What oil is best? and what ratio?

[Ron660]

follow up question just to be clear...

ME -

So obvious question just to be clear…

If I tested

87oct si-7
92 oct si-7

And 92 was faster.

Then between
87oct H1R
92Oct H1R 92 should win again right?

And that should be pretty much the case with all the oils I test?
--------------------------------------

Him -

If that was the case, with one oil, I would expect it to be the same with the rest, yeah.

-----------------------------
me -

I think the Stihl manual calls for 89oct on my stock saw. Which I want to say is around 170 to 175psi. Now with a ported saw where compression was raised to say 200-215..

Would you care to at least speculate on how much higher octane gas you’d want to use in that ported saw?
---------------------
him -

Unfortunately I would not like to make that speculation. Let me do a little research and I’m sure I can find a prevailing theory though.

Good questions

 

[Ron660]

Yes sir! You would be correct! Lol

Definitely port it

 

[laslabjohn]

Definitely port it

Oh I am

 

[Ron660]

Yes sir! You would be correct! Lol

Ya'll need a ported 3120 with a 20" bar for cutting those cants. Piped would help.

 

[laslabjohn]

I have got a good plan for this one too, I just need another cylinder.
I like the aftermarket one that Randy posted about ............ I might grab one soon

what cylinder and where do I find one?

 

[laslabjohn]

Ya'll need a ported 3120 with a 20" bar for cutting those cants. Piped would help.

Yea these are cants.

 

[Moparmyway]

what cylinder and where do I find one?

http://opeforum.com/threads/new-hyway-cylinder-kit-ms661.310/#post-15365

 

[laslabjohn]

http://opeforum.com/threads/new-hyway-cylinder-kit-ms661.310/#post-15365

thank you

 

[Ron660]

Yea these are cants.

That tree is to big for that Dolmar. Big wood.

 

[Keith Gandy]

That tree is to big for that Dolmar. Big wood.

I must say that 7910 would sing through there easily!

 

[bwalker]

High octane = slower combusting and unable to burn the whole mix intoduced completely in a short 2 stroke
High index/film oil= less combustible and slower combusting
tuned rich= worsens the effect of both which is leaving alota unburned oil and fuel that washes the piston clean. Go opposite on every account and u have faster igniting fuel and oil with more efficient complete burn resulting in more energy and a byproduct left behind thats visible

Your comment in regards to high octane fuel burning slower is totaly false. In fact a slow burning fuel would tend toward lowering the octane rating.

 

[bwalker]

That was about exactly my difference with 110 and 93....10%.

Most 110 fuels I have seen have distillation curves totaly wrong for a two cycle. So it makes sense 110 would perform poorly. AV gas is in the same boat IME.

 

[Keith Gandy]

Your comment in regards to high octane fuel burning slower is totaly false. In fact a slow burning fuel would tend toward lowering the octane rating.

How about resist igniting?

 

[bwalker]

Im seeing in my mind the shorter the stroke the lower the octane can be used and the longer the stroke the higher octance to a point can be used?

The bigger the bore the more prone to detonation and engine is. This is simply due to the time involved to combust a a large bore vs a small bore. The flip side is with a long stroke engine piston speed comes into play limiting rpm and thus output. One of the age old design comprises of two cycle design.

 

[bwalker]

How about resist igniting?

No.
Octane is a measure of a fuels resistance to detonation, which is a phenomenon that occurs after ignition.

 

[Keith Gandy]

No.
Octane is a measure of a fuels resistance to detonation, which is a phenomenon that occurs after ignition.

Ok lets start simple for everyones sake. When do u need high octane say 110?

 

[junkman]

Some of my old 250r engines would ping in the dunes if did not run over 100

 

[bwalker]

ok guys I emailed andrew for his point of view on this octane debate...

ME -

Big debate right now is how different gas will work with different 2t oils and thus affect the test results.

So let's take si 7 and h1r.

Si-7 low visc, low flash, in it.

H1r maybe double the visc or close to it, and more than twice flash pt.

So I'm thinking it's fair to say pretty different ends of the spectrum.


QUESTION #1-

How would
87 oct, eth free run different with each of these?
91 octane eth free same thing
94VP same thing

Question #2
What if anything would change if ratio changed? Say from 32:1 to 40:1 ?

Question #3
Is the octane going to be changed more than 1/2 of a pt either way ie. 87 to 86.5 or 87.5 94 to 93.5 94.5 with any of the above?


***Not sure if this will play into your response but...
stroke on most saws is 34-40 mm with bore sizes 8-16mm larger than stroke. So they're not square.
-------------------------
His response -

re question #1 -

For all the octanes, the oils will work fine, changing the octane should not warrant a change in chemistries and whatnot, perhaps just volume of oil. The assumption that I’ll make is that with higher octane, you are running at higher compression since that’s the whole purpose of high octane fuel. If you are running at higher pressure, than the oil’s applicable flash point (the temperature it volatizes in the crankcase in this situation) will increase simply due to the gas pressure. So the oil will remain liquid, and thus unburned at higher temperatures than normal.


There is a flip side to this though. If the higher octane is warranted due to increased compression, then the engine is under higher load and the pressure factor is going to be negligible compared to the more important factors of increased heat and load. So for higher octanes, I would expect a higher content of oil to be needed.


This all comes back to tuning the engine properly and finding the right ratio for the tune. Fuel should remain constant for that process or else when it is changed, the tune should be revisited. The autotune system isn’t going to take the load into account as far as I know, so you may want to go heavier on the oil even if the autotune is working properly. You’ll probably see performance drops with different octanes, but again, that’s all part of the tune, finding the right octane as well.


Question 2
What if anything would change if ratio changed? Say from 32:1 to 40:1 ?


In terms of octane rating, nothing.



Question 3
Is the octane going to be changed more than 1/2 of a pt either way ie. 87 to 86.5 or 87.5 94 to 93.5 94.5 with any of the above?


H1-R is tested specifically according to CIK-FIA regulations for MON and RON which measure octane changes and the change is always less than 0.1 difference from reference. So, no H1-R will not change the octane of the fuel. I don’t have the same data for Si-7, but I doubt it would affect it 0.5 or more.

Most decent oils have minimal effect on octane.
At one time Yam 2R used toluene as a diluent. Woukdnt be supprised if the oil when blended with the fuel actually raise octane slightly given this.
The bother thing is guys talk about their 200 psi saws being high compression. They are simply not and calculating the actual compression ratio woukd bare this out. Saws are really in a low state of tune and hence modded saws live on 87 octane.
With that said I run premium for a little added insurance and due to the fact premium doesn't contain ethanol at many stations in my area. Running race gas in a saw is retarded, unless yiur actually racing. And even then care needs to be made that the fuel has a distillation curve that is tailored to a two stroke or else your wasting money.

 

[bwalker]

Ok lets start simple for everyones sake. When do u need high octane say 110?

That would depend on the engine parameters.
However, as it pertains to OPE, likely never.

 

[bwalker]

Some of my old 250r engines would ping in the dunes if did not run over 100

My 09 yz250 pings pretty easily when running a PC pipe. In 2010 Yam reduced the compression ratio to solve the issue.