what is the best fuel to run !

[mailman003]

Been doing alot of reading and learning alot about porting.I am starting to understand how it works. I have a old 372 jug i am going to do first to see how i do. I have two questions i want to ask! THIS IS ALONG WAY DOWN THE ROAD I KNOW. First thing i would like to know is what is the best fuel to run. 87 octane, racing fuel or hobby fuel. Second, i have read on this site that if you decrease the size of your crank case you will get more power. How is that done! Once again thanks for all of your comments!

 

[Mr.]

Good ole pump gas will do fine until you need that last edge.

Then it's nitro and alcohol all the way.

Fred

 

[mike385]

Well this doesn't have anything to do with saws but.... I have a 3.5hp 22in push mower that I have running on 30% nitro RC fuel. I don't know why i did it but I did it. LOL Runs really strong especially through tall grass.
I got the fuel given to me so I had 3 gallons of it laying around and the curiousity of boredom overcame me. :jawdrop:

 

[Mr.]

Most of that stuff is around 18% oil.

Lots of top lube for sure.

Fred

 

[24d]

do you hav to mix the alky fuel or is that somthing you can just go out and buy?

 

[rahtreelimbs]

The stuff that burns!!!

 

[Crofter]

glow plug engine fuel is available at hobby stores for boats, cars and planes from 10 to 40% or so nitromethane in methanol with 18-20 percent castor or synthetic bean oil. I havent bought any for about 5 years but at that time it was 20 bucks a gallon. In the average small plane 6 oz will get you about 15 minutes flying time with a .40 cu inch engine. You go thru it mighty quick in a saw. It is a bit more oil than you need in a saw engine but the glo engines for the most part have plain sleeve rod bearings and no rings so they need the extra oil.

Yah Rich it burns. I wind up getting a lot on my fingers and it peels and cracks the skin. I get an allergic reaction to the smoke too. dont know whether it is the nitro methane or that oil is mixed in. You dont notice it when you are having fun but the next day like some other things, Lol!

 

[Al Smith]

Nitro will give you a dandy headache Frank.

I personally don't know sicem about mixing "rocket fuel " and don't care to learn at this age.What I do know is more often that not the fuels can be corrosive to the engine parts.

From what I've seen those rocket fueled engines either run real good or the run real lousey,no middle ground.I would lack the patience to fiddle with it myself.

 

[mike385]

Yeah mowing my grass is kinda difficult, that stuff smells good burning for like a minute then it really gets old. I found a company selling 99.9% nitro and was thinking of mixing it with methanol myself and that way I could delete the castor oil.
In a chainsaw what kind of oil do you use with them? I wouldn't imagine that the castor oil in RC fuel is enough for a saw. I am by no means an expert, mostly a tinkerer that understands air fuel ratios.

Another question, since it is the nitro that makes the fuel ignite in RC engines, does it lower the octane rating enough to be dangerous in a chainsaw? I mean dangerous as in preignition.

Just my ramblings
Thanks,
Mike

 

[mailman003]

nitro-alkey mods

I have been told when running nitro-alky fuel that you should chrome your piston and jug. The reason i was told it was to protect from the intense heat caused by the nitro in the fuel. If this be the case where can i get it done at. We only have 4-5 showes a year here. Is this a problem i should be concerned with! Thanks again for all the info!

 

[Crofter]

If you are thinking about running nitro and alky in a saw you are going to need a lot more correct info than you have. That is not to be insulting but there is a lot more to running it successfully in a saw without causing damage. There are a lot of totally different issues than running gasoline. As Al mentioned it is a LOT of trouble and totally useless in saws for anything but outright racing. When you get a saw setup to run it competitively it is also useless for anything else but racing too. Nothing matter with that either but it will cost you time and money to put it together.

 

[Al Smith]

Before anybody gets all carried away with old stories of mowing lawns or running super high contents of nitro meth in a street rod or pruning trees with a super saw,better look at what the stuff actually does.

In a top fuel dragster the stuff is blown into the engine at just about liquid content.If that thing as much as hiccups in the first 100 feet out of the hole that engine will come apart like a dollar watch. Those magneto sytems they run can knock a horse out for a week .In essence the valves burn out,the plugs are gone and the thing actually runs on diesel combustion about half way through the quarter mile.The engine is shot after it runs less than one minute.Don't believe me,"Google" it.

Besides all that the stuff costs a fortune,they don't give it away.That said run the stuff if you want and tell all the "sea storys " you want to about it.You can fool some of the people some of the time......

If you want a fast engine run it on laquer thinner.It will run like a scalded ape but it won't run long.

 

[mike385]

Very well put. Nitro is also creates toxic fumes that is the reason for the gas masks in the old dragstrer photos. My mower is just a toy and I have a regular one, I would never play with the stuff if it was a working tool.

Sorry to hijack the thread. I will quit now.

Mike

 

[oneoldbanjo]

I have heard lots of stories about Nitromethane and how powerful it is...truth is that gasoline has 3.7 times the energy per gallon that Nitromethane does. The reason that Nitromethane can make an engine have lots more power is that the air/fuel ratio of gasoline is 14.7/1 (12.7/1 for power) and the air fuel ratio for nitromethane is 3.57/1. Also the compession ratios for nitromethane are much higher than for gasoline - so a supercharged engine running nitromethane can run 8.7 times the amount of fuel in a cylinder that a gasoline engine could. Engines that are not running superchargers will not get any benefit from running pure methanol as they cannot get enough fuel/air into the cylinders to make a big power improvement - and methanol/nitromethane mixtures are used. A normally aspirated engine can not run more than about 10% nitromethane mixed with the methanol. Methanol has a fuel air ratio of 7.14/1.

Conversion of an engine to run on methanol or an methanol/nitromethane mixture will require an increased compression ratio and an increase in fuel flow through the carb to allow the engine to use about twice as much fuel. Starting an engine that runs on methanol often requires gasoline to be sprayed into the carb to get the engine running - then once running and warm the engine can continue to run on methanol.

I also feeel I should comment on the fact that Higher Octane fuel does not have any more energy in it than regular fuel - however it is used in high horsepower engines as it can better resist detonation caused by high compression ratios, big spark advance and high heat. If your engine can run on regular fuel it will not get any more power by running high test - it will however be better able to avoid detonation during heavy loads. The use of High Octane fuels certainly won't hurt your engine - it just may not be necessary and will only result in more horsepower if your engine is not designed or set up to run on regular.

I am an advocate of running good fuel and good oil in and engine - just not a subscriber to using exotic fuels in normal or mildly hot rodded engine.

 

[timberwolf]

A normally aspirated engine can not run more than about 10% nitromethane mixed with the methanol. Methanol has a fuel air ratio of 7.14/1.

Conversion of an engine to run on methanol or an methanol/nitromethane mixture will require an increased compression ratio and an increase in fuel flow through the carb to allow the engine to use about twice as much fuel. Starting an engine that runs on methanol often requires gasoline to be sprayed into the carb to get the engine running - then once running and warm the engine can continue to run on methanol.

From my experiences and what I have learned from others with respect to saw motors, I think there are many who would differ with these statements.

Many guys run 20%-30% nitro and more through primative naturally aspirated chainsaw carbs.

Because of the low octane detonation prone properties of Nitro, higher compression ratios are not always the key. For example a saw with 200 psi of compression might not tolerate more than 10%, however with compression backed off to 175 psi more nitro can be run, that gain from the added fule can be more than the loss from lower compression.

Twice the fuel quantity even on just plain methanol will be close, but add nitro to the mix and your going to need a lot more fuel yet. The 7.14 AF ratio mentioned for straight methanol is closer to the ideal in theory number, real world it is down closer to 6:1 where it will need to be run to get max power and get enough cooling to keep from running away into autoignition.

 

[timberwolf]

A saw run on a mix of Nitro and methanol may be down closer to an AF ratio of 4 or 4.5 to 1, based on the required jet sizes.

Top fuel cars running nearly straight nitro run down closer to 2:1.

Real world numbers are quite a bit richer than the in therory numbers.

 

[oneoldbanjo]

I was wrong.....I assumed the supercharger raised compression....but in reality I guess it gets more fuel and air in the cylinder while the resulting compression may still be low. I did find the following chart for compression ratios for alchohol/nitromethane mixes in cars - may not be applicable to two stroke engines.

Compression Ratio........Nitromethane ratio in methanol.

16 to 1........................10%
15 to 1........................18%
14 to 1........................28%
13 to 1........................38%
12 to 1........................46%
11 to 1........................56%
10 to 1........................66%
9 to 1..........................75%
8 to 1..........................85%
7 to 1..........................94%
6.5 to 1......................100%

I have no idea at what point supercharging becomes necessary.

 

[Al Smith]

Oh I suupose all this is interesting but I really have no idea where people think they have to run a concoction of rocket fuel to get power.

Heavens,acetone,laquer thinner,toulene .Great paint thinners but why run it in a engine unless you want to blow it up.Nitroglycerine would do a much better job.

 

[timberwolf]

Al, you can't play with the big dogs if you pee like a pup!

A gas saw can be made pretty fast, maybe even beat a so-so alky saw, but if you go up against a well built alky/nitro saw with pump gas there is just no way to win all other things being equal.

I think there is only one good thing about a methanol nitro fuel mix, it makes HP!

Other than that, it's toxic, expensive, absorbs water, eats saw parts, needs to be flushed out every time, makes the saw useless basically for any other purpose but to race, doesn't like to run in cold weather, doesn't like to run in hot weather, doesn't like humidity, more tempermental than a red headed girlfriend going from hot one moment to phycotic the next.

Not much point in runing alky/nitro in a mildy or poorly ported gas saw, IMHO better off to just build a beter gas saw.

 

[Cut4fun]

Al, you can't play with the big dogs if you pee like a pup!

A gas saw can be made pretty fast, maybe even beat a so-so alky saw, but if you go up against a well built alky/nitro saw with pump gas there is just no way to win all other things being equal.

I know this one first hand. My 3ci is pretty fast for a gas saw, but against the alky/nitro 3 cubes you can see and hear the difference :help: .