Biased Opinions on VW Aeroengines

Please read this excellent commentary on VW aeroengines before proceeding further. Justin Mace also shares his thoughts.  And this reality check by R.S. Hoover (Veeduber) is essential.

Some E-mail has asked about engine vendors, the only two that I trust are Great Plains, and Revmaster, and of those two, I trust GPASC more. Don't forget Limbach engines, particularly if you are in Europe. The Sonex people have an engine offshoot.  Their fixed advance ignition system looks simple and robust, but it makes hand propping impossible.  Their CNC conversion pieces look nice in the pictures; I’ve not seen one of these engines in person, or flown behind one. There is a new Australian vendor, with a Type IV conversion, driving the prop from the flywheel end with a prop extension and an outboard bearing, they also have helical gear reduction units.

If you are serious about hauling two people, 1835 cc is the minimum displacement, and please seriously consider a stroker Type I or Type IV engine.

Subscribe to the VW Aeroengines mailing list, and read their archives, particularly anything by Bob Hoover (not that one, the other one). Here's an example, on head rebuilding and why you need a spare set of heads. Bob has also come up with a serious of modifications he believes will increase the reliability of converted engines.

There is a promising new English ignition system on the market that looks appealing for minimum weight/complication conversions. The Leburg ignition is a bit complicated, but it is self contained, and with motorcycle dynamo bits, self-generating. If you want full electronic control of fuel and spark, you can have that as well. Probably the best value in ignition systems is a Bosch 009 distributor triggering a Universal Corporation CDI module. Many are believers in the Compufire dual coilwaste spark system. Maybe you’re interested in a homebuilt fuel injection system, but it’s not really set up for the firing order of VWs, although the previously mentioned Bob Hoover is working a such a system for his ’65 van, look for his posts in the Yahoo Group on this project to check on his progress Update: Bob finished his Megasquirt. It ran. He doesn't advocate you do the same.  Anything other than a magneto means you need a generator, or at least a battery.  There are belt drive Permanent Magnet generators that are small and light on Kubota and John Deere small equipment.  Vertex mags are supported by Mason Racing, 15 Second Ave, PO 101, Springmount, PA 19478, 610-287-1511 and Vertex Repair, as well as by the factory.

Type IV conversions are a bit heavier and more expensive than Type I/II/III derivatives, and there seems to be problems getting a decent stroker crank for this engine at an affordable price, but read what Mark Langford has to say about them anyway. Jack Lockamy built one for his Sonex and is quite happy about it – or was, until the crank/sleeve/hub arrangement cut loose and almost killed him.  GPASC is working on a fix, but at this point in time, Winter 2002, there is not, in my opinion, a safe “fan end” propeller hub/crankshaft arrangement for the Type IV on the market. Driving the prop from the flywheel end takes care of these Type IV specific prop hub problems!!!

If you need more than about 70 horsepower (and that assumes a stroker Type IV run pretty hard…), you should be looking elsewhere. A Corvair perhaps?

Why should you look elsewhere? The limiting factor is heat dissipation out of the heads and the exhaust valves. The stock heads are actually superior in this area to all aftermarket heads I've seen, including the SCAT heads on my old project. Thermal Barrier Coatings look like a very, very good idea for (in order of importance) exhaust valves, heads, and piston crowns.

Just hanging your cylinder heads out in the breeze is a loser. You will never achieve proper airflow through the heads that way, essential for long exhaust valve life. Richard Lamb shares how he did it:

I made my eyebrows thusly:  
Make patterns for the side pieces.  One goes at the base of the jug,
the other goes between the last pair of fins on the head. <Wrong, IMHO – RRY> Or make
them go all the way to the end of the head and add holes for your 
sparkplugs and intake manifold.  <Better, IMHO – RRY>
 Cut the side pieces so that the back end curves around the back
of the rear cylinder.  Make the top edge of the side pieces 1/2"
extra for a flange.  Bend the flanges by working around the curve
with a pair of pliers or ???
This will cause the piece to curl obscenely!  But by working around
the curved part of the flange with fluting pliers, the piece can
be straightened back up!  It's so cool.
Mount the eyebrows with a couple of #6 or #8 screws through the fins.
Pop rivet (or drive?) the top covers to the side plates.  
Don't forget to block off the bottom between the cylinders.  A piece 
of stainless or .063 thick aluminum between the fins on top of the jugs 
makes a neat place to tie in a piece of safety wire to secure the bottom

While we are on the subject of cooling, please look at this otherwise pretty sanitary VW installation. The problem I have with it is the lack of cooling air into the fins that surround the exhaust ports. See the area between the forward plug, and the forward exhaust valve? That's the most critical area for cooling, and in this installation, it gets NO AIR. That's not right. Even if your CHT's look fine, you're cooking your exhaust valves, and the temperature differential between various parts of the heads will promote cracking. Although I like and respect Richard, his plane, and his workmanship, his cooling setup as he implemented it makes this mistake; it doesn’t shove any air into the fins around the exhaust valves. Since his cylinders are out in the breeze, maybe he’ll get away with it. Same bad practice here. I wish I had a picture of prop maker Ed Sterba's Sonerai engine: his installation had it all done right, with little auxiliary plenums directing air UP (as I recall) through those exhaust port fins.  Blueberry’s engine does it right, Serge Vidal does it right, Jim Hardy’s engine does it right.  Look at the way the stock TOP tin is arranged.

The baffling patterns Great Plains sells are essential for any installation, even if the engine is out in the breeze, you can use the bottom of the patterns to save a lot of time building your "Elephant Ears". The Aerovee folks also sell baffle plans.

"Super Cool Tin", available anywhere performance VW parts are sold, is the easiest proper way to get a decent set of bottom baffles. Ideally, there should be a lower plenum, to build a LOW pressure area on the underside of the engine, with an outlet area 20-30 percent bigger than the inlets.

You can get brand new 1600 cc hydraulic lifter engines with full flow oil filtration for about $1400 long block. It a very tempting idea to just pop a shrink fit hub on one of them and go fly. GPASC's 1600 cc engine kits are only slightly more money, and have more parts you need, like prop hubs; they may be well worth it. A new trend in the VW business is “zero-time” engines assembled (in the US, generally) with all new parts. You can get them from many sources, at nice prices, but they are all solid lifter engines. However, after my initial enthusiasm for hydraulic lifters in Type I/II/III engines, I’m cooling my jets on that idea. A correspondent who fitted a BeetleMex “juicer” engine found the lifters would leak down, and would only pump up after 30 minutes of noisy running. My own engine will have solid lifters.

I've been asked about inverted oil systems for VW aeroengines, here is what I think.  More to the point, EVERY VW aeroengine should have a full-flow filtration system (NOT an aftermarket pump-filter, although the new VwdoMexico unit may be good enough), and a full-flow oil cooler, which could be the stock “doghouse” cooler laid flat with a suitable adapter from GPASC (although Veeduber points out some drawbacks with this attractively simple system…), or a J.C Whitney or Mesa stacked plate cooler mounted …wherever it will fit. Another link on how to full-flow a case.

I also keep getting asked about turbocharging. The short answer: it's generally a bad idea on Type I engines, it's marginally less so on Type IV. Turbos put more heat into the engine than the heads can deal with. There are other complications, particularly with the oil system. Read this Dan Diehl article almost 20 years old on his experiences. If you live some place (South Africa, for instance) where big cylinders and cranks for increasing your displacement are expensive and scarce, but turbochargers out of wrecks are cheap, it may make sense; all others should give this a miss. Dan took the turbo off after a few years, since he was too fast for his buddies to keep up with it on, and keeping it happy required a fair amount of attention.

Carbs: A Mikuni HS-42, a Tillotson Model X, a Revflow, or one of the new Aero-Conversions (Sonex) "POSA for the new Millennium" carbs. Or the Zeniths GPASC sells. I have more to say on the subject. And speaking of Posa's, yes, they can be made to work reliably.

The GPASC rear drive setup looks promising. The down side is that a complete package will cost about $500 more than a comparable setup using the Diehl case, there may be a slight weight penalty over a "full house" Diehl case engine (certainly some over an X-casting or other bare bones setup), and there are no cowlings yet to fit this setup - Steve's working on it. A guy on the VW Aero Engines list is working with one of them, and in a tractor setup, it's not easy to cowl. May be better as a pusher.

Speaking of driving from the flywheel end, there is was a German Type IV conversionthat doesdid just that. And Bob Hoover posted this message on the subject in the VW AeroEngines Mailing list, along with several related messages on how to build engine mounts for this configuration, etc. I strongly believe this is the right way to drive the prop, and the engine I'm assembling will be done this way.

As an engineer, I’m a little suspicious of the Valley Engineering reduction drive, also sold by GPASC, but I have not heard any experience-based bad things about it and I have heard some good. The things I don't like about it are the lack of an outboard bearing for the crankshaft pulley to keep the belt loads off the nose of the crank (Subaru redrive experience with this configuration is poor), and the way it mounts to the case.  I personally like Don Stewarts Maximizer better – but to be fair, it doesn’t have an outboard bearing either. Those blokes in Oz mentioned earlier will sell their reduction drive, which bolts up to the flywheel end. And the Airdrome Aeroplanes people are now selling a reduction drive.

Volksplane's have always used a very minimal approach to conversion. We should all consider the costs versus the benefits of a more complicated engine.

There is a lot of technical information about VW engines out on the web; not all of it applies to us.

I just found this really, really useful post on cooling on the KRNET FAQ page. The first part of this rap (I.E. my condensation of lots of research) is just as good, or better. It’s nice to have your assumptions validated though ;-)

I said I wasn't going to deal with 1/2 VW ultralights, then I went and listed the Legal Eagle. In the spirit of fair play, I'll mention that Bob Moore, and Morey Hummel also have 1/2 VW information, and plans for an early 1/2 VW are available on E-Bay. Great Plains now distributes the Carr plans. The most important thing to remember is to cut the oil pump capacity way down.

Two new developments of interest: aluminum (not magnesium) engine cases, and aluminum (not cast iron) cylinders. The first is heavier, but stronger, particularly in fatique (the way most cases fail, and fail they will, in time – why you should NEVER build an engine on a used case). The scuttlebutt on these Brazilian aluminum cases is VERY mixed, ranging from "they're awesome" to "absolute junk, never use them again. There are many vendors of these things, and apparently CB Performance has the best product. There are also US made CNC aluminum cases, twice the price and then some, of new magnesium VWoBrazil cases, and apparently spotty availability. The second new development, the jugs, are definitely lighter, WAY more expensive, and allegedly cool better.

Back to Ryan's Home Page

E-mail Ryan