3 into 1 pipe

[tz375]

Nothing like that. It's just another 3 into 1 pipe and a very modified 3 into 1.

Nitrous you say.. Hmmm.

I would use the 3 into 1 with the largest diameter collector and mid section. Cut it open and weld in three plates so the individual pressure waves have their own piece of the pie.

I don't think that would be very effective.

Large collector outlet creates a step which wrecks the pressure waves. If the collector is large enough, it acts as the end of the pipe and everything after that is just window dressing. Small hurts gas flow but increases density and gas velocity. So it's a compromise.

Inserting three dividers makes for three very small individual pipes in one shell. Novel but not very effective. three 90 mm belly sections would need to be 155mm to get the same area. A 120mm single pipe spilt into three sections makes them only the equivalent of 68mm each.

More to the point, all the angles would be wrong and it's the rate of change that creates pressure changes. If you would like to build that pipe I'd be interested to see how it works.

[tz375]

I thought i read somewhere that the middle cylinder has a slightly smaller displacement and that was the difference in jetting. Correct me if i am wrong but i am afraid of running the middle cylinder lean, heating it up and burning it down.

I read that somewhere too, but the bore and stroke is specified as 70mm and 64mm for all cylinders so don't believe it.

A stock GT750 is so underpowered and overcooled that you don't need to be concerned about the extra cooling that a richer main would provide to the center cylinder. Do you really want that extra unnecessary cooling at the expense of efficiency/horsepower? Add enough perfomance mods and maybe you'll want that extra cooling effect on the center cylinder.

And it's interesting that so many 750's burn holes in one or more pistons. The amount of cooling does not prevent or even do much to deter detonation meltdown. It can remove small amount of extra heat, but pistons will continue to melt in seconds - long before that extra heat can be soaked up and radiated to any meaningful degree. A cooling system is designed as a steady state device and is not able to deal with transient thermal spikes.

[ja-moo]

And it's interesting that so many 750's burn holes in one or more pistons. The amount of cooling does not prevent or even do much to deter detonation meltdown. It can remove small amount of extra heat, but pistons will continue to melt in seconds - long before that extra heat can be soaked up and radiated to any meaningful degree. A cooling system is designed as a steady state device and is not able to deal with transient thermal spikes.

It's the intake ports, they are so long the fuel just doesn't have the strength to stay in suspension and falls out...... (J/K)

[stcyr]

Many factors control what happens in the combustion chamber. I'm only stating what happens to the fuel and air due to to fact that a fully warmed up motor is going to have the most heat concentrated in the center of the mass. The ambient air (especially at speed) is going to cool the exposed parts but interior components are being more insulated. I won't speculate on the temperature differences but it exists and manufacturers have been adjusting A/F ratios for decades because of it. I mistakenly said "the hotter the intake gases are, the better they "atomize" the fuel" but I meant it's the greater amount of fuel that gets "vaporized" in the hotter tracts which displaces more air thus requiring less fuel. This is because vapor (a gas) volume is may times greater than fuel droplets (a liquid) so those carburetors with hotter tracts can't take in as much air as the cooler ones.

[tz375]

A properly designed (and tuned) engine will run the correct A/F ratio for best burn and still not overheat. But remember, an engine is most efficient when runing on the verge of destrucive detonation ............

I tend to disagree with that comment. it's an ages old myth that has led people up the garden path for years. Gordon Jennings did some work on that and many tuners claimed he was all wrong. he was right. Jet if right and get the right spark advance and the motor is not on the edge of destruction.

Of course a race motor is far more highly tuned and the distance from domination to disaster is diminished, but we have raced Yamaha and Aprilia twins for years at the front of the field without melting things very often.

Your previous post about better atomization was interesting and you realize that it was incorrect. Better atomization leads to more complete burn and hotter combustion chamber and hotter pipe temps leading to fitting LARGER main jets to cool it not the other way around.

You are correct that a warm inlet tract will flow less dense air and will in turn require less fuel to meet that magical A:F ratio, but the question is whether there is any evidence to suggest that the center cylinder has significantly higher temperature than the outer pair and the body of evidence seems to suggest that it's not the case - particularly on GT750 triples. If you have test data that refutes that, I would be very interested to see it. Our CHT and EGT tests suggest that's not the case, but I have not tried calibrated thermocouple in the inlets to test the temperature variations across all three at high speed.

[stcyr]

A properly designed (and tuned) engine will run the correct A/F ratio for best burn and still not overheat. But remember, an engine is most efficient when runing on the verge of destrucive detonation ............

I tend to disagree with that comment. it's an ages old myth that has led people up the garden path for years. Gordon Jennings did some work on that and many tuners claimed he was all wrong. he was right. Jet if right and get the right spark advance and the motor is not on the edge of destruction.

Of course a race motor is far more highly tuned and the distance from domination to disaster is diminished, but we have raced Yamaha and Aprilia twins for years at the front of the field without melting things very often.

Your previous post about better atomization was interesting and you realize that it was incorrect. Better atomization leads to more complete burn and hotter combustion chamber and hotter pipe temps leading to fitting LARGER main jets to cool it not the other way around.

You are correct that a warm inlet tract will flow less dense air and will in turn require less fuel to meet that magical A:F ratio, but the question is whether there is any evidence to suggest that the center cylinder has significantly higher temperature than the outer pair and the body of evidence seems to suggest that it's not the case - particularly on GT750 triples. If you have test data that refutes that, I would be very interested to see it. Our CHT and EGT tests suggest that's not the case, but I have not tried calibrated thermocouple in the inlets to test the temperature variations across all three at high speed.

On the verge of destructive detonation is not destructive and I'm only saying you get the most power per fuel consumed. Of course, you don't want to go racing that way. We back off the timing a bit and waste a little fuel to keep a good margin of safety. A plug check tells you how hot things are getting and you jet accordingly. Combustion chamber temperature and proper A/F ratio are directly related. I'm not sure what you're disagreeing about.

I corrected what I posted about fuel atomization. I meant to say "vaporize" which is totally different as fuel vapor has a much larger volume than atomized fuel (droplets). Vapor displaces air. Less air needs less fuel.

As I mentioned before, on V-twins, V-fours, triples and even inline fours, in areas of more heat, the carbs are jetted leaner. Again, I asked our service rep, he made a call and told me the reason. I can't find where I first read it but it was specifically about triples.

[stcyr]

I don't think that would be very effective.

Inserting three dividers makes for three very small individual pipes in one shell. Novel but not very effective. three 90 mm belly sections would need to be 155mm to get the same area. A 120mm single pipe spilt into three sections makes them only the equivalent of 68mm each.

More to the point, all the angles would be wrong and it's the rate of change that creates pressure changes. If you would like to build that pipe I'd be interested to see how it works.

I take it there is no 3 into 1 with a sufficiently large enough collector to separate into separate chambers. Oh well, it would be nice if it did. You're right, it won't be "very" effective but it will still be effective. It certainly won't be peaky.

Back in the day, I played around with chambers on model aircraft and even rolled my own from fiberglass and hi-temp epoxy. Very easy to make changes and get good solid results. The physics are all the same. The effectiveness is proportional to the angle of taper. An angle of 0 will obviously have no effect but anything greater will have some effect but, of course, unless the angle is great enough, you probably won't notice. 1/2 the angle of any given pipe will be roughly half as effective. My proposed mod would still have 1/3 effectiveness just like the original but the advantage would be that the other two cylinder's pressure waves won't be interferring. The typical 3 into 1 wastes 2/3 of it's returning positive pressure wave and half of that is pushing back the spent exhaust that's supposed to be leaving the next cylinder in sequence! Reminds me of a hit and miss engine.

[stcyr]

tz375, you seem like a pretty smart feller. Search for this document:

IC_Engine_Fuels_1_Volatility_characteristics.doc

Look under "Normal Running" and keep in mind that it's refering to fuel characteristics, NOT engine temperatures.

Notice the last sentence "Manifold design, length, hot spot etc are important."

Now, replace the fuel characteristics in each statement with manifold temperatures and it would read as such:

Normal Running

Low manifold temperature (low volatility) causes less fuel to evaporate – gives poor distribution. Requires over-fuelling. Gives more power but fuel consumption is high.

High manifold temperature (high volatility) gives better mixing; may even superheat the fuel vapor. But vapor displaces the air and reduces volumetric efficiency and gives less power. This is similar to using gaseous fuel.

Manifold design, length, hot spot etc are important.

They are still perfectly valid statements based on the original wording!

If you have test data that refutes that, I would be very interested to see it. Our CHT and EGT tests suggest that's not the case, but I have not tried calibrated thermocouple in the inlets to test the temperature variations across all three at high speed.

I don't disagree that EGT would be lower for the middle. It would make sense that besides diplacing some of the air, the greater amount of fuel vapor being created along it's journey probably aids in cooling the mix through the evaporation process.

I would love it if you could measure temps at the spigots and maybe a little further downstream, then swap the probes and measure again for accuracy. You may have to measure at the walls or floors where the difference is most likely be.

[ja-moo]

I still think you are splitting hairs. I seriouls doubt a few degrees difference is going to cause any need for different jetting. If it's that much.......

[tz375]

On the verge of destructive detonation is not destructive and I'm only saying you get the most power per fuel consumed. Of course, you don't want to go racing that way. We back off the timing a bit and waste a little fuel to keep a good margin of safety. A plug check tells you how hot things are getting and you jet accordingly. Combustion chamber temperature and proper A/F ratio are directly related. I'm not sure what you're disagreeing about.

We all understand that A:F is related to combustion chamber temperature though it is far from a linear relationship and that is not the only variable in the equation.

We don't set up an engine at the edge of detonation and then choose to waste some fuel as you put it. We jet and time the engine so that it operates at peak efficiency. No more no less.

I corrected what I posted about fuel atomization. I meant to say "vaporize" which is totally different as fuel vapor has a much larger volume than atomized fuel (droplets). Vapor displaces air. Less air needs less fuel.

That really has little or nothing to do with it. It's about what burns in the chamber. Smaller droplets burn faster because they have a greater ratio of surface area to droplet size. Fuel burns on the outer surface of a droplet, so more surface area means more will tend to burn within a given time. And for a given mass of fuel, the smaller the droplets the lower the A:F ratio (richer) and lower unburned HC levels.

As I mentioned before, on V-twins, V-fours, triples and even inline fours, in areas of more heat, the carbs are jetted leaner. Again, I asked our service rep, he made a call and told me the reason. I can't find where I first read it but it was specifically about triples.

And who did your service rep call for his "lifeline"? It is entirely possible that someone jets a hot cylinder leaner but jet it richer and cool the intake mixture and the intake duct seems to make more sense. Remember the old latent heat of vaporization?

[tz375]

I take it there is no 3 into 1 with a sufficiently large enough collector to separate into separate chambers. Oh well, it would be nice if it did. You're right, it won't be "very" effective but it will still be effective. It certainly won't be peaky.

Why? What is the rationale behind that comment?

The physics are all the same. The effectiveness is proportional to the angle of taper. An angle of 0 will obviously have no effect but anything greater will have some effect but, of course, unless the angle is great enough, you probably won't notice. 1/2 the angle of any given pipe will be roughly half as effective. My proposed mod would still have 1/3 effectiveness just like the original but the advantage would be that the other two cylinder's pressure waves won't be interferring. The typical 3 into 1 wastes 2/3 of it's returning positive pressure wave and half of that is pushing back the spent exhaust that's supposed to be leaving the next cylinder in sequence! Reminds me of a hit and miss engine.

Again, not completely correct. For a start, 0 degrees (parallel wall) has significant drag which reduces the movement of a pressure wave as well as the flow of gas.

A large collector is the wrong thing in a two stroke because it creates a step change and that generates a shock wave type effect which interferes wih all wavbe activity past that point, so the sucking wave is much weaker and the stuffing wave is also much weaker. Obviously splitting the wave into 3 ducts also reduces the amplitude and then a long parallel header basically finishes it off. That's one reason that 3 into 1 pipes are as bad as they are and not any worse.

As for your rather naive idea of splitting a pipe longitudinally, you forgot that not only would each pipe be only 1 third of the existing area but two sides would be flat ie no taper. Not going to be very effective as you would have realized if you had thought it through.

[tz375]

tz375, you seem like a pretty smart feller. Search for this document:

IC_Engine_Fuels_1_Volatility_characteristics.doc

Thanks but you can keep the sarcasm.

AFAIK that "article" is part of a basic course on IC engines and is trying to explain to beginners that a really hot intake is different to a cold one. That's a pretty good course BTW form what I scanned so far.

I don't disagree that EGT would be lower for the middle.

Why do you say that? what is the rationale? EGT is impacted by a number of things including combustion conditions and fuel droplets. Large droplets lead to high EGT because the fuel is still burning in the pipe. There are too many variables to make that sort of blanket statement.

I would love it if you could measure temps at the spigots and maybe a little further downstream, then swap the probes and measure again for accuracy. You may have to measure at the walls or floors where the difference is most likely be.

Its not relevant. Check pressure and velocity gradients across the cross section of a port and different points and it will be obvious why that is so.

Besides, as JA already noted, the temperature differences across intake ports is so small that it's not a significant factor.

Good day to you sir.

[stcyr]

Thanks but you can keep the sarcasm.

What's that supposed to mean?

Why do you say that? what is the rationale? EGT is impacted by a number of things including combustion conditions and fuel droplets. Large droplets lead to high EGT because the fuel is still burning in the pipe. There are too many variables to make that sort of blanket statement.

I said "I DON'T DISAGREE with you"

Good day to you sir.

Sorry if I said something offensive. No disrespect intended.

[Suzukidave]

This program claims to aid in design of 3 into 1 chambers ? http://www.buildandclick.com/" onclick="window.open(this.href);return false;

[tz375]

Thanks Dave,
I bought that one and to be sure it's cheap. The pipe it comes up with is the same single or triple and the only difference is tailpipe diameter.

No collector suggestions or anything else useful unfortunately. I also found that MOTA isn't wild about the pipes shapes it comes up with which was interesting.

It was worthwhile trying it and not too expensive a learning curve, but it's worth what I paid for it I guess.