bentgear

Not sure if this should be poll to see how folks answer it or just a starting post on debunking myths that get passed around about the little engines we run. Lets use it as a starting point and put several myths to rest. I am sure many of you have your favorites.

I’ll start off with one I see repeated all the time.

If you switch fuels to one with more oil the engine will run hotter or the other side of the coin - if you swap to a fuel with more oil you can lean the mixture because the oil lets it run cooler. Truth or myth? Its myth.

Reason: You tune the engine based on the amount of methanol in the fuel to air entering the carb. When you increase the oil percentage the methanol percentage goes down. To get back to the correct fuel/air ratio you must richen up the mixture to the point you are allowing the same volume of methanol to enter as before. Due to the higher oil contents passing thru the engine the temps will go down. If you were to make no changes and just run it you would be running lean. If you leaned it like some people think you would wind up with a well oiled engine trying to cook itself to death from a really lean mixture.

What’s your favorite?

Ed M.

Reindeer

My Feedback: (25)

Heli flyer I know is under the impression that adding castor oil to the fuel means that he doesn't need to worry about doing the after-run proceedure.

Nitro Fumes

I've always felt it was a myth about fuel getting old and losing its potency or being bad for the engine. If you have it stored properly, that is sealed, in a cool, dark place it will never go bad. Because I've stored fuel like that nad have never had a problem with it. But something people may not realize about stored fuel is that before you use it again you have to shake it up because the ingredients will eventually seperate.

Philster

I agree with the fuel myth. Consider the fuel myth busted: 15 year old Byrons 25% nitro: Performed flawlessly.


My FAVORITE ENGINE MYTH: "Wow, if I get a bigger, more powerful (expensive) engine, I can finally beat that guy in a drag race...or raise my cars top speed with 33% nitro!!! What super duper big motor shoud I buy to beat my friends XYZ car!?"

Nope - can't have a simple answer. There are way too many factors/variables, including clutch set up, gearing, engine RPM redline, the 'power band' of the engine, the tune, the break in, the final drive ratio, traction off the line, oil % in fuel, type of oil, fuel and glow plug harmony (call timing), etc, etc.

If it were that easy, racing wouldn't be about setups, clutch and gearing knowledge...or driving.

HEATsynk

I was laughing at some of them....Keep em commin.

Nitro Fumes

I definitely agree with you on the engine myth too. I used to race 1/8 nitro on road racing in the 80's. I've beat many a car with more powerful engines because the drivers couldn't handle the power. They just did a lot of slamming into the boards. And even more so for off road racing because you really can't use all the power. In fact (although I do know how to use the powere and throttle) I was racing last week. I have a Losi XXX-NT Adam Drake with an OS Max .12 TR w/#10J (slide valve carb.) and my friend has an Associated RC 10 with an OS Max CV. My Losi is lighter, you feel the difference and my engine is twice as powerful. But off road being a great equalizer I didn't have an advantage on our small track. He took 1st place and I took 2nd place in the main. (I did take 1st on the 2nd heat though) It's all in how you drive and how well you have your suspension set up. Right now I think his car's suspension is working better than mine. Mine is new, I'm new to offroad and been away from the hobby since '92, that was my truck's first race, and once I get it set up right I will go faster too. But not because of the engine, because of the suspension. Only then I might have a slight edge with more power.

But with the on road racing I used to do, my club had a big track and you could make use of all the power. But you had to have your car's handling correct and you had to be a skillful driver that knows when to slow down for a turn. You know the expression, "you have to drive slow to drive fast".

Fuelman

My Feedback: (6)

This is not always true, in fact it is very rarely true.
If I made a fuel with 18% oil and ran it in a car engine, tuned to peak performance (not lean mind you, just peak). That engine would run hotter than a fuel made with 10% oil, tuned in exactly the same manner.
Nitro contents, plugs, engines, etc... all remaining the same.


The one myth that makes me laugh is "the colder an engine runs, the better"
Did everybody forget that heat makes horsepower and these little engines were designed to run OVER a certain temp, not under.
Airplane and heli guys generally do not have heat guns and could care less about what temp things are running at, but their engines typically run much hotter than 300 deg F even in the wind blast of the prop and still last years of heavy flying. I have one engine that does not get to good friendly operating condition untill it gets over 350.

bentgear

Fuelman, then I would have to say our experience with hgiher oil content has met with opposite results.

Ed M.

Nitro Fumes

[quote]ORIGINAL: Fuelman

I never heard that one before: "the colder an engine runs, the better". When I raced my Serpent Excel (1/8 scale) I had a 6 port REX. I ran that at 285ºF. It ran geat at thet temp. I don't think I could have taken it up too much higher but if I ran cooler (like 265ºF) it still ran just as well but I couldn't finish a 5 min. heat race. Those cars only ran a 4 oz. tank. My current car, the Losi XXX-NT AD2 has an OS Max .12 TR. It seems to like 200ºF. When I had it up at 220ºF it was bogging on acceleration. But you certainly should run an engine at its highest optimum temp.

Reindeer

My Feedback: (25)

Here's another one...

MYTH: A nitro (car) engine is only good for about 3 gallons, then it needs to be rebuilt/replaced.

FACT: There are simply too many variables to determine how long an engine will last. Who is the manufacturer? How was it broken in? What was the state of tune? How was it cared for? How was it driven? While some engines are probably good for only 3 gallons or so, I've seen too many reports of people who have gotten over 10 gallons in their engines here on these forums alone. One friend in our local club has at least 2 years on his T-maxx... he runs it nearly every weekend he can and usually runs about 1/2 quart during that time. While I have never asked him what his total fuel consumption is, I'm certain he's got at least 6 gallons through it by now. For that matter, the .70 BX on my EK-4 is ringed as opposed to ABC construction, and with a somewhat conservative tune should last a VERY long time!

nitrosportdecals

OK, we are all forgetting about the portion/percentage of the mix that has the intoxicating effect on us. What is it about the scent of the fumes that is so addictive? What dark sinister conspiracy have the fuel manufacturers come up with that keeps us drooling? I'm fairly certain that all things considered, there is an additive that has us hooked beyond good reason. Truggy time takes precedence over all, eg:bills/wife/eating etc. Am I alone on this or are the majority as hopeless as I am? I for one am past just inhaling the good fumes. Can you snort, smoke, or take it intraveinously?

Dr Nitro

Yes, addicting is'nt it!
I do research and extended run testing by contract for a fuel company. I have had conversations with the owner about exactly the same thing- what do you put in there to cause the addiction??? Of course there is nothing special in there but the addiction comes from the sound, smell, the heat, and the experience of tuning, running, driving, racing, flying thiese things that all comes together to cause the addiction.

Bentgear,
I would have to agree with fuelman on this one. If I take a 20% nitro w/ 20% oil airplane or heli fuel and compare with a 20% car fuel with 10% oil, both from the same manufacturer. Run them car fuel first or plane fuel first, does not matter but its in the same engine, same truck, same morning, same track, same plug, etc... Tune each blend so it is at maximum performance, any leaner it would be losing performance.
The results would be that the high oil fuel will not only run hotter, but I would lose a lot of the snappyness and response to the throttle. Going to the lower oil car/ truck fuel and tuning it to the fuel exactly like before, the engine will return to its previous state, regain its snappyness and power and run (in this case) about 40 deg. F cooler.
I have done this with several engines, stock and modified OS, Fantom, DuraTrax, OPS, Traxxas engines.

Here's the best part: it works that way too in airplane and heli engines, If I have a significant drop in oil content such as switching to a car fuel from an airplane fuel, same as above, the lower oil car fuel will run significantly cooler than the higher oil plane fuel. I have a theory as to why, but I will not get into it here because I can not scientifically prove my theory. Fact is, it just happens in most cases with modern engines.

As far as the "running colder" thing, if this myth was not true, the aftermarket head business that all provide extra cooling would not exist. I see it frequently, people just have to make their engine run cooler than it is and buy that super heat sink for it or run it too rich, etc, etc... Lets face it, a lot of old school thinking about cooler runs better and longer is still out there and over-cooling these little engines and then leaning them too much is very common. Nearly every hobby shop I have been in promotes the "blubbery rich break-in" and the super duper after market extra cool heat sink head for their customers. They also have a ready supply of pistons/ rods/ sleeves on hand too. Coincidence?, NO.

One of the great myths I love is the longevity thing- As I heard a shop owner explane to a customer one time "This is one of the good engines, it will last about 5 gallons of fuel!!!"
Well for $400 that the engine cost, I would expect it to last for ever. In the airplane world, a $400 dollar engine would be a Saito 180 (1.8 cubic inch engine) that develops about 3 to 4 horsepower, It will take more than 5 gallons or up to 5 hours of run time just to break it in and last with proper maintenance and tuning well over 100 gallons of fuel.
Bottom line is, if that 400 dollar car engine was broken in correctly and tuned correctly (not necessarily to the instructions) then it would more than likely last a lot longer than 5 gallons, even if is a race engine.

bentgear

Dr Nitro, while I agree that performance will drop with a higher oil content, what I have seen is a lower temp reading after tuning. The fuel I normally run has 10 % oil. (8 % syn 2 % castor). In the past I have run 14%, 16 % 18% even some YS 20/20. I have taken 16% and added castor to raise it to 20%. All ran, some better than others. But each time I raised the oil content I have noticed a decrease in temp, I think its the unburned fuel/oil carrying away the heat. I also think it is much harder to tune correctly with a higher oil content as the needle settings are masked somewhat by the mix. The engine must be richened for the decrease in methanol by volume and the increase in viscosity of the fuel and this tends to screw a lot of folks up.

I may be completely off base, my testing has been limited compared to what one would do if they set out to determine the correct answer under lab conditions with dozens of engines and fuels.

Ed M.

Fuelman

My Feedback: (6)

Dr Nitro and I both run a lot of engines, I do it for a living with my fuel company. He does it for a company as an independent contracted engine tester.
To be perfectly honest, if you are to run a modern engine and peak it out with the same load beams or props on different fuel and use a tachometer to find the peak rpm, and use a thermocouple to measure heat, you will notice what I do and what Dr Nitro does. If you go by seat of the pants tuning and a standard hand held temp gun, you may not achieve peak power and therefore not have a valid comparison.

When going up in oil (when everything else is the same) does cause you to run richer than when going down in oil, to keep the amount of methanol and nitro at the correct air fuel mixture ratio. Even though that happens it will run hotter since each stroke for the piston will still need to consume a burnable amount of methanol and nitro to the air volume, but it is carrying with it a lot more oil, in the above case twice as much. Problem is the combustables in the fuel will vaporize and become a gas and the oil will be in micro droplets and not vaporize. Gas will be compressed and the liquid micro droplets will not be compressed since a liquid can not be compressed. This has the same effect as increasing the compression (my theory) and when that happens with all other variables remaining the same, the temps rise (what happens when you compress a liquid?, it gets hotter as well as its surroundings).
Also take into consideration that the methanol in the fuel takes most of the heat out of the internals of the engine, and nitro to a lesser extent since it is absorbing all that heat to change it from a liquid to a gas. Oils having a much higher flashpoint will not absorb as much heat and actually help trap and retain it to a minor extent. Even though the mixture is richened accordingly to run on higher oil fuel, still only so much fuel / oil mixture can be "inhaled" by the engine at a time, (and that remains constant regardless of how much oil you have since the space is only so big inside the engine, (that is why you get less power with higher oil), for every intake charge of air it is now carrying more oil than before so that has displaced some of the methanol and nitro and therefor has cut down slightly on the amount of coolant the engine is ingesting.

That is your answer to that myth.

In very few occasions, an engine will act inversly to this and cool down. For example- an old Fox 35 bushing engine with a lapped iron piston and iron sleeve. These engines were such that they needed 25 to 29 percent all castor oil to: #1 give a good piston to sleeve compresson seal, and, #2 to give enough cushion to the crankshaft so it would float on a thick film of oil in its brass bushing (no bearings in these engines).
In these engines and others like it, is where cutting down on oil will actually make them run hotter since the friction is increasing rapidly.

Nitro Fumes

To Fuelman & Dr. Nitro. I have a question. First I should add I do know how to tune and engine but I originally got into this hobby in '83 with 1/8 scale on road nitro racing. I learned about engine tuning from the more experienced guys of course. One thing I learned that I hear now is the opposite is this: When the weather is cooler I would lean the engine a little to bring it up to it's optimum operating temp. I had a .21 REX 6 port engine that ran great at 285ºF. Sure, it ran fine at 265ºF but I would run out of fuel on a 5 min. heat at 265ºF. Anyway, now I hear when the temp is cool you are supposed to richen the mixture because the air is more dense and therefore you need to richen it to bring the stoichiometric ratio back to optimum. And therefore when its wamer you lean it as the air is less dense for the same reason. BUT I've always felt leaning it to bring it to optimum temp makes more sense. You make more power too. I'm not talking about overleaning, just 1/16 to 1/8 of a turn. But I also feel since the air is denser as it is being sucked into the carb (which is a venturi tube) and this would increase its velocity into the engine. And with a higher velocity there is a greater pressure drop and this would in turn suck in more fuel, and that is why I make it leaner. So what do you guys think?

I should add since this is based on Bernoillis principle as my logic you might say comes from airplane wings. In cooler denser air and airplane gets more lift for a given airspeed than it does in warmer less dense air, more lift is the same as more vacuum in a venturi.

SManMTB

Always tune for performance, not temperature.
Cold air is denser ---> richen up
Warm air --> lean out

Fuelman

My Feedback: (6)

Nitro Fumes,
Yes, carbs are little venturies, thats how all of them suck in fuel, by lowering the pressure of the air moving through it to suck the fuel through the tube.
Forget the temp gun. The best way to tune is to start with a half tank and make a few laps, dial it in to max performance, back it off just a slight amount, fill up the tank and go run.
If you are running at 285 then the engine will probably handle a lot more than that, only you can find out by searching for its max. If you are running out of fuel, get a bigger tank or go to a slightly colder plug where the mixture must be leaned slightly to keep it running strong.

Nitro Fumes

Thanks, that was a car from the 80's I used as an example because I raced it quite a bit. I've been out of the hobby since '92 and just got back in with an off road truck, the Losi XXX-NT AD2 with an OS Max .12 TR. When I set this engine up it seemed to have liked to run at 200ºF. The weather was cooler so I'll just adjust accordingly. I do have a BSME so I understand all that basic physics involved.

bentgear

Then would you feel that maybe what I have experienced is because the engines that I noticed this on have been well used, but still runable. The extra oil was taking up some of the slack in the piston/sleeve fit returning the working compression closer to new conditions?

Ed M.

ryan_t888

I hate the "tune to temps" and "exhaust smoke" deal!

All engines run differently and depending on what fuel is used will determine the amount of exhaust smoke.

Ryan

Fuelman

My Feedback: (6)

If your engine was a lapped iron piston and sleeve engine without ball bearings, I would agree 100%

My thoughts are that you have not peaked the engine to its maximum rpm before going too lean, then and only then will you have a good comparison.
If you invest in a thermocouple, tachometer and some load beams and an engine run stand, you will no doubt see the relationship.

nitro_redneck

i have about 25 gallons through one of my engines

AJsToyz

I totally agree with you !! Go to the Traxxas web sight and they are fueling that mith though. I was very supprised to see this. Here is the link. http://www.traxxas.com/support/index...ighlight=omega

bentgear

When you lean it out til it falls flat on its face and then back off some I don't think running rich is a problem.


Ed M.

Nitro Fumes

Sounds like Traxxis wants you to use only their fuel. Just a ploy to keep making money. You can use any brand of good quality fuel. Just stick with the same brand all the time if you can.