thestratcat

My Feedback: (12)

how big of a performance difference is there between the two grades of nitro? does the 30 percent shorten engine life? if so how long?

A.B.U

I'd say you would probably get a good 1-3 mph out of an upgrade to 30%. It will shorten engine life, probably by a gallon at most.

gerwen

You can tell the difference.

I'm not convinced that it will shorten engine life. I've heard no real evidence of this, just people stating that it should shorten engine life because you're making more power.
I can tell you my engines run cooler on 30% than on 20%, and 20% ran cooler than 15%. This would lead me to believe that higher nitro doesn't shorten the life of your engine. While it is contrary to what you might think, it makes sense. You have to run richer with higher nitro, pushing more of the coolant (fuel/oil) through the engine, cooling it better. Higher nitro would probably create more stress on the con-rod, wrist pin, and possibly crank because of the higher compression, but those aren't the typical first-fail items anyway. It's the piston/sleeve that generally gets replaced.

More nitro does make it more finicky with tune though, same with lowered oil content. And i suspect the margin for error in going lean is greater. If you're confident in your tuning skills, go 30%.

You may need to go to a cooler plug, and add a head shim. I haven't run 30% in my evader yet, so i'm not sure if it runs right without one.

Frost_

My Feedback: (1)

Gerwen, that's my school of thought too. After running LOTS AND LOTS of DIFFERENT engines on both 20 and 30%, the idea that 30% kills an engine seems to be something that gets passed along between folks that have no idea. I challenege anyone that says that 30% shortens life over 20% to SHOW PROOF OF SUCH IN A CONTROLLED SETUP. Other than that, it's all opinions. Even if it were proven, there is no way it can be a significant %. It would be seriously overshadowed by the reduction in life engines see in the hands of the inexperienced anyway...

For that Evader (and 99% of what's out there) going to a medium heat plug is all you need to go with 30%.

jkulhanek

So a #8 should be fine with 30%?? I've been using A5's and they are just too expensive to keep using.

If I use an O.S. A3 what should be my maximum nitro content??

Dyehard

Anything that increases the Brade Mean Effectibe Presure (BMEP) on the piston of an internal combustion engine (that will give an increase in torque at any given RPM, which will give more horsepower at that RPM) will cause the pressure the piston excerts against the cylinder wall opposite the crank pin to increase. That will lead to more wear on the liner on that side. Thats exactly what the first liner on my grandsons DTX 18 looked like when we had to replace it. Anything that increases the power of an engine will cause it to wear quicker, if that power is used constantly, whether that engine is in a model car or a full sized car. In some respects an engine is an engine and size doesn't matter.

MonteEvader

My Feedback: (1)

Good point. The evader is my first engine of this size (.18). Prior to this I've only had .12 and .15. My local hobby shop told me to break the engine in with 10% fuel (first he said 15% but that sounded like plane fuel to me). The instruction tape said different. Is there a benefit to using 10% fuel during break in?

46u

My Feedback: (3)

You might find this article interesting.
http://www.rcnitro.com/rn/articles/nitro_fuel.asp

Frost_

My Feedback: (1)

Well no one would argue with your first sentence, however... There are soooooo many variables that dictate what the life of these tiny engines will be, based on what I have seen, I can't call the use of 30 over 20% a serious contributor.

A friend of mine (who is now my roommate) got an evader about 2 years ago as his first truck and went through 3 of these engines pretty quickly. The sleeves are garbage, hands down. His first engine was run for it's first 7 tanks with no oil in the dry foam air filter. The instructions with his truck and the video it comes with said nothing of oil. The truck that was "ready to run" from the box included no filter oil either. I discovered this on his tank 8 of breakin. I stripped it down and cleaned it thoroughly but it only lasted about a gallon. Engine number 2 had a text book heat cycle breakin. It was set very rich with the head and crank case wrapped in a gym sock to get the temps up quickly, and cooled at BDC for a huge number of cycles. He had learned a good bit and kept a religously cleaned element and ARO'd after each day. It made ok power and was not abused or run lean. This engine saw a sport type (18%oil) fuel of 20% with a hot plug. At about 2 to 2 1/4 gallons this engine would run hot quickly, had lost compression, and was hard to start. The sleeve looked like engine number 1. After some forum digging (places besides here!) it seems that this is not uncommon at all for that mill. Warranty engine number 3 was broken in the same way and spent it's life on 30% race fuel and a medium plug. Careful inspection for the first several tanks after switch-over showed no signs of detonation. This engine was pulled at about 2.5 gallons for something non-OE, and was still running well. This is not offered as any type of counter argument, just an experience.

I have yet to come across a BB or SB car/truck engine that doesn't run better and cooler with 30% and a medium to cold plug. I have many stock and worked engines. I'm not a blind cutter, or uninformed. I use a homemade degree wheel to measure port timing and know what there is to be gained at 1-1.3mm of the right part of the exhaust port. The same goes for the intake (to a lesser extent). I have had a number of engines to cut up. I have passed along to others four or five ported engines that are alive and strong (at this moment) at 3-7 gallons and have been run hard with 30%. A buddy of mine got just over 8 gallons out of a Picco 26 that I worked and reworked, and ran for 2 gallons myself!! This engine was beat on with 30% too. Many people see tired engines that aren't little RTRs at 4-6 gallons on 20% "sport" fuels like BT. Again, this is no counter argument, just experience.

I'm sure it's a variable that contributes to wear, but my experience tells me that it must not be a large contributor. I have seen breakin to be a large contributor to life, especially in my airplane engines that are somewhat comparable to these. I have seen tunes that always run the line of lean, and commonly fall over here and there for the whole life of the engine (about 2 gallons, and not an RTR engine). It had a rebuild that lasted over 3 times as long (now just over 6 gallons on new piston/sleeve/rod) and is still going on a more conservative tune. I like the speed, that's why I'm into this. I've never had an engine that made more power with 20%, and it doesn't seem like a large detriment, so I run 30.


/endlongwindedness

Dyehard

Yes, there are may variables that effect the life of an engine, proper breakin, contaminants in the incoming air, contaminants in the fuel, amount of oil in the fuel, initial piston/liner fit, metalurgy used in the piston/liner and how lean the engine is run to name a few. Some factors such as dirty air and lean run can kill an engine very quickly, others will do the job more slowly. The differance in wear between using 20% fuel and 30% fuel is one of the miner wear factors, simply because there is not that much more power produced with 30%. If all other factors are kept constant, I still stand by my statment. Any thing that increases cylinder pressure will lead to more wear of the piston liner on the side opposite the crank throw and will increase the pressure on the con rod bottom end, also causing wear unless plenty of oil is used in the fuel. There are only two ways to increase power, increase cylinder pressure and increase RPM. Race engines do both, that in why they are worn out in only a few hundred miles, whereas the street engines they are base on may last a few hundred thousand miles. A pylon racing forty that is raced every weekend will not last for years like a sport forty that flown every weekend. With power comes a price.

Trbo323

Iv never ran 30% all iv had is a nitro rustler running on various 20% Im hopfully gunna get a Mammoth st here soon and from what iv heard you can run 30% with a shim, my question is why do you have to run a medium to cold plug though??