Altitude Sickness - running weak in the mountains

[Scud]

On my recent trip the Sierra Nevadas the LeMans felt a bit weak, especially at higher elevations. During the weekend, I never got below 5,000 feet, nor above 9,000 (blocked by snow).

 

I've been running the valves kind of loose:  .008" I and .010" E.  My house is at 100 feet above sea level - so that's where I tune it.

 

So... I'm wondering if a loose valve setting could cause a bit of an intake restriction in thinner air. I can't do any quick tests... so this is a "theoretical" topic.

 

Edit - I am assuming that the looser the valve clearance, the shorter the duration of time the valve is open. So if the air is thinner, it might not get enough oxygen to burn the fuel. I also noticed some small pops on deceleration at the highest elevations - mini backfires - which made me think that unburned fuel was igniting in the exhaust.  Am I thinking about this the right way? 

[JBBenson]

If your theory is correct, they will also not open quite as much, as the rocker needs to first travel the gap before hitting the valve?

 

In any case, are you running closed or open loop? Do you have a Lambda?

[Scud]

1:  If your theory is correct, they will also not open quite as much, as the rocker needs to first travel the gap before hitting the valve?

 

2:  In any case, are you running closed or open loop? Do you have a Lambda?

 

1:  Good point, I hadn't considered that.

 

2: There are no sensors in the exhaust. I replaced the 2003 crossover headers with non-crossover headers from a 2002 bike. The original exhaust also did not have any sensors. So, I guess that means I am running an open loop system. 

 

FWIW - the bike also has FBF crossover, the factory Titanium exhaust and unmodified Titanium ECU installed.

 

I have to do some scheming to figure out how to get over 7,000 feet again soon... 

[JBBenson]

You are running rich at altitude....

 

Unless the ECU has a barometer in it (which my Aprilia does, with an air line running from the ECU to the filter box) and you are open loop, there is no way for the ECU to adjust the air/fuel ratio, as there is no Lambda to sniff the exhaust and adjust the mixture as you climb into thinner air.

 

There may be a way to hack this outside of tuning the bike again at altitude. I can't think of one. I would guess that as you climb, it will get colder and richen the mixture somewhat, causing the popping...

 

But running rich for a time is better than lean for sure.......

[docc]

Meinolf confirms that there is air pressure input to the V11 ECU:

 

((Fuel Map value x Fuel map value factor) + (CO trim value x CO trim value factor)) x trim factor_airtemp x trim factor_enginetemp x trim factor_airpressure x trimfactor_{batteryvoltage} x trim factor_n = injection time"

 

http://www.v11lemans.com/forums/index.php?showtopic=17865&p=221471

[JBBenson]

Hahaha, I actually wrote in my reply "that Meinolf guy would know" but then deleted it as it sounded presumptive....

 

Anyway, the ECU must have a pressure sensor inside of it.

 

But now, knowing that, I wonder if that doesn't create a worse problem for Scud, because now it's a mystery. The last time I rode above 5000 feet I didn't notice any performance issues....but I was looking out for patches of snow....!

 

Maybe a setting in Guzzidiag?

 

[Scud]

Well, it's not really a big problem - just a puzzle about optimum tuning for big elevation changes. I missed doing the Sherman Pass (9,500 feet) last season and want to try it again this summer.

 

The bike just didn't have the brutish punch on the high climbs, it felt like it would only go 3/4 throttle. However, it did manage to run sections of this long incline in 6th gear and 5-6k rpm. It idled a little rough when I stopped at the peak to soak in the view.

 

[docc]

Typically, I'm a *poor scientist* ("Dr. Venkman") and revamp all and everything. People say, "shotgun approach?"

 

I'd say more like an artillery barrage . . . 

 

But that's me. And this  The Scud.

 

So, what about setting the valves to "world specs" (0.006/0.008) and go out and find some altitude. See if that makes the difference?

[Scud]

 

So, what about setting the valves to "world specs" (0.006/0.008) and go out and find some altitude. See if that makes the difference?

 

That seems very scientific Dr. Docc. It would require a 130 mile ride to Onyx Summit to make a same-altitude test. I had forgotten how high that mountain is - thought I'd have to get into the Sierras again to get over 8,000 feet, which requires a weekend. But I could get to Onyx summit before breakfast.  Hmm... scheming in progress.

[JBBenson]

So, what about setting the valves to "world specs" (0.006/0.008) and go out and find some altitude. See if that makes the difference?

This is a really good idea.......

[docc]

That seems very scientific Dr. Docc. It would require a 130 mile ride to Onyx Summit to make a same-altitude test. I had forgotten how high that mountain is - thought I'd have to get into the Sierras again to get over 8,000 feet, which requires a weekend. But I could get to Onyx summit before breakfast.  Hmm... scheming in progress.

 

This is a really good idea.......

 

I could write you a *note* . . . doctor's orders . . .

[MartyNZ]

On my recent trip the Sierra Nevadas the LeMans felt a bit weak, especially at higher elevations. During the weekend, I never got below 5,000 feet, nor above 9,000 (blocked by snow).

 

I've been running the valves kind of loose: .008" I and .010" E. My house is at 100 feet above sea level - so that's where I tune it.

 

So... I'm wondering if a loose valve setting could cause a bit of an intake restriction in thinner air. I can't do any quick tests... so this is a "theoretical" topic.

 

Edit - I am assuming that the looser the valve clearance, the shorter the duration of time the valve is open. So if the air is thinner, it might not get enough oxygen to burn the fuel. I also noticed some small pops on deceleration at the highest elevations - mini backfires - which made me think that unburned fuel was igniting in the exhaust. Am I thinking about this the right way?

The thinner air at high altitude affects piston engine power a lot if it doesn't have a turbocharger or supercharger fitted. For example, a light aircraft piston engine full throttle power rating is:

- Sea level -100 hp.

- 5,000 ft - 84.6 hp.

- 10,000 ft - 74.8 hp.

A motorcycle will have the same loss of power as altitude increases, so if you think that your bike feels like it only has 3/4 throttle at 9,000 ft, then your butt dyno must be well calibrated.

The 15M ECU has an air pressure sensor, (under that little black vent on top) but Meinolf has improved the barometric correction tables for the 15M ECU in his .bin maps he has shared around, so the automatic leaning needed as altitude increases is closer to ideal.

http://www.v11lemans.com/forums/index.php?showtopic=19815&do=findComment&comment=217735

If you try one of his maps, you may find the decel pops in the exhaust lessen, but still the laws of physics do not allow you to get sea level power at altitude unless you fit a blower.

I don't believe that valve clearances will have any effect on the loss of mass airflow that is caused by low air pressure at high altitude.

 

That example is for an old Lycoming O-235 variant.

 

I asked a pilot about this, and he took me seriously. He wrote:

"Density ratio at 9,000ft is 0.7621 so a bike down to about ¾ power is about right for normally aspirated engines.

The Cessna 172RG Cutlass (180 BHP @ 2,700 RPM MSL) can make 77% BHP at 8,000 ft at 22” MAP and 2,700 RPM, and 70% BHP at 10,000 ft at 20” MAP and 2,700 RPM. Manifold pressure lapse rate in lower layers is about 1” per 1,000 ft on a standard day.

Induction interference causes max MAP ISA MSL to be just over 28’’ Hg."

 

So, yeah. That should make it clear.

Edited June 10, 2017 by MartyNZ

[Scud]

Great explanation Marty, thanks. I knew there was an effect of thinner air, but I had not seen it quantified so clearly before. Thanks also for complimenting my butt; that's a real self-esteem enhancer.

 

She's ready for her next routine service - so I started with the valves last night. The exhausts were at .010" and a tight .011" but the intakes were too loose at .009" - and I could force a .010" in there.  So I set them to world spec (.006 and .008). Seems a little better already. I assume that the effects of too-loose valves would be more noticeable at altitude.

 

Someday, I will try the Meinolf Maps. It's good to know that they won't cause me to violate the laws of physics. Laws of man, potentially different story... 

[LowRyter]

my '98 EV with the big computer has a trim screw that allows me to lean and richen the mixture.  

[Scud]

my '98 EV with the big computer has a trim screw that allows me to lean and richen the mixture.  

 

So does the carburetor on my Husqvarna. The '98 EV must have been in the carb-to-EFI transition zone for Moto Guzzi.