saws at high elevation

[royta]

I went camping over the weekend with my boys. We were at 8070 feet, and I thought I'd supplement some of the cedar and oak firewood that I had brought, with a killed by fire pine blow down. I leaned out the H needle on my 044 until I got to 12,500 RPM, and did about 10 8" diameter cuts. It seemed a little weak, but I since it was only a few cuts, I didn't do any extra tuning. After I was through, I seated the H needle just so I'd get an idea how much leaner I needed to set it. Only 5/8 turn out from seated. This is with the tabs on the limiter caps snipped off, so I was fully closed. Does this seem right? The tach said 12,500, but I was certainly lacking the power that I normally have down at around 1500 feet. Maybe it's the thinner air.

There were a couple snags, killed by the bark beetle I presume, just below us, that I really wanted to fall. However, I have zero falling experience, and didn't have a hardhat in the truck. It'd be nice to have somebody show me a few pointers before I try and drop anything.

Oh, my 7 year old isn't too shabby with the old Sheridan. My 4 year old doesn't get the whole sight picture thing just yet. He'll do fine in a couple years though.

 

[romeo]

Yup, that sounds about right for your 044 at 8k. I live at 9200 feet and have to deal with the thin air all the time. I think I have heard figures like 20% to 25% power loss at 8000 foot. I think my hotrod saws still cut slower up here than they do stock at low elevations.

Air at sea level is 23.5% O2, here at high elevation it is 15% to 17%.

 

[ShoerFast]

What a fine looking crew you have there! It is so nice to see that your raising them right, thanks for the pictures, that made my morning!

Make sure that your saw will 4-cycle burble and lean from there, but you would maybe see your best power at a higher free speed then 12,500RPM's,,,,try some timed cuts,,,,, you may simply be a little too fat there?

Your so right about less power, your 5.4HP saw will have 3.7HP ,,,,,here is a link: http://wahiduddin.net/calc/calc_hp_dp.htm

Plug this into the calculator,,,,,

80 Deg Air Temp

29.92 Altimeter Setting (standard day)

just for a say, say 65 Deg Dew Point

And your 8500' MSL [ Calculate ] ,,,,, you get a Density Altitude of 12,022' and a Relative HP of 68.9,,,,,,,, take 5.4 (HP) and x .69 = 3.726 , or about the power of an MS-280 ,,,, ever have a hertiz donut? ,,,,, hertiz don't it!

 

[Lou]

29.92 Altimeter Setting (standard day)

(standard day) Sea level @ 70 °F, clear and calm.

 

[Four Paws]

3% loss of power for every 1000 ft. of elevation gain - so at 8K, you are down about 24% from sea level.

 

[royta]

Thanks everybody. I was hoping it was the elevation. I was a bit nervous that despite the rich 12,500 RPM WOT, I was actually running lean and starving the saw for fuel.

 

[ShoerFast]

Thanks everybody. I was hoping it was the elevation. I was a bit nervous that despite the rich 12,500 RPM WOT, I was actually running lean and starving the saw for fuel.

I had hoped to make that point in mentioning coming from a "rich" 4-cycle burble and come down from there,,,,, I have made the mistake myself.

But here is a catch 22 that works for us, with less power, there more forgiving, if your saw like premium gas, you may be able to get by with mid-grade, or if your saw likes mid-grade (I wouldn't) you could maybe use regular?


Just a habit anymore, if I been doing any cutting high, and heading home, or at home and heading high (6000' vs 9500') I know that the saw is not close enough to run real well and get the tach out and start from too rich.

 

[Austin1]

I also cut my firewood at high elevation and a couple of times I took the tach with me and yes they do drop a bit every thousand feet above see level you go. I only go up about two thousand feet but the tach tells me I dropped 1000 or 1200 rpms from my back yard. I would like to hear more input from this from other people on here. I also find my small saw's and my big mac more affected by this I have to do some more experimenting.
Like the pix's of the little one with the pellet rifle I wish I was that age again!

 

[redprospector]

Yep, a lot of power is lost at 8000'. I don't live far from Romeo at 8700'. Some of our friends went to a competition Saturday at 4000', he said the saws really woke up at low elevations.:jawdrop:

Andy

 

[Patrick62]

I do all my cutting at 8000

I have never run a saw at lower elevation, It would probably scare me!

That percentage lost sounds about right. Little saws are even worse off.

-Pat

 

[ShoerFast]

Pat

Add a hot day, and a high humidity to that 8000' a 100 Deg. day, with a 95 Deg Dew Point, and an MS-660 is now just about an MS-361 , or 65.2%

But cut on the coldest of days, that 660 will keep up with a 460 at sea-level.

 

[LarryTheCableGuy]

I live at 6,800 feet.

Do y'alls think that I could use that as "justification" for getting a bigger saw or two?

...on the other hand, maybe I should lay low for a week or so as I just got a 31" computer monitor today...

.

 

[smokechase II]

Great photos

Four paws:

Bring me along:

1) where do you get that 3% stat?
2) why is there a loss in power? The air/gas mix changes, if properly tuned.
So is it just too little air?

Thanks for helping me.

 

[ShoerFast]

I live at 6,800 feet.

Do y'alls think that I could use that as "justification" for getting a bigger saw or two?

...on the other hand, maybe I should lay low for a week or so as I just got a 31" computer monitor today...

.

Good plan Stan,,,, or should I say Good plan Stan?

Hold out like nothings up till at least Thursday.

 

[Lakeside53]

Four paws:

Bring me along:

2) why is there a loss in power? The air/gas mix changes, if properly tuned.
So is it just too little air?

Thanks for helping me.

Simply the air is thinner.. so you need less gas, so the combustion is less.. so the power is also... Same way your body works at 10,000 feet...

 

[LarryTheCableGuy]

Good plan Stan,,,, or should I say Good plan Stan?

Hold out like nothings up till at least Thursday.

Cool! What do you think, maybe one for cool humid air and another for the warm dry days?



BTW royta - Awesome looking crew! Let me know if you make it up to Big Bear for woodcutting and/or fishing!

.

 

[oldsaw]

Simply the air is thinner.. so you need less gas, so the combustion is less.. so the power is also... Same way your body works at 10,000 feet...

No kidding. 20 years ago, I used to cut firewood above Estes Park, CO. I'd have to change the carb adjustments at almost every different place we would cut, and when we got "up there", it got really bad. Estes is like 7500 feet, so we were often well above 8000, and the saw would be a total dog. Fortunately, the trees get smaller up that far, so it was less of an issue.

The bummer was that I would come up from Denver, and I was about 25% weaker too. I was cutting with a 70 year old man who could out-work me on many days. Granted, I did the heavy stuff, but still, he was used to the elevation, and that lack of air is the great "equalizer".

Thanks for reminding me of a great time in my life. Frank is gone now, but the trouble we got into will live forever in my addled brain.

Mark

 

[Lakeside53]

yep... altitude.. I used to live at 5000 feet, so sking at 8,000 wasn't a problem. Now it wipes me out for days. My father-in-law lived at 8,600 feet at Alta -talking a quick ski hike up to 10,600 damn near killed me.. but he was 25 year older and in fine shape.

Unfortunately saws don't adapt!

 

[West Texas]

I do all my cutting between 5500' and 7000'. I tune the "L" jet for 'easy' starting, and set the "H" jet to where it just starts to '4 cycle.' Starting a cold or hot saw at higher elevations can sometimes be a problem. I find that the best "L" jet setting is usually within 1/8th turn of the recommended setting at my elevation.

I start the "H" jet at the recommended setting and then tune for the 4 cycle sound. When properly tuned the 4 cycle sound disappears when the saw is placed in the cut at WOT. And as a general rule I don't push my saws to the point that they bog down in the cut; at this elevation I like to maintain a high rpm in the cut and let the saw and chain do their thing.

Overall I think the primary influence of elevation, makes you more sensitive to good fuel, good oil, good tuning, maintenance and a sharp chain.

 

[ShoerFast]

Four paws:

Bring me along:

1) where do you get that 3% stat?
2) why is there a loss in power? The air/gas mix changes, if properly tuned.
So is it just too little air?

Thanks for helping me.

Smokechase,

Not so much for you, as this is oversimplified, and from what I know, that's not your speed. But if any would read this thread, and still be lost, picture this for a think.

Air pressure equals the amount of air above it, the higher you are, the less air above you.

Place 14.7* bricks on a stack, and your hand under the stack, smarts, no?

But up the stack a ways, slide your hand between brick 9 and brick 10, (top down) little easier on your hand? ,,,,, about between brick 9 and 10 would be the weight difference of air from sea level - 8000'

Now think of a hot-water bottle (think there extinct anymore?) or a strong balloon full of air under that stack of bricks, and hook the opening up to the carburetor, at sea level, there would be the full stack of 14.7 bricks squeezing air into the engine. Now if the balloon was between brick 9 and 10, it would only be 65% the weight of the balloon-pressure compared to the whole stack.

* If the bricks were 1 pound per square inch under 14.7 bricks, that would be close to the pressure of air at sea level.