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MG MGB Technical - exhaust gas temperature range

Hi!
Anyone knows what range of exhaust gas temperature is to be expected from a stock engine?
(as I plan to install an egt gauge to go along with a broadband afr meter)
Any input appreciated,
Jochen
Jochen Beyer

Jochen,

I have no data for you, but assuming you are willing to share, I would be interested in yours when you acquire it.

Sean
Sean Brown

Jochen.My infar-red thermometer normally reads about 350 deg F when checking the exhaust gasses out of the header. According to the instructions, the gas into the cat should read about 100 deg F lower than the gas output from the cat. This is what I have used the tool for and it has demonstrated that the cat is working correctly. If you need more accurate data than this, please let me know and I will fire up my 68 GT and take the exhaust header pipe reading tomorrow.

Les
Les Bengtson

Les,
You are obviously measuring something other than under-load exhaust gas temperatures. Maybe temps on the outside of the manifold or pipe? Meaningless, except for comparison of readings taken on the same engine and the same point. Temperatures must be measured at the center of the gas stream with a thermocouple, under operating conditions, ie loaded. Anything else is some average of current EGT with loss out the pipes. EGT gauges are calibrated 2-900C, or 8-1800F (Rotax Aircraft numbers) My old Cummins diesel was redlined at 1350F, and it could be put there pretty easily. Found some aftermarket instruments, again calibrated to 1600F/870C. Most are in that range, which is max operating for most engines that are not about to disintegrate; but Stewart-Warner sells a racing gauge at 2200F/1200C (unusual - that is meltdown range)
Jochen, suggest you ask on the supercharger board.
FRM
FR Millmore

Well, mostly EGT gauges seem to be interesting for people with turbo or supercharger, especially the Jap turbo guys who are really pushing it. They do expect much higher temps than I would in a normally aspirated MGB. I now ordered one that goes from 350-950 C, as I have checked the ranges of all sorts of aftermarket suppliers.
I'll share my data once it's here and installed (will take some more weeks, as Westach produces them to order)
BTW, anyone with experience regarding broadband afr meters?
Jochen
Jochen Beyer

Don't know about an MGB, but with the airplane I fly, I expect EGTs in the 1250F range on take-off (full rich) and lean to ~1350 to 1450F for cruise flight.

This is an engine with 8.5:1 compression turning 2500 to 2700 RPM.

Edd Weninger

Aircraft exhaust temperatures may not be "true" temperatures, but an artificial value used to set relative temperatures, including "maximum".

Temperature probes and their wiring that can withstand the heat get progressively more expensive and those able to survive over time and retain their accuracy prohibative.

Jet engine exhaust temperature probes have to be located far from the turbine where temperatures have dropped.

Rotary aircraft engines commonly used cyllinder head temperature.
Dan Robinson

Fletcher. You are perfectly correct. I am measuring the external temperature of the head pipe just below the exhaust manifold under idle conditions. Thus, the heat being radiated rather than the temperature of the exhaust gasses themselves which would be considerably hotter as you and others have stated. I am not sure why either temperature would be of concern when driving on the road, but am willing to be enlightened. Les
Les Bengtson

Jochen,
Again, go to the SC board; some of those guys are playing with WB AFR. Lots by Google, good one here:
http://www.techedge.com.au/vehicle/wbo2/default.htm

Les,
EGT is a measure of combustion efficiency, and extremely useful in setting fuel mixtures, etc. The temperature will be highest at stoichiometric (perfect) mixtures. There is a lot of info available on this, mostly from go-kart/snowmobile/ motorcycle sources, since they use it as a primary tuning parameter. Google away.
On turbo diesels, EGT gives the best indication of fueling, turbo, or driving failures. Lack of fuel gives low numbers; turbo failure, exhaust restriction, or lugging give high. When I rebuilt my 350NTC Cummins to 400+, with a custom big turbo, EGT at 1400rpm/full load dropped 200F (from 1500F to 1300F), despite the power increase. Previously I had to watch it at 1700/full load = 1350F, but under new turbo, it would only get to 1300F at 1400rpm and 1150 at 1700rpm or higher. Lugging reduces airflow from the turbo, causing higher EGT
Contrary to widespread myth, lean mixtures do not give higher exhaust temps, since combustion efficiency is down, but they DO give higher engine (like cyl head)temps as detonation sets in. A combination of falling EGT and rising Head temperatures means SHUTDOWN!(voluntary or not, your choice!)
Here's a really good link, which will lead to more:
http://www.factorypipe.com/Technical/Tech_Articles/Deto/deto.html
FRM
FR Millmore

Thanks for the links.
I opted for the LC1 so called lambda cable from innovate motorsports, as it's being officially imported to germany, so I have a competent dealer close by.

Basically, what I want is to get a real time lambda value during running conditions coupled with egt readings from front and aft header pipe as an added feature to look for synchronisation, thus being able to judge wether the chosen carb setup really works out for all driving conditions. (I also like a lot of gauges in my dash... all contemporary Smiths, though, except for a row of three)

I'll check the SC board.

Jochen
Jochen Beyer

Dan,

The aircraft exhaust temperatures are accurate and are measured with sensors installed in each of the 6 exhaust stacks about 6 inches from the exhaust valve. All six probes go to a single instrument that shows all 6 temps simultaneously on bar graphs. Individual probes are also used for oil temp and 6 cylinder head temps. It is interesting to note the slight differences (~50 to 70 degrees) between the different cylinders, primarily due to differences in the intake runner lengths, turns stc. Probable also unmeasureable differences in the injection orifices. In fact one company purposely makes injector sets with slightly different orifice sizes to get a better balance of the temperatures, to within 25 to 50 degrees or so.

Sounds like Jochen would like this in his dash. Google for JMI Instruments.

The probes last about 1000 hours or so. All a bit pricy for automotive use but worth the expense for an aircraft engine which costs $25,000 to overhaul.

Edd Weninger

This thread was discussed between 27/07/2005 and 01/08/2005

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