egt temps

[hairyuk]

hi all i know this has been answered before but i've spent days on the internet looking for egt temperature settings and still haven't found a definative answer. I've got a 1.9td aaz fitted with the kkk turbo in a vw t3 van and i've bought the gauges needed to keep an eye on temps, pressures, boost, etc but i don't know whats considered a safe reading for the egt gauge.
i've read that some people are going up to 1100c,
some are saying that aluminium starts melting at 900c,
some are saying that the oil squirters keep the engine below this temp so it doesnt melt,
some are saying that the kkk turbo will damage itself over 800c,
i'm coming to my wits end with this, i need to know what is a safe egt temp to be using all day on the motorway what temp i can push up too in short bursts and what temp i need to set the warning alarm on the gauge to.
Any help would be greatly appreciated thanks everyone.

[TDsamurai]

If im not mistaken aluminum melts at approx, 675*C and 1275*F so running those numbers as a maximum EGT would be safe as it would take quite some time for the metal to absorb the heat. I run my engine at 1200F for long periods of time without issue.

[RadoTD]

If im not mistaken aluminum melts at approx, 675*C and 1275*F so running those numbers as a maximum EGT would be safe as it would take quite some time for the metal to absorb the heat. I run my engine at 1200F for long periods of time without issue.

This.

1200F is a reasonable number to stick to. I've hit nearly 1500*F, never for more than a few seconds though, but nothing melted. I think timing also has a bit to do with it... if your timing is retarded, less energy is actually being forced into the piston, so it's less likely to get as hot. But unless you're doing anything crazy, 1200F is a good number to stick to

[dh13]

I have also seen 1500*F for short periods of time. This is on a NA block also. I don't try to get it there often, but if I hold it to the floor forever it can get there.

I usually run 1200*F to 1250*F for fairly lengthy amounts of time, and no problems yet. I don't know what my timing is exactly, but I know it is more then 0.95mm. I changed the timing belt and timed it to 0.95mm, turbo'ed it and just loosen the pump and moved it until I felt it was good.

[hairyuk]

High again and thanks for the replies.
Next question is what sort of revs are you getting to at these temps and are you using intercoolers or charge coolers?
i havent got as far as fitting either yet, but its next on my list as my egts are reaching these temps very easily, without even reving very high.

[lord_verminaard]

What I don't get about EGT's is why they have to be so much lower on diesels than gassers.  Audi's 2.7TT engine has factory EGT monitoring to prevent engine damage, but they don't start monitoring EGT's until 945C and will not start enriching until 980C.  That's 1790 F!!!  Other people have monitored 1400 F at highway cruise.

What's the deal with gassers being able to handle more EGT's?

Brendan

[Smokey Eddy]

I'm with Brendan on this one. the engines are constructed the same... what gives? Is the diesel exhaust supposed to heat soak its surroundings more so than petrol exhaust?

[theman53]

I could be wrong, but I think it is the way the fuel burns. The gassers get hotter the more air is in the mix and diesels get hotter when there is more fuel in the mix. There is different chemical reactions too IIRC like gassers making oxides the hotter things get. Maybe I am off.

[cyrus #1]

My understanding is it has to do with the relationship between the energy converted into motion and what goes out the exhaust as waste.  Our diesels convert more energy into motion than a gasser.  This translates into comparatively higher combustion temperatures but cooler exhaust going out.  Therefore a gas engine in theory has lower combustion temperatures and more waste energy going out the exhaust pipe.

[RadoTD]

I have a theory on this, nothing to back it up though... somewhat along the lines of what Cyrus said. I could be completely wrong though

Here's what I think - partly due to the higher compression of a diesel and their better efficiency, when a cylinder fires, a lot more of the energy from the combustion is pushed through the piston of a diesel. More heat is actually transfered to the metal than a gasoline engine.
If you advance the timing without touching anything else, it will increase fuel efficiency/power and decrease EGT's. You're still burning the same amount of fuel. I think more energy is being transfered through all the metallic components of the engine.
In a gasoline engine, your exhaust still has tons of heat that hasn't done anything for you... it just quickly blows out of the exhaust not spending enough time to linger and heat soak anything

[blackdogvan]

http://bankspower.com/techarticles/show/25-why-egt-is-important

[lord_verminaard]

I don't really care why diesel EGT's are lower really, what I want to know is why can a gas engine sustain more EGT's than a diesel?  Turbos are turbos, engines are engines.  The Banks article said sustained 1300F EGT is acceptable.  If the Audi 2.7TT can hit 1700 F without much trouble, why is that? 

Brendan

[vanbcguy]

I too have always wondered, especially seeing as how VW's diesels are essentially modified gassers... But then again, find anyone on here who has destroyed their engine due to high EGTs... Most I've seen is a turbo destroyed after running it waaaaaaay outside its efficiency range for a long time.

Not that I'm saying the 1300F limit isn't appropriate or that I wouldn't strive for it myself (if I had an EGT gauge in Jezzie) but what you say is true... Sodium filled exhaust valves, piston oil squirters, we have what it takes to take the heat.

[rodpaslow]

From older diesel books compression temperatures in a diesel with approx 20:1 compression range in the area of 1600°F (in the area above the piston when compressing the air) before the injector does it's thing.  Gasser has half the compression and I'm not sure about compression temps, But i would think start at a much lower temp until igniting the mixture.  With a gasser the octane rating and rate of burning the fuel has a lot to do with it as well.  With gas the fuel mixture burns quickly, diesel is much slower in comparison.  That's why F1 cars can rev to 18,000 rpm.  You may find an Audi TDI racer doing 5000 to 7000 at a maximum!

[blackdogvan]

I've read the Audi R10 TDi racer only revs to 5500 but apparently stays above 5000 for 70% of the 24hrs at LeMans.

Gasser EGT article: http://rusubaru.com/egts-101/

The guys putting tuned 1.8T's into Vanagons think the ECU is keeping them safe & therefore don't think a gauge is needed... Until one of them runs with one & posts some data i'm sceptical. Lean conditions under heavy boost could really heat them up.