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Exhaust Gas Temperature


Guest Martin F
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Guest Martin F

Oh Font of Knowledge

 

Could somebody please enlighten me to the intricacies of measuring Exhaust Gas Temperature.

 

I understand how you can do it etc, but am not sure as to all the reasons as to why you may want to do it.

 

As far as i am aware it is done to understand how well your mixture is burning in the chamber, and to avoid detonation (?). One would guess that if your timing is slightly off that some of the mixture will still be burning as the exhaust valve opens and hence your EGT will rise.

 

I couldn't find a website with reference info anywhere on this subject, so maybe if anybody knows of one they could point me in the right direction.

 

Ash - any chance of a pearl of wisdom on this one. :)

 

 

Thanks in advance.

 

Martin

 

 

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Keeping EGT's under control is very important for the long-term survival of a turbo engine.

 

Sitting smack-bang in the middle of the exhaust flow are the exhaust valves and seats. There is only so much heat these components can take before the edge of the valve, or the tip of the spark plug, begins to glow red hot. Then your engine's in big trouble, as this hotspot can readily act as an ignition source.

 

If the engine senses detonation it immediately retards the timing. This can have a spiralling upward effect on EGTs as, in retarding the timing, it cools the cylinder alright but all the heat of combustion doesn't just disappear - it simply exits the exhaust (which rapidly increases in temperature).

 

Excess exhaust heat can not only erode your valves and seats, it can also do nasty things to your turbos like crack the casing on No1; send your turbine blades on a trip through the exhaust pipe; overload the thermal capacity of the oil, etc.

 

As the turbo runs on heat, then too low an EGT has the direct effect of reducing turbo efficiency. So what you are aiming for is an EGT that doesn't send your engine into meltdown, yet is high enough to spin the turbo with good efficiency.

 

Aim for 900 deg C at the exhaust port under full boost. If you measure just after the turbos then subtract about 100 degrees to take account of the heat energy converted to spin the turbos.  

 

One MKIV owner I know regularly pushed EGTs higher than the above guidelines. I have just completed his total engine re-build: replaced all 24 badly eroded valve seats and detonation damaged valves, together with the cracked turbos, knackered big ends, etc.

 

In fact, he managed to virtually destroy his engine just a few thousand miles after upping the boost. Well it wasn't so much the boost that killed his engine, but excessive EGTs. By the time he'd got an EGT gauge fitted it was too late, the damage was done.

 

So an EGT gauge can be a very useful indicator if you regularly run increased boost, and can considerably extend the time between engine re-builds.  

 

Yours,

J  

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Guest Martin F

 

Most of the suppliers who make boost gauges, etc make an EGT one as well.

 

Check out HKS, Blitz etc and then ask the Shop for a price.

 

 

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Quote: from Martin F on 12:28 pm on July 17, 2001[br]

Most of the suppliers who make boost gauges, etc make an EGT one as well.

 

Check out HKS, Blitz etc and then ask the Shop for a price.

 

 

Not Halfords then? http://www.stopstart.fsnet.co.uk/smilie/jesterlol.gif

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Guest Martin F

I'd really like to see you go into Halfords and ask for an EGT gauge!!!!!!!!!

 

https://jza80.mkivsupra.net/imports/2002/04/1.gif

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just ran up into 1050 degrees or something didnt he? Like he was way over the recommendations.

 

I still agree that the EGT is vital to knowing what the car is up to, Im pushing my luck with my car and I know it so an EGT is on the cards eventually.

 

CW recommends never putting the sensor anywhere but pre-turbo, others have said post turbo is okay, but expect the figures to be less accurate and as Ash said, take off at least 100degrees.

 

JB

Shop!!

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Quote: from HardHead42 on 1:51 pm on July 17, 2001[br]
Quote: from Martin F on 12:25 pm on July 17, 2001[br]

Thanks Ash.

 

Best make that the second gauge that i purchase then.

 

 

Definately, it will look good in  that Trust A-Pillar Guage pod too. :) make sure you get 60mm guages.

 

Trust A-Pillar Guage pod? http://www.stopstart.fsnet.co.uk/Sounds/hell.wav

 

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