400c Rumors… or just internet trolls.

[bwalker]

ive been sawing in the pnw for over 30 years using 100 to 1 amsoil and never lost a powerhead....low octane gas is what hammers the bearings out from pre-ignition which in turn chips a bearing and sends it up top through mixing chambers

Low octane gas will cause detonation, but very rarely in a saw. Even a ported one. Low octane will not cause pre ignition.
So no, low octane gas isn't hammering bearings, but running 100:1 will certainly increase bearing wear.

 

[rahtreelimbs]

Low octane gas will cause detonation, but very rarely in a saw. Even a ported one. Low octane will not cause pre ignition.
So no, low octane gas isn't hammering bearings, but running 100:1 will certainly increase bearing wear.

Low octane gas will cause detonation, but very rarely in a saw. Even a ported one. Low octane will not cause pre ignition.
So no, low octane gas isn't hammering bearings, but running 100:1 will certainly increase bearing wear.

 

[rahtreelimbs]

I will never understand the interest in running 100/1. A guy spends $1600 on a new Stihl 500i and runs 100/1. The savings over 40/1 or 50/1 is moot.

 

[Ridgehiker]

i doubt a chainsaw has enough of a compression ratio that octane makes any difference, especially when you cut the gas with 2 stroke oil my guess is 5to1 compression ratio, somebody smarter has probably done the math

 

[sean donato]

i doubt a chainsaw has enough of a compression ratio that octane makes any difference, especially when you cut the gas with 2 stroke oil my guess is 5to1 compression ratio, somebody smarter has probably done the math

99% of saws don't have the compression to need High octane fuel.

 

[huskihl]

Tree monkey did the math on compression ratio of a ported 440 and even with the compression raised it was still only 8.5:1.
87 is fine as long as it’s fresh. You’ll run into issues when fuel loses octane points after it sits for months or years

 

[PV Hiker]

i doubt a chainsaw has enough of a compression ratio that octane makes any difference, especially when you cut the gas with 2 stroke oil my guess is 5to1 compression ratio, somebody smarter has probably done the math

99% of saws don't have the compression to need High octane fuel.

Though I might not have any issues but when I'm at 10,000 foot elevation on a hot summer day cutting long cut times, why take a risk. The price is cheap enough to burn 91 octane for added insurance to prevent detonation issues that I may or may not experience.

 

[sean donato]

Though I might not have any issues but when I'm at 10,000 foot elevation on a hot summer day cutting long cut times, why take a risk. The price is cheap enough to burn 91 octane for added insurance to prevent detonation issues that I may or may not experience.

Higher elevation requires less octane then sea level. Less air pressure = less air in the cylinder = effective compression ratio (doesn't matter if it's static or dynamic) goes down.

 

[huskihl]

Higher elevation requires less octane then sea level. Less air pressure = less air in the cylinder = effective compression ratio (doesn't matter if it's static or dynamic) goes down.

That’s my understanding as well, albeit rather limited. There’s definitely less compression at altitude. More compression would be the trigger for going up in octane

 

[bwalker]

That’s my understanding as well, albeit rather limited. There’s definitely less compression at altitude. More compression would be the trigger for going up in octane

A saw actually pulls over easier at high elevation and your carb settings go rich.
I live at roughly 3000', but alot of my saw use is between 7500 and 9000. You can tell the differance.

 

[huskihl]

A saw actually pulls over easier at high elevation and your carb settings go rich.
I live at roughly 3000', but alot of my saw use is between 7500 and 9000. You can tell the differance.

6 psi per 1000’ I believe. Or 10 psi per 600’. Something like that lol.

 

[stihltech]

Anybody ever read the owners manual? 89 is preferred. Yes 87 will detonate especially if old.

 

[RedneckChainsawRepair]

Wonder if really that close.

This guy I believe worked as a stihl tech.

620 60cc is 7cc smaller. List 629. Weighs close to 1lb more PHO dry.
400 67cc List 1029
He said both stock with muffler mod and running 3/8 7T.

 

[JKendrick87]

Wonder if really that close.

This guy I believe worked as a stihl tech.

620 60cc is 7cc smaller. List 629. Weighs close to 1lb more PHO dry.
400 67cc List 1029
He said both stock with muffler mod and running 3/8 7T.

Well guess I better sell mine then just wasted 1k bucks

 

[holeycow]

Well guess I better sell mine then just wasted 1k bucks

There's a lot more to a saw than cookie cutting times.

That being said, everyone should have an echo 590 so if you ever feel a need to throw a saw off a cliff, you can throw the cheap (but very effective) echo rather than one of your fancy saws.

 

[sean donato]

Wonder if really that close.

This guy I believe worked as a stihl tech.

620 60cc is 7cc smaller. List 629. Weighs close to 1lb more PHO dry.
400 67cc List 1029
He said both stock with muffler mod and running 3/8 7T.

He must have a Supreme running 600sx, cause I'll tell you first hand, my 400 out runs my neighbors 620p.

 

[jellyroll]

 

[RedneckChainsawRepair]

He must have a Supreme running 600sx, cause I'll tell you first hand, my 400 out runs my neighbors 620p.

I wish I had them to compare myself to see whats up. Surprised me.

Then run my 670 champ too just to see. 67cc old school 50x34

 

[OM617YOTA]

6 psi per 1000’ I believe. Or 10 psi per 600’. Something like that lol.

How's cooling effected at higher altitude? Lots of air-cooled electronics are de-rated at higher altitude, even though electrics don't care, they have reduced cooling capacity due to the thinner air.

Saw cooling due to altitude probably reduces in line with power reduction due to altitude, so likely not a consideration at all.

 

[huskihl]

Anybody ever read the owners manual? 89 is preferred. Yes 87 will detonate especially if old.

89 will detonate if it’s old also. So will 93 or 95, it just takes longer. Fresh is more important than the octane