newbie gauge question

[steve]

Question on EGT probe placement:
I've seen them installed in the exh manifold, and I've seen them installed in the down pipe after the turbo. I've got Autometer gauges, and the instructions say to install in the downpipe. Comments anyone?
Thanks.

[sperry]

Originally Posted by steve

Question on EGT probe placement:
I've seen them installed in the exh manifold, and I've seen them installed in the down pipe after the turbo. I've got Autometer gauges, and the instructions say to install in the downpipe. Comments anyone?
Thanks.

I don't know if popular opinion has changed any, but most people say to install it in the header 3 or 4 inches down stream from the block in the #3 cylinder runner. #3 tends to be the one that runs hottest (at least on WRXs).

On problem with the AutoMeter gauges is that some of the models won't read high enough for our turbo cars. 1600def F is the max on some of those gauges, and that's only a soft upper limit for a probe placed in the headers as described above.

Do some searches on NASIOC and I-Club for more up to date info... I'm just repeating the info I learned when I installed my probe 2+ years ago.

[Kevin M]

Originally Posted by steve

Question on EGT probe placement:
I've seen them installed in the exh manifold, and I've seen them installed in the down pipe after the turbo. I've got Autometer gauges, and the instructions say to install in the downpipe. Comments anyone?
Thanks.

I am a firm believer in installing them upstream of the turbo, but putting it in the uppipe is okay. If you're going to have to weld something anyway though, I'd put it where Scott described it.

[sp00ln]

I have mine in my o2. It really doesn't matter where you put it, just as long your EGT doesn't go above "normal" readings. Is your car stock? If so, just see where it normally is during WOT and as you upgrade, make sure not to go above, or too above, that mark. There is a big debate on DSM tuners about this. The problem with installing it in the ex.manifold, more so autometer (I'd suggest getting a greddy probe), is that the probe can break off and fall into the turbo.

[Kevin M]

Originally Posted by sp00ln

I have mine in my o2. It really doesn't matter where you put it, just as long your EGT doesn't go above "normal" readings. Is your car stock? If so, just see where it normally is during WOT and as you upgrade, make sure not to go above, or too above, that mark. There is a big debate on DSM tuners about this. The problem with installing it in the ex.manifold, more so autometer (I'd suggest getting a greddy probe), is that the probe can break off and fall into the turbo.

It does matter. The farther downstream you install it, the lower it reads. Particularly after a catalytic converter or the turbo. That's why the Autometer gauge reads lower and recommends downpipe installation. I'd rather not have to guess how much heat the turbo is robbing to know if my car is running hot or not.

[sp00ln]

Originally Posted by BAN SUVS

It does matter. The farther downstream you install it, the lower it reads. Particularly after a catalytic converter or the turbo. That's why the Autometer gauge reads lower and recommends downpipe installation. I'd rather not have to guess how much heat the turbo is robbing to know if my car is running hot or not.

It'll run about 150* cooler. But that's not the point, the point is to gauge normal activites. If you see anything ABNORMAL, you shut it down. Do you see my point or no?

[Kevin M]

Originally Posted by sp00ln

It'll run about 150* cooler. But that's not the point, the point is to gauge normal activites. If you see anything ABNORMAL, you shut it down. Do you see my point or no?

Your point seems to be that as long as you can see abnormalities, the mounting point doesn't matter. But I don't see any possible scenario where placing the probe before the turbo can have a negative effect on determining exhaust gas temperature. There is no advantage to placing the probe after the turbo.

Placing the probe in the downpipe has several distinct disadvantages however; primarily the fact that with factory serial fuel rails, cylinder 3 will run leaner than the others due to a slight drop in fuel pressure. Leaner = hotter, but if you're measuring the mixture from all 4 cylinders, #3 could be running at 1700F while the others are at 1550. That's a pretty good way to pop #3, even though your gauge was only reading 1250-1300 the whole time.

Further, the turbo is not a constant. You can't always say "add 150 degrees to get the true reading" because that isn't accurate. During warmup the turbo is stealing MUCH more heat than that, and the turbo isn't fully heatsoaked until after the engine coolant has reached thermostat temp. Also, it absorbs more heat during high temp runs, because of the larger heat difference, than it does during semi-steady-state cruising. Putting the temp probe in the downpipe turns it into an educated guess, rather than an exact measurement of what's going on.

I think you mentioned the possibility of the temp probe breaking and ruining the turbo and/or valves. But that's only an issue with cheap, bottom-of-the-line stuff. Subaru owners are encouraged by the rest of us in the online community to avoid low-budget mods, especially when it comes to reliability-affecting parts like gauges. The DSM crowd in general doesn't think that way. That's why they have such a poor reliability reputation- it's not the motor, it's the mentality of the average person who mods it. Don't get me wrong, I'm sure there are more than a few 12 second DSMs with 70, 80, 100k miles, and more than a handful of WRX owners with blown motors from cranking their MBCs. But every experienced car geek knows this mantra:

When choosings mods, choose two of these three; power, reliability, and cost.

DSMers choose power and cost. We choose power and reliability.

[sp00ln]

http://www.dsmtuners.com/forums/show...probe+location

http://www.dsmtuners.com/forums/show...hreadid=104367

Read up.


He's got an autometer gauge anyways - put it after the turbo.

[sperry]

Originally Posted by sp00ln

http://www.dsmtuners.com/forums/showthread.php?t=116765&highlight=probe+location

http://www.dsmtuners.com/forums/show...hreadid=104367

Read up.


He's got an autometer gauge anyways - put it after the turbo.

I read over a bit from those links but not in any great detail. All I saw were arguments that mirror Kevin's as to why *you shouldn't* put it after the turbo. The only argument to put it after the turbo was the one that you already proposed. We're those links supposed to refute Kevin's points?

The bottom line is this: on a WRX, #3 runs hot, so why not sample that one in particular? If your gauge and probe can't handle those temperatures, then you have the wrong gauge for your car. I guarentee you that placing a probe after the turbo will mean a huge variety in temps... you say "just figure out what's normal and look for changes", but on a cold day, with 20deg air flowing from the hood scoop, over the turbo, and down the DP, you'll be cooling everything off quite a bit, in which case "normal" will change depending on the weather. Meanwhile, a probe in the cast iron header 3" from the block will be much more insulated from external factors.

Autometer makes several EGT probes. If you get the race quality probe (the more expensive one) it will read temps up to 2000F. Granted most Autometer gauges only scale to 1600F... at least you don't have to worry about breaking the probe due to overheating, and you know that the accuracy won't be too haywire at 1600F. (Actually, when I had my Autometer EGT in the header, I *never* saw temps over about 1550F anyway.)

Also, it's not like there isn't a catalytic converter and the factory EGT already in the up-pipe before the turbo. I'd be much more worried about the pre-cat failing and blowing throught the turbo due to the altitude induced rich conditions we live with than an EGT in the header.

So basically the only reason to put the EGT probe in the DP is to "protect the turbo", when it's already at risk from the cat and factory EGT. I'd rather get accurate readings from the lean cylinder.

[sp00ln]

No, there are several arguments for the after turbo installation... if you would read the posts. Also, there is an argument there that "why does *cylinder 3* (#1 in the DSM case) run the hottest?" Do you really think it's struggeling for fuel? I doubt it. Every car is different, and I bet that every car's runner can vary in temps from what's the leanest, to whats the coolest. As far as external factors are conserned, you could make the same argument about the manifold too, however, I tend to think once the engine is warm, external factors wont cause a change in temp readings. Besides, the EGT is reading GAS tempretures, not o2 (up-pipe) housing temps. Plus, you should never TUNE with your EGT, a dattalogger is the choice here. And EGT is just a device for you to monitor while unleashing your car on the freeway, and make sure everything is reading NORMAL. If temps DO rise, in any of the runners, you'll be able to tell in your overall egt readings.

However, it seems that steve got the autometer, so *if* he does choose to install it in one of the runners and he's at WOT on the freeway with the EGT pegged at 1600*, how's he supposed to know what his ACTUAL temps are. He could be running 1800*? :?

[MikeSTI]

agreed if Auto Meter is maxed at 1600

[ArthurS]

Originally Posted by MikeSTI

agreed if Auto Meter is maxed at 1600

Mine was.

[Kevin M]

Originally Posted by sp00ln

No, there are several arguments for the after turbo installation... if you would read the posts. Also, there is an argument there that "why does *cylinder 3* (#1 in the DSM case) run the hottest?" Do you really think it's struggeling for fuel? I doubt it. Every car is different, and I bet that every car's runner can vary in temps from what's the leanest, to whats the coolest. As far as external factors are conserned, you could make the same argument about the manifold too, however, I tend to think once the engine is warm, external factors wont cause a change in temp readings. Besides, the EGT is reading GAS tempretures, not o2 (up-pipe) housing temps. Plus, you should never TUNE with your EGT, a dattalogger is the choice here. And EGT is just a device for you to monitor while unleashing your car on the freeway, and make sure everything is reading NORMAL. If temps DO rise, in any of the runners, you'll be able to tell in your overall egt readings.

However, it seems that steve got the autometer, so *if* he does choose to install it in one of the runners and he's at WOT on the freeway with the EGT pegged at 1600*, how's he supposed to know what his ACTUAL temps are. He could be running 1800*? :?

Again, you're bringing DSM arguments to the Subaru community and they don't work here. Like Scott and myself said, #3 WILL BE the cylinder to run hottest if you have stock fuel rails. Period. Every single time. So, that's where you want to monitor EGTs. And no, you don't tune with EGTs, you tune with your ears, a knock sensor, and a wideband O2 sensor.

If you have a temp probe that could fail at 1600 degrees, then it's not going to be very helpful. You should return it and get the one that can handle the heat, even if your gauge only reads to 1600, because that's hotter than you want the EGTs to be anyway.

[sperry]

Originally Posted by sp00ln

No, there are several arguments for the after turbo installation... if you would read the posts. Also, there is an argument there that "why does *cylinder 3* (#1 in the DSM case) run the hottest?" Do you really think it's struggeling for fuel? I doubt it. Every car is different, and I bet that every car's runner can vary in temps from what's the leanest, to whats the coolest. As far as external factors are conserned, you could make the same argument about the manifold too, however, I tend to think once the engine is warm, external factors wont cause a change in temp readings. Besides, the EGT is reading GAS tempretures, not o2 (up-pipe) housing temps. Plus, you should never TUNE with your EGT, a dattalogger is the choice here. And EGT is just a device for you to monitor while unleashing your car on the freeway, and make sure everything is reading NORMAL. If temps DO rise, in any of the runners, you'll be able to tell in your overall egt readings.

However, it seems that steve got the autometer, so *if* he does choose to install it in one of the runners and he's at WOT on the freeway with the EGT pegged at 1600*, how's he supposed to know what his ACTUAL temps are. He could be running 1800*? :?

Actually in the case of the WRX (I don't know squat about DSMs), yes #3 is struggling for fuel. It doesn't matter if the pump is flowing enough for fuel to be returning to the tank, because this isn't a flow issues, it's a pressure issue. The stock fuel rails leave #3 way out on the end, so it cannot generate the same pressure at the injector as the other 3... therefore it *can* run lean on cars that approach 100% duty cycle on the injectors. It's not really an issue on stock cars, but once you start boosting more and adding fuel to compensate, it can be an issue.

As far as the temp readings... having a probe *and* a gauge that can read 2000F is the right way to go (and one of the reasons I sold my Autometers), however, you can get by with only a 1600F gauge if your probe is fairly decent. 1600F in the header is pretty much the redline... so if you get there, back off... even if it's trying to go to 1800F, once it hit 1600F you're too hot. And, as I mentioned before, I never saw above 1550F and that's with a full turbo-back and mediocre tuning (via my old UniChip), driving like a maniac.

As far as uses for the EGT. I consider it simply a cheaper alternative to a Wide Band O2. Since I don't "unleash on the freeway" (), and since I don't tune the car off of a dyno, an EGT is just a piece of mind tool to let me know if something's b0rked and the car isn't supplying enough fuel.

[sp00ln]

In my personal experience when dealing with a WRX, it is optimal to place the probe in the passenger side exhaust manifold. This is going to give you an accurate enough reading to refer off of to how your car is running. Tuning off of an EGT gauge alone is never recommended. WRXs I tend to look for 700-800 (1400-1600) degrees. Going no higher than 850-900. This is only a reference point as I mentioned already. I was doing some road tuning with my WRX, and the EGTs were "safe" but AFRs indicated otherwise. My AFR was 11.8 - 12.2: 1, and on pump gas, WRXs do not like that and are inconsistent between fill-ups. When going WOT with my probe in the passenger side manifold, I saw EGT readings of 750-800 MAX with my GReddy gauge.

That was from a friend of mine that used to build stroker motors for the WRX. He also continued to say that the injector #3 "pressure" problem has since been fixed, being that it's only an early wrx condition.

In any event, you monitor your EGT's for a CHANGE in temp ONLY. So, if you even go as so far as in putting it in the TIP of your exhaust and your temp is rising, there's a problem.

[Kevin M]

Originally Posted by sp00ln

That was from a friend of mine that used to build stroker motors for the WRX. He also continued to say that the injector #3 "pressure" problem has since been fixed, being that it's only an early wrx condition.

In any event, you monitor your EGT's for a CHANGE in temp ONLY. So, if you even go as so far as in putting it in the TIP of your exhaust and your temp is rising, there's a problem.

He says to place it in the manifold, not the downpipe. Why do you still say otherwise? You keep saying that only changes in temperature matter, and we keep saying that's true, but to get ACCURATE readings of the changes, you need to be as far upstream as possible.

If he says the "problem" with leaning #3 has been fixed, I'd like to know how he came to that conclusion. WRX fuel rails still run in series, #3 is still at the end, and can still suffer pressure losses at high duty cycles.