Anatomy of EGTs

[btfarm]

Don't forget the lean burn aspect as well. That can alter the equation.

 

[buddy]

Yep, my calculations were purely from an air pump perspective how hot it gets inside our cylinder just from air compression alone. But to me it shows why IATs are best way to lower cylinder temps and EGTs. Maybe the reason the boost doesnt matter for temperature is explained in the conservasion of energy law, but I need to study that more. I had only considered the conservation of mass when using the ideal gas law between states of pressure. And this may be why DMax and others can run 40-50psi boost and not produce outrageous cylinder temps that melt the pistons because boost doesnt contribute to temperature, just peak pressure. The mass and lower volume always seemed to cancel out the affects of higher pressure perfectly, that it must be some law already written.

 

[Matt Bachand]

Perhaps the only reason higher boost creates more heat is the fact that to create the boost you are using drive energy to turn a turbine. This act will ALWAYS create heat in the process, thus raising IAT's as well as boost.

I don't think its possible to raise boost without increasing IAT's unless you are introducing a means to cool with.

 

[Missy Good Wench]

Just a note here.

Back many years when I was running an old Peterbilt with a 400 Cat engine, the EGT would regularly climb to near 1200F on along steep grade. Now the Pyro is after the turbo about a foot, so the temps at the valves is waaaaaaaaaaaaaaaaay Hotter.

Now jump ahead to todays technology.

My 500 HP electronic Kitty will pull that same hill far better and the EGT's never get over 850F at the pyro, which is located in the same relative spot.

Fuel makes power and drives the turbine, thus creating boost and so the cycle continues until the turbo runs up against its limits or the injection pump reaches its limits.

Somewhere in there the engines ability to use all the fuel efficiently is reached and anything more is simply HEAT that will if allowed to conrinue, Melt the damned thing.

The intake air temps on these engines (6.5) and any turbo diesel play a very important part in the overall picture of things.

1300F is way too hot for these engines. Now a couple seconds there is no biggy, but you are not going to find any real application where only a couple seconds is all you see.

The industry standard for the 6.5 (based on data collected by folks with big $$$$ and sofisticated test labs) is that 1100F is absolute tops for the EGT's on these engines.

The addition of an aftercooler is great but, really does little good unless the boost is being pushed to 15 PSI or more.

Intake air temp to EGT is IIRC 10F+ on the IAT = 100F in EGT increase.

The big issue with the 6.5 in stock trim, using the GM x turbo is the "drive side restriction"
These turbos reach a point that they basically choke and can't pass any more exhaust efficiently.

Beyond that point the temps go into the ozones and in a hurry.

The aftermarket turbos that allow lower drive side pressures really help elminate the choking and also drastically drop the EGT's

Free airflow through the heads really helps cool these things off.

With a stock engine and a GM x turbo, 1000F to 1100F EGT is the safe limit if you want the thing to live.

I have the Banks exhaust and the Pyro is post turbo about 8 inches.

I consider 900F to be the limit, Period.

There are many contributing factors to the EGT issue and all the rethinking in the world is not going to change the point at which these engines will give up.

If HP is what you want, the EGT can be cooled off a bunch with an water alcohol injection system.

The limits of boost are still relevant and the 6.5 engine design with the limits of the head gaskets are a very real concern.

15 PSI is just about all the little beast will take.

GM designed the engine to run happily, producing about 200HP and doing so using about 8 PSI boost.

We come along and change all this and try to make 300+++ Hp and boost the little critters to the moon.

Ya gonna melt it.

Stay within the reasonable limits and they will live a long time. Go beyond that point and your gonna be sweeping it up.

Really not too much more complicated than that.


Missy

 

[Matt Bachand]

Sure is my thoughts too Missy. I'm mainly stock with a very low tuned TM, and opend up air in, and air out, with an emphesis on fan&clutch to keep things cool.

It sure is fun though to watch these 6.5 enthusiasts push these little 'creatures! Some day when I don't absolutely depend on mine, I may push it into pieces too.

Threads like this make things fun. Thanks buddy for the time taken to do this, and time taken to share.

 

[buddy]

Its those of us that want to go beyond the traditional limits that must either use trial and error or science to understand how or why. Do the big guys with performance mods ever give you formulas and science? Never, they dont want you to understand, just buy their snake oil magic. They probably didnt actually think about it. Its awesome if you just get some data, or better yet data comparisons.

I run 20+ psi boost every day, thats just me and my lead foot with an empty truck, consider it a 1/4 mile race type driving a lot. Well, but I also run it up over 100mph a lot, a few times to 130mph. It just for a little fun. So if I can run my old tired train spout of an engine like that on diesel fuel alone, stock engine and heads, you ask why I might not be impressed with 158mph on gearing much higher than even I have? I had room to go too, but the PCM cuts out at 130mph max, unless I fool it with the VSSB, and I start to get nervous after like 110mph. 130mph at 3500rpm. Oh and I can tell when I do that the fuel tank ticks down, so its not all that smart to do often. Throw on the propane and WMI and it has even more giddy up in her.

When actually climbing hills, especially when loaded or pulling, which is not often, but I climb long steep hills often, my boost is not 20psi, it doesnt need that much to maintain 90mph up a 8% grade with the AC on, more like 12-15psi is plenty just to maintain. I'm that guy that flies past you when you were doing 10mph over the speed limit going up that steep hill thinking youre going fast. Not all the time, and not on long trips, but just for fun sometimes. My EGTs stay in check when the boost is there, at altitude it gets worse, and they are measured preturbo.

My engine may blow up soon or in a few years, time will tell, but I listen to the engine, and the exhaust and the turbo, if it doesnt sound right I back it out, and I watch the gauges and if anything gets hot I back it out. This 6.5 sounds remarkably good at 3500rpm over 100mph and 15psi of boost on at ATT, just hohumming along. The GMx will get you there too, but the engine is cursing you for making it do it, sounding very weak

 

[WarWagon]

We blow them up stock on a regular basis. Miles get to them. But it isn't that hard to pull the crank out of the pavement and drop in another engine. Esp if it was enjoyable and pushing you back into the seat before going BOOM!

Why 1100? What gets hurt over 1100 and how long do you have at higher temps? Can the failing component be removed, coated or cooled better? Will higher temps get more power when needed? From my view the precups crack and the glow plugs start to fail. Assuming the cooling system has been upgraded to handle it first as mine was. A little more EGT and who knows what sudden melting failure I could have had. An exhaust valve melting/breaking off comes to mind. That or the drive turbine melting and exploding. I would be curious as to the weak link that arrives at that number. The larger 6.2 head exhaust valves and different precups may have let my engine survive at higher EGT's or I am just lucky.

Low EGT's are desired on new engines for NOx emissions. Sacrifice compression and it's economy for that goal.

 

[buddy]

I think the weak link is the top ring of the piston, but thats why they use steel rings and put a steel insert in the piston for that ring. With however engines today are made even GM is willing to say 1300F EGT is OK to sustain. The DMax has the combustion chamber in the piston, the cupped pistons. Our combustion chamber is separated from the piston, and the precups are made out of much stronger metal.

Still, scuffing and rings is likely why we end up with blowby as an indicator of potential pending destruction. My truck has had terrible blowby since I bought it with 75,000 miles on it. It was originally used to pull horses, and I can imagine the original owner that did that probably didint worry about keeping it under 210F ECTs. I think scuffing/scratching cylinder walls would come as a result of high ECTs, which would show up from the metal becoming heat soaked and now transferring heat to the water. GM must have tried preventing the cylinder scuffing this with the oil squirters, and higher output water pumps. Engine temps were on their mind, yet they still put the red area of the gauge way too high and fan clutch engagement too high.

Although lots of people blow head gaskets, before anything else.

Using ceramic coated piston tops and piston skirts will help prevent scuffing and scratching. Head studs seem to help prevent head gasket failure. The gapless rings offered for the top ring may perform better and made from stronger steel. Oil cooler is also one of the best ways to keep engine temps down, especially in the cylinder.

 

[great white]

UNsubscribed....

 

[buddy]

UNsubscribed....

good riddance :hihi:

 

[buddy]

Latest versions of files

Since I posted the file in the first post I have updated it and I have this other file which can be useful if deciding how to lower CR or if altering Camshaft valve events timing