EGTS for boosted apex?

[kinger]

Has anyone used EGTs and have a range they like to say is "safe"? I will lean on AFR for overall tuning, but will watch EGTs for evenness across cylinders. If anyone had any learnings they would like to share I would love to hear it. Right now I am thinking less then 1300 degrees F or 700 Degrees C would be desirable.

 

[sxr70001]

Why are Exhaust Gas Temperatures so Important?

[ATTACH]Exhaust Gas Temperature (EGT) is an indicator of cylinder temperature and should be monitored to prevent detonation and engine damage. EGT...

www.theturboforums.com

Found this. Seems to me like a gas engine is a gas engine regardless of application at least for a baseline.

 

[kinger]

I may be a little light at 1300 looks like 1500-1600 max at full boost. It will be neat to see in my data what happens as my meth injection comes on.

 

[earthling]

From a theory perspective.. (and I am quite sure you know this but for those following along)

There is no perfect target temperature for EGT as it is all relative and related to a particular engine/configuration but if you had to pick a target, I might start with 1250. EGT is not like setting AFR. EGT is a byproduct of the combustion process so what you care about is HP/Torque curve and EGT as a way to understand the performance of individual cylinders relative to overall engine performance as you know. Max power is what you care about, EGT will be a byproduct of that no matter what the outcome is. It should only be used as a 'trimming' mechanism for the individual cylinders.

Lets say your AFR reading on a single wideband sensor downstream of where the exhaust pipes join and it says you are at 14:1. That could come from some cylinders being richer, others being leaner because you only see the average reading. You hope not but lets say your intake airflow is bad. EGT will tell you which cylinders are hotter or colder but those values fall or rise on both sides of stoichiometric. Look up aircraft EGT readings, you should be able to find a chart to exactly illustrate this. As a tool for root cause EGT is very useful because you can start by enrichening the cylinders that are 'off' and see what happens a cylinder at a time.

Your safety comes from knowing what is going into the cylinder and whether not you are getting detonation (or not). EGT won't help in this regard (detonation) because it is far to slow to react. Maybe it will save you from catastrophic damage if you catch it early enough but my guess is that the damage is already done by the time the EGT reacts.

Where EGT is used as a safety mechanism is right at the inlet to the turbo where there are definitely safety limits, if you have an extra sensor input that would be worthwhile.

 

[mysledblows]

Never played with them on a 4 stroke sled and certainly not with a compound boosted one, but back in my 2 strokes days I seem to remember about 1150 being the target. Now that depended on where they were located in the pipe because it doesn’t take much of a change in the distance from the combustion chamber to change that egg number pretty significantly. Aluminum starts to get pretty soft around 1200 - 1250.

 

[Srxspec]

There's alot that goes into the EGT number. Realistically the number doesn't mean jack sh!t! You have to correlate spark plug burn to an EGT number to get a baseline. I would start 1250ish as well, certainly not 1500-1600!! Ignition timing, boost level, your meth setup, etc will all affect the EGT number and how safe the tune is.

 

[kinger]

There's alot that goes into the EGT number. Realistically the number doesn't mean jack sh!t! You have to correlate spark plug burn to an EGT number to get a baseline. I would start 1250ish as well, certainly not 1500-1600!! Ignition timing, boost level, your meth setup, etc will all affect the EGT number and how safe the tune is.

Wait you said this engine will take 1600 degrees all day long

I kid I kid...I mainly got it to see variation between cylinders, I will let the number fall where it falls. It will be neat to see how it falls on the juice!

 

[earthling]

The 'juice' will help keep EGTs under control. It may not bring them down. It will be interesting to see how it actually works out for you.

 

[mbarryracing]

I agree with Allen... I would forget monitoring EGT's, that is old school low tech now in my book because there are too many other variables that affect and alter exhaust temps other than AFR, most significantly is ignition timing.
Monitoring AFR is way more of a priority...
Watching EGT's helps diagnose differences running between cylinders, but I wouldn't use it to tune for combined performance. I don't even use it for tuning 2 strokes anymore.

 

[kinger]

Thanks guys, I will just use them to balance the AFRs in Cylinders. I am not using them to control anything within the Motec.