EGTs, not just for breakfast anymore
09-21-08, 02:19 PM
#1
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
EGTs, not just for breakfast anymore
i have been digitally logging (Power FC/Datalogit) EGTs pre-turbo for a couple of years.
quite easy to fixture and inexpensive. get the FAST acting (instantaneous) thermocouples from TEAMRIP.com, around $50 each and the solid state signal convertor at simple circuitboards.com ($35 ea).
connect to your dataloggit and start logging.
recently i realized that i had been focusing on my egt target at one bar (1550 F preturbo) but had not really considered the transition area from zero to 15 psi.
a look at my logs showed good AFRs in that area but EGTs around 1050!
so i called my go to guy, Jose Le Duc, and found that the number should be 1420!
here's the point.... my AFRs were fine. BUT my egts were, uh, not fine.
so we worked the timing and before we ran into an unrelated problem (inconsistant alcohol pressure) had the egts up to 1350.
lots better spool, torque etc.
this points out that AFRs aren't everything.
get tuning.
howard coleman
quite easy to fixture and inexpensive. get the FAST acting (instantaneous) thermocouples from TEAMRIP.com, around $50 each and the solid state signal convertor at simple circuitboards.com ($35 ea).
connect to your dataloggit and start logging.
recently i realized that i had been focusing on my egt target at one bar (1550 F preturbo) but had not really considered the transition area from zero to 15 psi.
a look at my logs showed good AFRs in that area but EGTs around 1050!
so i called my go to guy, Jose Le Duc, and found that the number should be 1420!
here's the point.... my AFRs were fine. BUT my egts were, uh, not fine.
so we worked the timing and before we ran into an unrelated problem (inconsistant alcohol pressure) had the egts up to 1350.
lots better spool, torque etc.
this points out that AFRs aren't everything.
get tuning.
howard coleman
09-21-08, 06:32 PM
#5
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
yes, we increased the timing.
my setup is two garrett TO4s. total airflow is similar to a GT42 but at 25 psi.
i have an EGT probe in each of the two runners between the engine and turbo.
and yes, 1420 to one bar and 1550 after.
should be back on the dyno this week w my re-jiggered alcohol setup.
hc
my setup is two garrett TO4s. total airflow is similar to a GT42 but at 25 psi.
i have an EGT probe in each of the two runners between the engine and turbo.
and yes, 1420 to one bar and 1550 after.
should be back on the dyno this week w my re-jiggered alcohol setup.
hc
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09-21-08, 07:19 PM
#9
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IMO too many variables... why not move the bung pre-turbo? not really that much work involved.
Last edited by sunburn; 09-21-08 at 07:22 PM.
09-21-08, 08:58 PM
#11
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
"How much should we add to the temperature if the bung is 6" or so downstream of the downpipe?"
i did a study re pre and post turbo egts (i actually digitally logged both at the same time) and found the relationship is quite variable depending on where you are on the map. there are numerous posts on this board stating you add 200 degrees or whatever. unless you have tested post and preturbo i believe that post turbo egts are of low value. you really want to know the pre turbo number and it DOES matter.
"How did you calibrate the sensors so that the DL will record accurately?"
since the various translator circuits generally use the AD595 i just used the look up table from AD.
hc
i did a study re pre and post turbo egts (i actually digitally logged both at the same time) and found the relationship is quite variable depending on where you are on the map. there are numerous posts on this board stating you add 200 degrees or whatever. unless you have tested post and preturbo i believe that post turbo egts are of low value. you really want to know the pre turbo number and it DOES matter.
"How did you calibrate the sensors so that the DL will record accurately?"
since the various translator circuits generally use the AD595 i just used the look up table from AD.
hc
09-22-08, 12:49 AM
#13
The PLX Devices EGT units are also an alternative transducer choice. Not as cheap as the Simple Circuits units but nicely packaged. cf. http://www.plxdevices.com/products/sm/egt/.
11-27-08, 07:43 PM
#18
11-27-08, 10:01 PM
#21
LOL sorry man, but where is the heat coming from? Sounds like a violation of one of the thermodynamics laws to me. The exhaust gases heat up to their highest temperature at combustion, then they will shed heat from that point forward. The turbine heats by receiving energy from the gases, not the other way around.
The exhaust gasses will definitely become cooler as they travel downstream. As the gas moves through the exhaust components, it will shed heat primarily through convection to the exhaust side walls. The exhaust sidewalls will in turn shed heat through the three main modes of heat transfer: conduction, convection, and radiation.
So to answer some peoples' question, there is no generic "rule of thumb" offset that you can apply to thermocouples that are post turbine. Different exhaust materials, ambient temperature conditions, etc. will change this value on a case by case basis.
The exhaust gasses will definitely become cooler as they travel downstream. As the gas moves through the exhaust components, it will shed heat primarily through convection to the exhaust side walls. The exhaust sidewalls will in turn shed heat through the three main modes of heat transfer: conduction, convection, and radiation.
So to answer some peoples' question, there is no generic "rule of thumb" offset that you can apply to thermocouples that are post turbine. Different exhaust materials, ambient temperature conditions, etc. will change this value on a case by case basis.
