1/2 type 4?


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Well-Known Member
Apr 1, 2011
Palm Bay Fl.
anyone thought of or done this, i know not the cheap route of the type 1 but aftermarket performance is now starting to recognize the type 4, yes there is the problem of the crank snout not having enough material for a prop flange but could be set up for prsu or belt drive. just seems like a better engine to me without the case problems, already has the larger #3 main bearing, able to accept large stroke cranks and big bores, and the heads have better cooling already.

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
Nov 14, 2009
Rocky Mountains
It could be done. The Tp IV heads are arguably better units to saw in half due to the separate rocker arm shafts. This eliminates the "hokey" ways needed with the Tp 1 to keep the rocker shafts from twisting. For a prop drive you always have the option of machining the center of the crank when you cut it and using Hoover style prop drive from that end of the motor.

But Why? Type IV parts are expensive (for the good ones) and the engine will end up weighing more then expected. For another 30 pounds or so you could use a full Tp 1 and get the same Hp, or more.

If weight is the limiting factor for your use then consider a 1/3 Corvair. Parts for it can be had for the cost of shipping from someone that has parts, like a head with a dropped valve or a crank with a spun bearing, that can't be used for a normal Corvair build.


www.FlyCorvair.com - Home of the Recognized Authority on Corvair Powered Flight

I'm an old time VW builder, have all the needed tools, have built a 1/2 Tp 1, have several Tp Iv cores and I'd never build another 1/2 VW. It's just too much work for what you end up with. I've got 'Vair cores and the conversion manual, but would have to think long and hard before starting down that path as well.

The 1L class of industrial engines look like a better option than the cut case conversions - IMHO.
Last edited:


Mar 4, 2011
Vinton, Iowa / USA
The industrial V-Twins are attractive, especially since you get alternator, starter, electronic ignition at no extra charge. They are being used a fair amount on the powered paragliders. Of course an engine failure on one of those is a non-event.

The 1/2VW (and 4cyl VW) have a good track record in the air. And they can be built with better pistons, rods, crank, etc. than the industrial engine will have. Dual ignition is also a possibility. As with everything, you tend to get what you pay for. As far as weight and power, the 1/2VW will be very similar to the industrial V-Twins. Just look at the bore and stroke and rpm. I tend to be very cheap, so I would put an industrial V-Twin on my ultralight and land in a farmers field if necessary. Exciting, but survivable at 28mph. However, a serious homebuilder would IMHO be better off with a good 1/2VW with a magneto. Keep it simple and light but strong inside.


Well-Known Member
Aug 17, 2005
Newnan, GA
Just to play devil's advocate, a little web browsing will turn up many sources for stronger and lighter industrial v-twin parts - most from the cart racing world. You can spend as much as you like, but just the main parts - rod, crank, pistons, everything billet.

Performance V-Twins is one place