[2 stroke]exhaust temperature

Nombre de messages : 38 Localisation : valencia Date d'inscription : 03/03/2015

I am working on improving my 80cc engine, I'm making myself exhausts, I bought a temperature sensor koso my surprise is that only managed to rise to 350 degrees temperature, is this possible? normal is 500 or 600 degrees, this means that a large amount of fresh gases escape through the exhaust and lower the temperature? maybe have little compression in the cylinder head? ...

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ktuningteam a écrit:: I bought a temperature sensor koso my surprise is that only managed to rise to 350 degrees temperature, is this possible? normal is 500 or 600 degrees, this means that a large amount of fresh gases escape through the exhaust and lower the temperature? maybe have little compression in the cylinder head?

With your sensor so close to the cylinder there is a real chance that it is touched by washed-through fresh mixture that subsequently gets pushed back into the cylinder. You can put it another 100 mm further away from the cylinder and see if that makes a difference. You can also experiment with a later ignition timing; that will certainly raise the exhaust gas temperature. A leaner mixture will do that too, but retarding the ignition is safe, leaning the mixture is not.

Nombre de messages : 38 Localisation : valencia Date d'inscription : 03/03/2015

thanks for your advice, I have been inspired by his "FOS concept" and Gordon Blair studies, for pipes design. I have put a sensor to 100mm from the piston and another near the end, and the maximum difference is 50 ° between the first and second. So my question is, should I look for the highest temperature? what would be the optimum for a motor gp? would not be a good choice to design a shorter pipe calculated this temperature?

ktuningteam a écrit:: thanks for your advice, I have been inspired by his "FOS concept" and Gordon Blair studies, for pipes design. I have put a sensor to 100 mm from the piston and another near the end, and the maximum difference is 50 ° between the first and second. So my question is, should I look for the highest temperature? what would be the optimum for a motor gp? would not be a good choice to design a shorter pipe calculated this temperature?

As I wrote, retarding the ignition and leaning the mixture will raise the exhaust gas temperature, but that is not what we want; we want power.The optimum temp for a racing engine will be around 600° but you can only expect to reach that when every aspect of your engine is perfect.
Designing a pipe for the temperature you have actually measured is always a good idea; you will learn from it.

Nombre de messages : 1 Localisation : Germany Date d'inscription : 27/08/2014

could it be that your egt probe is rather short and the tip doesn't reach to the center of the pipe?

Nombre de messages : 38 Localisation : valencia Date d'inscription : 03/03/2015

It is not very long but reaches far enough to take a temperature, plus those achieved rpm and exhaust length are correct, so I take it for good measure. We are now testing different forms of head and compression, and we hope that this will improve the power and resulting temperature rise.

Nombre de messages : 38 Localisation : valencia Date d'inscription : 03/03/2015

Frits, Thiel , help!! you think of this cylinder head design?It is to 80cc, and a compression of approximately 14: 1 (real 7: 1 from closing the exhaust) squiss between 0.6 and 0.7.

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Nombre de messages : 38 Localisation : valencia Date d'inscription : 03/03/2015

finished head, now try the dyno

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Hi guys,
Find here some pics from a 125cc engine, head volume is 11cc, using a squish about 1mm, squish angle 4,5 degree parallel to the piston. I have light detonation but without any problem. I can't find the solution in carburation to stop this at 100%.

Any advices will be apreciated.

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Stinger may be too small , that's nothing close to safe deto !
Your ring will get stuck and no more compression quite fast ....

Seb4LO a écrit:: Stinger may be too small , that's nothing close to safe deto !
Your ring will get stuck and no more compression quite fast ....

Thx, unfortunaly the hole exhaust is fixed by homologation, not possible to change the stinger size.
Also the EGT seems not beeing to high with 630°C with that carb configuration, usually 680°C is used.
Should i try a narrower squish near 0,70mm?

If you have deto at 1mm , 0.7mm squish will go boom faster

Fuel used
Volume with or without plug hole

Seb4LO a écrit:: If you have deto at 1mm , 0.7mm squish will go boom faster

Fuel used
Volume with or without plug hole

Normal fuel 98 octane
Combustion chamber 11cc measured with plug insert 13cc
Not sure, like Jan use to say " where nothing is, nothing can detonate"
Thx

When you say "narrower squish," by "narrower" are you saying, "less clearance between the piston crown and the squishband"? Assuming that's what you mean, 1mm seems like slightly excessive clearance, although 0.7mm might be getting a little too tight . . . I'd think 0.9mm would be safe, and help with detonation (other things being equal), and if your engine allows 0.8mm without the piston hitting (incl. after the engine has run a few long races and loosened up), that should be better yet.

On the engines I worked on long ago, the crankshaft design and support and other factors discouraged us from going any tighter than 0.9mm, even though those engines didn't rev as high as modern ones.

Vortex a écrit:: Find here some pics from a 125cc engine, head volume is 11cc, using a squish about 1mm, squish angle 4,5 degree parallel to the piston. I have light detonation but without any problem. I can't find the solution in carburation to stop this at 100%.

Maybe the solution is not in the carburation but in the ignition. As you mentioned homologation, I assume you are talking about a KZ kart engine which means that both the compression ratio and the exhaust restriction are safe.
A 0,7 mm squish gap should be OK as well, and the pictures of your piston show a fairly rich mixture (or a bad premix oil).
You may want to retard the ignition timing by maybe 3° and see if it helps. That way you may loose some low-down power but it will give you an indication of where to look for a solution.
There is also the possibility that the ignition timing advances uncontrollably when the ignition unit gets hot. In that case you should change the unit.

Frits Overmars a écrit:

Vortex a écrit:: Find here some pics from a 125cc engine, head volume is 11cc, using a squish about 1mm, squish angle 4,5 degree parallel to the piston. I have light detonation but without any problem. I can't find the solution in carburation to stop this at 100%.

Maybe the solution is not in the carburation but in the ignition. As you mentioned homologation, I assume you are talking about a KZ kart engine which means that both the compression ratio and the exhaust restriction are safe.
A 0,7 mm squish gap should be OK as well, and the pictures of your piston show a fairly rich mixture (or a bad premix oil).
You may want to retard the ignition timing by maybe 3° and see if it helps. That way you may loose some low-down power but it will give you an indication of where to look for a solution.
There is also the possibility that the ignition timing advances uncontrollably when the ignition unit gets hot. In that case you should change the unit.

Thx Frits,
Yes, you are right it is a KZ Kart engine.
I will try to retard, now i use 16,5°-17° btdc

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