661 Oil Test 32:1 vs 40:1 vs 50:1 ?

[Ron660]

In regards to the viscosity comment while intuitively it sounds plausible I am not sure it's true. For instance castor can be of very light viscosity, you there isn't a synthetic or mineral lubricant that can take the abuse it can.

I've read that before. Castor-based oils did provide the most protection but the downside it's not clean burning.

 

[bwalker]

I buy quality 2-cycle for protection and cleanliness not because one might cut a second or so faster.

I've read that before. Castor-based oils did provide the most protection but the downside it's not clean burning.

The down side to any high viscosity fluid is its tougher to combust cleanly. Although castor takes it to the next level based on its decomposition path.

 

[Ron660]

The down side to any high viscosity fluid is its tougher to combust cleanly. Although castor takes it to the next level based on its decomposition path.

I'm thinking a big ported saw, like my ported 660 with 212 psi, might benefit using racing oils with viscosities higher than typical chainsaw oil viscosities. A ported saw produces more compression, more HP, and more rpms under load than a stock saw. I'm also thinking a large ported saw will produce different results comparing 2-cycle oils than a stock saw. After Redbull finishes his tests I could compare a few oils to see if I get the same results.

 

[Ron660]

The down side to any high viscosity fluid is its tougher to combust cleanly. Although castor takes it to the next level based on its decomposition path.

Do you think higher compression helps with combustion?

 

[Trx250r180]

Do you think higher compression helps with combustion?

what is considered high ?

 

[Ron660]

what is considered high ? View attachment 453903

I'd say 200psi+.

 

[Ron660]

what is considered high ? View attachment 453903

Hope your decompression button works.

 

[Moparmyway]

what is considered high ? View attachment 453903

230 ????
Meh ................

 

[bwalker]

I'm thinking a big ported saw, like my ported 660 with 212 psi, might benefit using racing oils with viscosities higher than typical chainsaw oil viscosities. A ported saw produces more compression, more HP, and more rpms under load than a stock saw. I'm also thinking a large ported saw will produce different results comparing 2-cycle oils than a stock saw. After Redbull finishes his tests I could compare a few oils to see if I get the same results.

Keep in mind the badest ported saw out there has a pretty pathetic HP output.

 

[bwalker]

Do you think higher compression helps with combustion?

Quit possibly.
Although the compression on these saws is pretty low. When a guy can get away with running 87 octane on a ported saw with 200 psi that tells you the compression ratio is low. Especially so given saws are air cooled.
My yz250 for instance will detonate with premium pump gas very easily if the main jet isn't fat enough for conditions. It has a stock head and cylinder btw.

 

[blsnelling]

Built sled engines typically run significantly less than 200 PSI.

 

[bwalker]

Built sled engines typically run significantly less than 200 PSI.

I have had them in the 190's but that was a race gas only chamber(had interchangeable combustion chambers).
The yz I mentioned above would be lucky to crack 180.

 

[blsnelling]

My point is that these saws with way over 200 is significantly higher than that found in other built engines. However, I'd assume that dynamic compression is higher on the sleds and bikes due to the tuned pipes.

 

[blsnelling]

I have had them in the 190's but that was a race gas only chamber(had interchangeable combustion chambers).
The yz I mentioned above would be lucky to crack 180.

I had that on my built Banshee. I ran a Pro-Design head.

 

[bwalker]

Any of the builders calculated the compression ratio for the saws they are building?

 

[bwalker]

My point is that these saws with way over 200 is significantly higher than that found in other built engines. However, I'd assume that dynamic compression is higher on the sleds and bikes due to the tuned pipes.

I would bet the compression ratio is lower on these saws in question.
I would also think the exhaust port height of a ported saw is higher than that of a sled or bike by virtue of the peak rpms each engine turns. This would limit compression ratio.

 

[KG441c]

Would anybody want to run say 250psi on a 390xp? The bottomend is already easy enough to let go isnt it? I built one saw at 230psi and ended up lowering it to 180psi and it ran better at 180psi

 

[bwalker]

Would anybody want to run say 250psi on a 390xp? The bottomend is already easy enough to let go isnt it? I built one saw at 230psi and ended up lowering it to 180psi and it ran better at 180psi

Pumping loses.

 

[KG441c]

Pumping loses.

Uneccessary wear and tear in the bottomend also

 

[Trx250r180]

These little bore saw engines are easier to crank over till the bore starts getting larget ,my hybrid pulls over not bad,but the 660 will rip the cord out of your hand if dont start it right ,the piston in a 250 dirt bike is much larget than our saws ,i would like to see someone put a recoil on the yz and try to pull it ovet,thats why the kick start on a bike