Octane Question

[lblac36315]

Hey Guys,
I Have been reading the thread about oil ratios and am now wondering about octane grades. I have always ran 93 in all my 2 stroke engines. does it make sense that if 50:1(less octane) at lower temps than 32:1(higher octane) that if you started with 87 for your mix that would be in your favor. or 87 @ 40:1 to be approx. the same as 93 @ 50:1 and gain additional compression & lube? Just an idle thought....I know I should spend more time working & less time on the web...but it is a holiday. And I'm tired of drawing aircraft this week. Beer Thirty!!!! Can't Wait.

 

[timberwolf]

Try a search on Octane, there is lots on the topic.

Oil actually reduces the Octane rating of the mixture, so if you start with 93 and add oil the end result will be lower than 93, if you start with 87 the end result will be less than 87 how much less would depend on the type and ratio of oil.

Timberwolf

 

[bwalker]

The change in octane when going from 32:1 to 50:1 is minimal. Some oils in fact use tolulene based diluents which could actually increase octane. With a stock saw octane really isnt much of a issue as the compression is fairly low. However, I always run premium as a little bit of cheap insurance. When it comes to pump gas you never know what you are getting so it pays to be a little conservitive in that respect.

 

[don]

Runnung Kart mixture in a saw

I guess (readings not experienced) they run a 20:1 mixture and have nitro in the mix. Don't know the % of Nitro but would this work in a saw?

I am guessing the carb would not feed the saw properly.

 

[bwalker]

I know quit a few cart racers and none use nitro. They do use oil ratios between 16-20:1 and race fuel doped up with a healthy(or unhealthy) dose mtbe.

 

[tundraotto]

i dont think you can mix nitro with normal gas - needs to be mixed with alcohol requiring rejetting etc. many types of oils are also not compatible with nitro (ie. straight synthetic I dont think is compatible with 2 stroke nitro mix, they use castor). I am not 100% sure but I this is the way it is.

 

[bwalker]

Otto is correct about nitromethane not mixing with gasoline. As far as the oil compatability with alchohol. Some synthetics are some are not. Some castors are not compatible with it also.
This topic on doped fuels is pretty interesting from a race saw standpoint. Especially stock classes. I can only imagine what some nutec race fuel ( formulated with mtbe and isoprene)doped with some proplene oxide or nitro propane would do for a saw.

 

[don]

Try to get a picture of the container

I think it is Nitro Methane.
Will go over the neighbors house and get a picture of the stuff.
He buys it premixed.

 

[bwalker]

I would bet its model airplane fuel if he buys it pre mixed. If that is the case it is a nitro?methanol blend. To take advantage of alcohol you have to change the ignition timing and the chamber profile.

 

[rupedoggy]

Nitro Methane mixes with gasoline, so will Nitro Propane and Propolene Oxide. The secret is in the oil/mix you use. As far as what they do for stock saws- not much. I have tried them and little is gained. If you want performance you have to SQUEEZE the charge before you light it! You have to light it at the right time and you have to have the correct intake, exhaust and port time figures. Then you are ready for a pipe and maybe some go fast juice. Mike

 

[bwalker]

Nitro Methane mixes with gasoline

Are you sure Mike? I have allways read/ been told that it does not mix with gasloine. I haver never actually fooled with the stuff though.

 

[tundraotto]

talked to some dragracers here and nope - the only way nitro mixes with gas is in a centrifuge, LOL. Trying to mix otherwise results in globs of nitro that when sucked up to your carb cause a kaboom.

 

[dbabcock]

Model airplane fuel is a mixture of methanol, castorbean and nitromethane. For many larger model engines (above 15cc) no nitro is used at all. Smaller engines may use as much as 50 or more percent nitro. Castor percentage is in the 5-10% range. Top fuel dragster engines can use upwards of 95% nitro and only 5% methanol (or other things like hydrazine which is only slightly less volatile than nitroglycerine). When I was at the World Dragboat Championships at Firebird Lake in Chandler, AZ a few years ago, Ron Braaksma's top fuel drag boat's 500 CID Keith Black hemi was running 93% nitro. Dip the tip of your finger in a puddle of it and touch it to your tongue and it actually tastes sweet.

 

[tundraotto]

The top fuel & funny cars can only run 98.5% nitro by NHRA regs. Used to be able to run 100% but, too many fires and dead people...

 

[bwalker]

I double checked my nitro commenst with a fuel guru I know. Here is what he said.

"Some words about Nitromethane (then forget about it):

It’s NOT a “powerful” fuel

It’s NOT even a very “flammable” fuel—it takes heating it to 96 F temp before flammable vapors even appear. Take a few degrees away from its desire to spontaneously ignite, and it wouldn’t even be considered a flammable! (don’t remember the numbers)

The reason it makes power is that it requires relatively little O2 to break a majority of its high energy bonds in the combustion process (to put it simply) . I think Top Fuel dragsters run 70-80% fuel to air ratios (vs. approx. 14:1 reverse air/fuel for our bikes/cars). So if you can imagine, a top fuel or model airplane motor at TDC on compression before firing is going to have about 70% of the cylinder literally filled with liquid nitromethane and combust almost all of it.

Using the Top Fuel as an example, since nitromethane needs horrendous spark energy, prolific fuel injection and compression ratios approximating 25:1 to ignite—I don’t think it’ll work too well in our bikes.

But by all means, feel free to go down to your local model airplane store, grab some up, fill her up and mix it 32:1 with some MX2T. I’ll stand there and watch you kick it over until you’re blue in the face, then throw a match in the tank for giggles.

I think Rich said once that you’d have better luck firing off some peanut butter with a match than nitromethane "

here is a website with more info. http://www.turbofast.com.au/racefuel6.html

 

[dbabcock]

I guess that nitro burns so slow that this is much of the reason that flames shoot so far out the zoomies on fuel cars. I've seen the fuel rails on top fuel engines. The ones that I saw were all 1/2". One running underneath the head and firing directly into each combustion chamber. Number two running along the top of the head near the rocker arms and injecting into the top of each intake valve and number three up above the blower. Fuel rail pressure was something like 250 PSI and at full tilt, each cylinder would literally be 1/2 full of liquid nitromethane at BDC. This is probably one big reason why if there was a misfire, she'd probably hydrolock and throw a rod, then launch the blower into low orbit after that. The ignited mixture would be burning through almost the entire travel of the piston from ignition to BDC on the power stroke. Three spark plugs were used per cylinder. Two in the top of the dome and one underneath the head near the exhaust. Serious stuff here to make 6000 or so HP.

 

[tundraotto]

6000hp was winning 4-5 years ago, winning usually takes about 8000hp nowadays (all cars in the top 10). The reason for the flames out of the pipes it the fat mix to prevent burned pistons etc. 2 fuel pumps also, 1 for moving, burnout and idling and the second one for extra pressure during time run.

 

[dbabcock]

I'm sure you're right, Otto. This was all back in 1995 when I was younger and smarter. At any rate, I've also heard that these HP numbers are all estimates because there isn't a dyno that can handle the HP and short pull times required before the engine self-destructs. It's also much more difficult to predict rear wheel HP based on terminal velocity because of the many multiorder variables that start getting into the act with speeds into the hundreds MPH.

Yep, it's OT action at it's best again folks!

 

[bwalker]

Imagine the waterbrake needed for a 8000hp dyno. YIKES!

 

[tundraotto]

very true Doug - now that you mention it, we are off topic again arent we. LOL, nitro still does not mix with gas, for long....