924Board.org

[bruce76-924]

Took my turbo'd n/a this evening for a short road test to try and set it all up since been rebuilt and it's down on power underload. Looking at the plugs it needs the mixture richening right up but since the're a real pain to get to when the engines hot could I use exhaust temperature as a guide to mixture or is it to vague?

Cheers Bruce.
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1976 924 LHD, full cage, semi tube chassis, 951 brakes, lightweight 951 body panels.
1.8t engine conversion with Holset turbo and 6 speed Audi gearbox.

[Min]

http://www.sdsefi.com/techegt.htm

Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[Racing]

Yes you could.Most def.
However,a word of warning with EGTs.

Most common mistake with these are installer faults.
It is imperative that they are installed rahter far into the gas stream to be of any use,and this is also fairly linked to diameter and type of probe.
I often see customers coming in the door with turbo cars claiming this or that as EGT reading.
I´ve had them in the door,jumpin of joy,to the tune of loudly explaining to me that they have an EGT of 600C....
Then...then i spend some time explaining to them that IF 600deg...your engine most certainly isn´t doing its job,and you´re NOT making power.

Fact is that most engines will have a TRUE EGT somewhere around 900degC+

Where it´ll touch down from there..is a matter of the indiviual(Ie-engine)

To make good use of the EGT its response time is also imperative,and again this is a matter of how you install it and what diameter it is.

In short you can say that you alter timing until the EGT reading for a given engine is at its LOWEST,and then fool around with fuel until the EGT reading becomes as HIGH it can again.
That´s how you make power..

Meanwhile it is IMPERATIVE(especialy so with the pistons of the 31 engine) to keep anal control of any and all detonation.

IMO an EGT would be wisely used(read this is not an option) together with a wideband lambda sensor.
Point being that a CALIBRATED WB will let you get AFRs in direct mode while being able to log EGT.
What´s more,is that most WB units carry the poss of multiple analogue inputs,and to log the WGTvsWBvsThrottle position vs MAP sensor load is a good idea as there´s no way in hell that a human will be able to keep track of all those numbers across the rev band.

Tech edge unit for instance comes with software that makes it possible to log a variety of inputs of your desire via a laptop.(Most units do this)

[Racing]

Another thing.
Most in dash EGTs should be outlawed IMO.
Point being that EGT probes break after being subdued to long term use.
..and having one of them probes going dead on into your turbine is a BAD thing.
Ie;you use the EGT to set the engine up,then take it out and plug the bung.

[bruce76-924]

Min and Racing, many thanks for that, I will investigate further and keep you posted.

Cheers Bruce
_________________
1976 924 LHD, full cage, semi tube chassis, 951 brakes, lightweight 951 body panels.
1.8t engine conversion with Holset turbo and 6 speed Audi gearbox.