2 cycle pre-mix oil

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The 2 cycle pre-mix ratios for air cooled engines changed in the 70’s – 80’s from 32:1 to 40:1 ratios. Now days, the standard is probably 50:1 (if Amsoil products are excluded).

What were the technological advances in either base stocks or additives that enabled the smaller volume of pre-mix to be added to a gallon of gas?
 
Mixture ratios for two cycle engines is largely driven by the epa and the fear they cause the mfgs. Two cycle oil tech has changed alot since the seventies mostly in the area of cleanliness and lack of smoke although this excludes the oem oil standard oils IE stihl, mac, tanaka, etc) as they are still formulated to circa 70 api tc specs.
While I do not know for sure amsoil 100:1 I bet they use a really high temp basestock and a hearty dose of mettalic adds to make a 100:1 ratio work ok. Porblem with thi strategy is the fact that both high temp base oil and mettalic adds lead to deposit problems.
 
So what happens when I put a modern oil in my old 16:1 Poulon? I have heard it is very important to use the right mixture.
 
Labman – I’m a newbie to this site, but I can respond to your question. My Remington SL9 chainsaw is early 70’s and lists a 16:1 pre-mix ratio. On the inside of the air filter cover it states “Mix ratio 16:1 using SAE 30 2 cycle oil”.
I mix any API-TC air cooled pre-mix oil at 32:1 which is 4 oz. to 1 gallon. A 16:1 ratio would require 8 oz. dumped into 1 gallon of gas (a lot of pre-mix). From a practical point, 8 oz. of pre-mix will cause the equipment to smoke & buildup carbon in the exhaust port and muffler.

And this is what we are discussing. The formulation of commonly sold 2 cycle pre-mixes has changed over the years & we’re trying to define the specifics.
 
Blano- I guess the issue is have changes in the commonly used API group1 petroleum base stocks allowed the amount of pre-mix to change from 4 oz (32:1) to 3.2 oz (40:1) ?

Has the viscosity index of the commonly used base stocks moved to the upper end of the API range of 80-119? This would improve volatility and more of the pre-mix oil would make it to the combustion chamber to lubricate the cylinder walls & piston rings.

Or have the base stocks remained the same formulation & it is an issue of % of solvent and additives?
 
Ben,

I'm still trying to figure out this mix ratio stuff ....

Is your goal to run the richest mixture ratio you can, to maximize compression and still get clean burning? It would seem to me as a engineer that for a particular oil and application, there would be a mix ratio that is the best compromise of:

1) subjective engine performance
2) wear protection
3) deposit formation
4) plug fouling
5) exhaust smoke
6) fuel octane degradation

If I was testing a new two stoke oil, I guess I'd start at the oil manufacturers recommended mix ratio and do some testing on either side of that ratio. Am I missing something here????
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TS
 
"Is your goal to run the richest mixture ratio you can, to maximize compression and still get clean burning?"
Too slick, To answer your question, yes! A good oil will burn clean at 32:1, protect better under extreme conditions, and leave an engine cleaner than these 100:1 wonder lubes. Keep in mind that 50:1 and leaner ratios are a product of the epa and public perception. A case in point is stihl chain saws. The basic engine designs of these saws hasnt changed since the late seventies when a 32:1 ratio was reccomended. Today a 50:1 oil ratio is reccomended and the oil that stihl sells hadnt changed much until last year when they came out with a iso egd jaso fc oil and labeled it as a premium product while still selling there circa 1979 formulation orange bottle oil. My point being is that stihl changed their oils reccomendations not because of any new tech, but because of other concerns. More oil is better and this can be easily recognized by pokeing ones head into the pits at a shifter cart or national mx race. .

[ September 29, 2003, 08:09 PM: Message edited by: blano ]
 
Blano,

What about engines that use oil injection ....It is my understanding that these are calibrated to run mixtures of 100:1 at idle, up to about 50:1 at full throttle. Do you tinker with the oil pump output on these as well? I am specifically talking about sleds and PWC's ....

TS
 
"Do you tinker with the oil pump output on these as well?"
Yes, although not on all sleds as some pump a exceptable amount. For instance my 98 xcr 440 used a little bit more than a quart of oil per ten gallons of gas. This is right around a 32:1 ratio. My 97 polaris xc 700 with a big bore kitted motor however used less than a quart per ten gallons till I turned up the oiler. I try to shoot for 32:1 as it seems to work well in most motors. I have ran as rich as 18:1 (125 mx bike that was ice raced) in certain applications where I was reving the heck out of the motor in high load conditions. BTW I beleive polaris oil injection pumps are suppose to pump 40:1 at wide open throttle. I would just ditch the injection sytems altogether if it where not for the fact the Polaris injects oil directly into each crank bearing. Good system IMO.
 
Another thought, If you are looking for maximum power out of your 2 stroke powered device. The best bet is to go with a 16 to 1 ratio. Testing I have done for race teams in the past show that more oil makes more power. As a matter of fact, using more quality synthetic oil will keep the small engine cleaner. I know many believe otherwise, however be my guest and try it for yourself, you will be convinced. Ratio's (using synthetic)such as 8 to 1 will keep an engine perfectly clean internally.

Chris
 
Cujet,

The di-ester 2 cycle pre-mix synthetics are reported to have the ability to dissolve deposits, tarnish and carbon in the cylinder & crankcase. From your testing, it sounds like the product could also be promoted as "Merry Maids in a Bottle".

Regarding the mix ratios in your racing testing,(more power from more mix in the gas), I'm assuming this is with synthetics. At 16:1, when you do a tear down, do you find an accumulation of synthetic in the crankcase? If not, then my thoughts are that the surface temp of the crank pulls only a set amount of ester base out of the gas & the rest is ported into the cylinder to lubricate or be combusted.

Also, at 16:1, does running the engine at idle create any problems with plug fouling? This is probably more of an issue with chainsaws, trimmers & leaf blowers than with racing engines.

Thanks for relating your testing results.
 
I have three small 2-cycle motors that each use a different mix - 16:1, 32:1 and 40:1. I keep a separated stash of mix for each motor.

I'm still confused on what everyone is saying. Am I correct in saying that these different ratios aren't needed for each motor?... that these ratios are specified not for technical reasons but for different agendas each manufacturer has for their product.

I'd like to simplify my stash of mix and do what's best for my equipment. Would it be okay if I used 32:1 for ALL of my small 2-cycle motors, regardless of specification?
 
Blue, our testing was with Mercury outboard engines. As such, we did not have the ability to pull the cylinders off and look inside the crankcase. I suspect the level of residual oil in the outboard remains the same no matter what the ratio.

We did test with synthetics and that wonderful oil provided for free by the factory (non synthetic). For racing use, we chose the free stuff. However there is no question that the synthetic was a better oil. Even so, both oils left near zero deposits when used at an 8 to 1 ratio, especially the synthetics.

Chris
 
Kestas, 32 to 1 is the old standard. Use a good quality oil and I am convinced you could do no better. High oil ratio's have not (in my experience) extended engine life one bit.

Chris
 
"If not, then my thoughts are that the surface temp of the crank pulls only a set amount of ester base out of the gas & the rest is ported into the cylinder to lubricate or be combusted."

Blue, This isnt the case. In order for a two cycle oil to lube it has to come out of suspension when it reaches the crank case. Its quit simple actually. The fuel enters the crank case in a liquid state(ie small droplets). The heat of the crank case at operating temps evaporates these droplets very rapidly causing the oil to drop out of suspension and coat all internal parts. This happens with oil oils, syn or otherwise. A example of this is not occuring is when the motor is first started. Since the crank case is not yet warm the fuel doesnt evaporate and the oil doesnt drop out of suspension. Instead sent directly to the combustion chamber where it partially burns. This unburnt oil is what causes smoke on startup. BTW There are many oils that use ester bases that are not di esters. polyol(redline) and carboxl(mx2t) are two of the most common.

[ October 03, 2003, 09:18 PM: Message edited by: blano ]
 
Blano, thanks for describing the activity of the pre-mix oil in the crankcase.

I’ll jump in & ask the next question that will pop up in this thread:

If the 32:1 (4 oz/gal) mix ratio provides good lubrication for a 2 cycle air cooled engine, why do the popular brands in the lawn & garden equipment field – Stihl, Husky, Echo, Poulan/Weedeater – specify a 50:1 (2.56 oz/gal) pre-mix?
 
Because of the public perception in regards to smoking two cycles. It also kept the epa of their back for a few years.

[ October 04, 2003, 12:42 PM: Message edited by: blano ]
 
Blano,

The oil is suspended in the fuel up to and including the time of combustion.

The combusted mixture burns with the oil in suspension, else why would the engine smoke at all, hot or cold at high oil-to-fuel ratios?

While conventional 2-stroke oils are based on mineral oils (mostly brightstocks) with detergent additives and some heavy napthenic solvents, most of the synthetic base oils used in 2-cycles are synthesized hydrocarbons such as polybutenes or PAO's, or oils using esters such as diesters of C36 dimer esters or trimellitates, and TMP polyols (tri-esters). The later three offer less engine fouling through cleaner burning, and lowers levels of deposits on ring grooves, skirts, and undercrowns, and better lubricity (even at lean burn ratios) than even PAO's and polyisobutylenes. Ester solubility alows them to be used without solvents. Esters provide operation down to -56 C or better.

[ October 08, 2003, 12:57 AM: Message edited by: MolaKule ]
 
On all my 2 stroke equipment (Stihl 021 saw, Homelite leaf blower and weed whacker, Lawnboy mowers) I use Amsoil 100:1 oil and mix it into a five gallon can instead of the recommended six gallons of gas. This makes about an 80 something to one ratio. One of the Lawnboys I bought new five seasons ago and have been using the Amsoil mix since it was broken in. I recently took the muffler off to look into the exhaust port and saw no excessive deposits and saw no scoring or scuffing on the piston or cylinder. The Lawnboy service manual recommends periodic cleaning of the top of the piston and exhaust port, but I didn't have to do this as there were such little deposits. I have been pleased with the results of Amsoil products in general (and no, I am not an Amsoil dealer).
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"The oil is suspended in the fuel up to and including the time of combustion."
Molkule, Respecytfully you are wrong. The oil does eventually make it in to the combustion chamber, but not mixed with the fuel. BTW this was explaned to me by a guy buy the name of Dr. Dave Redzus. He owns Presision auto research and helped develop Phillips 66 Xamax rrace oil. He also works with nascar teams on oil related issues.
 
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