Light Weight VW

Discussion in 'Volkswagen' started by wanttobuild, Dec 29, 2016.

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  1. Jun 15, 2017 #41

    cluttonfred

    cluttonfred

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    This has been kicked around before, and the short answer is: single ignition using an 009 distributor (or 009-based electronic ignition), dead-drain battery (simplest) or small dynamo/alternator (could be wind-driven) with very small battery, single carburetor or throttle-body injector, stub exhausts, Nikasil cylinders if you can afford them. Here's an oldie but a goodie from my site: Steve Bennett on FRED VW power
     
  2. Jun 16, 2017 #42

    dino

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    That leaves the crank. What could be done to make a lighter version at reasonable cost? Would an assembled crank like the 912 be workable. Something like what BBerson posted or a 912 assembly but welded instead of interference press fit.
     
  3. Jun 16, 2017 #43

    cluttonfred

    cluttonfred

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    For reliability I would go with an proven 69mm crankshaft with shrink hub (up to 1915cc) or 82mm crankshaft with tapered hub (up to 2400cc) from a proven supplier. I don't think the few pounds you might save are worth the potential compromise in reliability from an alternative crankshaft. VW engines have been used in little airplanes now for something like 70 years, keep them simple and don't push them too hard and they will serve well, hop them up and modify them and they will bite you. The best way to save weight is to leave stuff off that you don't need.
     
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  4. Jun 16, 2017 #44

    BBerson

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    Can't bore the 69mm crank anyway. The crank pins overlap the mains because the stroke is short.
     
  5. Jun 16, 2017 #45

    Pops

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    I agree with you completely. I think the most bang for the buck and still retain the max reliably is the 1835-1915 cc engine. You can do a major overhaul for about $500 in parts.
     
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  6. Oct 1, 2017 #46

    KWK

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    How much hp continuous do you feel a well executed VW Type 1 can reliably supply? 50, 60, 70? Some makers claim 80, but I have to think that's stretching it (so to speak).
     
  7. Oct 1, 2017 #47

    KWK

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    Looking at the Great Plains site, I have to wonder why that is. Much effort is expended to beef up the pulley end bearing to support a prop, but no one hangs a mag there. Great Plains has a housing to put it on the flywheel end only. I plan to talk with Casler this week, and I'll ask him, too. How's your project going?
     
  8. Oct 1, 2017 #48

    Topaz

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    What displacement? With what modifications? A "VW conversion" describes a range of engines of various displacements, modifications, and other adjustments for airplane use. A small-displacement straight-stock engine with just a Vertex magneto plugged into the distributor hole isn't going to be capable of the same "reliable" continuous power output as one of the more-thorough conversions with custom heads, reworked bearings, larger displacement cylinders, oil coolers, etc.

    It's rather like asking how much continuous power a "Continental" engine can reliably supply. Which one? You have to be more specific if you want a worthwhile answer.
     
  9. Oct 1, 2017 #49

    KWK

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    Fair question it seems, but it's a bit subtle. You can run a bigger bore at lower pressures, or a smaller bore at higher pressures and get the same load on the bottom end at the same hp. The bigger bore may cost you fin area, so maybe it can't get the heat out.

    So, again, how much can you get reliably, and allow me to amend the question with "in what configuration?"

    It seems to me heat rejection in the heads must be the limit.
     
  10. Oct 1, 2017 #50

    Topaz

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    It's not at all "subtle." You can't run a little 1600cc engine at the same power output as an 1835cc and expect the same kind of reliability, any more than you can push an O-200 to the same output as an O-360 and expect it to hold together. Reality doesn't work that way.

    Heat rejection in the heads is the limitation in most cases for VW's. Which is why just about all the higher-power, "more professional" VW conversions incorporate some kind of custom cylinder head. The higher-power versions also almost universally incorporate an oil cooler, which helps get heat out of the heads as well.

    The 1835cc "65hp" VW has been established for decades, putting out 65hp takeoff and 55-60hp continuous power with a "standard" TBO of about 1200h, depending upon manufacturer. This is for a professional conversion with custom heads, bearings, etc. The 70+hp versions from Great Plains and AeroVee seem to be doing pretty good, and I hear good things about the "new" Revmaster engines in this range. Once you get up to engines in the 80+ hp (takeoff) range, you're pushing the limits of what a 1835cc-2100cc VW can do and still provide a roughly 1200h TBO, IMHO. I've heard whispers and rumors that AeroVee is having some difficulties with their 85hp conversion, but I have no actual facts with which to substantiate those rumors.

    1600cc and smaller displacements are not capable of these kinds of power outputs reliably. People try, put the engines in airplanes that need more than 70ph, burn up the engine, and then blame the conversion for the results of their own idiocy. All in the name of saving a buck or two.
     
  11. Oct 1, 2017 #51

    Pops

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    Revmaster is the only one that uses a custom head. Larger fins for better high HP cooling. Everyone else including AeroVee are using stock VW heads that are made for the VW car market. Revmaster also has the best stroker crank and #4 Main Bearing
    The most bang for the buck along with the reliability of the 1600 cc engine is the 1835/1915 cc engine. When you go bigger with a stroker crank the reliability takes a large hit.
     
  12. Oct 2, 2017 #52

    N8053H

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    Revmaster claims no more 25 hr valve adjustment when using their heads.
     
  13. Oct 2, 2017 #53

    KWK

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    So unless you're running the compression ratio to the point detonation becomes a concern, or rpm to the point the valve train is being hammered to death, displacement isn't everything, as far as the continuous rating?

    If heat rejection is the limit in the basic VW design, more displacement would mostly allow you to get a lower (propeller) rpm at top continuous power, no?

    Assuming a reasonable displacement, then, what is the limit hp for continuous operation? 60, 65, 70? It sounds as if 60 may be the limit with 70 briefly.

    edit: Looking at the Great Plains reduction units, it appears 65 is roughly their limit.
     
    Last edited: Oct 2, 2017
  14. Oct 2, 2017 #54

    Pops

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    If building your own VW engine the Bob Hoover HVX oil mods that allow an increased oil flow to the heads helps for more continuous HP because of additional cooling. I used these mods on my 1835 cc, 60 hp VW engine and could climb at WOT on a 100 deg day as long as I wanted with no heat problem with the CHT's or Oil temps. But 60 HP is not generating the heat as 70 or 75 HP.
     
  15. Oct 2, 2017 #55

    MikePousson

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    The following statement was posted on the Yahoo group Starlet site, by another member. There are trade offs with the larger displacement VWs.

    A second Revmaster (VW) head has cracked between the intake and exhaust
    valves on my Corby. It had 40mm intake, and 36mm exhaust valves, which
    left precious little metal in between, and that's where it cracked, just
    like last time. To be on the safe side, I ordered two new heads from
    Great Plains with 36mm intake and 32mm exhaust valves which leaves more
    metal to beef up this area. Don at Great Plains said he mainly ships the
    larger valve heads and they have not had a problem, but I decided to be
    on the safe side.
     
  16. Oct 2, 2017 #56

    Pops

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    Even with stock valves in the VW dual port heads ( 35.5 x 32) they have a history of cracking between the valve seat and spark plug hole. For sure if you run high CHT's. One of the reasons I use single port heads. Don't need large valves in a straight drive at prop rpm's below 3000-3200. IF you are flying a VW in a slick, low drag airframe at higher airspeeds running high rpm's then use the dual port heads, but be sure your cylinders have good cooling to keep the CHT's in check.
     
  17. Oct 3, 2017 #57

    pictsidhe

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    The rocking couple can be fixed with a balance shaft. Toothed belt drive to an external one, cranked suitably weighted and Bob's your smooth talking uncle!
     
  18. Oct 3, 2017 #58

    BBerson

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    So cut a balanced 4 cylinder VW in half and then repair the damage with a balance shaft?
    I would prefer a lighter 4 cylinder at low rpm and big prop.
     
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  19. Oct 4, 2017 #59

    KWK

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    I spoke with Hummel Engines today. Based on his user reports, he thinks VW heads can deal with 70, maybe 75, hp continuous. (He didn't have any dyno data, though, so I'd be inclined to go with less than that.)

    Separately, I asked him about using his largest engine in a full weight, LSA class two place, and he recommended against that. He felt around a 600 lb empty weight is the limit for a direct drive VW two place, and mentioned the 701 as a possible application. That said, wing loading, prop diameter, etc. didn't enter the discussion at all, so this is not definitive. Most LSA are designed around the 912S, which is a 92 hp engine, so at 75% will be running under 70 hp, yet he shied away from recommending a VW in such an application. His straightforward, "not recommended" was refreshing, and I'll keep him in mind should I ever dust off those Zenith 601 plans sitting under my bed.
     
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  20. Oct 4, 2017 #60

    BBerson

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    High cruise speed will cool better than cruising full power at 60 mph. The cooling is proportional to dynamic pressure.
     

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