrod tube seals due to the *#@@% compromise of a cam in the VW. AND unlike a standard VW where we can change the seals by installing a 2 piece pushrod tube, with the flathead the head will have to be removed to change the seals.... but that is only 4 bolts per cylinder and no other gaskets or adjustments to worry about.
Regarding the hydraulic valve adjustment. Almost mandatory. Adjusting the lash with a mechanical system would be a pretty nasty job and require a bunch of custom built parts. I really like the OTS solutions.
I'm looking for alternatives. Right now I have 3:
The easy one - just using a VW Tp IV lifter inverted at the head is kind of heavy.
Using a tappet bucket from a water-cooled VW is another but would need a custom 'shim' on the bucket to adapt to a spherical pushrod end.
A rocker arm unit like found in Subarus. This too would require an adapter.
Any ideas?
Straight Off The Shelf parts are ideal but if the part can be modified by the builder with little more than a hacksaw and file, that fits my desired design philosophy too.
Well, it was a good idea but................................
It just isn't possible to put a flat head on a stock VW case. Space is tight, but using shorter VW Rabbit valves fixed most that problem. The Rabbit hydraulic lifters also enabled good oil flow to the valve area. Castings and machining was gong to be pretty easy.
But that $%@##$$$ cheap a** camshaft just can't be worked around. The pushrod angles are too great.
If anyone ever decides there is an aviation market for a new VW case take a long hard look at the Corvair.
2 days 'wasted'.
It just isn't possible to put a flat head on a stock VW case. Space is tight, but using shorter VW Rabbit valves fixed most that problem. The Rabbit hydraulic lifters also enabled good oil flow to the valve area. Castings and machining was gong to be pretty easy.
But that $%@##$$$ cheap a** camshaft just can't be worked around. The pushrod angles are too great.
If anyone ever decides there is an aviation market for a new VW case take a long hard look at the Corvair.
2 days 'wasted'.
Thanks for giving it a hard look. While it is still fresh on your mind, did you get a WAG regarding the highest practical CR that could be achieved with standard VW Type 1 crank, conrods, and pistons but in a flathead config?
A flathead was always going to be a huge project, just getting the valve opening, durations, push angles right after eliminating the rocker arms, etc. Deciding it wasn't going to be feasible this early may be a blessing.
You aren't abandoning your quest for an improved (conventional, OHV) head for the airborne Type 1s, are you? There's still a lot of progress to be made there, IMO.
A flathead was always going to be a huge project, just getting the valve opening, durations, push angles right after eliminating the rocker arms, etc. Deciding it wasn't going to be feasible this early may be a blessing.
You aren't abandoning your quest for an improved (conventional, OHV) head for the airborne Type 1s, are you? There's still a lot of progress to be made there, IMO.
Just a SWAG, but with modern software* to help shape the chamber and lost wax casting it was looking like 9:1 was going to be a practical target - and still have decent flow and flame propagation.
Yes, in the grand scheme of things the amount of time spent down the wrong rabbit hole was small - and not all wasted. Still, frustrating and disappointing.
No, I'm not abandoning the project, but it is going on the back burner again. The simplicity of the flat head was tempting enough to change my project priority. With the apparent demise of the O-100 I've been back to playing with my 2 cyl project again. It could use either a 1/2 VW or a 1/3 Corvair but really needs it's own head. I have kind of a double incentive to figure this out..
It's really unfortunate that Hoover and Bennett didn't live longer. Steve was thinking about a purpose built case back when I was trading e-mails with RH about a new head design. They had planned to meet to brainstorm the project, but that meeting never happened.
*Solidworks is kind of a PIA for organic shapes, but still faster than hand carving each thought.
Yes, in the grand scheme of things the amount of time spent down the wrong rabbit hole was small - and not all wasted. Still, frustrating and disappointing.
No, I'm not abandoning the project, but it is going on the back burner again. The simplicity of the flat head was tempting enough to change my project priority. With the apparent demise of the O-100 I've been back to playing with my 2 cyl project again. It could use either a 1/2 VW or a 1/3 Corvair but really needs it's own head. I have kind of a double incentive to figure this out..
It's really unfortunate that Hoover and Bennett didn't live longer. Steve was thinking about a purpose built case back when I was trading e-mails with RH about a new head design. They had planned to meet to brainstorm the project, but that meeting never happened.
*Solidworks is kind of a PIA for organic shapes, but still faster than hand carving each thought.
Hephaestus
Well-Known Member
Considered that yamaha phazer like marc's doing?
Almost like a 582 but without the headaches and a bit more oomph.
Yes, it and others. It has a big plus that is also a big negative: water-cooling. From a pure technical way of looking at it those of us still interested in the VW as a base are on a fools errand.
But all, or the overwhelming majority, of the existing air frames were designed around an air-cooled engine. Trying to package the radiator and required ducting into the nose of them seems to be a task beyond most builders. Whoever tries to go down the water-cooled conversion path is probably going to have to offer complete FWF packages.
If it hadn't been for a guy named Nader; Revmaster, AeroVee, HAPI and GP probably would have never existed?
