When talking to a BANKS guy about a 6 gun he commented that some of the D/Max guys have POPPED 1700 DEGREES with NO failure for a brief burst.

 

Plenty of guys have passed the 2000F mark with their Cummins with no failures for a brief burst... but it's gambling, that's for sure...

 

The two main areas of immediate concern with high EGTs is piston meltdown and turbocharger turbine rotor overheating. The pistons in our motors are forged aluminum, and are most likely a 4000 series (high silicon) content. The melting point of pure aluminum is 1220 degF, and when alloyed (4032, 6061, etc) it generally drops, not raises. If you took one of our pistons and left it in an oven at 1200 degrees you'd come back to find a puddle of molten aluminum. Furthermore, once most aluminums get over the 400 degree range their strength starts to drop dramatically.

So why don't our pistons just melt away when the pyro sweeps past 1200? They are "saved" due to boundary layer effects (a thin layer or fuel & air that sticks to everything inside the combustion chamber and acts as an insulator to heat transfer), a fresh charge of cool air entering the cylinder every other stroke, cool fuel being injected, and the pistons ability to conduct & convect heat away from itself. It can take spikes of 2000+ degrees of air temperature since it never sees 1200 degrees of surface temperature. You're basically saved because of the fact that heat transfer takes time. The higher above the melting temp, though, the shorter the amount of time you have to play with... literally.

The turbocharger inlet is much the same way, but it is more determinant on the bearing's ability to pull heat away. Almost all turbos have a rated inlet temperature that they are not supposed to exceed. Like with the pistons, you can push past it, but as I've heard before "Every time you push the pyro past 1300 you better put a little money away to pay for the rebuild you're contributing to"

John

 

Banshee, I stand corrected. Thanks for the insight. Why does the alloy process drop the melting point? And second...I thought most diesels did not use aluminum pistons because of the high cylinder temps? I have never looked at one personally (plenty of gas, motorcycle, and small engines though).

 

cquestad,

In general it is the bonding of the elements in the metal that determine properties such as melting points, etc. That is determined by a number of factors such as the types of bonds present, any changes in the element packing due to the alloy, and phase changes due to any treatments. There are really a bunch of different factors involved, and some materials are more complex than others. All the diesels up to large truck motors use aluminum as far as I know.

john

 

Most of the heavy diesel engines are using a two piece piston with a steel crown. Some have an aluminum skirt. Some a steel skirt. Our little B's use an all aluminum piston with a NI-Resist insert in the top and sometimes second ring groove. All aluminum though. Very heat resistant alloys.

The steel pistons are not old technology, but have kinda been in remission until the higher power densities came back around in the last 10 years.

Many little tricks like hard anodized crowns to provide rim stress relief, etc were being use on the aluminum pistons in the L10 Cummins.

Both the M11 and the L10 now use a two piece design. Steel and aluminum. The big N14 went to a larger connecting rod with additional material in the small end to accomodate the newer two piece steel/aluminum piston they designed in 1995.

BMEP was the biggest factor in going back to a steel crown or a single piece all steel pistons in the big engines. High BMEP and aluminum pistons just wont last long.

Don~

 

So Don,

Dive in and give us your opinion on EGT's, when a piston melts, what goes first with high EGT's etc. Thanks!

 

Don,
Gives us some EDM's so we can test the max EGT theory!

-Richard

 

everyone says the edge juice adds timing only no fuel. then why is it so hot? it should be the coolest chip box out there?

 

Even the BEST high dollar alloys start to spall/crystallize, and MELT above 1500F

Every time you go above 1250F, start putting money in the bank.... Thermal damage is cumulative damage. it weakens parts over time (thermal expansion and contraction over many cycles). Thermal fatigue in pistons usually starts changing the metal itself from temperature and pressure (same conditions it was alloyed in!) All it takes it time to weaken the alloy enough where it will turn into a puddle.

1250 is my own personal limit. These are not F1 engines with super high $$$ aluminum alloys in them.

 

but...but. with my edge completely unhooked last summer i EASILY (easily) got up to 1350 F . thats with my pyro in the manifold where edge says to put it.thats stock with a heavy foot going about 110-130 km/hour.....you tell me whats up?

 

With conservative timing of factory, and their 'in cylinder' egr i believe it.

But they are also achieving this on a limited amount of fuel.

With us changing the amount of fuel and timing, how much heat are we building in the piston itself, not including the exhaust stream

There is some cushion in piston temps based on flame front and WHERE the ignition even is happening. Is it happening close to the wall or all in the bowl?

There are a lot of dynamic changes we can make to these motors that will effect that.

I personally know of 1 motor melting pistons at 1000F (indicated on pyrometers) because of too much fuel and timing.

As you can see, you can be well within 1250 and still melt the slugs out the bottom.

It depends on timing, flame front, combustion area, amount of fuel, amount of air, dwell time, cam overlap.

So there is not a definate 'hard and fast rule.' only the best guidelines we can come up with'.

 

Oh, I forgot to mention, Duramaxes seem to take higher EGT's a little bit better because of better airflow in and out of the heads, and the AL head itself acting as a big huge heatsink.


Much of the time we see their pistons dying because of too much timing AND high EGT's

EGT's by themselves, they are pretty tolerant.