Nitro Engine Operation (pls review for accuracy)

[jgorm]

I'm pretty new to nitro, and it has frustrated me to say the least. I'm giving it one serious attempt before I go brushless. I've very experienced with tuning real cars, and I could have tuned 5 blown mustangs for $500 each in the time I've spend messing with this 'toy'. I didn't know much about how the little 2 strokes worked, but some local guys helped me out and schooled me a bit. (mostly 2revo1maxx and olds97_lss). Thanks guys! I wanted to summarize my view of how these engines operate so I know better how to make them run great.

1. Air enters the air filter and goes into the carb. The LSN (point) actually sticks into the HSN (tube) to slow the fuel flow for low rpm / load conditions. As the throttle opens it allows more air, and when its WOT, the LSN no longer protrudes into the HSN. This is not the best picture, but the LSN is on the right side, HSN on the top left.

2. The air fuel mixture exits the carb into the crankcase. The piston creates vacuum in the crankcase as it goes up towards TDC. The crank has a rotary valve that blocks the mixture from getting pushed back into the carb as the piston comes down on the power stroke. You can see the rotary valve about half way closed in the port under the carb.

3. The mixture travels through the center of the crank into the crankcase. You can see the port in the picture above if you look close down the crankshaft center on the right side.

4. The mixture gets pressurized on the power stroke and gets forced through these ports on the piston sleeve as the piston reaches BDC.

5. The pressurized intake charge fills the combustion chamber and helps (?) push the exhaust out the exhaust ports on the opposite side. I'm not sure if the port at the top of this picture is intake or exhaust, but I suspect its intake. The exhaust ports are on the right side.

6. The piston rises towards TDC and compresses the mixture to critical temperature and pressure before it detonates. (does it detonate, or does it ignite off the glow plug?)

4CH3NO2 + 3O2 → 4CO2 + 6H2O + 2N2
The amount of air required to burn 1 lb (0.45 kg) of gasoline is 14.7 pounds (6.7 kg), but only 1.7 lb (0.77 kg) of air is required for 1 lb of nitromethane. Since an engine's cylinder can only contain a limited amount of air on each stroke, 8.7 times more nitromethane than gasoline can be burned in one stroke.

The stoich point of nitromethane is SUPER rich, 1.7:1:whhooo: The stoich point of methanol is 6.4:1 so the stoich point of 20% nitro is about 5.5:1. But none of this really matters because we can't easily measure the mass of air on these little engines.

7. The piston comes down on the power stroke and the combustion gasses / still burning fuel, etc gets pushed out the exhaust as the new mixture enters the combustion chamber. You can see the internal sleeve ports looking through the exhaust port with the piston at BDC.

I had a new thought I had after learning a bit more on nitro operation.

When these engines get flooded, I'm assuming that the entire crankcase gets flooded too. I used to see no need in pulling the glow plug and spinning it over with the fuel pinched off, but now that seems like a great idea! This is also the reason that you need to 'clear it out' with heavy throttle, to minimize the mixture that is in the crankcase.

These pictures are before I cleaned everything up and I'm resealing everything mentioned in some thread. I'm getting a new exhaust seal thing too.

Please critique, fill in the details, tell me everything is wrong, etc. I'm trying to learn as much as I can.

I built this 'dyno' when I first got the truck so I could adjust the mixture while at wot. I have plans to add some more load to it via some sort of braking device. You guys might get a kick out of it.

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[Punisher]

I can't see your pics, but your theory seems right.

The exhaust plays a huge roll in the 2 stroke cycle.

Changing the length of the header, the pipe, and stinger makes a big difference to the power band and how the engine runs.

Do some research on 'tuned pipes' . . .


I know a bit about 1:1 carbs too, but tuning nitro is a art in itself. As for engine mods, I tried my hand at porting, and minor timing changes but proper mods (ie real timing changes) are best left to the pros - http://www.extremercmods.com/

Check out Robin's site . . . .



I like your dyno . . . need to add some resistance . . . dont forget little rc nitros are air cooled - so make sure you have a fan on the engine (may have had one there - I didnt notice) . . . also, often guys will start tuning before the engine is warm . . . before you make any adjustments, make sure your engine is at proper running temp.

No AFR meters for RC (probably is but out of the reach of the common man) - get a temp gun and learn to read what the engine is doing by sound.

I started off with Lipo, sold it all and moved to nitro - it's frustrating at times, but I would never go back to electric.

---------- Post added at 1:59 AM ---------- Previous post was at 1:52 AM ----------

"5. The pressurized intake charge fills the combustion chamber and helps (?) push the exhaust out the exhaust ports on the opposite side. I'm not sure if the port at the top of this picture is intake or exhaust, but I suspect its intake. The exhaust ports are on the right side."



The piston acts as a inlet valve would in a four stroke . . .

The 'cam shaft' in a two stroke is the position of the inlet and exhaust ports in relation to the piston stroke . . . . the crank also contols timing . . . .

There is only one exhaust port, that's at the rear . . . yes, the inlet charge pushes the exhaust out, the pipe also sucks exhaust out/charge in - reverb tuned by the pipe and header length helps fill the cylinder - see tuned exhaust. . . .

As I mentioned, I can't see your pic, but the ports you labelled 'exhaust ports on the side' are probably booster ports - they assist cylinder filling and produce swirl.

 

[jgorm]

Thanks! I'm familiar with exhaust scavenging, and understand its roll in tuning the power band. My engine has 2 exhaust ports that you can see when you look into the exhaust port form the rear. See if you can see the pictures here. I've linked to G+ in the past and it seemed to work. Can anyone else see the pictures?
https://plus.google.com/photos/105856624487263703214/albums/5848974273549683713

I'm still wondering if nitro detonates like a diesel, or ignites like a gasoline engine.

 

[Extreme RC Mods]

Glow fuel shouldn't detonate, when tuned properly it will ignite. That engine also only has one exhaust port, the port directly across from it is the boost port and the ports on the sides are called transfer ports. Some sleeves have ports that are below the top of the piston at BDC, these are called bypass ports and only function if the piston is drilled to match with them.

 

[2revo1maxx]

The platinum in the glow plug also has a catalytic reaction with the fuel, in addition to the coil staying hot enough to ignite it.

Your engine looks like it's spent, and that exhaust gasket could have been causing some tuning issues.

 

[jgorm]

The platinum in the glow plug also has a catalytic reaction with the fuel, in addition to the coil staying hot enough to ignite it.

Your engine looks like it's spent, and that exhaust gasket could have been causing some tuning issues.

Thanks. why do you say it looks like its spent? It has maybe 5 tanks of gas so far.

 

[Greywolf74]

Thanks. why do you say it looks like its spent? It has maybe 5 tanks of gas so far.

Looks like its been through hell and back. It also looks like its rusting on the inside. If i bought that engine (assuming the outside of it was clean) under the assumption it only had 5 tanks on it I would promptly send it back and ask for a refund because i wouldnt believe you. just my .02 on it.

 

[Extreme RC Mods]

It does look like it sucked in some dirt as the crank looks marred, it does appear to have what looks like a substantial amount of fuel run through it. Just by looking at the pictures, if there really has only been 5 tanks run through the engine, you are running it way too hard too soon and could have caused a lot of damage.

 

[jgorm]

I'm assuming that you are basing your comments on the combustion deposits on the piston? My guess is that is from improper storage. I'll be the first to admit that I have not taken the best care of this engine. I've left fuel in it for weeks (months?) at a time. Never run after run oil, etc. I figure that there was evaporated fuel on the piston for a while and it turned nice and black the past few weeks I've been running it. It's also possible that its been closer to 10 tanks. The compression is still strong. The damn thing would act up all the time so I've actually only run a tank out of fuel 2x so far. If it doesn't work right this time, then I'll sell it and go electric.

 

[lesclaypool]

You are the first owner of this engine??

 

[jgorm]

yeah 1st owner

 

[uberbricky]

If you are neglecting your engine then thinking you can't get it right, I'd start with proper maintainence. I've never seen an engine looking that rough with 10 tanks though it.

Clean her up, seal it and give it a go, it just might be recoverable. But you shouldn't try to sell the engine (unless you meant the whole truck)

 

[2revo1maxx]

10 tanks? I thought you said 5 gallons.
I can tell that engine has been too hot, and yes the crank has seen some dirt. I'd replace the exhaust gasket before trying to run it again, but before that you can do a simple test. Spray a little wd-40 in the cyl and turn it over by hand, if there's no tight spot at the top of the bore then it's safe to say she's spent.

 

[jgorm]

10 tanks? I thought you said 5 gallons.
I can tell that engine has been too hot, and yes the crank has seen some dirt. I'd replace the exhaust gasket before trying to run it again, but before that you can do a simple test. Spray a little wd-40 in the cyl and turn it over by hand, if there's no tight spot at the top of the bore then it's safe to say she's spent.

yeah, 5 or 10 tanks, not gallons. The compression is good and it gets tight near TDC even without wd40. It will 'pop' back down if you let go at the right spot. I already have a new exhaust gasket. I should have time to test it this weekend. I'll keep my fingers crossed!

 

[Punisher]

I'm assuming that you are basing your comments on the combustion deposits on the piston? My guess is that is from improper storage. I'll be the first to admit that I have not taken the best care of this engine. I've left fuel in it for weeks (months?) at a time. Never run after run oil, etc. I figure that there was evaporated fuel on the piston for a while and it turned nice and black the past few weeks I've been running it. It's also possible that its been closer to 10 tanks. The compression is still strong. The damn thing would act up all the time so I've actually only run a tank out of fuel 2x so far. If it doesn't work right this time, then I'll sell it and go electric.

Two words - 'mechanical empathy'.

. . . you find nitro frustrating?! . . . Your engine doesn't think much of you either . . . And people let you tune their supercharged cars?! :whhooo:

 

[jgorm]

Two words - 'mechanical empathy'.

. . . you find nitro frustrating?! . . . Your engine doesn't think much of you either . . . And people let you tune their supercharged cars?! :whhooo:

haha, you must be the guy all the girls love: This is a toy that I obviously don't care too much about. The blower for my mustang was well over 10x what this truck cost, so this is more of a disposable toy. I bought it because I figured I wouldn't have to wait for batteries to charge and could run it until I was bored. I lost interest and put money into real vehicles instead of this. It sat in my shed with a $2 broken starter pin for over 4 years because I didn't feel like fixing it again. I picked up a electric crawler and the RC bug in me decided to give it another shot.

If my next 2 trips out with this truck give me any trouble I'll put everything on craigslist for $50 and buy a savage flux. I'm a busy guy and I don't have time to screw with toys to make them work. When it's "play time" I want it to work. I don't mind tweaking the carb a bit, but when I spend 20 minutes trying to start it, it's time to move on. I know something is wrong and this is the last attempt to fix any issue. If you want to help out, I'll appreciate it. If you just want to bust by balls for not being a 'hardcore' nitro guy, go for it, doesn't bother me a bit

When I tune real cars, I use a computer and know if there is any aspect that is not working correctly within 1 minute of datalogging. My tunes don't change with the weather either I wont mess with carbs, or even cars older than 96 because there is always too many things wrong with them and I like OBDII Nitro cars are finicky, and there is little feedback. Having fuel in the crank case just seems like a terrible idea compared to injecting a fine mist on a burning hot intake valve, milliseconds before it opens up and sucks in the vaporized fuel. Imagine tuning some customers $20,000 engine by "pitch" :\

 

[2revo1maxx]

I can't imagine being a tuner and not realizing that the future is direct injection. It's already in some cars, and simplifies things tremendously.
Nitro engines are made to be simple, and they work very well for what they are.

 

[jgorm]

I can't imagine being a tuner and not realizing that the future is direct injection. It's already in some cars, and simplifies things tremendously.
Nitro engines are made to be simple, and they work very well for what they are.

When did I say anything about direct injection?:kookoo: I love direct injection, but it sure doesn't simplify anything. You still have the intake valve and now you need to control 1500-3000+psi psi of fuel pressure with multiple injections. The ability to inject the fuel even before the intake valve opens is the coolest thing because the piston cooling allows more timing and more power. As soon as you start modding cars with direct injection it gets REALLY complicated. Lots of cars with DI don't have any aftermarket fuel systems that allow more fuel for boost. You can push them to do a fair bit more than stock, but there is no way to double the boost without doing something to support the extra fuel flow. Fuel pumps cost way more, injectors cost WAY more, etc

 

[Extreme RC Mods]

I would think that with a stand alone you could control the DI injectors just the same no?

 

[jgorm]

Stand alone ecu's are for race cars that never see street duty Imo. I am also not aware of any stand alone that will control Di injectors especially with a piston cooling pre squirt. The base cost for a decent stand alone is about $2000 and it goes up quickly from there. That still leaves you with the issue of finding new injectors and a fuel pump that may not even exist. The stock ecu is far more sophisticated than any stand alone and you just need a flash tuner to be able to adjust it properly (and $5k+ in software)

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