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Keith,

Very interesting info. I played around with LOP on my O360-A1A after the Lancair Ada Seminar many years ago. Like you, I ran into issues down low but didn’t think to try it up high, so perhaps there is still hope. I was able to get LOP down low, but had to cock the throttle plate so far that I was losing too much MP to be practical. For stretching range on long trips, I simply go up to 17.5k/16.5k. Even with my less than ideal ROP fuel distribution I am flowing about 7.5 gph. Book values say it should be closer to 6, so I figure my rich cylinders are throwing away about 1.5 gph. It hasn’t quite been enough to drive me to fuel injection just yet.

On the CHT front, the 360 inlets are very small relative to the required cooling air mass flow. This drives the velocity through the inlet to be very high. Typically inlets are sized so that the oncoming air is slowed prior to reaching the inlet throat to recover some pressure externally. With the 360, the inlet velocity is roughly the same as cruise speed, so all pressure recovery is internal. Unfortunately internal pressure recovery is much more difficult and really requires controlled diffusion of some sort. The stock inlet lip creates a jet that turns most of the energy into turbulence. After many partial fixes I resolved my temperature issue once and for all with a complete makeover: new inlets, diffusers and a plenum. The inlets retain the original diameter, but the internal flow expansion is now controlled. At 2,500 rpm, WOT and leaned for best power, my hottest cylinder runs 360 +/-15, depending on time of year. The next two cylinders are 20 degrees below that and the last cylinder is 40 degrees lower.Chris ZavatsonN91CZ360stdhttp://www.n91cz.net/

On Tuesday, October 15, 2013 9:49 AM, George Braly <gwbraly@gami.com> wrote:

Try using some carb heat. It will smooth out that engine significantly when LOP.

The warmer induction air does a much more uniform job of distributing the fuel as vapor with less liquid drop outs in the induction plumbing.

-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of vtailjeff@aol.com
Sent: Tuesday, October 15, 2013 8:21 AM
To: lml@lancaironline.net
Subject: [LML] Re: LOP ops on O-360 A1A

Have you checked your baffling?

Sent from my iPad

On Oct 15, 2013, at 7:53 AM, Keith Smith <keith.smith@gmail.com> wrote:

> Hey all,
>
> I'm waiting for winter to come around but it seems like my O-360 A1A has been running warmer than usual, requiring me to power back very shortly after takeoff to avoid an excursion north of 425 degree CHT's.
>
> In any case, I know that LOP ops are hard to come by with an O-360 due to poor fuel distribution. Indeed, my #4 cylinder peaks well before the others, making it tricky to get them LOP.
>
> I've been running in two modes...one is around 20 LOP to cool it down to around 385 CHT while the others run just slightly rich of peak. I can do this without much effort, and under a wide range of throttle positions, and density altitudes.
>
> On a recent flight, though, I found #1 and #3 settling on temps that were just too high to be happy with. I would go well ROP to get them cooled, but burned a lot of fuel in the process and still had a warm 4th cylinder due to the fact that it runs quite a bit leaner. This was all done at 75% power or less, btw, density altitude was well above 11k (I was at 11k and it was +10C)
>
> Eventually, I tried something somewhat dramatic. I was determined to get ALL the cylinders LOP. I leaned relatively rapidly and ignored the disconcerting knocking/shuddering associated with the uneven amounts of power being produced between the 4th cylinder and all the rest.
>
> It all happened a bit quickly, but with cylinder 1-3 roughly 20-40 LOP and #4 70-90 LOP, the CHTs dropped like a stone, seemingly in seconds, down to 380-385 across the board for #1-3 with #4 now in the 350-360 range. With careful fiddling of the mixture, and countless experiments with throttle position, I got the vibration down to the point where it was barely noticeable. Eventually it just felt smooth...but I can't tell if I got used to it, or things just settled down, although I wouldn't think it was possible.
>
> Final fuel flow was around 8.8-9.0 gph.
>
> Finally, living the LOP dream with my O-360 :)
>
> I tried repeating this later on, down low and wasn't able to repeat it (ie, never got it smooth).
>
> So, it's elusive, but possibly doable under just the right circumstances. Since I do long trips on a regular basis, I'm definitely interested in making this work.
>
> Separately, I'll try to find out why it's running warmer in general. I did have a mag replaced, the other rebuilt, and 4 new plugs installed in the last year.
>
> Honestly, I'm going to try to save some clams and get this converted to an IO-360 (didn't realize it was relatively inexpensive until my mechanic suggested it), get balanced injectors and run LOP as SOP. The difference in cooling really is staggering. I know I'm probably preaching to the choir, but I thought that O-360 owners might find it eye opening. Get up high and give it a try if you have a 4 point engine monitor. You'll know it's working when your leaning results in EGT and CHT's coming down :)
>
> The trip, btw, was N07-KFTW-KSAV-N07, around 2600nm.
>
> Keith

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