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LexusTico
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3,172 Posts
Discussion Starter #1
How's it goin? I'm installing a fuel system right now so I've got some of the car apart. I installed an EGT gauge when I was BPU but when I went single almost a year ago (4,500 miles ago) I didn't drill a hole for it.

I'm debating now whether or not I should install the EGT gauge as I now have a wideband gauge. My uncertainty stems from the fact that from what I've read, the EGT probe after the turbo doesn't really say much as it's way cooler than before the turbo. And putting the EGT probe in one runner won't tell me if another is running lean, not to mention the runner is real thin. Then I got a suggestion from Dave H. to drill into the turbo exhaust housing right where it joins to the header, which is where he likes it.

I'm reluctant to put it pre-turbo because I've heard the probe can break off which will then destroy my turbo.. and so I'm debating whether I need it at all or not since before the turbo can cause carnage to the turbo and after the turbo it's pretty much useless. The only thing I'd see it good for is the warning setting that will blink the red light @ me when it reaches a certain temp - which will help me in the event that I don't notice my wideband going lean when I'm going WOT and looking @ the road.

Discuss! :bigthumb:
 

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Boost Junkie
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12,616 Posts
It is always better to run both as a wideband can fail just like any other gauge. By running both you have some sort of redundancy built in. I like to check my peak EGTs after a nice pull through the gears on the highway just to make sure things are where they should be. You are right that it won't tell you when one cylinder gets hot (unless you run 6 of them), but neither will a wideband.

Steve K.
 

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95 Hardtopper X 2
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1,709 Posts
Running pump gas and 11-11.5afr's at 18 psi on a small 63mm turbo in high gears I have seen EGT's go as high as 860C which I would be clueless about without an EGT gauge and probably due damage if I didnt back off. I have seen on a stock ECU it can pull timing quite often and raise your EGT's pretty dangerously so would definately recommend having one especially now that you are singled.
 

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I've posted this about 659 times over the past few years, but regardless of what others might say, EGT probes post-turbo are FUCKIN' USELESS. If you do a search for my posts on this subject you'll see that I've probably had the most elaborate EGT monitoring system on my car of anyone here other than the big race teams like Titan. It's hard to get any definitive info even with a PROBE IN EACH HEADER RUNNER, but once you move the probe post-turbo, THE READINGS ARE PRACTICALLY MEANINGLESS.
:end of rant for the moment:

:D
 

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Spencer
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823 Posts
Pre turbo is the way to go, dont worry about the probe going through your turbo. I had mine in my runner for over 4,000 miles and I took it out to inspect, it looked good as new. With a inspection every 10K you should be safe.
 

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LexusTico
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3,172 Posts
Discussion Starter #7
Thanks for the responses. So what I'm understanding from the first 2 posts is that it's not so important whether the probe is pre or post turbo as long as I get a base reading of where the temps would be in a WOT pull - preferably on a dyno - and then set my warning for a bit above that for everyday use?

Boost Junkie I actually wanted to put the probe pre-turbo when I was reading one of your posts but then came the concerns of the probe breaking off and :gaysex: my turbo and therein lies my uncertainty.. I'm wondering if the difference in temperature as measured pre and post turbo is linear or if the temperature drops exponentially post turbo.. ie. would a 20deg. increase pre turbo show up as a 20 deg. increase post turbo - but in a cooler part of the scale? If it's the loss is linear then I'd think it doesn't matter much where you put it as long as you get a base reading and set your warning at the highest peak. However if the loss is exponential then it's totally useless unless you have a conversion table in your head.

A buddy of mine (blklabl) said that if my probe breaks off it's essentially because it's melting and the little pieces probably won't do anything to the turbine.. also I think if I'm melting my probe I've got a bigger issue to worry about.
 

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The problem is that the readings in the DP just don't have enoughn resolution to mean anything. IF, IF, IFFFF you used the same fuel all the time (same exact fuel, not just a similar octane mix derrived from various fuels), took your readings after the same exact amount of time at WOT at the same exact boost presssure, then you might get a number that could, after a lot of careful correlation, kinda sorta serve as a warning.

If the above still leads you to want to put some stock in what the EGT reading in the DP says, then consider the following:
1. With all else being equal (fuel quality, ignition timing, boost, engine load, thottle position, etc.), there is ONLY 35 degrees C difference in one full AFR point (say, 12:1 to 13:1).

2. With the probe in the DP, the temp reading generally increases the longer you stay in the throttle, finally leveling off after several seconds. So, if you make a pull through a single gear, you might get a reading of, say, 630 C. Make a pull through 3 gears and you might get 730 C due to having more time for the piping and probe to heat up. (Keep in mind that the ACTUAL temp of the exhaust coming out of the head is probably 880-910 C all along.) Stack all of that up and you're talking about relying on some very shaky assumptions, and you are almost guaranteed to be looking at numbers that have no reliability, and you'll never know when you have a problem and when you don't.

Now, I suppose that on an AEM car it might be worthwhile as I've heard of some cases where the timing was soooo screwed up that the header was glowing red at idle. :barf: So, I will conceed that with a non-factory ECU there could possibly be a case where timing could be off so bad that you could see something meaningful in the DP temps, but frankly, I suspect that you'd have already melted something before you really know what's happening based on EGT readings in the DP. If I had an aftermarket ECU I might be more inclined to run the probe in the header. With the Factory ECU I'd trust timing and wouldn't pay any attention to EGTs.

SupraTico said:
Thanks for the responses. So what I'm understanding from the first 2 posts is that it's not so important whether the probe is pre or post turbo as long as I get a base reading of where the temps would be in a WOT pull - preferably on a dyno - and then set my warning for a bit above that for everyday use?

Boost Junkie I actually wanted to put the probe pre-turbo when I was reading one of your posts but then came the concerns of the probe breaking off and :gaysex: my turbo and therein lies my uncertainty.. I'm wondering if the difference in temperature as measured pre and post turbo is linear or if the temperature drops exponentially post turbo.. ie. would a 20deg. increase pre turbo show up as a 20 deg. increase post turbo - but in a cooler part of the scale? If it's the loss is linear then I'd think it doesn't matter much where you put it as long as you get a base reading and set your warning at the highest peak. However if the loss is exponential then it's totally useless unless you have a conversion table in your head.
 

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Trust me, if you install the sensor in the turbine-inlet tract, you better make sure it is a good quality probe. I have seen plenty of twisted turbine wheels due to fatigue of the probe. Only If you take are to insert the probe properly, you can reduce the chance of this happening.
 

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I'm not a proponent of EGT gauges at all, but I was just saying that IF someone was determined to have an EGT gauge, it must be ahead of the turbo to have any semblence of usefulness. And IMO, even if it IS in front of the turbo, it's of little use in most cases.

From what I've seen, the Greddy probes are reasonably durable (some of the others have a history of breaking off), but after about 9K miles on my original probe it was leaning a good bit in the direction of exhaust flow. :eek: Since I already had the gauge in the cockpit, I just moved the sensor to the DP immediately aft of the turbo. With no other changes I and saw ~200C reduction in EGT readings vs. in the collector.

But I agree with you.... if you are running a probe ahead of the turbo, it should be a good quality probe AND replacing it should be part of a routine maintence schedule just like changing fluids, spark plugs, etc.


MtFujiSupra said:
Trust me, if you install the sensor in the turbine-inlet tract, you better make sure it is a good quality probe. I have seen plenty of twisted turbine wheels due to fatigue of the probe. Only If you take are to insert the probe properly, you can reduce the chance of this happening.
 

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Boost Junkie said:
I'm not a proponent of EGT gauges at all, but I was just saying that IF someone was determined to have an EGT gauge, it must be ahead of the turbo to have any semblence of usefulness. And IMO, even if it IS in front of the turbo, it's of little use in most cases.

From what I've seen, the Greddy probes are reasonably durable (some of the others have a history of breaking off), but after about 9K miles on my original probe it was leaning a good bit in the direction of exhaust flow. :eek: Since I already had the gauge in the cockpit, I just moved the sensor to the DP immediately aft of the turbo. With no other changes I and saw ~200C reduction in EGT readings vs. in the collector.

But I agree with you.... if you are running a probe ahead of the turbo, it should be a good quality probe AND replacing it should be part of a routine maintence schedule just like changing fluids, spark plugs, etc.
Actually, my experience is stricktly on the engine dyno but it's interesting to see some "field" experiences. Thanks for the good post.
 

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LexusTico
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3,172 Posts
Discussion Starter #12
Good info in here..

Ok maybe I'm :deadhorse: with this whole probe breaking off thing since I only drive about 6,000 miles a year and I wouldn't mind checking/replacing it periodically but do you guys think it'd be a good idea to put the probe at the inlet of the wastegate? That way you'd still be getting the exhaust temperature reading pre-turbo at WOT but if the probe did decide to break off it'd just go out the wastegate.

Granted you won't get as good a reading under normal driving due to too little or no exhaust flow unless you're WOT with the wastegate open, but I wonder if it'd be worthwhile for those people weary about putting their probe pre-turbo. It'd diminish the risk of the probe going through the turbine should it break off during a WOT run.
 

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Boost Junkie
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Sorry,

Yes mount it in the header, pre-turbo. Anywhere else and your readings are inaccurate.

Steve K.
 

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My thoughts are:
-- Putting the probe in the WG port might further delay the response to increasing EGTs since it wouldn't see high-velocity exhaust gas until the WG opened
-- I wouldn't bet on it NOT going through the turbine if it broke off -- it might break off from vibration while the WG wasn't open, or it might not go out the WG even if it did break when the WG was open because it might be too large or not positioned correctly to make its way out the WG.
-- If I wanted a probe pre-turbo, I'd just bite the bullet and install it in the collector and check it every 3-4K miles for damage/bends, replacing it when needed. Is it a bit of a risk that it'll take out the turbine? Yes. But it's not like you don't already have some things at risk on a high-powered car like a single turbo Supra. :) Bottom line is MOST people never have a probe breakage issue. Several do, but most don't, and putting probe inspection on a mtce. schedule could help minimize the chances.

SupraTico said:
Good info in here..

Ok maybe I'm :deadhorse: with this whole probe breaking off thing since I only drive about 6,000 miles a year and I wouldn't mind checking/replacing it periodically but do you guys think it'd be a good idea to put the probe at the inlet of the wastegate? That way you'd still be getting the exhaust temperature reading pre-turbo at WOT but if the probe did decide to break off it'd just go out the wastegate.

Granted you won't get as good a reading under normal driving due to too little or no exhaust flow unless you're WOT with the wastegate open, but I wonder if it'd be worthwhile for those people weary about putting their probe pre-turbo. It'd diminish the risk of the probe going through the turbine should it break off during a WOT run.
 

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Turbo Pilot Since 1983
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Well I have my probe post turbo at the moment and looking to make changes in the future with my setup. I don’t see the value in location it in the WG opening over the DP myself. I somewhat agree with the earlier statement that locating it post turbo and using the pervious measured values as reference would also be of useful value and better than none at all as you could set the alarm at a point just above that of a controlled pull. If I were to reinstall my probe post then where is the best location, in the primary collector just prior to the turbo inlet?
 

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LexusTico
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Discussion Starter #16
no i think you guys misunderstood me. I put it right smack in the collector, but just in front of the opening to the wastegate. If the probe melts or breaks during a WOT run (when you'd expect it to being that it's so hot) it would mean that my wastegate is open, and having the wastegate open and being a path of less restricted air flow I'd hope that the probe would just go out the wastegate. It may or may not, but I've got a better chance of it going out that way than if I had placed it somewhere else in the collector.
 

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When cars say, "NO MORE!"
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2,112 Posts
an egt gauge is completely unnecessary. If your EGT gets too hot your A/F ratio will go nuts. Put all the EGT gauges you want and I would rather have just the wideband, besides with all the conflicting results about what is too high of egt temps varies with location, person, source yadayadayada.

They are good on diesel engines though. :)

Now go ahead and flame...because I am sure someone on here know more than me.
 
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