Melted #6

[Diesel Power]

What Diesel Power is saying might have some fact. A truck with 1300 deg stock might be different than 1300deg with a truck that has lots of timing. But still About a mounth ago I was on a dyno with all kinds of load on it running 1400-1550deg and the boxes all of the way up, and held up fine.

with allot of timing the cylinder and pistons dont have time to cool down from the last combustion event, and melted pistons will result---even at 1300 degree----------its the consisitently high combustion temps that worry me, steel melts at 1200*, so that is probably what happend :{ good luck dude

 

[Forrest]

How much timing are we talking about here?





tia

 

[AK RAM]

My probe is just after number #3 exhaust port on the manifold.

This really sucks man.



I know I have shared this before. On my truck, when at WOT, there can be over 250*F difference between the gasses coming out #3 and the gasses coming out #6. That is with the probes about 1" from the head, right outside the exhaust port so it catches the exhaust as soon as the valve opens. The further away from the head you get, the lower the temps will be from actual chamber temps. If your probe is down in the collector as most are, your getting a mixed average at best and actual will be much, much warmer.



I personally wouldn't be concerned about any extra heat from timing advance. Many other variables involved that keeps that from happening and becoming an issue. More than likely your #6 was just way, way hotter than you realize.

 

[ACoffel]

I don't mean to hijack, but can it be gathered from all this that the best location for the pyro probe is on the manifold right out of the number 6

exhaust port ? I'm very sorry to here of a member having this kind of problem

and I hope everything works out as well as possible !!

 

[nps]

What Diesel Power is saying might have some fact. A truck with 1300 deg stock might be different than 1300deg with a truck that has lots of timing. But still About a mounth ago I was on a dyno with all kinds of load on it running 1400-1550deg and the boxes all of the way up, and held up fine.

I pull grades at 1300* with an HO motor (timing and compression) plus an EZ. No melted pistons yet - and I don't think they radically changed the characteristics of the pistons between 24V and HPCR motors.



On the other hand you are saying recently you had your motor up to 1550* . With a termocouple reading on the low range of its scale in the number 3 tube that 1550* could have easily been 1700* or more.

 

[RustyJC]

I personally wouldn't be concerned about any extra heat from timing advance.

1. If you've run an engine on a dynamometer at fixed load with templugs and/or thermocouples in the piston crown and cylinder heads, (our company is an engine manufacturer, and we do that), then one can watch as the timing is advanced with no other changes. EGT drops, and piston crown/cylinder head (i. e. , combustion zone) temperatures increase. The heat balance of the engine is changed - less heat is rejected to the exhaust, and more heat is rejected to the coolant and lube oil (with oil-cooled pistons).



2. My stock 2002 HO would run 1300 degF pre-turbo EGT towing a large 5th wheel RV. Dodge and Cummins apparently do not have heartburn with this EGT under stock timing and fueling conditions as that's how they tested and released the engine configuration for production. Now, we've seen a number of cases where someone added larger injectors and a timing/fueling box with increased boost and roasted/scored a piston and cylinder (typically #6) at this same 1300 degF pre-turbo EGT when towing a heavy trailer up a long grade. The point is, with more fueling and timing, a given 1300 degF pre-turbo EGT doesn't mean that the same amount of heat is being absorbed by the piston crowns and cylinder heads as it would be with the same 1300 degF EGT under stock fueling and timing conditions.



Rusty

 

[Diesel Power]

yet another good point

 

[hotram03]

I've made short burst of no more than 8-9 secs and have hit 1600-1700 deg, quite a few times and no problems and heard of numerous other dodge guys going that high but only for a short time, I've heard as long as you dont go over 10-12 secs thermal expansion hasn't time to take place, I try not to go there much but have been there, and so far so good, but I have added many things to help combat high egt's, but the main one is some constraint

 

[Vaughn MacKenzie]

This really sucks man.



I know I have shared this before. On my truck, when at WOT, there can be over 250*F difference between the gasses coming out #3 and the gasses coming out #6.

I blame that on a couple things. . . cylinder #6 is at the far end of the intake, and sorta gets what air is "left over" in the intake chamber. The further you get from the air horn, the less boost pressure there is (same principle as the garden hose, the further you are from the spigot the more the pressure drop. . . the more the pressure to begin and the faster the flow, the greater the drop). The higher the boost and RPM the greater this becomes an issue.



Add to that the crapola stock manifold, with its tortuous exhaust passages for #6 and especially #5. For anyone who hasn't looked at a stock manifold taken off #5 passage essenitally shoots at #4 but the gases exit at 90* to the passage channel.



RustlyJC: interesting point about timing, one I hadn't considered before that makes sense. Another thing about the 3rd Gens, with the tiny injector tip holes and high pressure I believe the injection duration is longer than the 24-valve and 12-valve trucks. Even if you are putting in the same amount of fuel during a combustion event, if it's being sprayed in at a slower rate over a longer period of time guess what? Gives the heat more time to soak into the piston crown.



Last thing. . . I can think of 3 cases of 24-valve engines melting down after pulling grades at 1200-1250F. In those cases the problem could be blamed on inaccurate pyrometers. That's one thing I've posted about over and over. . . if you're pushing the limits, don't assume your gauge is accurate.



Vaughn

 

[AK RAM]

I always understood that crown heating, or cylinder heating in general, as a result of timing advance was a problem for gas engines only. When you advance timing on a gas engine, you are advancing the spark. It is all ignition driven. When you advance the spark, you lengthen the burn time, and everything gets hotter as you go. On diesels, advance timing all you want and ignition still does not happen until TDC, just as always. The burn time doesn't increase at all. On a diesel, all you have done is introduced more cool air and fuel earlier, giving both longer to mix in the combustion chamber, with the side effect being the crown and everything else is cooled more and more as you advance more. The only draw back to advancing timing on a diesel is extremely high cylinder pressures. The effects of timing advance on gas v/s diesel should be totally opposite.

 

[betterthanstock]

On diesels, advance timing all you want and ignition still does not happen until TDC, just as always. The burn time doesn't increase at all. .

And how does a chemical know where TDC is?

If the air is hot enough, it will start burning before TDC, and pushes your piston backwards, and creates high cylinder pressures. That's why you lose power if you over-advance past optimum timing.



The reason we can improve MPG and power with a small advance, like 2-4 degrees more than what Cummins makes them, is because they have to retard it to keep the fire cooler, and thus limit NOx at the expense of more smoke, CO, CO2, HC, and of course more wasted fuel. Then they add the catalyst to clean up the smoke and the other gasses. Pretty simple.



If you dump huge quantities of fuel, you need a lot more timing advance, but for street use, you don't need that much more over what Cummins already gives us. I would rather be 2 degrees retarded from optimum, and lose 1% power while keeping the engine on the safe side, than be 2 degrees overadvanced and lose the same (or more) power, while creating high stresses and temperatures.

The power loss is non-linear, so the first 1-2 degrees are maybe 1-2%, but then the losses become a lot bigger. By the time you retard it 4 degrees the losses may reach 5%, for 6 degrees about 10%, 8 degrees maybe 18%. So bringing it to within 2-3 degrees of optimum (from 5 or 6 that they have retarded it) will give you pretty good fuel economy and power, and still keep it reliable.



Pressure boxes make the fuel jets penetrate deeper, and the flame itself can reach 3000 F, which will cut right through the piston.



For the racetrack, I would try using ceramic coated pistons. There are some guys out there that custom make them.

 

[Vaughn MacKenzie]

The injection event begins before TDC, but fuel does not light instantaneously. There is a delay period of several microseconds, depending on the cetane rating of the fuel. I think depending on RPM and power level (and if it's a 12v, 24v or 3rd Gen) combustion could start a little before TDC. Just because it starts a little before TDC doesn't necessarily mean there will be an instant pressure spike because it takes a few microseconds to heat the air.



Injection starts before TDC and continues spraying fuel through TDC and beyond by several degrees (depending on how much you have your foot on the Go pedal). The reason timing is advanced is to remedy the stock retarded timing, but on 12-valves it is done because p-pump timing is fixed and so as RPM increases the piston is further down the hole before the fire really gets going, so advancing it compensates for this, with the tradeoff being more noise and rattle (probably due to a high pressure spike at TDC from early light-off).



Vaughn

 

[jwilliams3]

There are plenty of trucks out there running gobs of timing with the stock pistons and are not melting down. I ran 3 boxes all last year and none of my pistons melted and that was sled pulling with my electronic egt gauge maxxed at 1700* most of the way down the track.



There are many trucks that have ran over 2000* while drag racing or sled pulling and have not melted a piston and they have plenty of timing.



I dont think its timing that melted the piston.

Most of the time timing reduces EGT's at least thats what I have found with load dyno testing and many road miles.



With the introduction of the 2004. 5 timing was retarded even more resulting in higher egt's or combustion temps whatever you want to call it.

 

[banshee]

even at 1300 degree----------its the consisitently high combustion temps that worry me, steel melts at 1200*, so that is probably what happend

Steel doesn't melt at 1200 degrees F. Try 2050 and higher.

 

[Matt S]

This is a great discussion. I have 2 questions. How would you calibrate your pyrometer? How come the extra heat from the timing advance wouldn't translate into the exhaust stream to be picked up by the pyrometer?

 

[Tinman]

This timing issue is confusing me. I see some say advancing timing on the 600 motor by 2-3 degrees brings is closer to optimum, inproving MPG and performance. But then I read on TST web page that the powermax advances timing 6 or 12 degress. That can't be advanced by 12 degrees. Is it advanced to 12*. What is optimum timing and where does the stock motors fall. How much is a safe timing advance. I want to advance timing on my 06 at some point for throttle response and MPG, but I want to do it safely.

 

[Tinman]

Optimum Timing??

I am confused. I read where advancing timing on the 600 motors by 1-2* is helpful. Then I read on the TST web page that the powermax advances timing 6 or 12 degrees. Could that be advance to 12* not by 12*. Seems like a lot. What is optimum timing and how far do the stock motor retard timing? I would like to advance timing on my 06 for mileage and throttle response but would like to do it safely.

 

[Diesel Power]

Steel doesn't melt at 1200 degrees F. Try 2050 and higher.

i'm sorry i meant aluminum melts at 1200*-----i should know that, coming from a ironworker background :-laf

 

[MAshley]

SO I have to ask... seeing as no one else has... . When was the last time the fuel filter was changed... . If it’s plugged up, that mean less fuel, and less fuel in a diesel engine means a lot higher temps. I saw a posting at a dealer ship on Cummins Letter head reminding dealers and owners that 15K miles is the max for a fuel filter. . In fact the whole thing was brought to my attention because of a long block sitting on the floor; with a melted piston on #3 ... ... customer is out 6K he said because he didn't change a filter...



Moral of the story if you mod, or even if you don't. . And you don't change filters often you may melt something because at the worst possible time your engine runs a little lean... Doh

 

[jwilliams3]

Were not talking gas engines here.

Ooohhh no... . not letterhead.



They want you changing the filters because they dont want dirty fuel contaminating the fuel system.

Not because of a mythical "diesel lean" condition.