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this is aimed at the tuners out there...... I'd like to start a conversation about tuning with dual EGT probes in front and rear runner of the turbine manifold, and the methodology.
What kind of differences front to back are 'acceptable' for different running conditions?
I've been around enough setups to know that some cars run fairly even front to back, or can be tweaked/tuned to do so. I've seen a BW S362 setup run almost even EGTs with (gasp) a stock LIM.
My current FD is seeing some pretty serious split. The car runs wonderfully so I'm not terribly concerned but want to investigate further. Example, highway cruising at 3000ish rpm I'm seeing 1420F front and 1170F rear.
For many years I had EGT in the downpipe on my old 500R setup and all was good..... Sometimes I think "Mo' Gauges Mo' Problems"
^^Rich, I'm not a tuner, but mine runs 30C warmer in the rear versus front rotor housing (on average). This is with large street port and Ground X LIM.
I have looked into this while tuning my haltech, and like you, have had uneven egts. I have ruled out variation from the sensors by switching them around from front to rear and back. For the most part on my car, the rear rotor runs hotter by 150*F during boost, uncorrected. With fuel correction of about+6% to the rear rotor, they now run within 100 F of each other at most. From research on this forum and otherwise, 100*F difference is acceptable.
In regards to your cruise egts I think some adjusttment to the tune(pri inj trim) is needed.
Under cruising and idle situations, compression and intake leaks play a big role in how the engine runs and egts. I have noticed similar number to what you are seeing with lower compression on one rotor. When in boost the egts will level out. I have also seen this number in cases when the air, fuel combustion isn't burning properly; burnt out plugs or weak coils. Goodfella, I'm not saying your situation is the same, but I would definitely look into those first before looking at other things and plus it's probably the easiest thing to check.
Like most other responses here. I too see about 100f difference on a properly running engine, rear rotor always being hotter. It's gets cooled last.
Under cruising and idle situations, compression and intake leaks play a big role in how the engine runs and egts. I have noticed similar number to what you are seeing with lower compression on one rotor. When in boost the egts will level out. I have also seen this number in cases when the air, fuel combustion isn't burning properly; burnt out plugs or weak coils. Goodfella, I'm not saying your situation is the same, but I would definitely look into those first before looking at other things and plus it's probably the easiest thing to check.
First, I'll agree re-iterate some points that have already been made:
1) making some changes in individual rotor fuel compensation can change the egt a small amount
2) rotor to rotor differences in the condition of the sealing could potentially have an effect, and the coolant circuit cools the rear rotor after the front
3) 100 to 200 degrees F difference between rotors is common
There are other things to keep in mind. The difference in exhaust temperatures can also reflect stuff going on in the combustion chamber besides the ratio of and fuel taken during the intake stroke.
It can reflect a difference in combustion speed between the rotors. A lot of that is affected by exhaust manifold design, because exhaust manifold runner length and diameter affects the residual gas content. Backpressure in the turbine housing affects it too. A higher residual gas content means slower burn and higher EGT. Individual cylinder spark compensation can help with that - it's not something that a basic ECU like a Power FC can do.
Originally Posted by GoodfellaFD3S
My current FD is seeing some pretty serious split. The car runs wonderfully so I'm not terribly concerned but want to investigate further. Example, highway cruising at 3000ish rpm I'm seeing 1420F front and 1170F rear.
I suspect this is a result of pulsation effects that occur at that rpm and at that given level of manifold vacuum and exhaust pressure. It's specific to a given engine's porting, turbo, exhaust manifold.
Originally Posted by gxl90rx7
i wonder how much of the difference is caused by divided turbo manifold runners being different lengths and/or driving front/rear of the turbine wheel
ding ding ding, you're on the right track
One rotor has a lot higher dilution because it's ingesting more of its own exhaust during overlap. Or the fuel isn't atomizing as well in that rotor, making mixing worse.
You see this kind of EGT and combustion imbalance on your normal oddfire cross plane V8 [the typical design] all the time--a couple cylinders that run cooler due to higher internal EGR, or run hotter because it burns slower and there isn't enough spark advance. A lot of that is due to the uneven number of crank angle degrees between cylinders firing in that case, or some compromises made in manifold design. It varies greatly with speed and load though.
Originally Posted by GoodfellaFD3S
I'd like to start a conversation about tuning with dual EGT probes in front and rear runner of the turbine manifold, and the methodology.
In these kinds of setups, just normal street project cars that happen to have EGTs in the manifold, I usually ignore EGT. A gauge itself is nearly useless for understanding what's going on doing pulls at high loads because it doesn't respond fast enough. Analog gauges were really meant for big diesels or piston powered aircraft that run at mostly steady speed and loads with slow transients.
If your data acquisition system can dump EGT into a datalog at a fast sample rate, it's a nice thing to have but hardly essential. That means you need to convert thermocouple signals to analog, or have something that reads thermocouples directly.
If you have the ability to read combustion chamber pressure or emissions, you can corroborate what you are seeing with EGT. For example, if I see low EGT, slow combustion, and high HC emission coming out of that exhaust port it's likely to be poor mixing. That's not project car stuff though. That's lab work.
Originally Posted by GoodfellaFD3S
Sometimes I think "Mo' Gauges Mo' Problems"
Yep. EGT just isn't an engine critical metric for a normal project car in normal street use. For [not drag] racing or engine dyno work the concern can be damaging whatever is in the way of the hot gases right as they leave the exhaust port - the manifold itself, the turbo, exhaust valves in the case of piston engines. Even if those components do get super hot for a split second they are usually ok if it's just excursions of accelerating through onramp for a seconds.
My experience with EGT is that it is heavily influenced by the positioning of the probes in the manifold.
I am running an "SDR" split pulse manifold on a 13b turbo. I'm working in degrees Celsius. I had up to 80 degrees Celsius difference between rotors. The depth of the probes in the manifold is critical, they need to be matched as exactly as possible. I marked mine up with a vernier and ensured they descend into the runner the exact same amount. They protrude about 7mm into the runner.
I also have the probes mounted very close to the same distance from the exhaust port.
A data log of a dyno run from three weeks ago is below. The difference is within 10 degrees Celsius under power and increased to within 20 degrees Celsius under over run
Analog gauges were really meant for big diesels or piston powered aircraft that run at mostly steady speed and loads with slow transients.
i flew a few flights with my dad's friend, and take off rpm is 2400, and cruise rpm is 2200-2300. most speed changes are done with prop pitch. additionally ignition timing is fixed.
the mixture adjustment starts at best power, and then pulling it removes fuel, and you just do it, until egt is a little colder than the mark on the gauge. which is ironically a snowflake.
One rotor has a lot higher dilution because it's ingesting more of its own exhaust during overlap. Or the fuel isn't atomizing as well in that rotor, making mixing worse.
This is why I personally wouldn't go *****-nilly trimming fuel based on EGT differences.
First off, you have things like EGR passages and port air passages that aren't even on or working on both exhaust ports always.
Second, you have exhaust manifolds that aren't perfectly symmetrical.
On my TII with modded S5 TII manifold/turbo and 60mm external WG it would run ~100C cooler on one rotor than the other at cruise, but as soon as the WG opened EGTs would even out.
Third, the two scrolls in a dual scroll turbo aren't even symmetrical to the turbine wheel.
Fourth, the myriad of other variables such as compression/sealing differences between rotors.
Sounds like we are all of the same opinion about EGT differences on this thread. My take on it is-
You are probably better off getting your intake manifold and injectors flow matched on a test bench and while everything is fresh watch your EGTs to see the trends in your motor so you know when they start acting out of the ordinary.
Hmmn, motor/exhaust smells hot (usually this is subconscious thing)- look at EGT gauges. Yup its hot- better slow down and find out what is wrong. Its just like having a trusted 2nd opinion to me.
In tuning EGT is very handy to figure out under what driving situations you get really high EGTs when you are learning to tune.
For instance, you might figure out why OEMs run the engine so rich at high rpm even under low/smedium loads so you don't melt your motor down doing long burnouts, drifting, donuts, general hooning or even cruising at high speed on the freeway.
Abel used my EGT's last during my tune. He would glance at them every once in a while but this is his methodology. I think a lot of good tuners would agree that there is more art involved in tuning a rotary than piston motors. But At the end of the day at 8400 RPM at 100% TPS.. 18.4 PSI, I have a 3 Celsius (37.4 F) Degree difference between front and rear rotors. My rear runs hotter of course. But front is 670 Celsius \ Rear is 673 Celsius or Front 1238 F\Rear 1243.4 F. I think this is one of the main reasons my Car is still running sound with over 13 Track drift events and 6 of those being Judged Events. The car is run on E85 and does have full ducting but I think Heat really is the killer on most motors....especially so with our wee little 1.3 liter rotaries =-). Abel has been teaching me quite a bit and this next build he'll be mentoring me as I tune the car, but it's to my understanding that you really don't want to be edging close to higher egts.... especially for prolonged periods. So if 1400F is a normal number at cruise... and you'll be cruising around quite a bit, It should probably be addressed to get that number down. Maybe pull some timing and add some cruise cell fuel. May be time for an ECU upgrade rich!!! =-)
EGTs are especially critical on turbo cars and street NAs because you have the exhaust manifold pressure from exhaust restriction that will reflect/concentrate the exhaust heat right back into the motor like a pressure cooker.
Still, I wouldn't worry about EGTs at cruise as long as it richens up on tip in AND when climbing hills/high speed cruising.
My TII did 1,000C+ EGTs tuned lean under cruise, but would drop to 700 and climb to 800C under any load.
Only time I ever had heat related issues with motors (sacked out springs, worn/warped seals/plates/raised spark plug area, etc) was when I also had detonation that killed a motor (EGTs are extremely high during detonation).
Any other time I took a motor down in the last 15 years it looked great inside with very minimal wear and no signs of heat damage.
I have seen over 1000C but those temps were with an exposed tip egt probe. An exposed tip won't last as long but give you the quickest response and I believe a more accurate and usually higher temp compared to a protected tip (most K type sensors).
I run the protected tip sensors from Exhaust Gas Technologies, and they are most definitely at different probe depths..... when installing I was on my back at midnight and they somehow ended up being like 1/8th of an inch different in depth
Also, check the pic below..... the inconel does shed a *lot* of heat, and the front runners are getting the brunt of it.
given the posted picture which shows your turbine close to the front runners and the fact that your front EGT is much hotter than the rear it is my opinion that your heat shielding is the most probable cause. front to rear EGTs should be no more than approx 50 F if you have a Ground Zero LIM and your injectors are O K.
comparative heat transfer
Aluminum 205
Stainless Steel 16
Inconel 9.8
Mica .71
given that the aluminum manifold is HIGHLY receptive to heat proper shielding is critical.
Cam Worth was tuning an FD w the turbine situated as yours w no heat shield and after a few runs he grabbed a piece of stainless steel and placed it between the turbine housing and the LIM. the AFR changed more than a full point on the next run!
we are logging the average of two distinct entities. it is probable that the AFR from the rear rotor didn't change much. IF that is the case the front rotor changed two full points.
as you can see from the material properties listed above Inconel is not something that you would place at the top of your list as to heat shielding. Inconel's primary attribute is high melting point (25-2600 F) which is why it is often used as a turbine wheel material.
assuming your shielding comes from Turblown it apparently contains a "proprietary" heat blocker in addition to the inconel.
the simple question is... what is the temp of the shield after running a bit. for that matter what is the comparative temp of your front and rear runners.
a friend of mine runs (from the floor) a large industrial operation. i have always listened to him. one day he showed up w a piece of Mica, saying that is what they use to combat heat transfer. after checking material properties i found a very nice home for it. see pics.
prior to mounting it i hit it w a propane (1300 F) torch for over a minute. i could touch the other side of the 1/8 inch sheet!
McMaster Carr sells a 10 X 12 piece (1/8th inch) for $67. you can saw and drill it.
PN 85165K81
following along the same material lines i discovered PTP's LAVA turbo blanket. way different that the typical fiberglass product. they have a video on their site of a dyno pull w someone holding their hand on the blanket. they also have an interesting PDF on a U Texas study on turboblankets.
here's my setup:
i am not knocking the inconel shield as it looks tidy, just suggesting you check to see how it is performing as to heat blocking. i also believe other companies are picking up on the lava (which is similar to Mica) infused turbo blankets.
it will be very interesting to find out what is going on w the 1400 F EGTs.
Howard
Last edited by Howard Coleman; 08-15-15 at 11:51 AM.
One rotor has a lot higher dilution because it's ingesting more of its own exhaust during overlap. Or the fuel isn't atomizing as well in that rotor, making mixing worse.
This is why I personally wouldn't go *****-nilly trimming fuel based on EGT differences.
First off, you have things like EGR passages and port air passages that aren't even on or working on both exhaust ports always.
Second, you have exhaust manifolds that aren't perfectly symmetrical.
On my TII with modded S5 TII manifold/turbo and 60mm external WG it would run ~100C cooler on one rotor than the other at cruise, but as soon as the WG opened EGTs would even out.
Third, the two scrolls in a dual scroll turbo aren't even symmetrical to the turbine wheel.
you got me thinking.. the rear rotor will naturally have higher egts because the coolant has to pass through the front rotor first, on the spark plug side, correct? Im thinking that is why in the factory turbo manifolds, mazda always had the straighter runner on the rear rotor, which would help balance the egt's between rotors. Even the S4 and FD twins, the rear rotor always has a clearer shot at the turbine wheel(s)
I read through this thread to try to figure out what's going on with my ride. I'm a little confused and believe it's just some kind of issue with the sensor, but would like the collective input of the board.
While cruising on the highway - fifth gear - I'm seeing EGT on one rotor of about 1,400* F and the other rotor doesn't even read (analog gauge goes from 900*-1,900*F). The funny thing is, when I left off the throttle, the temp immediately drops, as it should since it's no longer under load, but as that needle drops to the 900* or less, the other needle that wasn't reading at all before suddenly jumps up to that 1,300*-1,400* range and then begins to drop slowly from there. If I then touch the throttle again to accelerate, that needle that was not reading and now is, immediately slams downward to the 900* mark, and the other returns to it's normal temperature, roughly 1,400* F...
I don't quite understand what's going on. At first, I noticed that the one wasn't really reading and the other was, so I said to myself "Something must have come unplugged or something" but then when I let off the throttle, it comes to life and then immediate pegs back down when I get back on the throttle.
Does anyone have any idea what the heck this could be? I'm not really sure where to start.
Yeah, I will have to look into it, but I didn't install them, car came with them so I will have to figure it out as I go.
I was thinking as I was discussing with a co-worker, it is strange but it seems as though the two needles for the EGT gauge are working inversely. It's almost as if the one is connected backwards...? Higher temperatures would make the needle go upwards, but in this case, the one needle goes downwards when temperatures rise. Conversely, as temperatures lower when the throttle is released, the needle goes upwards.
Maybe that's not really possible, but it seems like that's basically how it's working.
Really excited to see all of this development action going on here. Thank you Howard for the McMasterCarr link! I'd definitely prefer a Mica IM shield and Lava Turbine Cover like this Synapse Unit:
To the guys claiming EGTs go up with detonation or advancing ignition timing, have you ever actually logged this? With my limited experience it has always been the opposite with ignition timing, thermodynamics also backs this up (earlier burn and more heat energy rejected into the rotor/housing due to both time and gas/energy density in the combustion volume), as does Ben Strader from EFI university (and he instruments and logs the **** out of his/numerous race team engines in a lab).
As you say regarding timing I have always seen retarded timing raising EGTs on the rotary and not advanced timing.
As for detonation, I have never observed raised EGTs during detonation since it has always happened quickly and with engine destroying force.
I have only looked at the melted and poorly lubricated internals from engines that were destroyed from detonation and surmised higher EGTs...
but you could be quite correct that EGTs did not rise at all- just more heat was transferred into the engine internals and thus less out the exhaust port.
08-08-15, 05:17 PM
Tuners--Dual EGT probes, temp differences
