Surefly electronic ignition

[pecanflyboy]

Scott,
DO NOT CAP THE MP PORT! It will seal the manifold pressure sensor which may throw a fault to the unit. A cap could pressurize or depressurize the manifold pressure sensor, thereby making the unit think the MP is faulty. It will result in a rapid flashing LED. Let it breathe.

[Scott Hersha]

OK, I won’t cap it. My install manual says to do that, but it’s a year old. Checking the online install manual - no mention of capping it...... THANKS for the heads up, Jimmy and George.

[DanH]

Originally Posted by Scott Hersha

With a wasted spark EI system, when I set my timing to 5* ATDC, that also influences the wasted spark on the opposite cylinder. That wasted spark is supposed to occur at TDC on the exhaust stroke of the opposite cylinder when the exhaust valve is fully open.

It was fully open back around 100 degrees before TDC.

When I fool it to fire 5* later, that wasted spark is occurring after the exhaust valve is starting to close. How much is it closed? Who knows...

BY TDC, it's been closing for quite a while, but won't fully close until well after TDC. The TDC overlap period, during which the intake valve and the exhaust valve are partially open at the same time, is (ballpark) 30 to 50 degrees of crank rotation for a low speed engine like our trusty Lycoming. The actual number quoted depends on the arbitrary valve lift point picked to designate open and closed. In the context of spark timing at cranking speeds, the exact number doesn't matter much, because it's a lot more than the 5 degrees you proposed. Next time you have the valve covers off, rock the crank around #1 TDC and watch the valve action on #2.

FWIW, you know EMag incorporated a cranking retard. As an experiment I clocked the EDIS on my 390 by 10 degrees for a few years. The typical EDIS module fires a few degrees before TDC, so 10 degree clocking put spark delivery (ballpark) about 6 ATDC. Made for very smooth starts. I've since returned it to a TDC set, as I have a metal Hartzell with lots of inertia.

One other thing he asked me that I hadn’t considered was how I am timing my ignition. I timed it just like I would time a Slick. He said there is quite a bit of slop in the gearing in the engine and in a traditional mag that doesn’t exist in the SureFly SIM - it is very precise. He recommended finding TDC on cylinder #1 compression stroke using a dial indicator riding on the piston to find the exact TDC.

A dial indicator is a fine idea to check the location of the flywheel's TDC mark....once.

Slick points are on the main shaft. As such, internal Slick gearing has no effect when setting timing. The gearing drives the distributor rotor.

The engine's gear freeplay is the same for any ignition driven from the accessory case. Using a dial indicator to find TDC when setting the timing will not in itself eliminate the slack. Doing so simply requires good procedure, i.e. rotating the crank in the normal direction of rotation to arrive at TDC, or to trigger a buzz box.

[DanH]

Originally Posted by bjdecker

Thanks Dan -- What do the numbers look like if the RPM is the same (2nd set of pictures -- 2430 vs 2530).

Can't find the 23/2430 photo, sorry. The speed difference would be less of course, but still faster at 23 degrees. In fairness, at this altitude and mixture, an advance of perhaps 28 would have been fastest by a wee bit. See Marvin McGraw's past posts with detailed variable timing inflight data for the 390.

I was playing around with a few things here.

Over in the Bonanza/GAMI/APS world, the LOP procedure has the pilot setting mixture, then adding MP to regain the lost speed. Can't do that with a 390 above 8000 or so (no turbo), but we can add RPM.

Cooling demand is proportional to mass flow, i.e. RPM. Note that using the mild timing, I can turn up the RPM, yet maintain CHT and oil temps well below the advanced timing example.

The result here is a fuel burn about 4% higher in return for speed 3% higher, not a bad trade in the world of internal combustion. Note groundspeed is over 200 knots at 7.8 gph; the tailwind and settings would get me home non-stop quickly, with range to spare. The subsequent switch to 35 degree timing pushed CHT up so far I never went to 2530.

Reminder...this is angle valve stuff.

[pecanflyboy]

What ignition and plugs are you using to get this data?

[DanH]

Originally Posted by pecanflyboy

What ignition and plugs are you using to get this data?

What difference would it make?

[sailvi767]

Ignition and plugs should not matter. Dan’s engine is I believe a angle valve that responds quite differently to advancing the timing.

[pecanflyboy]

Originally Posted by DanH

What difference would it make?

It’s a Surefly thread. If you are presenting data and it is not a Surefly system, you should at least be willing to disclose on what system your data is based.

[DanH]

Originally Posted by pecanflyboy

It’s a Surefly thread. If you are presenting data and it is not a Surefly system, you should at least be willing to disclose on what system your data is based.

As noted a few posts above, it's based on a Ford EDIS module. Again, what difference does it make? Please be technical.

https://vansairforce.net/community/s...d.php?t=135476

[DanH]

Crickets eh?

Ok, good for the goose, good for the gander.

Originally Posted by pecanflyboy

Do you have an engine monitor? If you pay close attention to your CHT's, you will see any "stress."

Higher CHT, sure. But that's not the only stress of interest.

I have an RV6 with dual SIM's, in variable timing mode, on a high compression IO-360. I flight a lot of formation below 4000' without any problems.

May I ask which 360 and propeller you're using? I ask because high compression 360's and 370's without crank pendulums and with ignition advance are generally subject to propeller restrictions...for good reason.