Need info on a pyrometer .
02-09-2003, 12:01 PM
#12
1.0 BAR
Join Date: Dec 2002
Posts: 296
Re:Need info on a pyrometer .
if you want to tune use a wideband.... here is a little write up one of my friends did for the FJO wideband company about it.. sorry if its long but to me it explains why...
Why not tune AFR based upon EGT (Exhaust Gas Temperature)?
You can only get a general idea of AFR based upon EGT IF, and only if, you have correlated your car's AFR with its EGT under a given set of conditions. And even at that, you can only get a general idea of the AFR. You can not tell with accuracy just where the AFR is. Perhaps at best you can get within a full point or so, and that's not very close.
Here's an example of the variation in EGTs from car to car. Several months ago I helped tune 3 single turbo Supras on the same day on the same dyno using the highly regarded Horiba wideband O2 system. All 3 cars were tuned to about 11.4:1 AFR across the boost and RPM range. Peak EGTs ranged from 770 to about 880 C on the various cars according to the GReddy gauges (one car's EGT at 770, one at 790, and one at 880). All 3 had GReddy EGT gauges but with identical probes mounted in different places. The coolest EGT reading was from a probe mounted in the #6 runner, the middle temp one was mounted in the front passenger corner of the collector, and the hottest reading came from a probe in the center of the collector directly under the turbine inlet. This in itself proves that EGT readings can not be trusted because there is no physical way that the EGTs in the collector are actually hotter than those in the runner close to the combustion chamber, but this is a function of heat-sink effect happening with the probe and we won't get into that concept here.
If one were attempting to tune the above cars based upon EGT readings, what would he have done with those 3 cars? Conventional wisdom says that EGTs of up to 900 C are allowable prior to the turbo on most turbo motors. If the 770 C car were leaned out to approach 900 C, the AFR would have been in the 15:1 range! That could prove disastrous for an engine running boost. A similar circumstance exists for the car indicating 790 C. What about the one with the 880 C readings? Would that car be dialed back a bit richer because the 880 C readings are approaching the generally accepted MAXIMUM of 900 C? If so, that car would probably end up in the 10.5:1 range and needlessly sacrifice power.
Perhaps the biggest downfall of EGT as an AFR tuning tool is the fact that there is no possible way for an EGT monitor to react quickly enough to spot lean and rich spots in the RPM curve. Most engines will exhibit an AFR curve that varies a good bit throughout the RPM and boost range. At best, EGTs can only give you some indication of peak temperatures. It is not possible for them to point up a dangerously lean area spanning a few hundred RPM somewhere in the range (even though many cars exhibit AFR curves of this sort that need to be tuned to flatten them out).
The bottom line is that EGT readings don't really provide much useful information when it comes to AFR.
and heres a little about using the a/f gauges...
Why not use a 'narrow band' O2 sensor for tuning ?
Only a true wideband O2 sensor provides accurate AFR information outside the narrow range either side of 14.7:1. The narrow-band sensors are incorporated on OEM vehicles simply to tell the ECU if the AFR is on the rich side of 14.7:1 or on the lean side. That is all. They are not designed to provide reliable information down in the 10:1 - 13:1 range where we need to work with high output engines under load.
One should note that GReddy, a highly regarded supplier of quality products, cautions strongly and repeatedly that one SHOULD NOT rely on their 4-wire sensor (one step down from a 5-wire true UEGO wideband sensor like the FJO) and associated Air/Fuel Ratio gauge for tuning purposes. They strongly recommend that a "laboratory spec" quality system be used. The FJO is an affordable system that provides the same level of accuracy as the so-called laboratory spec system. (See the GReddy Air/Fuel Ratio gauge owner's manual for specifics of this warning and other details on the GReddy system.)
Why not tune AFR based upon EGT (Exhaust Gas Temperature)?
You can only get a general idea of AFR based upon EGT IF, and only if, you have correlated your car's AFR with its EGT under a given set of conditions. And even at that, you can only get a general idea of the AFR. You can not tell with accuracy just where the AFR is. Perhaps at best you can get within a full point or so, and that's not very close.
Here's an example of the variation in EGTs from car to car. Several months ago I helped tune 3 single turbo Supras on the same day on the same dyno using the highly regarded Horiba wideband O2 system. All 3 cars were tuned to about 11.4:1 AFR across the boost and RPM range. Peak EGTs ranged from 770 to about 880 C on the various cars according to the GReddy gauges (one car's EGT at 770, one at 790, and one at 880). All 3 had GReddy EGT gauges but with identical probes mounted in different places. The coolest EGT reading was from a probe mounted in the #6 runner, the middle temp one was mounted in the front passenger corner of the collector, and the hottest reading came from a probe in the center of the collector directly under the turbine inlet. This in itself proves that EGT readings can not be trusted because there is no physical way that the EGTs in the collector are actually hotter than those in the runner close to the combustion chamber, but this is a function of heat-sink effect happening with the probe and we won't get into that concept here.
If one were attempting to tune the above cars based upon EGT readings, what would he have done with those 3 cars? Conventional wisdom says that EGTs of up to 900 C are allowable prior to the turbo on most turbo motors. If the 770 C car were leaned out to approach 900 C, the AFR would have been in the 15:1 range! That could prove disastrous for an engine running boost. A similar circumstance exists for the car indicating 790 C. What about the one with the 880 C readings? Would that car be dialed back a bit richer because the 880 C readings are approaching the generally accepted MAXIMUM of 900 C? If so, that car would probably end up in the 10.5:1 range and needlessly sacrifice power.
Perhaps the biggest downfall of EGT as an AFR tuning tool is the fact that there is no possible way for an EGT monitor to react quickly enough to spot lean and rich spots in the RPM curve. Most engines will exhibit an AFR curve that varies a good bit throughout the RPM and boost range. At best, EGTs can only give you some indication of peak temperatures. It is not possible for them to point up a dangerously lean area spanning a few hundred RPM somewhere in the range (even though many cars exhibit AFR curves of this sort that need to be tuned to flatten them out).
The bottom line is that EGT readings don't really provide much useful information when it comes to AFR.
and heres a little about using the a/f gauges...
Why not use a 'narrow band' O2 sensor for tuning ?
Only a true wideband O2 sensor provides accurate AFR information outside the narrow range either side of 14.7:1. The narrow-band sensors are incorporated on OEM vehicles simply to tell the ECU if the AFR is on the rich side of 14.7:1 or on the lean side. That is all. They are not designed to provide reliable information down in the 10:1 - 13:1 range where we need to work with high output engines under load.
One should note that GReddy, a highly regarded supplier of quality products, cautions strongly and repeatedly that one SHOULD NOT rely on their 4-wire sensor (one step down from a 5-wire true UEGO wideband sensor like the FJO) and associated Air/Fuel Ratio gauge for tuning purposes. They strongly recommend that a "laboratory spec" quality system be used. The FJO is an affordable system that provides the same level of accuracy as the so-called laboratory spec system. (See the GReddy Air/Fuel Ratio gauge owner's manual for specifics of this warning and other details on the GReddy system.)
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