Oil ratios verses air temp

[JIM]

Does anybody know how to calculate oil mix ratios to keep jetting the same for different temps.? THANK YOU, JIM

[Recovered]

I have never thought of it in those terms.

Since the carburetor is a pressure sensitive device, once you have your tune up close, you should be able to use the air screw and needle to keep the tune up in shape (and maybe a colder plug in good weather and a hotter plug in the bad weather).

Good weather for me is defined as spring and fall. Winter and summer would be bad weather.

Seems like a lot of work adjusting premix ratios while chasing weather conditions...........................

[JIM]

I have been doing it, but I am guessing at the ratios. I ride from 10 degrees to 90degrees. too much hassel to change jets all the time.

[Recovered]

I have been doing it, but I am guessing at the ratios. I ride from 10 degrees to 90degrees. too much hassel to change jets all the time.

Snowmobile or dirtbike?

I'm not sure temperature is the complete picture here. In drag racing it's called "density altitude" and encompasses temp, baro pressure, water grains etc. They have weather stations to calculate all this.

That being said, IMO, if the air gets better, you need more fuel. This means if you mix at 40:1 you may go to 32:1 to add fuel. Are we on the same sheet of music here? And you want to know how much to change the percentage of oil to fuel to compensate for this???

Seems like I have seen a formula somewhere. If we are on the same page I can make a couple of calls and see what I get. Just want to make sure we are saying the same thing.

[JIM]

Yep same page, I thought I seen a chart too. It was about 30 years ago.

[Recovered]

I'll make a phone call and see what I can find out.

[theeternaltwostroker-mr.h]

Some really simple basics:

When you mix more oil, aka going from 40:1 to 32:1, you actually will lean out the engine.
This is because you now have MORE oil than you did taking up part of the mix running through you jets...and less fuel.

A change from 40:1 to 32:1 is minor, but larger changes would become more critical.

different terms are used regarding altitude, pressure, humidity as one sum, some call it RAD or relative air density, some call it density altitude etc...

They all are a means to correlate all the factors necessary to jet your engine....
Basic rule, the hotter it is outside, the leaner you go, the colder it is the richer.

More humid: Go leaner (less air getting in replaced by some amount of moisture)

Higher altitude go leaner reverse for lower.


Regarding oil ratios, while it's been argued and argued, you will find that the fastest engines often run at really high oil ratios, and the correlation has ALWAYS been more oil, more power, and more lubrication and longer life.

It's not uncommen on highly stressed engines to have oil ratios at 20:1 or even greater.

I am told the absolute highest level two strokes (moto GP 125s) are mixed at 24-32:1 using extremely high tech synthetics.  These engines have I think 2 hour life expentancy (at most) and it was found that with the new cool synthetics being so slick, the roller bearings would skid and not roll when there was too much oil...

With the oils most people run, the skidding issue is not an issue. 
There have been tests showing more oil more power, but NEVER a test showing less oil more power....
Run whatever floats your boat and budget, but I highly suggest more oil than less oil

[Recovered]

Some really simple basics:

When you mix more oil, aka going from 40:1 to 32:1, you actually will lean out the engine.
This is because you now have MORE oil than you did taking up part of the mix running through you jets...and less fuel.

A change from 40:1 to 32:1 is minor, but larger changes would become more critical.

different terms are used regarding altitude, pressure, humidity as one sum, some call it RAD or relative air density, some call it density altitude etc...

They all are a means to correlate all the factors necessary to jet your engine....
Basic rule, the hotter it is outside, the leaner you go, the colder it is the richer.

More humid: Go leaner (less air getting in replaced by some amount of moisture)

Higher altitude go leaner reverse for lower.


Regarding oil ratios, while it's been argued and argued, you will find that the fastest engines often run at really high oil ratios, and the correlation has ALWAYS been more oil, more power, and more lubrication and longer life.

It's not uncommen on highly stressed engines to have oil ratios at 20:1 or even greater.

I am told the absolute highest level two strokes (moto GP 125s) are mixed at 24-32:1 using extremely high tech synthetics.  These engines have I think 2 hour life expentancy (at most) and it was found that with the new cool synthetics being so slick, the roller bearings would skid and not roll when there was too much oil...

With the oils most people run, the skidding issue is not an issue. 
There have been tests showing more oil more power, but NEVER a test showing less oil more power....
Run whatever floats your boat and budget, but I highly suggest more oil than less oil

I have heard of the skidding issue before. When I asked the oil company I was selling for, they called BS. At the time, we were discussing V-8 engines with 370-380 lbs of seat pressure and 1000 + lbs over the nose.

I don't consider 32:1 too much oil. Those GP bikes turn outrageous RPM's  and I'm not sure if the are liquid cooled.

I'll ask again, but I'm pretty sure I've been told before that more oil theory is ok down to 32:1. After that it was a waste.

I'll ask............

[theeternaltwostroker-mr.h]

Sorry, I will try to put it more clearly!
It has been conclusive in every instance of testing that a two stroke will make more power with more oil all the way to point of ignition failure!
That's in the 12:1 range.

However the improvement drops off dramatically at "some point" usually around 24:1 for most big bikes and 20:1 for most "minis"

The GP bikes are water cooled, and actually dont turn RPM's all that incredible...peak power usually around 13k.

The truly incredible engine are the kt100 class shifter karts turning upwards of 20k.

Skidding is for real...just not for most "mere" mortals, as not many truly high tech oils are for sale...I have not personally seen skidding with ANY oil even at 20:1.


Of course oil ratios depend on use and the jetting, a trail rider who puts a bike designed to scream will not need high oil ratios, where road racers, karters, and most fast mini and schoolboy kids will need more oil, as the engine stays high RPM all the time and doesn't allow oil to accumulate in the cases near as much as a trail rider's bike....

Despite the modern advances in lubrication, I have not seen ANY synthetic compare anywhere close to the performance of a castor oil under extreme duress.  castor oils have an interesting molecular structer that actually turns into a better and better lubricating oil the hotter it gets.  So much so it eventually sludges at extreme temps (it's pitfall...it requires frequent rebuilds do to carbon build up in power valves and exhaust ports...sometimes ring lands.)  All other oils, syn or not, reach a temp at which it's bonds dissapear and it fails as a lubricant, not true of castors (the opposite)

Anyways, not trying to step on toes...just the knowledge I have gained from too many engine failures and many long phone calls.

[Recovered]

Sorry, I will try to put it more clearly!
It has been conclusive in every instance of testing that a two stroke will make more power with more oil all the way to point of ignition failure!
That's in the 12:1 range.

However the improvement drops off dramatically at "some point" usually around 24:1 for most big bikes and 20:1 for most "minis"

The GP bikes are water cooled, and actually dont turn RPM's all that incredible...peak power usually around 13k.

The truly incredible engine are the kt100 class shifter karts turning upwards of 20k.

Skidding is for real...just not for most "mere" mortals, as not many truly high tech oils are for sale...I have not personally seen skidding with ANY oil even at 20:1.


Of course oil ratios depend on use and the jetting, a trail rider who puts a bike designed to scream will not need high oil ratios, where road racers, karters, and most fast mini and schoolboy kids will need more oil, as the engine stays high RPM all the time and doesn't allow oil to accumulate in the cases near as much as a trail rider's bike....

Despite the modern advances in lubrication, I have not seen ANY synthetic compare anywhere close to the performance of a castor oil under extreme duress.  castor oils have an interesting molecular structer that actually turns into a better and better lubricating oil the hotter it gets.  So much so it eventually sludges at extreme temps (it's pitfall...it requires frequent rebuilds do to carbon build up in power valves and exhaust ports...sometimes ring lands.)  All other oils, syn or not, reach a temp at which it's bonds dissapear and it fails as a lubricant, not true of castors (the opposite)

Anyways, not trying to step on toes...just the knowledge I have gained from too many engine failures and many long phone calls.

Interesting!

I may not get to it tomorrow, but this week I will call the company who manufacturers what I consider to be the most advanced oils available to the general public. I will print your info so I get it correct when asking questions. I will then post what they have to say. Which doesn't mean it's gospel.