> ----- Original Message ----- > From: brian.kraut at eamanufacturing.com > Sent: 07/12/13 02:27 PM > To: KRnet > Subject: Re: KR> Additional testing data with P-mag timing > I would think that the increase in oil temp would be directly proportional to the increase in CHT since it is the more complete burning of the fuel in the cylinder that causes a temperature increase. ?Therefore I would be more inclined to do something to increase the cylinder cooling with the baffles, air inlets and outlets from the cowl, etc. than to try to directly cool the oil. ?Even if your CHTs are not overly hot the cylinders are obviously getting hot enough for long enough to increase the oil temp. --------------------------------
Actually, at BDC on each stroke, the oil port in the rods squirt oil against the bottom of the piston head of the opposing cylinder to cool the pistons. ?That's the genesis of the higher oil temperature. ?Additional burn time in the cylinder equals higher piston head temps, which gets absorbed 100% by the oil. ?The CHTs do go up a small amount with the advance in timing, but my CHTs are well under control with all of them running in the 300 - 340 range. ? While I have no doubt they would make a difference, I'm not really interested in adding heat sinks or an oil cooler to the engine. ?220*F is still in the green and that is as high as it goes under summertime conditions. ?There is really no drop off in performance for selecting the more conservative timing curve, so I really don't see any down side to adding a switch to simply select the more conservative timing curve on a hot summer day, then the more aggressive curve any other time. ?That's why they put the multiple timing curve option in the Pmags. ? Something that's probably worth pointing out here is that the way the Pmags operate causes the temps to run differently at different times from what you have learned to expect while using magnetos with fixed timing. ?For instance, with magnetos, my oil temps would always peak during a long climb, then cool back down a bit once I throttled back to cruise. ?That is not the way it works with the Pmags. ?My oil temps are pretty much the same as I have always seen during take off and climb conditions. ?Once I settle in at cruise, the oil temp climbs a bit until it reaches it's peak temperature, then stays there. ?The reason for that is the timing curve. ?During full throttle and climb operations, the timing runs a bit more conservatively to give a significant margin to prevent detonation, which causes less burn time in the cylinders. ?Under worst case conditions (low altitude, full throttle), the ignition timing will be the same as you would see with the fixed timing on a magneto. ?It's when you get to altitude and start pulling the throttle back that the timing goes to full advance, which causes a significantly longer burn time (14 degrees longer burn) in the cylinders. ?That additional burn time is creating more heat in the piston itself and that is what is driving the oil temp higher than what it used to run. ?The actual power output isn't any higher, so the CHTs are not significantly higher than they were before. ?But the oil cooling the bottom of the piston heads has to absorb a lot more heat, and it shows up as higher oil temps. ?This probably wouldn't be seen at all in an engine with an adequate oil cooler, but shows up in the O-200 due to the lack of any kind of oil cooler. ?As another side note, the additional burn time in the cylinder means there is less fuel burning in the exhaust. ?All of my EGTs have dropped between 200 and 300 degrees from where they used to run. ?The good news there is that the exhaust valve and exhausst valve guide life should be significantly longer as the exhaust valves are seeing less heat than they were before. Anyway, I was asked to report back on my experience with the Emag/Pmag set up. ?My overall impression is that I like them. ?But don't buy them thinking it's going to improve your performance. ?It's not likely to make a big impact. ?However, the additional timing advance will allow you to save fuel by burning more of it in the cylinders and less of it in the exhaust, especially if you fly throttled back or at high altitudes. The other benefit I see is with the much hotter spark supplied by the electronic ignition and automotive style plugs. ?The engine simply runs better and will fire marginal mixtures that a magneto won't fire. ?With the current high cost of magnetos, the cost to buy a set of Pmags is only marginally more and will pay for itself over time. ?So I recommend them as a buy. -Jeff Scott Los Alamos, NM
