light/mid load EGT
light/mid load EGT
(OP)
What is an acceptable EGT range for light/mid cruise?
Right now they hover in the 1350-1400*f range while at cruise (50-60 kpa @ 3000rpm)
the engine is a 1755cc mitsu 4cyl
9.5:1 compression
Ive tried AFRs from 14.5 to 17:1
and ign lead from 36 to 42* btdc
No mater what Ive done they wont seem to go down
Right now they hover in the 1350-1400*f range while at cruise (50-60 kpa @ 3000rpm)
the engine is a 1755cc mitsu 4cyl
9.5:1 compression
Ive tried AFRs from 14.5 to 17:1
and ign lead from 36 to 42* btdc
No mater what Ive done they wont seem to go down





RE: light/mid load EGT
Are you sure your timing marks are correct. If you have a dial in timing light throw it away and get a good non adjustable timing light and put accurate marks on the pulley or flywheel if you have access to it.
Regards
Pat
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RE: light/mid load EGT
The timing is correct. (I would never even own a dial-in timing light) I had the same thought though so checked my base timing from idle to 3000 rpm , it doesn't fluctuate from the 5* its set at and the programmed advance is spot on.
I also forgot to mention that the Engine is turbocharged, if that makes any difference
RE: light/mid load EGT
Regards
Pat
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RE: light/mid load EGT
Regards
Pat
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RE: light/mid load EGT
All 1.8Turbo cars of German manufacture I have driven seem to have a lot of back pressure taking your above known statement into account,
That is, any time I take one for a moderate run and return to base, the exhaust manifold glows red hot, Im talking red now, like a poker in a blacksmiths forge (I have witnessed this on 20 plus cars)
Could this be the fact that a small turbo was fitted in an attempt to reduce lag at low rpm, but at the cost of flow through the unit at higher rpm, thus creating excessive back pressure within the manifold?
Appreciate your answer Pat, you havent failed me yet in the years of reading Ive done on here.
Brian.
RE: light/mid load EGT
Then how much back-pressure is to much?
RE: light/mid load EGT
The red heat is an artifact of using the engine's hot exhaust gas, instead of some room temperature gas supply, to provide the pressure.
Both are perfectly normal when the turbo is spooled up and working. They track each other because the turbo is sort of a bootstrap device.
Mike Halloran
Pembroke Pines, FL, USA
RE: light/mid load EGT
I understand that Mike, but surely you can have an excess of pressure too pending flow resistance through turbo?
A pretty large red hot part in a 1.8T engine bay always amazes me everytime I see it.
Thanks for the reply,
Brian.
RE: light/mid load EGT
You trade power for response and can only make the compromise that suits you best. The size of the restriction relative to other dimensions is the AR ratio. I would need to refresh my memory to know exactly how it is calculated, but for a given turbo, I think low AR equals quick response and high IR equalspoor response but big top end.
To much restriction is when the exhaust gets so hot that things fail or the power is unacceptably low.
Regards
Pat
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RE: light/mid load EGT
Brian.
RE: light/mid load EGT
The exhaust manifold pressure is a measure of the load on the engine, or of the engine's response to the load, depending on your perspective, but in either case, you don't particularly want to minimize it.
The backpressure at the exit of the turbine is one pressure that you do want to minimize, because the engine always responds happily to doing so.
I don't think it's correct to call the exhaust manifold pressure 'backpressure'. Sure, that's what it would be in a normally aspirated engine, but in a turbo engine, that flow is not at the back end of anything; it's right in the middle of a strong feedback loop of energy flow.
Mike Halloran
Pembroke Pines, FL, USA
RE: light/mid load EGT
I was trying to keep it more simple than cylinder blow down pressure.
It is pressure that backs up behind the nozzle orifice in the turbine housing.
There is an obvious relationship between the load on the compressor wheel due to volume of air pumped and the head of pressure it is pumping against.
There is an obvious relationship between load on the compressor wheel and load on the turbine wheel.
There is an obvious relationship between load on the turbine wheel and exhaust gas flow through the turbine.
There is an obvious relationship between power developed and mass of exhaust gas per unit of time.
There is an obvious relationship between exhaust gas pressure and exhaust gas temperature.
Regards
Pat
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RE: light/mid load EGT
No lag, or ''boost coming on kick'' can be felt when driving it, it behaves pretty much like say a 2.5n/a engine when driven.
Maybe this characteristic> the fact that the turbo spools and starts to make boost very low in the rpm range has an effect on manifold temperatures due to the fact that higher up the rpm range a lot of the gas is being directed electronically out the waste-gate in order to prevent the turbo over spooling?
The bottom line is , to Pat and Mike I dont know why the 1.8T reddens its manifold so much from the factory, everytime I see one It makes me wonder, surely all the energy used to do this could be made better use of?
One thing I do know(or think), and keep in mind Im more a n/a guy that a turbo guy, is that I feel compressor maps are sometimes too looked into or over studied taking into account all the rest of the variables the turbo can encounter throughout the load/rpm range.
Dont shoot me down for saying that but Ive seen folk analysing the map, wondering, worrying, calculating, re-calculating, simulating, etc, for days on end before making the final choice and still not being happy how it performs in real life.
To Pat and Mike, I want to say thanks again for your fantastic replys, I value your opinions as Im sure your aware that each reply is very valuable given the fact that real life testing can be a costly route and often a waste of time when direct answers can rule out some ideas or ways of thinking immediately.
Ill always be learning.
Brian.
RE: light/mid load EGT
However I'm still curious why the EGTs are higher at low load and not during high load .If it were due to a restrictive turbine housing (small AR) or a restrictive manifold the EGT should higher all the time or at least during high airflow
The temperature issue only seems to occur at low load constant speed .I could understand if the problem was at time of high airflow but this is at low throttle, less than 20% .I know that a restriction will cause temperature to rise but why would it rise more when its lower ?
Pat and Mike I do appreciate your incite and thanks to all of you
Aaron
RE: light/mid load EGT
Im not familiar with your engine but the temperature range seems reasonable. I have seen cruise EGT's as high as 1600f.
RE: light/mid load EGT
Brian.
RE: light/mid load EGT
http://dodgeram.org/tech/dsl/FAQ/turbo_faq.htm
About half-way down the page, it lists effects
and causes. High EGT is associated with a too-
rich mixture and mis-matched boost levels.
<als>
RE: light/mid load EGT
the EGT problem only occurs at lean AFR and Low manifold pressures
...The problem has gotten better since I added more timing to my spark map in the problem areas but there still in the 1300*f range
RE: light/mid load EGT
Mike Halloran
Pembroke Pines, FL, USA
RE: light/mid load EGT
If anything I've noticed that post turbine EGTs on a turbo car are a bit lower at cruise than they are on N/A cars. Granted it's comparing apples to oranges but turbos are pretty good at converting thermal energy into mechanical energy after all :P
RE: light/mid load EGT
I had a turbo failure yesterday so I spent the better part of to day pulling all of the turbo stuff off and putting my old 4-1 header and N/T exhaust back on .While I was at it I welded an egt bung on.So after it all was back together, I took a test drive and egts under the same circumstances temps were 1100-1150*f
So I guess the turbo/manifold combination was to restrictive ...so that combined with the failure means its time for an upgrade
Thanks to all of you for the help