tazamazoo

i have been running 20% fuel in my cars.but now i am in a tight budget with money i was wondering if 15% would be ok to use in my cars since the diffrence in price at my hobby shop is 8dollars a gallonof 20% runs 30 bucks while 15% runs around 21 bucks. i heard mix views on it . so what do you all think ???????

proanti1

My Feedback: (2)

Is it car fuel? Because airplane fuel is high in lubricants, and runs hot in car engines. You can always buy a liter and see how it runs, if you have a newer motor, you may have heat issues running a lower nitro content fuel.

Smiff 24

If you do try it youll probally need to tweak your carb settings a bit.
It my bogg and foul the glo plug.

yakfish

My Feedback: (27)

you will definantly have to adjust the need setting but it will work. I mixed up some 15% nitro with 8% oil and my engines run great on it! What is the oil content of the fuel you are considering buying?

1QwkSport2.5r

Less nitro = narrower tuning window = less heat = less power = less $$$. Not a noticeable amount of power loss from 20% down to 15%.

More nitro = broader tuning window = more heat = more power = more $$$.

Needle settings will need to be leaned slightly since not as much fuel is needed because of there being less nitro.

1QwkSport2.5r

The engine would be a bit rich, but you wouldnt foul the glow plug. I've yet to ever "foul" a glow plug from a rich mixture. I have an engine I ran so rich during break-in, I was burning 6oz of fuel in 2 minutes. 2 gallons of fuel later, I'm still using the same glow plug.

proanti1

My Feedback: (2)

Higher nitro content almost always runs cooler, especially in newer engines. Higher nitro content + higher compression = efficiency. Higher efficiency engines run cooler. Nitro content does not directly correlate to power, the compression ratio does.

1QwkSport2.5r

I am not going to argue, but 95% of what you have said is wrong.

tommygun32

tazamazoo, what brand nitro fuel is it you're thinking of buying?

lez1troubles

Hi Tommygun, I used to run Sidewinder 16% but it really overheats your engine some thing terrible. If you do use it you could end up breaking more con rods and wearing out cylinder liners rather quickly and you'll deffinatly see the performanse decrease.

lez1troubles

By the way, Higher nitro content = lower heat.

proanti1

My Feedback: (2)

Nope, it's not. You are wrong. In a properly tuned engine, higher nitro fuels burn more completely, and quicker, which means less methanol has to be burned. More nitro = less methanol. High nitro fuels are also thinner, requiring a slightly richer tune. The more fuel you can pass through an engine, the cooler it will run.

Argess

I may be adding to the list of people who are wrong, but I can see where both scenarios can cause higher temps.

Low Nitro Fuel + CR designed for Higher Nitro Fuel = Less efficiency = excess heat

High Nitro Fuel + CR designed for Low Nitro Fuel = Less efficiency = excess heat

Just speculation on my part as I've never tried it.

Back to the OP though. If the OP's engine is running fine on 20%, I doubt switching to 15% would cause a significant problem. The cost difference is attractive enough to try it. If it doesn't work, he could try mixing the remains of the 15% with some 20%. If that works better, he won't waste the 15% and there will still be some cost savings.

What I do have expereince is with 16% oil fuel. My engines always ran hot and were touchy to tune with that fuel (Backyard Basher). When I switched to a fuel with 12% oil, things improved greatly. My theory (which might be wacky) is the extra oil takes up space in the combustion chamber and artificially increases the CR. To support that theory, I have had some improvement with the 16% oil fuel by switching to an OS shorty plug, which reduces the CR a small amount and helps counteract the excess oil.

Anyway, speculation isn't all that useful unless it generates better input (from others). These forums are essentially a "discusion board", where hopefully something useful will arise. When someone is worng, a little tact is nice. It makes things polite. Seperates us from the animals, so to speak.

1QwkSport2.5r

From: http://www.dynamiterc.com/Articles/A...ArticleID=1638
Fuels with a higher nitro percentage, like 30% for example, burns hotter and creates more power, but the engine also consumes fuel faster and you have a greater chance of overheating your engine. 10% nitro burns cooler and is a little more efficient fuel, but it doesn’t create as much power. 20% fuel is a good all-around mix between the 10% and 30% as you’d assume; it burns hotter and creates more power than 10%, yet is cooler and doesn’t deliver as much power as a 30% fuel would.

From: http://bentley-flyer.tripod.com/aboutfuel2.html
Hardly a month passes that someone doesn't call to ask, "I hear more nitro will make my engine run cooler. Is that true?" Nope. The higher the nitro content, the higher the operating temperature. Fortunately, in most of our sport engines, the difference in operating temps between 5% and 10% is negligible, and there are lot of other factors (proper lubrication, etc.), that are much more important.
The latter was written by the former president of GBG Industries, former maker of power master fuels which is now owned by VP Racing fuels.

You can believe what you'd like. This stuff wouldn't be published in such a way if there weren't some factual evidence to it. I'll talk to a chemist to put the subject to bed once and for all.

proanti1

My Feedback: (2)

You do know that Don Nix article is about 15 years old right? Powermaster was a pretty low grade plane fuel back then, which ran hot in all my OS motors (go figure), and it's still pretty crappy. I like how he gives absolutely zero facts to support his theory. Just "NOPE".

"High performance racing engines, for example, are tuned entirely differently.... Compression ratio, intake and exhaust timing etc.... and are usually intended to run on much higher nitro."

Most current RTR engines are higher performance than the 'high performance' engines designed 10 years ago.

http://www.optifuel.co.uk/Home.aspx?...mid=64&smid=-1

"The reason it runs cooler is because burning more nitro liberates more oxygen and therefore burns more methanol, the more fuel you burn, the more oil goes through the engine and it is the oil that disperses the heat"

DaveG55

I don't intend to get into the whole "what runs hotter/cooler" thing. It seldom ends with a concensus and, IMO, is not terrably relevant to the OP's question. He's only changing 5% and I seriously doubt that he notices much difference in temp or power.

As to the oil question. That IS the real question here as oil content will make a big difference in how the engine tunes and how hot it runs.
Argess, I'm not sure what you mean by "CR" but this is a paraphrase of what I've read on the subject. It seems that when you use fuels with high oil content (12% an up) that there is a good bit of oil that remains in the combustion chamber after the burn. This oil tends to retain heat from the combustion and cause an overall rise in engine temps. I have also read a couple of articles that say that the optimum oil content for our engines is 8%. The problem with that level is that it becomes imperative that the tune be dead-on at all times. It's real easy with that low a content to get too lean anddamage the engine. The article went on to say that, as a compromise, a fuel w/12% oil is a great balance between the optimum oil content and a content that gives good results and stilll offers a larger, safe, tuning window.
Now I'm sure that there are several other factors that play into the engines heat and the relationship to oil content but those things I have read made sense to me and corosponded to my personal experiences too so I tend to believe them.