FlyingMonkey Posted February 23, 2016 Report Share Posted February 23, 2016 Todd, I pretty much agree with you, the 912 likes the revs. Mine loves 5400rpm in cruise. I also flew all the way to Oshkosh and back (~600nm each way) at 5500rpm, it was fine even in the dead of summer. I don't get nearly your fuel efficiency, because I'm using the stock mixture circuit. But leaning to the numbers you are getting might scare me a bit; I'd be afraid of frying something running that lean. What do your CHTs and EGTs look like when leaned out like that at 5400-5500rpm? Link to comment Share on other sites More sharing options...
GravityKnight Posted February 23, 2016 Report Share Posted February 23, 2016 Todd, I pretty much agree with you, the 912 likes the revs. Mine loves 5400rpm in cruise. I also flew all the way to Oshkosh and back (~600nm each way) at 5500rpm, it was fine even in the dead of summer. I don't get nearly your fuel efficiency, because I'm using the stock mixture circuit. But leaning to the numbers you are getting might scare me a bit; I'd be afraid of frying something running that lean. What do your CHTs and EGTs look like when leaned out like that at 5400-5500rpm? I believe a large part of the increased efficiency came from the zipper kit (higher compression). It really noticeably picked up then, I already had the hacman on before that. When leaned out in cruise I usually see in the 1450 area max egts. CHT stays at ~180 along with water (thermostat). And oil around 180-210 (I have 2 oil coolers, so it depends on time of year and how much tape I have on the second one etc.) I also have a wideband o2 gauge so I can see real time air fuel ratios (makes adjustments instant, instead of waiting on the egts to respond). Climb/WOT in the low 12's to 1, cruise in the 13:1 to 13.5:1 area etc. I am building equal length headers right now to see if I can extract some more of something: power/efficiency etc. and bring EGTs closer together (the rans headers and exhaust are different from the rotax stuff, too small, massively different lengths on the primaries etc.) What was weird is going from the 68" warp drive to the 72" KOOL I saw no noticeable reduction in fuel economy, yet my cruise RPM went up ~200rpm (in order to get that good climb rpm). And this prop drags noticeably more under no throttle (like another notch of flaps suddenly now - which is actually nice). I can't explain in.. I'm guessing it did go down, just not enough I've been able to detect it when measuring? They say the scimitar blades are more efficient but come on now lol Link to comment Share on other sites More sharing options...
IrishAl Posted February 24, 2016 Report Share Posted February 24, 2016 Gravity knight - any possibility of starting a new thread and giving us a rundown on your views and experiences with the zipper kit? Link to comment Share on other sites More sharing options...
GravityKnight Posted February 24, 2016 Report Share Posted February 24, 2016 I'd be glad to, it's been an interesting / fun experience so far.. I'll do that Putting it in the Engine/Rotax subforum Link to comment Share on other sites More sharing options...
FlyingMonkey Posted February 24, 2016 Report Share Posted February 24, 2016 and the HacMan too please! Link to comment Share on other sites More sharing options...
Roger Lee Posted February 24, 2016 Report Share Posted February 24, 2016 Most I know that have had Hacman for a while have taken them out. Just had an RV12 remove one for complications. The Hacman basically changes the air pressure to the carb and lies to it. No one has gone to TBO or been around long enough to know it's long term side effects. It will be interesting to see what happens. I have seen a few detonation issues over the years with Hacman so adding the Zipper Kit may be interesting in the long haul. Did Ronnie Smith install this? Link to comment Share on other sites More sharing options...
GravityKnight Posted February 24, 2016 Report Share Posted February 24, 2016 I do all my own work. I would be more concerned with the 11:1 compression if not being at such high altitude. I dropped some richer main jets in, in case I visit lower elevation so I have some headroom. Probably wouldn't be a bad idea to run some avgas at that point to (which I would have to most likely be running anyway, away from home). At my altitude, there is a pretty good chance I'm still not even making stock 912 power. In that other thread I started to blab about the zipper and such I mentioned having the wideband for the HACman, I really think it's a good idea to run one as you can see your air fuel ration in real time and make quick adjustments to what you want, I could see someone getting into a little more trouble with the hacman without that (egts definitely are a must of course too). Flying in the mountains in CO, the hacman is a big help... I've been high enough that without it (turning it off) the motor was running rough and chugging due to being richer than 10:1 afrs (rich as the wideband goes). But we can discuss all that sort of stuff in the thread in engine/rotax subforum if you guys would rather, before we get way off topic in this thread. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 24, 2016 Report Share Posted February 24, 2016 You can get detonation so fast the gauges won't have time to react. I have seen way too many 912 junked detonation parts from owners. takes just a few seconds. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted February 24, 2016 Report Share Posted February 24, 2016 You can get detonation so fast the gauges won't have time to react. I have seen way too many 912 junked detonation parts from owners. takes just a few seconds. A little JB Weld will fix that right up. Link to comment Share on other sites More sharing options...
GravityKnight Posted February 24, 2016 Report Share Posted February 24, 2016 A little JB Weld will fix that right up. little JB and a little buffing should be good as new! Many years ago, I killed a 22RET (1987 turbo 4runner) that I threw big boost at, on pump gas, with no real ability to tune it. Well it still ran when I tore it down to rebuilt it, but the edges of the pistons had all gone missing. Big learning experience. Tuning is everything. I'll keep that in mind Roger when playing with the leaner, especially when I visit lower elevation where everything is far less forgiving! Link to comment Share on other sites More sharing options...
Roger Lee Posted February 24, 2016 Report Share Posted February 24, 2016 Rotax purposefully runs rich at WOT to help prevent detonation. It runs leanest in midrange around 4600-4900 where they would rather you did not run for long periods which is more due to vibration rather than lean conditions. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted February 24, 2016 Report Share Posted February 24, 2016 Rotax purposefully runs rich at WOT to help prevent detonation. It runs leanest in midrange around 4600-4900 where they would rather you did not run for long periods which is more due to vibration rather than lean conditions. It runs leaner when the needle circuit has control, that's dependent on throttle setting not RPM range, right? Still can't figure out why the Rotax runs so well at full rich and 12,500' Don't seem right. Austria has mountains yet the Rotax lack the ability to lean at WOT, don't seem right either. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 24, 2016 Report Share Posted February 24, 2016 Yes it is dependent on throttle setting and not rpm. Once you are approx. 3K rpm the idle circuit is no longer in play and it's all needle and main jet. Link to comment Share on other sites More sharing options...
GravityKnight Posted February 25, 2016 Report Share Posted February 25, 2016 The wideband agrees with Roger. Down around 4500 it runs a leaner, and progressively gets richer as you feed it more throttle. The idle circuit is also pretty rich. Same day, same climb, wide open, mine will go from having air fuel ratios of say 12:1 at 6650ft (ground level) to 11:1 or maybe a bit richer by 15,500ft, and worse on up.. (without the leaner). There is some kind of compensation taking place, it's just not enough to keep up. I've seen it slightly leaner down around 5k altitude which makes sense, but I have not been lower yet with all these modifications to see how far it will go. Hence keeping the bigger main jets in for now. Going to Sheridan WY again soon and so I'll get some 4k testing in. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted February 25, 2016 Report Share Posted February 25, 2016 My understanding is that above 10,000ft or so the stock altitude compensation is maxed out and is no longer a factor and the engine goes progressively richer after that the higher you go. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted February 25, 2016 Report Share Posted February 25, 2016 My understanding is that above 10,000ft or so the stock altitude compensation is maxed out and is no longer a factor and the engine goes progressively richer after that the higher you go. Its not an altitude thing its a throttle setting thing. At idle its full rich, I think. Advance the throttle and the needle circuit gets control and while it has control the bing can lean from differential pressure adjusting the needle. At 93% throttle the main jet gets control and its full rich from there. Link to comment Share on other sites More sharing options...
GravityKnight Posted February 25, 2016 Report Share Posted February 25, 2016 I believe the main jet has effect before that. The needle and main jet are working together. (For example, at half throttle, changing main jet size would have very little if any effect, at wide open, the needle position has very little effect, but in between they both have an effect).. Just like changing the idle screw for mixture has an effect everywhere, but it's too small to actually notice above idle. This has been my experience anyway after testing different needle positions, and several different size main jets etc. so it's not gospel... But essentially what you said yes. Wasn't it the 912i that puts itself into economy mode anything under 93% TPS? That number stood out, but I may be remembering that wrong. Anyway, I personally think the leaner is very worthwhile when you want to go real high and have your ship run correctly/efficiently. It can also be touchy though. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted February 25, 2016 Report Share Posted February 25, 2016 Sure the main jet has effect when needle circuit has control but you have to change the main jet in order to adjust its effect. The 93% stood out to me too because I would have expected leaning when cruising above WOT 7.5DA and the injection could easily do that but they didn't bother. It seems the mimicked a weak point of the bing. Link to comment Share on other sites More sharing options...
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