EGTs, not just for breakfast anymore - RX7Club.com - Mazda RX7 Forum

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EGTs, not just for breakfast anymore

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Old 09-21-08, 03:19 PM
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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
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Old 09-21-08, 03:28 PM
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awesome advice and well explained
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Old 09-21-08, 05:59 PM
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did u end up increasing the timing overall? is this on the stock twins or a single? and finally are you running dual EGT probes or just one? interesting observation on the EGT's during spool
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Old 09-21-08, 06:00 PM
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So you're shooting for

0"-14psi 1420 and 15psi+ 1550

Is this correct?
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Old 09-21-08, 07:32 PM
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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
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Old 09-21-08, 07:51 PM
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How much should we add to the temperature if the bung is 6" or so downstream of the downpipe?
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Old 09-21-08, 08:13 PM
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wouldnt you reduce the temp if it was on the downpipe? since its further from the combustion area
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Old 09-21-08, 08:19 PM
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Yes, EGT's post-turbo are lower than pre-turbo. Lower because the turbine absorbs heat that's wasted from the combustion.

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Old 09-21-08, 08:19 PM
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Originally Posted by Dudemaaanownsanrx7 View Post
wouldnt you reduce the temp if it was on the downpipe? since its further from the combustion area
nope... the exhaust gets heated up at the turbine.

Originally Posted by RX7 RAGE View Post
How much should we add to the temperature if the bung is 6" or so downstream of the downpipe?
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 08:22 PM.
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Old 09-21-08, 09:47 PM
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Howard,

How did you calibrate the sensors so that the DL will record accurately?
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Old 09-21-08, 09:58 PM
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"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
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Old 09-21-08, 10:31 PM
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can info like this get stickied? this is EXTREMELY valuable.
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Old 09-22-08, 01:49 AM
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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/.
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Old 09-22-08, 11:28 AM
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did increased EGT's during spool correlate with actual quicker spool times, or more area under the power curve? Did you have a quantifiable improvement in performance?
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Old 09-22-08, 12:07 PM
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yes, yes and yes.

back on the dyno this week.
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Old 09-22-08, 12:09 PM
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Originally Posted by sunburn View Post
IMO too many variables... why not move the bung pre-turbo? not really that much work involved.
If someone is running the stock twins manifold, it may not be an option.
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Old 11-27-08, 12:53 PM
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any updates on EGT's we should target and their effect on the boost and power curve?
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Old 11-27-08, 08:43 PM
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Originally Posted by Mahjik View Post
If someone is running the stock twins manifold, it may not be an option.

https://www.rx7club.com/attachment.p...6&d=1169056439

Actually... It Is an option.
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Old 11-27-08, 09:18 PM
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what is the ideal distance from the motor for the probes? I would imagine a few inches would make a difference.
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Old 11-27-08, 10:00 PM
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Originally Posted by Monkman33 View Post
not everyone (me) has the resources to do something like that. It's much simpler if one can be placed in a certain position in the exhaust and we have a temperature to aim for from there.
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Old 11-27-08, 11:01 PM
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Originally Posted by sunburn View Post
nope... the exhaust gets heated up at the turbine.
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.
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Old 11-28-08, 01:53 AM
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Thats what i was thinking as well. The only thing i could figure is if it was actually combusting in the turbo maybe it could be hotter. But thats not really a typical system unless we're refering to a rally car with anti lag.
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Old 11-28-08, 10:25 PM
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It is worth it in my opinion, to pay a machine shop $75 bucks to get it done.

Then you can get readings from front and rear rotor separately. The front and rear tend to have balance issues.... especially if you are running a stock LIM.
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Old 11-28-08, 11:30 PM
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Howard, do you have any pics of your turbo manifold?
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Old 11-29-08, 06:13 AM
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Originally Posted by RX72NR View Post
Howard, do you have any pics of your turbo manifold?
id like to see the complete turbo system!
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