Silverhawk FI - any adjustments for a high altitude home?

We've now got about 280 hours on our RV-3 (Tsamsiyu), and have had flawless performance from our Mattituck IO-320 with Silverhawk fuel injection and P-Mags. We have been based in Houston, which is basically sea level, and most of the flying has been done in the center of the country. Aside from the usual care with hot starts, nothing special has been required for operation, and it worked right out of the box.

I transferred Tsam to her new home near Carson City a couple of days ago, and have noticed that starting and ground operations seem a little different, and am wondering if we need to make any adjustments for a higher altitude "base" (Density Altitudes about 6,000 msl or greater). In particular, the idle has changed - if I pull the throttle all the way back on the ground, she'll die - I'd say that the idle has changed about 150 rpm for the same throttle position. Starting mixture seems to be a little more finicky as well - I already figured out not to go all the way to full rich when she fires, but settle in somewhere below that.

I'm just curious if anyone has done any re-adjustment to operate routinely at higher altitude fields - performance is just as it has been before when we get out of the mountains, so I don't think that there is anything "wrong" per se'. ANd maybe it is just a matter of needing to retrain the operator.... If nothing else, it should spark some discussion!

Paul

I'm sure Don will jump in here, but I'd like to think the engine should be baselined for sea level. If you adjust it to better deal with your new home and drop down to the Bay Area, you're in a world of hurt. I make my ground ops adjustments at home with the red knob. Takeoff is often with the red knob pulled out a bit - full rich delivers 250 degrees ROP, which is well fat of best power.

Toobuilder said:

I'm sure Don will jump in here, but I'd like to think the engine should be baselined for sea level. If you adjust it to better deal with your new home and drop down to the Bay Area, you're in a world of hurt. I make my ground ops adjustments at home with the red knob. Takeoff is often with the red knob pulled out a bit - full rich delivers 250 degrees ROP, which is well fat of best power.

Click to expand...

That's pretty much I have been assuming, but the low idle surprised me. It might be a coincidence that the idle needs adjusting after the trip from Oshkosh, but I hate coincidences....

The lightweight prop does make us run the idle a little faster than if we had more of a flywheel up there to keep it turning.

Paul

Hi Paul,

I have nothing factual to add as I am not flying yet but am very interested in this discussion. I have a similar setup: IO-360 Silverhawk with Pmags.

I would think that you would only want to modify the procedure for the high altitude starts so as not to affect ops at lower altitudes. Assuming that the FI was set up correctly for sea level.

Are you running straight 100LL or a mix or one tank of each etc? I think there is merit to the idea of avoiding extended idling and taxiing at full rich due to spark plug fouling.

Bevan

Paul, I went to Precision Airmotive's forum at Oshkosh on fuel injection system maintenance. Nobody brought up this good question, so I don't have an answer. However, the presenter, Alan Jesmer, told us that he's very willing to answer emails and phone calls with technical questions. He also has a really good CD-ROM with all the tech manuals, etc. that he'll send you for free just for asking.

Here's his contact info: [email protected]

Injection

Lean the mixture aggressively for all ground operations. Do a ground run to determine best power fuel flow at full throttle and note the fuel flow for your airport elevation. Then on subsequent takeoffs you can lean to say 1 gallon rich of this fuel flow as you power up for takeoff. For landing leave the mixture set for cruise or just very slightly richer. At Dayton you will not develop enough power on a go around to hurt the engine, just a bit richer than cruise on a go around if it makes you feel better. For multiple local flights you may want to make a mark on the mixture control for takeoff and another for ground operations. Don't go full rich on start, go to the mark, not too quick on the mixture on start.

Thanks All for the comments. As a "flatlander", I have always used full rich for start, but lean very aggressively in flight. Once I started flying out west, I have rarely used full rich. What puzzles me most is the quitting at idle. I have to fly down to Davis tomorrow (elevation less than 100' msl), and I'll see if it runs normally at sea level or if I actually have an idle speed shift that I need to adjust.

Paul

Too rich at idle

You need to keep the mixture away from full rich on start. You can do several cold starts attempts with half mixture, and go up from there. Find a mixture that will sustain idle power rpm that you want. You won't be fouling plugs.
The home folks at Leadville, Co field elevation 10,000 feet have a laugh when "flat landers" make the start attempts with full rich, and then the low idle, because of too rich a mixture at idle rpm. When shutting down lean the mixture slowly to find the sweet spot for idle. Then when you go to start set the mixture "red knob" in that position. As previously stated in another post, take off is similar, do not use full rich at high density altitudes during start, taxi, and take off. FWIW

Yes, the Davis trip is a good opportunity to see what kind of a rise you get with the red knob before if falls on its face. After that, it's time to alter your process. Welcome to the high country!

Just as a data point, I can pull an additional 30 rpm during run up from full rich. The knob is WAY out at max rpm. But at sea level, the idle mixture is spot on with the knob all the way in.

I would think you should keep the adjustment for sea level operations, and learn high altitude operating techniques, because you may fly back to low altitude airports (on your many travels to come) where you will still need that setting for safe ops.