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Old 07-02-2001, 01:05 PM   #1
8Complex

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Default RS-T EGT advice needed... (pt. 2)

Ok, so <a href="http://www.i-club.com/forums/showthread.php?s=&threadid=65237">part one</a> of this was very informative, but since then I've made a few new observations and all of a sudden the whole concept of what could be wrong might not be has come into view.

Situation :

5-6psi on boost guage
~80psi on fuel pressure guage
EGT probe located at pass. side collector (4-5" from the head)
A/F meter says I'm rich while under boost - sits about 3 o'clock on A/F meter

For some reason in 3rd+ my EGT's creep up to damn near 1700. While this seems insanely high, it was brought to me attention that the location of my EGT probe (in the collector, not in the primary runner off the head) could be causing some problems since it is mixing together the output from cylinders 1 & 3 right where the probe is at.

There is no audible detonation, and the A/F meter doesn't go any leaner then that 3 o'clock position on the Autometer A/F meter, though occasionally it goes 1 LED richer. Yes, the A/F meter acts normal at idle, so I know it's working right (found that the wire hadn't been connected while I was working on it last night - doh!). The O2 sensor I am using is a K&N single wire sensor located just after the turbo outlet in the downpipe.

Does anyone else think that the convergence of gas there may be causing the EGT's to be read falsely, much higher then they actually are? The car is running well and pulls VERY hard.
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Old 07-02-2001, 02:16 PM   #2
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Given all of those things, sounds like maybe the EGT probe is reading falsely - but not because of the confluence of gases. If anything, that would make the number lower....

What type of EGT probe do you have?
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Old 07-02-2001, 02:25 PM   #3
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Glad that O2's working now. I think you are getting a false reading at the hottest point in your header. I will buy and infared heat gun this week and we shall do some testing. Talk to ya soon.


Jeremy
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Old 07-02-2001, 02:53 PM   #4
8Complex

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I've got the Autometer competition probe (mid-level). Wish there was a way to check it somehow. :-/

I was thinking maybe that since the gasses aren't flowing quickly past it there, that it picked up more of the just-going-out combustion air. Or maybe even that since the front runner is longer, that maybe the heat from each cylinder is hitting that point at the same time.
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Old 07-02-2001, 04:07 PM   #5
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8: think about this...
1. A tray of ice cubes sits at -10C.
2. A thermometer will read -10C whether or not it is touching one or a dozen ice cubes.

1. An engine produces 1650F from each combustion cycle at a certain RPM.
2. A thermocouple probe will read 1650F whether or not there is one cylinder or six cylinders (e.g. V-12) feeding that exhaust header.

Make any sense? You're measuring temperature, not mass or velocity. The only thing that may affect your measurements is if there is a large heat loss through the exhaust header, and there's less heat loss with fewer cylinders/exhaust ports. Even in that case, it means you're losing a lot of energy before the exhaust gases even get to the turbo.

-WaC
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Old 07-02-2001, 04:15 PM   #6
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1700F at 4-5" from the port should mean the cc is getting pretty soft.

inspected the plugs recently? if so, any signs of melting?
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Old 07-02-2001, 04:53 PM   #7
8Complex

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wac - While that is true to some extent, fluid dynamics state that when gasses converge and run into a larger path then which they come from, gasses slow down and drop in pressure (which would result in lower temps). The case might be that I'm too close to the collector end and it is seeing a smaller area then it is coming from, increasing velocity and also pressure... which just might raise the temperature. Maybe? Any fluid dynamic experts out there?

Colin - I just put the plugs in on Tuesday (IIRC), they are BKR7E-11's (1 step colder for the MY00-01, 2 steps for the MY99-98). I haven't taken a look recently, but I think I just may have to.
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Old 07-02-2001, 05:04 PM   #8
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I just talked to one of the engineers here at work (hmmmm, anyone at Safety-Kleen know anything about fluid dynamics? duh...) and he was saying that yes, in theory the temperature would go up, but it's more on the molecular level rather then the measurable one. *shrug* There goes that idea. Time to dump more fuel on it.
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Old 07-02-2001, 06:50 PM   #9
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I don't know if it would make that much of a difference anyways. The two cylinders don't fire at the same time (in fact are the opposite?) and being that close to the engine I would guess that the pulses would be out of phase rather than in phase. Also, I'm just wondering, how much could one expect the EGTs to go up if you get your header coated for better insulation. I would guess that it would make the turbo more responsive because less of the energy (heat) would be bleeding out of the headers before it got to the turbo but that heat must make it hotter too. Anyone know?

-Brian
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Old 07-02-2001, 09:58 PM   #10
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Could one of your injectors not be up to par? Wouldn't this cause less fuel to be put into the chamber resulting in higher egt's. I would think you would be able to hear the pinging though...

Be careful 8, it doesn't take much to start blowing stuff up...

Aaron
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Old 07-02-2001, 11:04 PM   #11
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dump more fuel, you're nuts. there is such a thing as too much fuel.
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Old 07-03-2001, 03:50 AM   #12
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The question i possed to 8 when he and i last spoke was where are most people running thier egt probes, and what are the safe readings?

i run mine about 2 inches past the turbo, and have been told by very relighable sources that 1500 egts are just fine, like i should be between 1400 and 1500, so being much closer to the motor would result in less heat loss so higher egts, if 8 has no detination, either audible, or on the j&s, what is wrong with his egts? they seem ok to me. if he is running correct a/f on the gage, and isn't experiencing any wierd surging, or power band problems, isn't he ok.

so all those out there who are turbo and have egt probes, please tell me where they are, and what they are reading.

jon
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Old 07-03-2001, 07:20 AM   #13
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Let your mouse do the walking: http://www.i-club.com/forums/showthr...threadid=66864

-WaC
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Old 07-03-2001, 07:24 AM   #14
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Quote:
i run mine about 2 inches past the turbo, and have been told by very relighable sources that 1500 egts are just fine,
2 inches PAST the turbo and you're seeing 1500F? And, if I recall, you recently posted in another thread how you "melted a piston"?

Absolutely NO REASON to put an EGT probe AFTER the turbo. If you're going to do it, why not just do it correctly?

Steve
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Old 07-03-2001, 10:39 AM   #15
8Complex

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Well, regardless of where it is, 1700 is near melting point. I'm going to have to go back in and make sure that it isn't going back towards any part of the motor, and make rerun it around any electrical sources, etc. I just can't believe that it's running 1700 with all other conditions going on.
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Old 07-03-2001, 11:07 AM   #16
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Actually Corky Bell advocates the EGT probe after the turbo, because (not his words) he is concerned about the probe breaking and being inhaled by the turbo.

I've seen few people that agree with that sentiment. Most would rather know exactly what's going on in the exhaust port instead of "guessing" how much energy is lost through the turbo. Hint, hint for Jon-- 1500F after the turbo means it's definitely over 1500 before the turbo and could be as hot as what 8 is seeing. If the probe melts, you've got much bigger problems than damaged fins on the turbo so it's best to have the most accurate picture of what's happening.

8, don't allow this to happen. We all know there's a fair chance you've already done lasting damage, but if you continue on you are sure to break stuff. Open the wastegate and buy some books, including Maximum Boost. Do a little reading and start over from the beginning... clearly there's a problem somewhere. Start with the lighter wastegate spring too.

If you don't do that, bring it to a shop and pay to have it done right. Otherwise it WILL be in the shop when you need a new longblock.
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