Hi guys,have you ever think that Nitro eng doesn't have a timing device,but there is no problem of detonation,why?

If you run glow fuel with more than 20% nitro you will need to change the timing. I think timing and fuel grade has been taken into account during design of the engine, and this is why different engines perform better with different amounts of nitro (from 0% up to 20%).

The engine is designed to combust at the correct point (near TDC). Increase your nitromethane content too high or use a really hot plug (without shimming the head) and you could get pre-ignition or detonation. The process of compressing the mixture heats it up. Near the top of the stroke the heated mixture is ignited by the glow plug. The glow plug stays hot because it is getting heated through catalytic reaction because of the chemical reaction between the platinum element and the methanol in the fuel. Like I mentioned, throw off the heat range too much (higher nitromethane content/hotter plug - without increasing cylinder volume) and you can experience pre-ignition or detonation issues.

The timing on a 2 stroke glow engine is done with the placement of the intake and exhaust porting, or in the case of a rotary valve engine, the placement of the opening in the disk, or the hole in the crankshaft. The glow plug actually never goes out, unless it burns out, and then the engine gets real quiet. With a 4 stroke, if you allow the mixture to become too lean, the engine will backfire and normally will toss the prop and spinner into the high weeds, where the prop gremlins will spirit it away never to be seen again. With the 4 stroke engine, the camshaft lobe placement serves to set the timing of the engine. Ignition is constant, and when the engine compresses the fuel and air mixture to the correct amount, ignition occurrs. It ain't rocket science, but it works pretty well. This system is one reason that the glow engines are so messy to operate. consider this, a gasoline ignition engine that uses spark timing burns much less fuel for the same displacement than does the glow engine, and is far less messy, even though the oil content in the mixture is about the same. The glow engine is not very economical to operate in terms of fuel efficiency. Back when I was into Formula 1 racing, we used to run the Moki 3.6 twin on ignition and with Glow fuel. This was done in order to gain the maximum RPM and power from the engine, and to do that requires a more lean mixture. The NitroMethane percentage was bumped way up, and I have even seen a touch of Hydrazine added (often leading to the catastrophic failure of the rotating mass).

Bill, AMA 4720
WACO Brotherhood #1

Edited for punctuation

Bill. I saw my first glow fuel ignition enginge Saturday. It was a converted O.S. 300 Twin. It really got my curiosity up. I started a thread a couple days back on the topic of ignition and glow fuel. Really interesting.

One thing that susprises me is the top end performance imporvement with it. What has turned up so far is that it imporves idle and slow speed and works best with FAI fuel. Quite different than your comments. I'm interested in hearing more. Oh yes, these were for a four stroke.

Don

Don't own a gas engine (on the market though..) from what i read gas engiens use different ratios, 32:1 (break in) 50:1 and 100:1 seem to be the most common. so that ranges from 3 to 1% oil, can glow engines this? if so why in the world are we running about 18% oil in our glow engines

It has more to do with the improvements in engine machining, and metalugerical advances than anything else. It used to be common to run 20 to 25% in ignition 2 strokes. Back when I was first starting to run model engines, we ran White gas (coleman fuel) mixed with 70 wt. oil. The lifespan of some of those engines were measured in minutes. Some of the slag engines would wear out in a short time.

Bill, AMA 4720
WACO Brotherhood #1

Needle bearings on the rod ends. We don't have them on glow engines and they do on the Gas engines.

I remember when the standard mix for 2 cycle engines, IE outboard motors, was around 10 to 15 to 1 gas to oil. Then they redesigned the engines to the point that they would live on 40 to 1. Needle bearings and better oil allowed this. Oil won't do it on it's own

Don

Fuel injection is a timed event for a reciprocating engine. The ignition is still always there, but the fuel charge can be made more precise with the injection than with a carb. Same reason that a 350 chevy gets better fuel economy with fuel injection than it did with a Rochester Carb.

Bill, AMA 4720
WACO Brotherhood #1

I know why, i was just wondering if he could explain 1- how to run a glow engine on 32:1 or less oil or WHY you'd run a gas engiens on 18% oil...

Steven

Bill, This is very true. I've got an old 1991 Lexus with a big FI V8. I'll bet it would turn the 1/4 in around 15seconds. Not bad for a 4 door sedan. The thing gets 26mpg on the highway and around 23 in town and I don't baby it. Quite a difference From the rochester Carb days, or even from the early Vett FI days.

Don

When you adjust the fuel mixture with the needle valve, you are effectively fine tuning the ignition advance. With spark ignition, the spark fires at a very specific point, usually around 25 to 30 degrees before the piston reaches the top. With glow ignition, the exact point of fuel ignition is determined by the compression ratio, hotness of the glow plug, and the richness of the fuel air mixture. A lean mixture fires sooner than a rich mixture. That's why there is such a drastic increase in rpm when the mixture is leaned just a few clicks, not only is the mixture being leaned, but the ignition timing is being advanced also.
The fixed spark timing of our cars and motorcycles is one of the main reasons we don't have to carefully readjust the needle in the carb every time the weather changes.

Steven. the glow engines have oilite/bronze bushings in the rod. They require a good supply of oil for lubercation. The ball bearings on the crank can run with a lot less oil that the bronze bushings can. With the gas engines, and they are usually a bit larger than the glow engines, they have the room for the needle bearings. Now the oil requirements is greatly reduced.

You can run run your glow engine on a 40 to 1 mix, untll the rod go out. You can run a gasser at 18% oil also, but it won't run it's best. They have diesel engines that take all their lube from the diesel fuel. A few years back I saw where a Japanese company made an all ceramic engine that didn't use any oil. What's the old saying? Different strokes for different folks. What works for one wonn't for the other.

Don

There are alot of guys in the nitro car market that mess with the timing on their engines, but not sure exactly how they do it. I have seen them port out the crank alot too.

Most of the car guys alter the crank timing and port timings, polish the crankshaft and cut extra flow channels in them. All of this can result in a 20-50% boost to the imagination .

I've got a friend that's had his 63 Vette with the old Rochester injection system since 1965. He gets fuel economy in the mid-20's even with that old system.

And most of them would have been better off just buying fuel, finding a good racing coach, and practicing instead. But, we all seem to think that the only reason the other person won was because he had better equipment.

We are getting way off topic, but it's fun stuff.

First, collor me green. I always wanted a FI vette. I owned two vetts, a 59 with a 350hp 327 and the what I though was a 62 but turned out to be a 61 trickeed out. I never got that one restored.

In the 60's, the there was an intersting thing going on. The cars they were advertising as their economy cars were getting way less gas milage than the muscel cars. I had a 61 Pontaic Catalina with the 348 HP tri power, four on the floor, 390 positraction, etc. My first "new" car. Cost me $2900.00 and a 47 Plymouth coupe for trade. That car would get near 18 mpg even the way I drove it at 19 years old. The same car with the Econnomy package was hard press to get 12 MPG. But at $0.25 a gallon, who cared, that was only 6 minutes pay.

Don

My cousin had a black 59 Vette. He's never been without a Vette since.
And a guy down the street from me had a 66 Dodge/Hemi 4-speed 6 MPG [:@] in good weeks.

Back on topic, the glowplug is a wonderfully simple device with very complex behaviors.

I believe the OP was asking about ignition timing, not port timing (valve timing in 4 strokes), which is fixed on most engines, barring vvti/vtec etc. advanced engines.

In a gasoline engine, the timing at idle is usually 10 or so degrees BTDC, while at full throttle it will be closer to 30 degrees BTDC. This allows time for the gasoline to burn before the compression is released in the power stroke, allowing complete combustion and efficient, powerful operation. This can be accomplished with manual advance (as in early IC model engines), with mechanical advance, like in early automotive engines, or with electronic advance, as in most modern gassers, be they in cars, chainsaws, or models.

In a glow engine, there seems to be no advance control. There is, tho! And it's all in that little coil of wire in the glowplug. Timing is retarded by colder plugs, by lower compression, by lower nitro content, rich needle settings and by lower throttle settings (ie. lower effective compression). This is because the plug element, under these conditions, sees either less fuel in contact with it (lower compression and throttle settings), or insufficient oxygen to allow it to work efficiently coupled with being doused by fuel droplets (rich needles), or by the lower nitro. Any of these will cause the element to catalyze less efficiently, it cools a bit, and the ignition occurs later in the stroke.

Conversely, if the mixture is leaned, or the throttle opened, or the compression raised, or the nitro content raised, the plug will burn hotter, the charge will ignite earlier, and the timing is effectively advanced.

In practice, if the same plug is to be used, and optimum mixtures are set (as they should always be), an engine's ignition timing can be tuned by the user by changing the nitro content of the fuel, or by adding or subtracting head shims to change the engine's compression ratio. Most engines today are shipped with compression ratios suited to nitro contents in the 5-15% range, and will run pretty well within that range. Some, notably european engines and racing engines, are designed to run on 0 nitro fuel. They typically are higher compression than the common US market sport engines. Running 15% nitro in them will often lead to pre-ignition, unless extra head shims are used (lowering compression, and thus retarding the ignition timing).

Tuning engines with compression changes isn't really common in North America outside of a few specialized facets: 1/2a engines (think cox, Norvel, CS etc.), and competition engines, where that last bit of performance is very important.

Hope that explains stuff a bit.

J

This is my baby! '65 292, roush heads, compcams, MSD, Hurst 4-speed, actually does well with the stock gearing on the highway, but I don't have exact numbers. It gulps fuel when I tell it to. Sorry, it's off topic but I had to show it.