Wow, lots of things I could add and say about this thread ; ) Oddly enough, I am in Mark?s camp when it comes to turbocharging a VW in a plane, at least at this point. While I have about 8 flight hours on my turbo motor, I don?t/can?t approach the plane like I used to. It used to be a pretty fast sport plane that I trusted, even when I ran it wide open at 4100rpms for hours on end. With the turbo, its an entirely different animal. I wear a fireproof suite, shoes, gloves and a helmet every time I fly it. I may get more comfortable with it, bit its got to prove itself first.
I will contested the idea that the VW cannot run cool at high RPMs. I don?t have a ton of time on my engine (about 80 hours) before I tore it down for the turbo build. I can tell you a few things however. During that time, I usually cruised it at 3600 RPMs, sometimes slower to make fuel stops and it has spent many hours above 4000. It ran the same temps at 3200R RPM?s as it did wide open spinning up to 4100 straight and level, more in a full power race descent. The bottom end looked like the day it was first put together. Working on cleaning up the heads is a big deal when it comes to getting them to cool. I have a set of Revmaster 049?s on the plane now and have been abusing them pretty badly during flight testing with the turbo. They have seen 500F a few times at 45? MAP, but for now at lest have had zero issues with the valves. The did require a bit of clean up, but nothing crazy. Too bad the "soon to be officially mine" Corvair powered KR has taken to circulating the better part of the cam gear teeth throughout the engine? But that is a different story for a different thread ; ) Jeff Lange Race 64 - Skye Racer Blog: http://schmleff.blogspot.com <http://schmleff.blogspot.com/> Youtube Channel: https://www.youtube.com/schmleff <https://www.youtube.com/schmleff> > On Jun 21, 2016, at 7:13 PM, Mark Langford via KRnet <krnet at > list.krnet.org> wrote: > > Some random thoughts that I feel must be said: > > Turbocharging a VW would be a recipe for disaster IMHO, and insurance that > you wouldn't do much flying. Don't forget...it's all about flying, not how > fast you can say your plane would go if it were running. > > GPASC has proprietary parts...flywheel, adapter, hub, crank, bearing, and > case come to mind quickly. Having built one of these several times, I'm not > a fan of the keyway setup. The slots are in hub and crank are shallow, and > the key is provided as a square key that you need to grind (or mill) down to > something way thinner to fit between hub and crank. Getting a good fit with > maximum material is trial and error. The key is only there to ensure the > timing mark stays constant if the hub is removed. The taper is where the > power is transferred. > > Crank and hub are also matched sets due to tolerances on the angle. The hub > still needs to be lapped onto the crank, which is a two-hour chore by hand. > > The hub/bearing clearance is not consistent. The crank and bearing are sold > as a set, and getting a new bearing for an existing crank is iffy. I've > torqued the case to 8 ft-lbs and the crank still spun, then when I torqued it > to 14 the crank seized. No amount of refitting cured that one. I'm not a > great fan of the prop bolt...1/2" RH threads. Revmaster's is .75" LH threads, > which can be torqued higher for a better connection. Otherwise, a simple > engine backfire can unscrew the prop, despite proper torque and Loctite 620 > on the bolt threads. > > If the crankshaft's oil seal leaks, the hub isn't going to come off without a > 20 ton press, so tear the engine down to replace the seals, and hope the next > seals work better. My luck with those seals has not been good either. > That's the only place my engine has lost oil. > > If you're working with the hub before it's torqued and remove it while the > keyway is facing down, the tiny key falls down into the cavity below the cam > gear, and you get to tear the engine down again to retrieve it. Yes, I'm > stupid, but it could happen to you as well. > > Buy the GPASC manual and read it. There's a lot of trial and error work to > be done in there, not to mention the basics of case and other clearancing > when boring and stroking a VW engine. I guess the 2700cc Corvair really > spoiled me...no machine work or trial and error. > > Generally, VW heads have a tiny area of air passages between the top and > bottom of the head, even after serious deflashing. This has gotten even > worse over the years, rather than better, now that factory VW heads have > dried up. Corvairs have way more cooling passage area, hence they cool far > better. N56ML would fly around on the hottest of days at cruise speed and it > might be 320F. This VW is closer to 380F. The "cure" for this is to move > the CHT probes to the head studs, so the temperature will read a lot lower. > Makes you feel better, at least. Fiberglass plenums are my next experiment, > and probably a set of heads with larger cooling air passages, if I can find > them. > > Keep in mind that I used to be a VW mechanic, and am no stranger to trial and > error with details like chamber volume, but this is ridiculous, and > apparently never ending. > > GPASC is on its third owner in less than a year, so consistency is not > something I'd count on. > > I could write more, and someday I'll have time for further details, but I > feel obligated to get this said. For the moment I'm off to adjust the valves > again. > > Stirewalt's right, I "make" time by not getting enough sleep, and it's not > getting any better... > > > Mark Langford > ML at N56ML.com > http://www.n56ml.com
