Ready-made VW fat fin heads?

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cluttonfred

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The late R.S. "Bob" Hoover was working on a project to develop a VW-based standard, affordable homebuilt aircraft engine, basically a big bore VW with low-cost accessories and mods for better performance.

A key element of Hoover's approach was the "fat fin mod" which involved brazing or welding on additional fin area to allow the VW heads to shed more heat.

I came across these ready-made "fat fin" VW heads and there many be others as well. My question is, why aren't all the large VW conversions using these or something similar?

Mofoco 042 Performance VW Heads - Highest Flowing Unported Heads

Cheers,

Matthew
 

dino

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Modifications to cowling and baffling would probably be easier and more proven than a limited production niche head. There's a lot more going on in a head than the cooling fins. If possible stick with what works. Even high output pusher VWs can be cooled.

Dino
 

Pops

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Unless you are running a redrive, you don't want big valve heads. Will hurt power at the low RPM's that you will be turning. High flow heads are for high rpm. If you want fat fin heads buy the heads that Revmaster sells.

http://revmasteraviation.com/

Dan
 

Hot Wings

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My question is, why aren't all the large VW conversions using these or something similar?
Because they are just another "Band-aid" approach and don't address the fundamental problem with the VW Tp1 head that is the limiting factor. They do cool a bit better overall, but not in the right places.

Hoover knew this and in our conversations during this point in history he said that what he really wanted to do was move the exhaust port so that there was more flow available to directly cool the exhaust valve/stem area. But that was more work then he really wanted to take on at that time. He did have some basic sketches* of a weld and grind method that would have helped. I was of the opinion that it was too much work for the gain and what was needed was a clean sheet casting. I didn't have the time or the skill** at the time to do such a casting. VW with their Tp IV and the Corvair point the exhaust straight down for a very good reason.

*I no longer have a copy of them due to a hard drive failure several years ago.

**That was in my pre CNC/Solidworks era. I still don't have time.
 

Pops

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When Bob Hoover said anything about the VW engine, you better listen.
I did Bob's HVX mod's on my 1835 cc VW engine.
Dan
 

Aviator168

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Just read Bob Hoover blog about not enough oil getting to the head. Makes perfect sense. Circulating oil carries away much more heat than fins, no matter how large they are. I wonder if adding an accessory pump to pump the oil from the crank case directly to heads will do the same thing.
 

103

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The late R.S. "Bob" Hoover was working on a project to develop a VW-based standard, affordable homebuilt aircraft engine, basically a big bore VW with low-cost accessories and mods for better performance.

A key element of Hoover's approach was the "fat fin mod" which involved brazing or welding on additional fin area to allow the VW heads to shed more heat.

I came across these ready-made "fat fin" VW heads and there many be others as well. My question is, why aren't all the large VW conversions using these or something similar?

Mofoco 042 Performance VW Heads - Highest Flowing Unported Heads

Cheers,

Matthew
Matt I am running the Mofoco 040 heads with standard size stainless valves. They stock them with dual 12mm plugs and know why you buy them. :) Work great Friday OAT was 80f and the heads never exceeded 380f on climb out. Level flight 2900 19.5 inches of mercury and CHT at 330 steady. Lucky to have Mofoco in my home town easy to pick up consumables like valve cover gaskets.

https://www.mofoco.com/item/Mofoco_040A_40mmX35_5mm_Cylinder_Head_12mm_spark_plug_holes_92mm_bore_/3520/c52
My engine 82x94 with GP crank with front bearing, Sterba 58x34 prop,
4316 mag, Comufire DIS secondary ignition ,Revflow carb with carb heat.

Flies great

Bob Hoover's DIS recommendation makes a great secondary or primary ignition if you have Electric. I have a slick primary and the DIS. If I were hand propping it it would be on the electric ignition with variable timing provided by simple mechanical advance. See:
https://bobhooversblog.blogspot.com/search?q=dis
 
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103

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More stess testing the new heads above.

This past Friday OAT was 95.

Cygnett climbed 6-700 ft/min stedy from 850ft to 2500. Max CHT was 385 MAx oil temp 202.

Cruise 2900 rpm 18.5 inches of MP all heads quickly settled down to 308f.

Flight duration 1.1 hours one landing 2.5 gallons of 100ll.

Surprisingly sprightly take off dor sucj q hot muggy day.

Matt
 

karmarepair

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The late R.S. "Bob" Hoover was working on a project to develop a VW-based standard, affordable homebuilt aircraft engine, basically a big bore VW with low-cost accessories and mods for better performance.

A key element of Hoover's approach was the "fat fin mod" which involved brazing or welding on additional fin area to allow the VW heads to shed more heat.

I came across these ready-made "fat fin" VW heads and there many be others as well. My question is, why aren't all the large VW conversions using these or something similar?

Mofoco 042 Performance VW Heads - Highest Flowing Unported Heads

Cheers,

Matthew
Those heads look better than most aftermarket heads, in that they DO NOT cut down the NUMBER of fins compared to stock, which many drag racing oriented heads do. BUT they are NOT "fat fin" in the way the Bob Hoover was working on. He was tig welding additional fin AREA, so the whole head would get grow, in planes parallel to the valve cover gasket sealing surface. See below, which is a NOTIONAL plan view. The magnenta is the added fin area.
FatFinHeadPlan.png
 

Bill-Higdon

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Those heads look better than most aftermarket heads, in that they DO NOT cut down the NUMBER of fins compared to stock, which many drag racing oriented heads do. BUT they are NOT "fat fin" in the way the Bob Hoover was working on. He was tig welding additional fin AREA, so the whole head would get grow, in planes parallel to the valve cover gasket sealing surface. See below, which is a NOTIONAL plan view. The magnenta is the added fin area.
View attachment 86918
I remember seeing a Brazilian engine that was VW based that had redesigned heads with way more fin area.

An interesting question has anyone looked at using a 3d printer to make head form out of PLA for investment casting?
 

103

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Those heads look better than most aftermarket heads... BUT they are NOT "fat fin" in the way the Bob Hoover was working on. He was tig welding additional fin AREA, so the whole head would get grow, in planes parallel to the valve cover gasket sealing surface. See below, which is a NOTIONAL plan view. The magnenta is the added fin area.
View attachment 86918
I agree the MOFOCO heads could be further improved with Bob Hoovers' FAT FIN add-ons. After Friday I have little reason to do so in my application since I can get to altitude without broaching 400f and in cruise run cool sub 330f.
Check the valves and change the oil every 25 hours. Read the plugs every 50 or as needed and the VW will commit aviation with very little complaining. Don't ask too much too long stay in limits and the VW will deliver reliability.

That said I may add margin some winter but I will give priority to a oil bath heated induction like Dan used to promote fuel atomization on his SSSC.
REF
https://www.homebuiltairplanes.com/forums/threads/hot-oil-box-oil-cooler.24527/#post-314821

I did spend about 1 hour with sawzall blade in a hand holder and many rat tail files to remove all flash between the fins. Time well spent and easier to do before installation or a fat fin conversion makes them deeper.
 

pictsidhe

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Cleaning up flash etc between fins is often very well worth doing on many air cooled engines. I've used an angle grinder in the past and likely will on my experimental Briggs too.
The webs you find on many finned heads and cylinders are there to damp vibrations and reduce ringing. One of my higher specific output air cooled bikes had mould rubber inserts pressed in to the outside of the fins. I could hear a big difference when run without them. They didn't block much air. You could probably drill and tap and use a length of threaded Al rod to get a good ring reduction with much less airfow impediment than the webs. A little JB weld and they should stay put.
 

Vigilant1

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An interesting question has anyone looked at using a 3d printer to make head form out of PLA for investment casting?
We've had a couple of good threads here talking about what an aviation-specific VW head would look like. There's agreement that, at our RPMs, smaller valves (compared to the large-valve racing heads) would help increase reliability/longevity by reducing cracking between the valve seats, and probably improve volumetric efficiency, too. Pops has pointed out the advantages of single port heads for the smaller displacement engines (??maybe 1915cc and below?? We did some calculations on this in a previous thread). And, of course, more fin area especially on the exhaust side of each head. Oh, and the plugs should have steel inserts from the get-go.
 

Hephaestus

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An interesting question has anyone looked at using a 3d printer to make head form out of PLA for investment casting?
No reason you couldn't other than it wouldn't be cheap. Splitting the form and sand casting would probably better at the end of the day wouldn't it be?
 

Hot Wings

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No reason you couldn't other than it wouldn't be cheap. Splitting the form and sand casting would probably better at the end of the day wouldn't it be?
Way back when we first started down this path - when Hoover was still alive - I did some fiddling with lost foam for this. Sand casting, other than maybe CO2 set, is too much of a pain to get good consistent results*. Lost foam looked like it was going to require some expensive molds for the foam so the fall back was good old lost wax. This was all taking place when a good 3D printer was a large $5 figure tool. If I had access to modern 3D printers and Solidworks back then we wouldn't be having this discussion.

If I had the time and inclination to revisit this project I'd probably use a 3D printed master to use as the base for lost wax. Even then the master might well be several pieces with the resulting wax getting assembled in the final form. This gives us a lot of options to direct the airflow to exactly where it is needed that can't be done any other way, that I know of, other than lost 3D print.

*At least for me.
 

Hephaestus

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Ah I see where you're going.

We (@ makerspace) much stopped doing lost wax style casts with pla because it never quite seemed to work out, wierd porosity issues & hunks of remnant pla crust left behind. But using a wierd slurry sand mix (almost like Portland cement) we got pretty good casts. Not sure how adhesion would be if you tried to glue multiple pieces together to acheive the same?

But we were also playing with recycled computer parts so not exactly precision casting lol.
 

pictsidhe

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I'd be tempted to try CNCing XPS. You need a lost plug that will burn out cleanly, not all plastics will. I think olefins burn out fairly cleanly. It could be educational to try samples in a crucible in your burn out kiln. I would like custom Briggs heads...
 
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