Big Type 4 VW

[dannobee]

Call up ARP and see if their VW studs are in stock yet.

WRT aluminum, the alloy usually used for high temp applications are RR350 or the less common NASA398.

[Mummert]

One of the best things you can do to keep a type 4 alive is have the heads re seated with nickel bronze or beryllium copper seats. They are notorious for dropping seats. High performance air cooled engines need valve jobs on a regular basis, lots of seat insert movement.
We used to cut Vw heads for much larger seats than valve o.d to help seat stability.

I think we used to have rimco sleeve the lifter bores down to type 1 spec so we could run the big mushroom lifters. Its been 20 years or so .

[modok]

Not sure what your talking about with gas filled o-rings, but since I don't like o-rings in any form, I can advise against it with total confidence.
Can only imagine what the design is, and what the point is.
I suppose the wide bore spacing of the type-4 engine would be useful feature since you intend to aircool the cylinders.
Keeping it primarily aircooled, but liquid cooling the heads in only specific areas might be a great idea.

If the aim is more like a "Spread bore subaru with aircooled cylinders".....I don't see the point of that, but then again I've never seen anything like that so... who knows. Generally it is MORE sense to air cool the head because that's the hot part. The larger the temp differential the more effective the cooling.
Many engines "get away with" only cooling the top inch or two of the cylinder because that's where most of the heat is, and "oil cool" the lower end of the cylinder, and if your looking to make a very lightweight design that might be the way to go, is figure out how to extend your water cooling slighly down the cylinders.... but then again if it is DOHC I bet that's not going to be particularly light anyway, so....maybe I guessed close or maybe I'm way off, if so I apologize, tho I'm sure my advice is worth every penny you spent for it.
Try looking at Deutz and Tatra aircooled/oil cooled engines for design ideas.

LN engineering sells aluminum cylinders, they have studs to go with them.
it is common to use 55mm rod journals in a type-4, but very few choices of bearings. Very frustrating. I am tempted to convert them to subaru bearings.

[dannobee]

Maybe look to see what Porsche did on their air cooled race engines and get some ideas on how they handled the heat.

The Porsche "Moby Dick" 925/78 had water cooled 4 valve heads with air cooled cylinders. They did the goofy cooling just before throwing in the towel on air cooling altogether and going to all water cooling.

Incidentally, Porsche used the straight down "Flat Fan" on the air cooled race cars for more even cooling.

The critical juncture between the top of the cylinder and the deck of the head was always problematic on the turbo cars. The solution on the later cars was to electron beam weld the heads to the cylinder. Obviously not ideal for rebuilding.

The production air cooled turbos used no head gasket and relied on the machining of the cylinder's top surface and the deck portion of the heads to seal combustion gases. In practice the two surfaces are often lapped together hoping for an even better fit.

The factory and several aftermarket companies have tried and failed to make 4 valve air cooled heads work. The consensus is that there simply isn't enough room to adequately cool the heads with the 4 valves taking up so much space.

[hoffman900]

There are plenty of air cooled 4 valve heads floating around in motorcycle circles from the 1970s and 1980s.

There are plenty of 911 / 914 Porsches road racing making well above 100hp/L.

The op has liquid cooled heads and “plenty of airflow”, so I think he’ll be good in that regard.

[englertracing]

Not sure what your talking about with gas filled o-rings, but since I don't like o-rings in any form, I can advise against it with total confidence.
Can only imagine what the design is, and what the point is.

https://www.imps4ever.info/tech/engine/ ... rings.html

[modok]

The only times you have an o-ring which never fails.... is when none was needed in the first place. Which is certainly the case with the engine he's starting with.
if he re-designs it into something that has head gasket problems then yeah sure maybe.
"VW head gasket" is right up there with blinker fluid and muffler bearings. I'm not sure if it's a joke or not. o-ringing it is next level humor.

[PackardV8]

Time to talk to air-cooled Porsche guys. I have this vague recollection Porsche had the same problem and came up with some unobtanium Dilavar alloy studs as a solution.

[Fusion Works]

Seeing as how my first car was a 914, I learned a lot about these engines. Find another platform is the lesson I learned. LOL

That said, the T4 has a bunch of issues that you get to address. OE cylinder heads are weak, they do not do boost well. There were several guys that tried drag racing these engine back in the day. With 6 and 7 stud mods they finally gave up and went to the Pauter heads at a minimum. The OE heads flex too much and the port configuration is only moderate for good performance. The exhaust ports are very weak on flow.

There is a reason Porsche never did anything with these engines. They suck compared to the 911 engine. The T4 is a true air cooled engine. The 911 engine was oil cooled with secondary cooling with the fan. The T4 is fairly fragile when you really up the power and start adding boost.

The lifters are pretty small and its hard to find reliable sources of good lifters these days. Three main bearings went out with the old engine designs. The 911 fan shroud kits cool the T4 engine poorly as the distribution of air across the cylinders is compromised. There were some kits to run a Corvair type arrangement, but never super successful. The old setup for converting these engines to an upright fan using the shroud kit sold by Joe (I can't remember his last name) was probably the best option for other fan upgrades.