Can TIT be 100F Higher than EGT?

[BrianL29]

I was experimenting with lean of peak settings in my Bravo that others have used.  29-30 MP 2200-2300RPM 13GPH.  My engine runs fine, but my EGT's & TIT never drop even when CHT's are dropping and my TIT is over 100F higher than my EGT's? (over 1700F).  So I enrichen to prevent turbo damage.  Is it even possible for TIT gas to be that much higher than EGT? Doesn't make sense to me.  Or why my EGT's aren't dropping when CHT's are?  Maybe my TIT is just reading too high?

[kortopates]

Entirely normal, TIT should be 50-100F higher than the EGTs since its represents all 6 EGTs hitting the turbo. Only time TIT will get lower than EGT is when you either have a worn out TIT probe or a partially blocked injector driving that cyl EGT high.

Plus please note its not very kind to lean slowly through peak at 29-30" even with RPM pulled back. At Savvy we recommend you to do the Gami sweeps and LOP Mag test at around 20-22" MAP to keep you TIT down; especially when you do the LOP Mag test which will cause TIT to spike.

[BrianL29]

Thanks Paul.  Good talking to you on several platforms! I did pull the mixture back to 13 GPH quick.  I was pretty sure I would be lean of peak at that point based on others data.  CHT's are dropping dramatically, so I'm still not sure how I'm not lean of peak at that setting.   

I'll perform the LOP Mag test again.  

[A64Pilot]

TIT should be higher, it’s from pressure I believe as combining cylinders doesn’t drive temp higher, even if you accept the argument of the heat is in pulses coming from the exh and the egt probe averages temps

Its sort of similar to how steam at 212F will burn you more than water at 212F, because the steam is at a higher energy state.

If you had downstream temp, known as EGT in a turbine it’s markedly lower than TIT, as in much lower because the energy has been extracted from the gas flow to drive the turbine.

Edited March 29 by A64Pilot

[Will.iam]

  On 3/29/2025 at 2:54 PM, A64Pilot said:

TIT should be higher, it’s from pressure I believe as combining cylinders doesn’t drive temp higher, even if you accept the argument of the heat is in pulses coming from the exh and the egt probe averages temps

Its sort of similar to how steam at 212F will burn you more than water at 212F, because the steam is at a higher energy state.

If you had downstream temp, known as EGT in a turbine it’s markedly lower than TIT, as in much lower because the energy has been extracted from the gas flow to drive the turbine.

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But isn’t the temp of exhaust leaving the turbo lower also because the pressure is lower on the exit side of the turbine than the entry point of the turbine and since gases cool as pressure drops i would think that would be more of the contributing factor as well as the turbo itself absorbing heat from the gases hitting the housing and impeller blades acting like a big heat sink too. I know some reference heat as doing the work but i always thought of it like pressure does the work since i can take compressed air that’s even cold and push it through the turbo and it would work but if i just had a oven heat on the intake and cold air on the exit, i don't think heat alone would be the driving factor. 

[A64Pilot]

A turbo extracts energy from the exhaust stream. That energy is primarily heat as there isn’t much pressure, there is of course significant gas flow that comes from expansion from heat and mass times velocity squared = energy.

I don’t know the HP a turbo makes but it’s considerable, a turbo is similar to a turboprop or jet engine. Massive HP but I think the max pressure in a jet engine isn’t but about 40 or 50 PSI? Not sure really but if the HP was derived from pressure it would be massive pressure. I don’t know what the max pressure is in a turbine but am pretty sure it’s orders of magnitude higher in a piston engine.

If you search glowing hot exhaust or similar you’ll see some turbo systems where the exhaust is yellow hot while the turbo side is a dull red, there is a large drop in temp.

Argued a different way, heat is solely the driving force behind the entire engine, we could argue I suppose the pistons are driven by pressure, but the pressure comes from the heat from burning fuel. Chicken or Egg?

Like arguing I guess that John died from blood loss and not the gun shot, but the gun shot caused the blood loss.

[A64Pilot]

You know now that I think about it I think the compression ratio of the newest and most efficient PT-6’s is about 14 to 1,I think, older designs were much lower like half that.

But say the new ones have 200 PSI coming off of the last compressor stage, that is the highest pressure in the entire engine, if it were higher in the hot section then you would get reversion or backwards gas flow like you do in a compressor stall.