EGT

[miniman82]

From another thread, to avoid pollution.

[The Noof]

I have mini, and seen the results of high SUSTAINED egts over 1400.The pistons can, and do melt.
Our first adventures on our SB chev/nitrous race car engine was where we discovered it.We data logged every pass, and were doing well untill we had a hardware failure(fuel solenoid).It was a big shot,about 300 hp.The a/f went very lean @ 20:1,egt topped at 1433,and melted 3 pistons before it could be shut down in a 9 second pass.Thats all the research I need to do.

[miniman82]

Detonation is what melted your pistons not EGT, Noof. That's totally different. It's possiblt to crack pistons via detonation on N/A engines without even trying, and the EGT's can still be low as you've noted. Your EGT of 1433 was still not all that high, the guys at my machine shop who bracket race 3 stage systems tell me they see well into the 1600*F range all the time. It takes a whole lot of EGT to melt heads without detonation doing any work as well, especially on a waterpumper.
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[Jimmy111]

High EGT's cause high Exhaust valve and seat temperatures which cause detonation and melted pistons. The heads wont melt. Just crack especially between seats and sparkplug.
Most diesel engines start to fall apart after 1350 and that is with piston squirters and water cooling of the exhaust valve.

Personally I think it is too hot and 1200 is more like it. But racing is racing and you do what it takes to win. Durability has little to do with it as long as you finish.

[The Noof]

[kielbasa]

[miniman82]

I'm not even sure what to call it anymore.

I must have heard at least 13 different names for so far, but they all describe the same phenomenon. Preignition, detonation, ping, knock, ect. It's all destructive, regardless of the name you give it. I always use the word detonation, to avoid confusion. Detonation doesn't always cause the same thing to happen, either. Sometimes it will melt a piston under low loads, other times it will happen incessently to where you can hear it but nothing melts and the ring lock up instead. But thing to do: stay away from it.


Jimmy: diesel engines are nothing like gasoline, so the EGT numbers are useless by comparison. The only thing they share is being 4 stroke, and having intake and exhaust valves. Not trying to rub you the wrong way, but you know it's true. And for the record, I don't race this car- it's one of my DD's.

[The Noof]

...and I will take your instrumentation with a HUGE grain of salt.

[Jimmy111]

My point was that diesel engines are designed for high EGT's Much more durably constructed than gasoline engines.
If you use steel exhaust valves they will soon reach their maximum operating temperature. The valve which has an initial tensil strength of 60,000 psi looses half of its strength by 1100 degrees and 80% by 1400.
You would need to use titanium exhaust valves for any life expectancy at those temps.

Since you are still a Squid you might have access to NAVAIR manuals. There is a very good section in the AD-1 (Skyraider) R-3350 engine that has a lot of testing of the hows and whys of EGT's effect of cylinder head parts and materials.

[Vee Dub Nut]

[The Noof]

[Splitdog]

Also, it would seem to me, melting is melting. High temperatures. Detonation causes a different kind of damage. Cracked cylinder, broken ring land, etc. Also, way before aluminum melts, it gets soft. The steel seat starts to sink, etc. Bottom line=excessive heat is a killer.
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[The Noof]

[SGKent]

obviously based on your compression you are choosing the correct fuel. If however you run too high an octane for your engine it may not hurt it but it will slow the burn and extend it out into the exhaust stack, raising EGT. That is one of the reasons you see flames from methanol fueled engines. The burn is so slow that with the short stacks it extends out into the open air. There the unburned fuel has extra oxygen to burn with as well. I don't want to suggest a lower octane because detonation could be fatal to the engine, however if you are running the 110 av gas on the street, and you have stock compression you might consider 91 - 93 octane.
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[miniman82]

[Jake Raby]

I also have Gb's of data.. I gathered 2Bg on my 2006 cross country trip, EGT was logged the entire time on all 4 cylinders. I tune by EGT and have been for years.

EGT thats measured at anything less than WOT isn't very indicative of anything and at part throttle EGT will always be higher. This part throttle EGT isn't going to harm the engine at all because the engine is hardly under a load at all. I have been cruising at 16:1 and 1500F EGT in my 912E for 155K miles, it only has 6% leak down hot and still makes as much power as it did when the engine was new 8 years ago.

You guys with Turbo engines can't stay on the throttle long enough at once to see the effects of high EGT very well, because the engine is so powerful and the car is so light... You'll kill yourself first. This is why boosted Beetles fair well in longevity.

With moderate CR and/or boost you can get away with higher EGT for much longer than high CR / high boost. As the CR elevates the quicker the EGT will do things to the engine that it doesn't like.

I have found WOT EGT sweet spots to be around 1275F, anything higher than that and the valve job is compromised fairly quickly, I have wiped out valve jobs in two pulls on a high CR engine when I missed the tune...
I see EGT impact valve seats and exhaust valves more than anything else, different head castings can deal with elevated EGT better than others, the same goes for different valve seat materials.

Lots of things impact EGT, but the engine's combo is the biggest.

For one to fully understand how EGT impacts an engine you'll need to force a failure under data logging to see what happens when things go south.. It takes a crazy bastard like me to do that.

Miniman, what DL system do you use?? I have used a race Technology DL-1 and my current set up is a Race Technology DL-2 expanded to 24 channels with AEM thermocouple amplifiers and I monitor the data real time with Race Technology DASH 2.
where are your EGT probes attached to the exhaust system? What sensors do you use?
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Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell"

[koolkarmakombi]

[The Noof]

Jake: I won't question your knowledge, or authority, but i HAVE to question your findings:how can you have a SUSTAINED egt well past the past the melting point of the best aluminum alloys?

[Jake Raby]

[The Noof]