High altitude saws.

[drf256]

Have a question for you guys who have done saws intended to be run at higher altitudes.

Just did a 462 for a buddy that lives at 10,100 feet.

It’s MT, so I shouldn’t have to worry about a smaller carb jet to keep it in tune, one less variable.

Other than more compression, are there any other changes anyone does in porting for saws meant to run where the air is thin?

I typically take 30 from the band in 462’s. This one has 65 out and .022 squish. Runs well here, @230’ asl. Hoping it runs well there as well.

Thanks.

 

[Duane(Pa)]

That’s some damn fine looking work

 

[David Young]

Jasha

went by treeslingr. He was out west somewhere I’m not sure exactly where. He would take 40 from the band set squish and widen all the ports. He would never even look at port timing. I don’t know if this is the best way but he seemed to get good results.

the challenge is the thin air. So the primary compression is obvious. I would think secondary/ case compression would be equally important. So with that in mind I would think case stuffing or longer case compression duration would be beneficial.

 

[Redfin]

Intake landed fairly long on this one Doc?

 

[SteveinUT]

I can tell you my non-autotune saws have the H jet turned all the way in and are still too rich where I cut (8,000-10,500 above sea level). I even hit up Randy asking about max RPMs on my MMWS 346 before I took it up on the mountain for firewood this year and he predicted I wouldn't have enough adjustment in the carb to lean it out at those elevations and he was right. The good thing is, they aren't going to burn up from a lean condition. One of the reasons I bought my 562 was for the autotune, because I live at 6,000 and cut at 10,000. My 562 is managing to tune, I think. I am pretty deaf, but it sounds like the four-stroking is cleaning up in the cut with the 562.

 

[Ketchup]

I live at 9,400. Saws can be real dogs up here. I port them to run at my elevation and that seems to have good results when they’re taken lower.

More compression and more air seem to help. A bigger carb bore can be good. I like a higher intake. Sometimes wider too. In strato saws, a minor increase in cold air timing can have good results. I open the muffler a bit more as well.

But no matter what you do, there isn’t as much air. The saw will never be as strong as sea level. At my elevation, I still need to be careful not to make them too lean. I’ve smoked a couple saws by adding too much air.