EGT Measurement Position of Sensor

I'm about to change out my manifold and turbo assembly and have a query.

The current setup came with an EGT sensor drilled and tapped in the collector, just before the turbo.

To save drilling the new manifold and positioning the sensor in the same place, would there be any significant difference/ effect/ good reason not to mount it in place of my now redundant stock O2 sensor? My thinking was to get an M18 bolt, drill and tap it to 1/8" and mount the sensor here. This would be post obviously be post-turbo, would EGT be that different to pre-turbo?

The image I've attached is a full frame Evo kit, it's all I had to hand. I'm fitting a stock frame, but hopefully this illustrates my point! :-)

I'd strongly advise that you go to the extra trouble of mounting the sensor pre-turbo. There is a significant temperature drop across the turbine wheel so the reading post turbo can't directly be related to the pre turbo EGT (which is what we are most interested in). To make this more complex, the EGT drop across the turbine wheel will also be dependent on the size of the turbocharger. This means that post turbo EGT is all but useless for tuning purposes as you won't be able to relate the temperature to anything.

Is there any merit in using a post-turbine EGT purely as a safety measure? I am using a cast manifold so not really an opportunity for pre-turbine sensor placement. I'm thinking about setting a threshold and using the sensor to add fuel/pull boost duty as EGT rises above this threshold?

Certainly there is a correlation between pre turbine and post turbine EGT, but it's not possible strictly speaking to say for example that you're going to drop 200 deg C across the turbine as there are too many variables that will affect this. Post turbine EGT may be marginally better than nothing as you can log this temperature and see what values you're experiencing but it would be difficult to say outright what is safe and what is dangerous.

There isn't necessarily a problem with fitting a sensor to a cast manifold either. Rather than welding to the cast material you normally have sufficient wall thickness to drill and tap the manifold instead which in my experience works out to be reliable. It is of course a pain in the ass removing the turbo/manifold and everything else to do this install but I feel the effort is rewarded.

Thanks Andre :)

No problem to remove the manifold, I was worried about it cracking if the EGT boss expansion ratio was higher than the cast. It's an expensive aftermarket cast that are no longer available!

Thank you for the replies. I had a feeling there would be losses across the turbo itself- guess we could go all sciencey and how energy changes forms?!

Anywho, the manifold that is coming off is a single scroll and the sensor is at the common point. The one going on is a standard fittement upgrade/ replacement, which is twin scroll. Am I right to assume that measuring cylinders 3 & 4 as per my pics will be OK? Does thebsensor need to be in ge middle of the port, or would having it to one side (as there's slightly more material there to drill and tap) be OK?

1 thing is temp drop in pre vs post turbo. Another thing is even bigger delay, that is nature of EGT sensors anyway. For this reason there are open-tip sensors available. Also for same reason you want to install sensors as close to exhaust valve as possible. You have to ask yourself what is the reason you`re installing sensors, what you gonna do with this data and then you know where and why sensor(s) have to be installed.

If individual sensors going to be installed to individual cylinders, the depth have to be adjusted same for data being comparable.

@Adturbo with a twin scroll housing you really only have the opportunity to measure one scroll if you're using a single sensor. Of course it's reasonable to assume that the temp for 3/4 'should' be the same as 1/2 but that's not necessarily the case. In this situation though the only useful data you can hope to achieve is measuring the EGT at the turbo inlet as opposed to cylinder trimming or the like and in this application you'll be just fine.

In the perfect world it would be ideal to have the tip of the sensor located in the middle of the exhaust flow but often the ideal location must be balanced with what is practical. Even with the sensor offset significantly you'll still be measuring EGT and since you're only using one sensor it's not like it will effect a comparative reading like it could if you were fitting a sensor to each runner.

Thanks again for the replies.

I'm keen to keep an EGT sensor as it has been a really useful (albeit uncommon, in the UK Evo scene) tool. It's surprising the difference adjusting the injector timing makes as well as retarding ignition timing. On that basis I think I'll crack the drill out and get busy on the collector for 3&4! It's a shame I don't have a 5th temp sensor input on my G4+ PNP or I'd happily fit 2 (or maybe even 4!) sensors. Maybe I should buy a Thunder..... :-)

Out of curiosity, can anyone advise on 'safe' maximum temperatures? I've seen a wide range out there. Currently my peak is 950 Deg C, the original map, from a tuner had it hitting almost 1100.

In my opinion EGT absolute value is not so important and is very relative to particular application and is dependent on many factors. For me it is not main tuning parameter, rather another data to understand particular engine tendencies. Just have to understand principles how leaner/richer mixture and timing advancing/retarding affects exhaust temp. EGT is also helpful parameter, for protecting turbo and exhaust components in general, especially on applications where a lot of cutting/retarding used (launch, ALS, traction). EGTs, especially if installed in individual cylinders, are helpful with troubleshooting.

@Adturbo if you've run out of inputs you could always purchase an EGT-CAN module such as the Haltech TC4 we're using on our engine dyno. This can transmit 4 EGT values via CAN to the Link ECU.

Advising on a maximum safe temperature is a little tricky due to the variations that can be generated due to sensor location, sensor type (exposed or encased tip), fuel and even ignition advance. As a maximum value I aim to keep the EGT below 1000 deg C as most turbos won't enjoy sustained EGT much higher than this.

As ever, thank you for the responses.

I will look into the TC4, although I think it's unlikely I will go down that route with my current setup.

I'll update my thread when I get the turbo back from being overhauled and fitted :-)