2015 TM MX 125 engine in a 125 cm^3 kart

[gridslammer]

Hi, first post here would of thought it to be for cars on our snowmobile we run the EGT roughly about 100mm from piston, it usually ends up being in the header section. EGT temp should be in general lower than aluminum will melt, and should be only for prototyping not a tuning device. O2 is usually put in the center section it will get you close. The best way is on the dyno and check BSFC and read you plugs and wash on piston. Pipe pressure can be a great tool for developing pipes via stinger length and size and is usually measured in the belly also.

[brentry]

X2 on what vannick said. I have had wobbly help me design some of my stuff.

[David Redszus]

Hi, first post here would of thought it to be for cars on our snowmobile we run the EGT roughly about 100mm from piston, it usually ends up being in the header section. EGT temp should be in general lower than aluminum will melt, and should be only for prototyping not a tuning device. O2 is usually put in the center section it will get you close. The best way is on the dyno and check BSFC and read you plugs and wash on piston. Pipe pressure can be a great tool for developing pipes via stinger length and size and is usually measured in the belly also.

In my opinion, the location of the EGT in the pipe is subject to incorrect readings. The header section was used in the early days when closed end thermocouples were used. Their very slow response time required their location to be very close to the port. This no longer applies when an open tip sensor is used.

An EGT does NOT indicate the true exhaust gas temperature at all. The gas pulse temperatures will vary from about 2300F to 400F within one cycle. The TC reflects a time weighted average, not a mass weighted average. As a result we might see EGT values of about 1075F to 1250F, but neither temperature is correct. If the sensor is located in a collector, the indicated temperatures will be even higher, but still wrong.

If three sensors are installed; in the header, mid-section and in front of the stinger, we will record three different temperatures. Which temperature should be used for correct pipe tuning?

When attempting a tuned pipe design, an assumption is made regarding probable pipe temperature so that the pipe lengths (by section) can be calculated to produce the proper negative and positive pipe pressures, at the critical crank angles.

The problem of tuning a two stroke is complicated due to the fact that optimum combustion will produce a certain EGT.
But optimum scavenging requires a different temperature to make the pipe work properly. We wind up with a tradeoff; combustion vs scavenging, neither being optimized.

EGT values are greatly affected by ignition timing; along with rpm, port height and time at full throttle.
I have yet to meet a two stroke engine tuner who knows what the optimum EGT reading should be for a given pipe/engine combination, due to the complexity of the process. To make matters even worse, what we see on the dyno is not replicated on the track.

But we keep trying. The new computer controlled, fuel injected two stroke engines bring a new set of complexities to add to the confusion.

[gridslammer]

I agree, there are so many variables when developing a pipe elevation and ambient temp change a lot what works at 500ft will be a total dog a 6000ft!
Pipes are also fuel mixture dependent, to rich and gas temp drops lengthing the reflect of wave.

There is some awesome things happening with modern 2 stroke design using combustion chamber and timing to Get around the ecm And not have the computer Retard the timing but still retain very efficient combustion.



Awesome discussion David!

[GRTfast]

In my opinion, the location of the EGT in the pipe is subject to incorrect readings. The header section was used in the early days when closed end thermocouples were used. Their very slow response time required their location to be very close to the port. This no longer applies when an open tip sensor is used.

An EGT does NOT indicate the true exhaust gas temperature at all. The gas pulse temperatures will vary from about 2300F to 400F within one cycle. The TC reflects a time weighted average, not a mass weighted average. As a result we might see EGT values of about 1075F to 1250F, but neither temperature is correct. If the sensor is located in a collector, the indicated temperatures will be even higher, but still wrong.

If three sensors are installed; in the header, mid-section and in front of the stinger, we will record three different temperatures. Which temperature should be used for correct pipe tuning?

When attempting a tuned pipe design, an assumption is made regarding probable pipe temperature so that the pipe lengths (by section) can be calculated to produce the proper negative and positive pipe pressures, at the critical crank angles.

The problem of tuning a two stroke is complicated due to the fact that optimum combustion will produce a certain EGT.
But optimum scavenging requires a different temperature to make the pipe work properly. We wind up with a tradeoff; combustion vs scavenging, neither being optimized.

EGT values are greatly affected by ignition timing; along with rpm, port height and time at full throttle.
I have yet to meet a two stroke engine tuner who knows what the optimum EGT reading should be for a given pipe/engine combination, due to the complexity of the process. To make matters even worse, what we see on the dyno is not replicated on the track.

But we keep trying. The new computer controlled, fuel injected two stroke engines bring a new set of complexities to add to the confusion.

Yes finding that balance between optimized combustion events and getting EGTs that make the pipe work is tedious in my experience. The old variable length "slippy" pipes uncoupled these parameters somewhat. I can imagine a modern version that is servo controlled. Obviously not legal in most or all sanctioning bodies these days.

[David Redszus]

In my opinion, the location of the EGT in the pipe is subject to incorrect readings. The header section was used in the early days when closed end thermocouples were used. Their very slow response time required their location to be very close to the port. This no longer applies when an open tip sensor is used.

An EGT does NOT indicate the true exhaust gas temperature at all. The gas pulse temperatures will vary from about 2300F to 400F within one cycle. The TC reflects a time weighted average, not a mass weighted average. As a result we might see EGT values of about 1075F to 1250F, but neither temperature is correct. If the sensor is located in a collector, the indicated temperatures will be even higher, but still wrong.

If three sensors are installed; in the header, mid-section and in front of the stinger, we will record three different temperatures. Which temperature should be used for correct pipe tuning?

When attempting a tuned pipe design, an assumption is made regarding probable pipe temperature so that the pipe lengths (by section) can be calculated to produce the proper negative and positive pipe pressures, at the critical crank angles.

The problem of tuning a two stroke is complicated due to the fact that optimum combustion will produce a certain EGT.
But optimum scavenging requires a different temperature to make the pipe work properly. We wind up with a tradeoff; combustion vs scavenging, neither being optimized.

EGT values are greatly affected by ignition timing; along with rpm, port height and time at full throttle.
I have yet to meet a two stroke engine tuner who knows what the optimum EGT reading should be for a given pipe/engine combination, due to the complexity of the process. To make matters even worse, what we see on the dyno is not replicated on the track.

But we keep trying. The new computer controlled, fuel injected two stroke engines bring a new set of complexities to add to the confusion.

Yes finding that balance between optimized combustion events and getting EGTs that make the pipe work is tedious in my experience. The old variable length "slippy" pipes uncoupled these parameters somewhat. I can imagine a modern version that is servo controlled. Obviously not legal in most or all sanctioning bodies these days.

A few years ago, SkiDoo used an EGT sensor that fed data into the ECU. As the EGT values changed with operating conditions, the ECU would retard or advance the ignition timing to bring the pipe back to a pre-determined temperature.
When EGTs were very cold, the timing would be retarded so much that the combustion process was impacted.
It often ran like shit. But then, it may have been that tuners modified the porting without any knowledge of the possible effect on ECU temperature response.

If we invade the realm of computerized engine mapping, we must be sure to correctly optimize every map in the system.
If we only knew what they were and what they did.

[brentry]

New pipes need to be ran and get a coating of suit on them. Seen that before. Old pipe and new pipe ,big difference on dyno. And yes they where exactly the same pipe. Same stinger diameter The suit acts like insulation and changes the pipe temp. Not saying this is always the case. But it can happen. Goes on and on. Thats part of the reason i started making pipes.