Ready-made VW fat fin heads?

Discussion in 'Volkswagen' started by cluttonfred, Oct 31, 2014.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Oct 31, 2014 #1

    cluttonfred

    cluttonfred

    cluttonfred

    Well-Known Member

    Joined:
    Feb 13, 2010
    Messages:
    6,366
    Likes Received:
    2,231
    Location:
    World traveler
    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
     
  2. Oct 31, 2014 #2

    Aviator168

    Aviator168

    Aviator168

    Well-Known Member

    Joined:
    Sep 21, 2012
    Messages:
    2,205
    Likes Received:
    249
    Location:
    Brookville, NY. USA
    Ah. I wonder if this mod has better heat extraction that the stock ones.
     
  3. Oct 31, 2014 #3

    dino

    dino

    dino

    Well-Known Member HBA Supporter

    Joined:
    Sep 18, 2007
    Messages:
    598
    Likes Received:
    82
    Location:
    florida
    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
     
    Topaz likes this.
  4. Oct 31, 2014 #4

    dino

    dino

    dino

    Well-Known Member HBA Supporter

    Joined:
    Sep 18, 2007
    Messages:
    598
    Likes Received:
    82
    Location:
    florida
    Topaz likes this.
  5. Oct 31, 2014 #5

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,131
    Likes Received:
    6,022
    Location:
    USA.
    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
     
    pictsidhe and Topaz like this.
  6. Oct 31, 2014 #6

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,382
    Likes Received:
    2,306
    Location:
    Rocky Mountains
    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.
     
    sotaro, Pops and Topaz like this.
  7. Oct 31, 2014 #7

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,131
    Likes Received:
    6,022
    Location:
    USA.
    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
     
  8. Oct 31, 2014 #8

    Aviator168

    Aviator168

    Aviator168

    Well-Known Member

    Joined:
    Sep 21, 2012
    Messages:
    2,205
    Likes Received:
    249
    Location:
    Brookville, NY. USA
    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.
     
  9. Jun 9, 2019 #9

    103

    103

    103

    Well-Known Member

    Joined:
    May 3, 2015
    Messages:
    124
    Likes Received:
    67
    Location:
    Wauwatosa WI
    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_...ead_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
     
    Last edited: Jun 10, 2019
    fly2kads and akwrencher like this.
  10. Jun 10, 2019 #10

    akwrencher

    akwrencher

    akwrencher

    Well-Known Member HBA Supporter

    Joined:
    Oct 16, 2012
    Messages:
    1,104
    Likes Received:
    393
    Location:
    Gustavus, AK
    Sure sounds like a real airplane engine to me:)
     
  11. Jul 20, 2019 #11

    103

    103

    103

    Well-Known Member

    Joined:
    May 3, 2015
    Messages:
    124
    Likes Received:
    67
    Location:
    Wauwatosa WI
    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
     
    TerryM76 and BoKu like this.
  12. Jul 21, 2019 #12

    karmarepair

    karmarepair

    karmarepair

    Well-Known Member

    Joined:
    Jan 13, 2011
    Messages:
    63
    Likes Received:
    19
    Location:
    United States
    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
     
  13. Jul 21, 2019 #13

    Bill-Higdon

    Bill-Higdon

    Bill-Higdon

    Well-Known Member

    Joined:
    Feb 7, 2011
    Messages:
    444
    Likes Received:
    139
    Location:
    Salem, Oregon, USA
    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?
     
  14. Jul 21, 2019 #14

    103

    103

    103

    Well-Known Member

    Joined:
    May 3, 2015
    Messages:
    124
    Likes Received:
    67
    Location:
    Wauwatosa WI
    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.
     
  15. Jul 21, 2019 #15

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,858
    Likes Received:
    1,844
    Location:
    North Carolina
    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.
     
  16. Jul 21, 2019 #16

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member Lifetime Supporter

    Joined:
    Jan 24, 2011
    Messages:
    4,053
    Likes Received:
    1,796
    Location:
    US
    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.
     
  17. Jul 21, 2019 #17

    Hephaestus

    Hephaestus

    Hephaestus

    Well-Known Member

    Joined:
    Jun 25, 2014
    Messages:
    1,177
    Likes Received:
    256
    Location:
    YMM
    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?
     
  18. Jul 21, 2019 #18

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,382
    Likes Received:
    2,306
    Location:
    Rocky Mountains
    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.
     
    MadRocketScientist likes this.
  19. Jul 21, 2019 #19

    Hephaestus

    Hephaestus

    Hephaestus

    Well-Known Member

    Joined:
    Jun 25, 2014
    Messages:
    1,177
    Likes Received:
    256
    Location:
    YMM
    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.
     
  20. Jul 22, 2019 #20

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,858
    Likes Received:
    1,844
    Location:
    North Carolina
    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...
     

Share This Page

arrow_white