- Joined
- May 28, 2001
- Messages
- 16,747
from another forum..
Speed Talk: Interviews - Racing Books - Racing Forum
Quote:
I've come to the conclusion that EFI is the only way to properly fuel a turbocharged, methanol burner. Coming from a background of only using mechanical, constant flow systems my main issue is understanding what input from the oxygen sensor means and how it tunes based on that.
Over the years, turbo charging has resulted in massive piles of scrap and tons of wasted dollars. It was only when the computerized ECU emerged that it became possible to use high boost turbocharging with any assurance of consistency and durability. The most successful of course was Porsche.
Reading the output from any oxygen sensor is more complicated than most folks think. The lambda signal is temperature dependent (unless corrected) and does not understand when combustion misfires occur.
Quote:
With a constant flow system, we run a datalogger and add fuel if EGT's get too high. The EGT's and spark plug color are the only true information we have to change a tune up by.
Fuel and EGTs have very little in common. EGTs respond primarily to ignition timing and combustion burn rate, and very poorly to fuel ratio.
With high quality fuels, spark plug color is no longer available as a tuning aid.
Quote:
Is there a quantity that goes with it or only some electronic signal change as the exhaust gas chemistry changes based on engine inputs and parameters that affect combustion?
Exhaust gas chemistry, or more properly, exhaust gas composition does have an effect on lambda values. Depending on the presence of certain exhaust components there can be a rich or lean shift; but the effect is small and not worth worrying about.
Quote:
I have also been told an O2 sensor reads data at 20Hz and an EGT thermocouple may only read at 5Hz.
A lambda sensor responds much faster than 20Hz but the response rate is dependent on the size of the step change. A small step change is read very quickly, a large step change takes longer. A response rate of 200Hz is more reasonable. However, the limiting factor is not the sensor but rather the signal processing required to convert millivolts (which is all that a lambda sensor can output) to some engineering units such as lambda or A/F ration. Be very, very wary of any system that claims to output A/F ratio as all are very innaccurate.
The response rate of a thermocouple is not measured in Hz but in full seconds. Most thermocouples being used are not much better than wall thermometers. To be useful, a very fine wire, open junction thermocouple must be used. But even that is slow and very inaccurate since the TC will output an average of the high and low temp pulses that it sees.
Do NOT tune engine fuel mixture by EGT; use quick response EGTs to help determine proper ignition timing balance between cylinders.
Do NOT tune engine fuel mixture by A/F ratio or lambda value. Use dyno measured engine torque values to determine proper A/F ratio. After optimum torque has been determined, the corresponding lambda value can be used as a control target.
Speed Talk: Interviews - Racing Books - Racing Forum
Quote:
I've come to the conclusion that EFI is the only way to properly fuel a turbocharged, methanol burner. Coming from a background of only using mechanical, constant flow systems my main issue is understanding what input from the oxygen sensor means and how it tunes based on that.
Over the years, turbo charging has resulted in massive piles of scrap and tons of wasted dollars. It was only when the computerized ECU emerged that it became possible to use high boost turbocharging with any assurance of consistency and durability. The most successful of course was Porsche.
Reading the output from any oxygen sensor is more complicated than most folks think. The lambda signal is temperature dependent (unless corrected) and does not understand when combustion misfires occur.
Quote:
With a constant flow system, we run a datalogger and add fuel if EGT's get too high. The EGT's and spark plug color are the only true information we have to change a tune up by.
Fuel and EGTs have very little in common. EGTs respond primarily to ignition timing and combustion burn rate, and very poorly to fuel ratio.
With high quality fuels, spark plug color is no longer available as a tuning aid.
Quote:
Is there a quantity that goes with it or only some electronic signal change as the exhaust gas chemistry changes based on engine inputs and parameters that affect combustion?
Exhaust gas chemistry, or more properly, exhaust gas composition does have an effect on lambda values. Depending on the presence of certain exhaust components there can be a rich or lean shift; but the effect is small and not worth worrying about.
Quote:
I have also been told an O2 sensor reads data at 20Hz and an EGT thermocouple may only read at 5Hz.
A lambda sensor responds much faster than 20Hz but the response rate is dependent on the size of the step change. A small step change is read very quickly, a large step change takes longer. A response rate of 200Hz is more reasonable. However, the limiting factor is not the sensor but rather the signal processing required to convert millivolts (which is all that a lambda sensor can output) to some engineering units such as lambda or A/F ration. Be very, very wary of any system that claims to output A/F ratio as all are very innaccurate.
The response rate of a thermocouple is not measured in Hz but in full seconds. Most thermocouples being used are not much better than wall thermometers. To be useful, a very fine wire, open junction thermocouple must be used. But even that is slow and very inaccurate since the TC will output an average of the high and low temp pulses that it sees.
Do NOT tune engine fuel mixture by EGT; use quick response EGTs to help determine proper ignition timing balance between cylinders.
Do NOT tune engine fuel mixture by A/F ratio or lambda value. Use dyno measured engine torque values to determine proper A/F ratio. After optimum torque has been determined, the corresponding lambda value can be used as a control target.
Seen a few do it to. Kinda funny but REAL expensive.
