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I have been researching this topic for awhile now and the general anwser seems to be EGT is hotter at the turbo collector by about 50-100F, although I havent gotten a solid anwser why...I have heard that you need to think of it like a flame(being hotter at the end than at the start), exhaust gases"backing up" before the turbo,etc. I was just wondering if you guys have any input on this subject.
 

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Run me on Nuts...
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The Reason that everyone taps the #6 Collector is because it runs the leanest. Therefore, if your car is gonna fucking blow up or something, the #6 will show it before taping it at the collector.

In Closing, if you wanna just have an extra gauge in your car...mount it in the Collector, but if you spray nitrous, etc...your best bet is in the #6 Runner.

Suprdave
 

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wut
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This is good to know, it just answered the same question I had and was about to ask.

Hey Suprdave: Did you do the install of your egt probe into the #6 runner yourself? Just curious because once my guage gets here in a week or two, a friend and I are going to attempt to install it ourselves. How hard was it to install/how long did it take you? Did you actually take the manifold out or just drill into it while it was on your car? Reason I ask that is because I am hearing different opinions. Some say you have to take it off due to shavings entering the manifold and then the turbo while others say that after drilling you can just crank over the engine a few times (without starting it) to get rid of the shavings.

I can see it is probably better to do it the hard way and take apart the whole hot side and do it right. Any tips/info you or anyone else have about an egt install would be greatly appreciated.
 

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Travis,

The collector should be hotter. Why?

Initially, your first "blast" out of the #6 exhaust port will be hotter when starting up the car. However, as the car heats, 2 exhaust pulses will be hitting the collector. (That assumption is predicated on header design however) The Law of Heat Conduction says:

H=-kA dT/dx where...

H=Thermal energy transfer rate, -k=thermal conductivity of the element, A=cross area, dT=change in temp, dx=change in temp over the area. (dT/dx=temp gradient, it may be easier to think about it like that)

Basically, the less the temperature gradient, the less the transfer rate. Since exhaust pulses are hitting the collector in a much more regular pattern than the relative sporadic pluse from the #6, the amount of energy transferred into the collector is greater, and since there's less of a gradient, the heat tends to remain. (vs the #6 runner where it will cool off)

Now, if you had the perfect EGT gauge with incredible resolution (and eyes to read it :) ) you would see the pluse is slightly hotter than the collector as it cools in the runner. After all, when have you ever applied a heat source (exhaust pulse) and heated the object above that of the source?

In practice, the collector becomes an average of all exhaust pulse temperatures. As with any average, the more pulses, the worse the resolution. For instance, if #3 detonate for a few revolutions, it may only appear as a 20 C degree jump at the collector. Of course, if you're probe is on #6, you wouldn't see anything. Likewise, if the #6 were detonating, the probe in the #6 runner may change ~80 degrees C and you may actually be alerted to the problem.

Ok, that was clear as mud. lol
 

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We're all aware that detonation/knock show up in EGT's, I am under the impression that the rise in EGT's is actually from the ECU retarding timing when reacting to knock..... basically dumping some fresh air & fuel into exhaust manifold vs a more complete burn in the combustion chamber..... so basically an EGT probe in any one runner should show knock in any of the cylinders. Am I just totally off here?

-Mike



In practice, the collector becomes an average of all exhaust pulse temperatures. As with any average, the more pulses, the worse the resolution. For instance, if #3 detonate for a few revolutions, it may only appear as a 20 C degree jump at the collector. Of course, if you're probe is on #6, you wouldn't see anything. Likewise, if the #6 were detonating, the probe in the #6 runner may change ~80 degrees C and you may actually be alerted to the problem.

Ok, that was clear as mud. lol [/B][/QUOTE]
 

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Run me on Nuts...
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Ok...

The Collector will show an overall increase in EGT.

BUT! If the #6 Cylinder Runs the Leanest first, and if your running the EGT Gauge for safety reasons...wouldn't it make sense to run you gauge off the cylinder that runs the leanest?

EGT gauge shouldn't be used to tune a car anyways.

If I'm a fucking moron, someone please tell me.

Suprdave
 

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wut
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Is it possible for any other cylinders besides #6 to run leaner than the #6 itself, or will it ALWAYS be the one to show detonation first?
 

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V8THIS said:
We're all aware that detonation/knock show up in EGT's, I am under the impression that the rise in EGT's is actually from the ECU retarding timing when reacting to knock..... basically dumping some fresh air & fuel into exhaust manifold vs a more complete burn in the combustion chamber..... so basically an EGT probe in any one runner should show knock in any of the cylinders. Am I just totally off here?

-Mike
[/B][/QUOTE]

Hey Mike,

To properly answer your question, you have to see what detonation really is and how it occurs. The base answer is: it is the spontaneous igniting of fuel from pressure, and makes extreme heat (mainly from the increased pressure). Detonation is much more concerned with cylinder head pressure than intake air temp, as it's the compression of the air/fuel that really creates the heat.

Also, as the name implies, detonation is an explosion. The main property of an explosion is the shockwave.. It is the shockwave you hear in knocking hitting the cylinder walls. It is also the shockwave which can "sweep" the air/fuel coating from the cylinder walls/piston. When there is no insulating coating, the temperature rises rapidly which will correspond also to EGTs. So as you can see, EGT/detonation is kind of two tailed... Actual detonating creates its own heat, and cylinder head pressures create a high EGT which can bring about detonation.
 

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Suprdave said:
Ok...

The Collector will show an overall increase in EGT.

BUT! If the #6 Cylinder Runs the Leanest first, and if your running the EGT Gauge for safety reasons...wouldn't it make sense to run you gauge off the cylinder that runs the leanest?


Sure, if that's the problem cylinder. You'll see "real" race cars with all exhaust ports EGT probed.

EGT gauge shouldn't be used to tune a car anyways.
I completely agree with this, but I have talked to some very accomplished tuners who swear by the EGT method. That said, they have all of the exhaust ports probed. No one would seriously tune on a one runner EGT.
 

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red94tt said:
Is it possible for any other cylinders besides #6 to run leaner than the #6 itself, or will it ALWAYS be the one to show detonation first?
It's like throwing dice.. #7 is the most likely single number to come up on any one throw, but it's more likely to be some other number.
 

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AZWildcat said:


I feel very confident that you wouldn't have anything to add to that...
Why would I?? I'm just a dumb redneck troll, right? Besides what do I know about going fast and/or tuning?
 

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booost said:


Why would I?? I'm just a dumb redneck troll, right? Besides what do I know about going fast and/or tuning?
Good question. Of course this topic concerns physics and chemistry far more than rudimentry "tuning" and "going fast." Though, I'm sure you're aware of that.

In case you missed it, this is "MKIV Tech." If you would like a shit talking battle (and we both know you don't), take it to Anything Goes.

If you have nothing to help the discussion, don't post.
 

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OK.. Well here are my questions..

Why does it matter what the temperature is 14 inches away from the parts that you dont want to hurt?? Are you worried about the turbine wheel on your turbo?


Do you know why your EGT's are hotter that distance away from the combustion?? I wasnt aware of the combustion taking place in the header..


I'm not here to talk smack to you.. I just dont want to see Travis get theories that mean squat in the REAL world.. Sure your smart, and I wont argue that.. But from what I have seen you’re not a tuner, not saying that I am either. Besides this post wasnt about tuning it was about a comparison of EGT's.

Travis, The REAL world theory is.. We all run turbo cars a little on the safe (rich) side.. What you are seeing is what we Rednecks call afterburning... Its just the rich A/F mixture still burning in the header after the combustion process.. Hope that answers your question.
:)
 
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