Typical EGT for I.C.E.'s 4

[kahlilj]

can anyone tell me what typical exhaust temperatures (at the header) would be for a 4-cylinder normally aspirated, gas-fired engine.

secondly, what about that same engine with a factory turbo installed? (e.g. mitsubishi eclipses 1990 - 1999 models, lancers,.. ) would there be a dramatic temp difference or would they be within the same range?

i'm asking because those temps influence/determine which header materials would be suitable. i tend to think there will be little temperature difference between the two engines esp as exhaust gas reaches the exhaust manifold/header pipe.

any thoughts?

 

[patprimmer]

The turbo engine will have substantially higher EGT.

You will need a substantially heavier gauge steel for the turbo exhaust manifold than is normally used on NA engines.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[kahlilj]

thanks pat, but what temp ranges are we talking for each?
i thought the N/A engine & turbo would both have temps ~1000 to 1400°F. does that seem about right or way off?

i'm really looking for values here.

 

[NickE]

My WRX (2.0l, 8:1cr, 14.5psi, 94octane, ~11:1AFR) will hit 1600°F (at the outlet in the head on the cylinder with a known lean condition when highly tuned, I'm stock ECU/stock boost) on a long WOT pull, in the winter. I dont know about summer yet.

The headers are cast iron.

Most aftermarket headers are constructed of 304ss (although I think it should at least 304l if not 321/347 -thats more of a personal opinion.)

I do know that one company makes an inconel up-pipe (headers -> turbine inlet) it adds about 200-300$ to the price.

Try some of the hobbiest fourms (IE:

http://www.nasioc.com)

for the motors you are interested in, this is a pretty well known piece of information needed for tuning aftermarket timing/fueling controls.


Nick
I love materials science!

 

[kahlilj]

thanks nicke. would you say that that same engine without turbo would approach that temperature too?

also i noticed the same about a lot of aftermarket headers. from what i read about the two material props, 321 would seem more suitable for header material because of its higher heat tolerance. i guess 304SS is cheaper than 321?

does any one else have knowledge of what the temp ranges could be for a non-turbo engine?

 

[Rob45]

Temperatures of 1600+ F are not uncommon for NA SI engines.

A drawback to 304 is that when welded (heat sensitized) it is susceptible to intergranular corrosion if exposed to road salt.
And it doesn't take much salt or very lengthy exposure to cause a part failure.
304L seeks to minimize this effect by reducing the amount of carbon in the alloy, with some success.
321 doesn't have this drawback, nor do the much less expensive stabilized ferritic alloys such as 409 and 439.

All of these have much greater elevated-temperature strength yield strength than do any carbon steels.

 

[NickE]

Rob45- and cooling slowly through the temp rage of 700-1400F can also sensitize the alloy.

I do know that 409/439 (I dont know wich) forms a nice hard oxide scale at turbine output temps after ~18mths. (salt dirt soap exposure).

I am going to throw my opinion with Pat. Although I've never measured EGT on a NA motor. Rob might be right then.

 

[kahlilj]

thanks folks. rob, may i ask what you base your statement in about +1600°F for na engines? source you have read? or personal experience? or ?? don't get me wrong; i tend to agree with you. & is this applicable to 4 cylinder engines

also does SI mean "straight, inline"? as opposed to "horizontally opposed" or a "vee" configuration.

if you live in an area where road salt is uncommon then that corrosion concern with 304SS becomes less of an issue right? does that then leave concern with thermal fatigue as nick eluded to?

 

[patprimmer]

I have never measured either, but I do know turbo exhausts fail if you use std NA construction methods and materials. Maybe it is more to do with load due to exhaust gas pressure and the weight of the turbo, or the stress of the braces restraining thermal expansion.

However, I would think that both NA and Turbo engines would be limited by detonation and piston meltdown when trying to get maximum power. In that case, both combustion chamber temperatures would be similar.

Even though the temps might be the same inside the chamber, I would also think that as the gas passes out the exhaust valve and expands into the port it will cool a bit. As an NA will not have as much pressure in the exhaust port, I would think the NA engine will allow the exhaust to expand more and therefore cool more.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[kahlilj]

interesting thoughts pat. see this is why we need measured values - to confirm or deny our theories or introduce new phenomena!

 

[NickE]

" does that then leave concern with thermal fatigue as nick eluded to?"

I did nothing of the sort.

I stated the well known point that not only does welding sensitize 304; so will exposure to temps in the same region as exhaust temps.

This sensitization is the precipitation of chrome carbides, 304L is a low carbon grade and minimizes it to some extent as Rob states, 321/347 have Ti/V as alloying elements, the kinetics are such that the carbon prefers those over chrome, leaving the chrome to provide corrosion resistance.


Nick
I love materials science!

 

[mattsooty]

Kahlilj

I dont think that you are comparing apples with apples. The two engines you mention will not be the *same* in turbo/non turbo guise. There will be myriad changes, compression ratio, piston & valve material, valve timing etc etc

However I get your gist and a modern SI (spark Ignition) engine will generally have max exhaust temps of ~950degC.

For a given engine set up (NA or FI) one is const

1) Detonation
2) AFR
3) Exhaust Temps

To increase the torque at a given engine speed (and therefore power) the amount of air in the combustion chamber must be increased. However as with everything there is a compromise: -
As the airmass per stroke increases so does the tendency to detonate.
To stop this detonation the spark must be retarded.
As the spark is retarded the exh temps increase.
As the temps increase the AFR must be reduced.
This 'richening' can only continue until such time as rich misfire occurs - or no more torque is produced because of the extreme retarded spark.

At wide open throttle the modern Bosch Motronic EMS systems run closed loop exh temp control (with AFR being the control parameter). This allows best fuel economy and also means that different octane fuels can be used with their active knock system without fear of overtemp in the exhaust.

MS

 

[kahlilj]

MS,
i appreciate your input. however don't let my simplification mislead you into thinking i presume the engines (esp. internals) are exactly the same. that was not the point. i fully understand there are substantial, as well even slight, differences between a NA & turbo engine.

my point was simply to use the same engine block for comparitive basis of EGT not to compare the engines in of themselves. i did not want to compare say 12-cylinder to a 3-cylinder or a 2-stroke versus 4-stroke, etc. i suggested a common "platform" such i did to minimize other variables.

e.g. i pointed out that the 1990's version of mitsubishi eclipses (& talons & lasers) did just that. they used the "same" 2.0 liter, 4 cylinder engine, but had different internals (& other accessories) for the NA versus the turbo. however, when you look at the engine block & they appear identical.

that being said, you indicated a max EGT of ~1700°F is typical. are you saying this applies to both NA & FI engines? would this be temp be at the exhaust header/manifold? & as i said before, i am not doubting anyone's veracity, but what is your source for that value?

thanks again.

 

[mattsooty]

Kahlilj

The temp I quote is the max exh port temp within the head and is the most recent that I have worked on in an SI application. However I would expect that some OEMs might be anywhere up to 50-100deg less than the 950degC I quoted.

MS

 

[kahlilj]

i gotcha matt. was this SI application normally aspirated or was it forced induction?

kj