Sam,
Great write up! I was certainly curious about what an “AA” head is. Your right, these look pretty good except for the part about not being able to set up dual spark plugs. Thanks, Rob Schmitt N1852Z Lee’s Summit, MO From: KRnet <krnet-boun...@list.krnet.org> On Behalf Of Samuel Spanovich via KRnet Sent: Monday, July 10, 2023 2:21 PM To: krnet@list.krnet.org Cc: Samuel Spanovich <spanovich...@gmail.com> Subject: KRnet> Update - AA VW Cylinder Heads The net seems fairly quiet, so I figured I would give some supplemental info on another set of VW heads that are not covered under Mark Langfords page of VW heads. I posted about these heads a couple weeks ago, asking about machining a second spark plug, but never gave an update, so here we go. These are the heads I’m currently using on my N6399U https://aapistons.com/collections/cylinder-heads-components/products/new-vw-1600-dual-port-high-performance-cylinder-head-40x355 The Goods 1) Comes standard with stainless steel intake and exhaust valves 2) Lot of air cooling passages (I don’t have pictures, but I would say they are on par with the DRD heads Mr. Langford has on his page, in terms of air passages), before any de-flashing. 3) Ready to use out of the box - for better or worse, I installed these on my KR2 about a year ago after one of my older MOFOCO heads failed, and I other than a simple water leak down test, I didn’t do a single thing to these heads. The heads were able to be used right out of the box. A valve job was not necessary. **additionally, after I eventually did have to break down one of the heads, after about 100 hours on one (due to one of the exhaust valves leaking ever so slightly on #3), the valve guides were still in great shape, and there was no “gap” in between the valve guide and the cylinder head, how Mr. Langford discussed on his set of DRD heads. 4) CHT spark plug sensor fits with ease - the pictures I posted above incorrectly portray this (or maybe I just got lucky), however on my set of heads, there was lots of room in the spark plug area to install a 12mm CHT plug sensor with no machining/dremeling required. This is different than my previous MOFOCO heads, that required me to grind down part of the circular “edge” that usually surrounds the spark plug, in order to install a plug-style CHT thermocouple. 5) the valve seats do not appear to “recess” like they do on older VW heads. Usually the valve clearances between oil changes are just about where they should be when I go to adjust them; I never have to make any drastic changes. I’ve gone through about 4 oil changes on them so far. 6) Lastly - they got me to and from the gathering last year, all the way from WA to IL (and back) in some pretty harsh flying conditions. Out of all the things that went wrong with my airplane, the heads were not one of them. Now for two “others” 1) my #3 exhaust valve began leaking ever so slightly (compression was 125 psi vs 150-155 psi on the other three good cylinders) which required a lap job to get it to seat again. However, after lapping, and about 5 hours of run time, it appears to have seated nicely again. 2) now for my BIGGEST complaint, which is almost certainly a dealbreaker for most people - Eh Hem - Dual ignition is pretty much impossible. Because of the geometry of these heads (when compared to something like a MOFOCO 042 or a CB 044 head), there just isn’t enough “beef” in the secondary plug area to drill a second spark plug. No way you could get anything close to a 12mm x 3/4” spark plug in there; probably the most you could do is something in the realm of a 10mm x 1/2”. After talking to Great Plains (who recommended against that plug size), and a very experienced local machinist and engine builder, I decided that the juice wasn’t worth the squeeze and just decided to keep single ignition. If nothing else, I’ll have that much more metal in the cylinder head for support. Now for my typical performance numbers on a fairly hot (80-90F) day at sea level. The engine is an upgraded Revmaster 2100 (75-80HP), Sterba 56x56, single electronic ignition. Standard baffling (no plenums). Temperatures are all taken from a type J thermocouple, directly under the spark plug. Static RPM - 2800-2900 CHT climbout at full power - absolute max 430-440F on the hottest cylinders (full power for an extended period of time), and 400F on the coolest (front) cylinders. Usually I apply full power on takeoff, then once safely airborne throttle back to 2600-2700 to keep the CHTs under control; I can still usually manage a safe 600-700 FPM climb when solo, or about 350-450 FPM at gross at this power setting. CHT climbout at 2/3-3/4 power - 390-410F on the hottest cylinders, and 350-375 on the coolest cylinders. Typical CHTs during cruise (all altitudes) #1 - 350-375F #2 - 300-325F #3 - 350-375F #4 - 300-325F It appears that the hotter cylinders run about 25-50F hotter than the two most forward cylinders. If nothing else, this can serve as some supplemental info for somebody looking for a new set of heads. Just don’t expect a dual ignition setup :D. Very Respectfully Sam Sent from my iPhone
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