Pyrometers
"The secret weapon when used correctly."
We have been racing 2-strokes for 40 years. Pyrometers are a beautiful thing. After years of working on any 2-stroke, the pyrometer gives you a look at an engines heartbeat. Numbers are relative but I will never run an engine without all cylinders monitored. Spark plug reading is the true magic to successful WFO mapping. We are still learning this art.
There seems to be a lot of confusion and misinformation about using exhaust gas temperatures to tune engines. Claims by many about being the best way to tune an engine must be qualified. The BEST way to tune a 2-stroke engine is on an engine dyno. PERIOD. Bottom line. No argument. After 40 years of doing this I can honestly say this is true. EGT’s are a good reference for where the engine made maximum torque and hp at all rpm’s at WFO. Once removed from the dyno, a similar air/fuel ratio can be established at a later date by dialing in the mixture to achieve the target EGT found on the dyno. If you work on a good dyno and have a properly calibrated ECU you should have to do nothing. It is really the AFR that is important not the EGT. Most engines will make maximum power at an AFR of between 12.0 and 13.5 to 1, however, the EGT may vary from 1100F to 1400F and is dependent on many factors such as timing, squish, fuel, compression and ceramics. On multi cylinder two-strokes, EGT’s are the only true way to balance all cylinders at idle besides cylinder combustion pressure so they are happy, ready to rip your head off when you smack the pedal.
It should be mentioned that the target EGT is valid only on the same engine configuration as was used on the dyno. A Merc 2.5 with one set up can see totally different numbers than a pro fuel OMC. Their optimum EGT's are most likely different. Never compare yours to theirs. Raising the compression ratio with no other changes will drop the EGT at the same AFR. Retarding the ignition timing will generally raise the EGT at the same AFR. One engine might make best power at 1250 degrees while a very similar engine might be happier at 1400. You can't guess at this or you are simply wasting your money on the instrumentation. When you don’t have a dyno, EGT’s are the only true look at cylinder pressure and temperature. Way better than nothing.
Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7-15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at about 1 lamda: about 14.7 to 1 for most purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1, EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT. I see this every dyno test.
You can sometimes feel a lean peak condition when driving as the mixture is hard to ignite and power will be down. Once the AFR gets lean at WOT, generally the engine will start to lean misfire (very hard to hear and feel in the seat) and usually ends up with a giant hole in the piston. On the dyno the torque simply falls off and you richen it up. In the boat when logging all EGT's and using GPS you can see performance changes better or worse based on time vs. distance helping you make a more educated guess to the next mapping change. Most good tuners always begin mapping from a known very rich initial setting and carefully lean until torque falls off slightly, then go back richer to the point of max torque. Note the EGT at this setting. Be aware that altitude, barometric pressure and ambient air temperature may affect this optimal temperature to some degree.
At DBR, we log all six cylinders and both collectors through the ECU or dash. In doing this while dyno testing it enables you to maximize the tune on all six cylinders resulting in more torque. More horsepower. When you are out on the water your dash can recall all temps to see if you are still in the ballpark. If not, a simple fuel trim on the dash can help keep things stay alive or increase performance. If you don’t have a dash you can download the ECU and get a good look at what just happened. Again a conservative approach to this leads to prolonged engine life.
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There seems to be a lot of confusion and misinformation about using exhaust gas temperatures to tune engines. Claims by many about being the best way to tune an engine must be qualified. The BEST way to tune a 2-stroke engine is on an engine dyno. PERIOD. Bottom line. No argument. After 40 years of doing this I can honestly say this is true. EGT’s are a good reference for where the engine made maximum torque and hp at all rpm’s at WFO. Once removed from the dyno, a similar air/fuel ratio can be established at a later date by dialing in the mixture to achieve the target EGT found on the dyno. If you work on a good dyno and have a properly calibrated ECU you should have to do nothing. It is really the AFR that is important not the EGT. Most engines will make maximum power at an AFR of between 12.0 and 13.5 to 1, however, the EGT may vary from 1100F to 1400F and is dependent on many factors such as timing, squish, fuel, compression and ceramics. On multi cylinder two-strokes, EGT’s are the only true way to balance all cylinders at idle besides cylinder combustion pressure so they are happy, ready to rip your head off when you smack the pedal.
It should be mentioned that the target EGT is valid only on the same engine configuration as was used on the dyno. A Merc 2.5 with one set up can see totally different numbers than a pro fuel OMC. Their optimum EGT's are most likely different. Never compare yours to theirs. Raising the compression ratio with no other changes will drop the EGT at the same AFR. Retarding the ignition timing will generally raise the EGT at the same AFR. One engine might make best power at 1250 degrees while a very similar engine might be happier at 1400. You can't guess at this or you are simply wasting your money on the instrumentation. When you don’t have a dyno, EGT’s are the only true look at cylinder pressure and temperature. Way better than nothing.
Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7-15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at about 1 lamda: about 14.7 to 1 for most purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1, EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT. I see this every dyno test.
You can sometimes feel a lean peak condition when driving as the mixture is hard to ignite and power will be down. Once the AFR gets lean at WOT, generally the engine will start to lean misfire (very hard to hear and feel in the seat) and usually ends up with a giant hole in the piston. On the dyno the torque simply falls off and you richen it up. In the boat when logging all EGT's and using GPS you can see performance changes better or worse based on time vs. distance helping you make a more educated guess to the next mapping change. Most good tuners always begin mapping from a known very rich initial setting and carefully lean until torque falls off slightly, then go back richer to the point of max torque. Note the EGT at this setting. Be aware that altitude, barometric pressure and ambient air temperature may affect this optimal temperature to some degree.
At DBR, we log all six cylinders and both collectors through the ECU or dash. In doing this while dyno testing it enables you to maximize the tune on all six cylinders resulting in more torque. More horsepower. When you are out on the water your dash can recall all temps to see if you are still in the ballpark. If not, a simple fuel trim on the dash can help keep things stay alive or increase performance. If you don’t have a dash you can download the ECU and get a good look at what just happened. Again a conservative approach to this leads to prolonged engine life.
Back To Technical 101
