A good location for a Pyrometer Thermocouple?

[houdel]

I'm planning on installing EGT and Turbo Boost gauges on my Deuce (also an exhaust back pressure gauge for a silencer project I'm working on, but thats another post). Most everyone seems to drill and tap the exhaust manifold just before the turbo to install the EGT thermocouple. I'd like to avoid the drill and tap exercise since I'm not very enthusiastic about pulling the fender so I can yank the turbo out just to clean the drilling chips out of the exhaust manifold.

While contemplating this project, I noticed a pipe plug at both ends of my exhaust manifold, one at the #1 cylinder and one at the #6 cylinder. The photo shows the one at the front at the #1 cylinder. Assuming I could get one of these plugs out (probably with a little help from an oxy-acetlyne wrench), would this be a suitable location for the EGT thermocouple? Or does the thermocouple need to be closer to the turbo for better exhaust gas mixing/more uniform EGT?

 

[ken]

That's where i put mine. But you will have a better reading just before the turbo. You'll only be reading that cylinder. I've had mine there since 2001 and i've been meaning to relocate it, but there was always more important things to do to the truck.
If you use grease on your drill bit and tap you can catch the chips instead of letting them fall into the turbo. Just clean and regrease the cutting tool often. But i STRONGLY sudjest you remove the turbo if you decide to install the probe by it.
I've removed mine and i didn't have to take the fender off. Just remove the clamp at the expansion joint and let it move back. Take the oil lines loose and the charge air off, then the 4 bolts holding it the the exaust manafold and it's off. But you'l probally need new gaskets.

 

[Djfreema]

There is no need to pull the fender. I just swapped out a turbo today and it took 2hrs between watching my 2 1/2 year old. When I installed my pyro, I completely took out the air filter canister assembly, unbolted the turbo and dropped it down 1/2 an inch, placed some sheet metal over the turbo exhaust inlet to catch all the shavings, drilled it out tapped it and she was done. Very easy. Good luck getting those plugs to come out at the ends of the manifold.

 

[houdel]

Ken, Djfreema - You are probably right. Most likely it will take me more time with the heat wrench getting the plug out than it will to drop the turbo, and I'll get more accurate readings at the turbo input. Thanks for the feedback!

 

[rdixiemiller]

I've seen people drill exhaust manifolds with the engine running. Go slow, drill a 1/8 pilot hole. The exhaust coming out of the pilot hole will blow the fine cast iron chips out as you drill. This was on some turbo site on the internet, so your mileage may vary.

 

[cranetruck]

They are probably selling turbos....

 

[Recovry4x4]

I might drfit out into the yard today and swap out the turbo in the wrecker. While its off I plan to drill and tap the exhaust manifold just above the turbo. Reckon I'll go 1/4 npt and bush it to 1/8 npt if needed. I'll just plug it for now. How difficult it that cast iron to tap, anyone? Hey Dman, can you tig aluminum?

 

[cranetruck]

The cast iron exhaust manifold is easy to drill and tap, just use plenty of oil.

 

[Armada]

Yes, easy. Go slow, lots of oil. Use antisieze on fitting. Remember, there is a plenum in the center of the manifold.

 

[SasquatchSanta]

When I installed my pyro we positioned the thermocouple in the echaust header pipe approx 2 inches from the turbo.

I've debated moving it upstream of the turbo but being a little on the lazy (and busy) side hate to do so especially
since I'm running a stock pump setting.

Does anyone have an educated (or even wild) guess as to what the temp spread most likely is from an upstream thermocouple reading versus a downstream reading? (If I'm reading 900 downstream what would you guess the actual upstream temp to be)?

If it's 100 or 200 or 300 degrees I think I'd rather "factor it in" and keep out of trouble that way.

 

[Ambulancechser]

egt spread...

i seem to remember reading somewhere that there is a linear relationship between the two...that is at idle it is likely no more than 90 or 100 degrees- f.
At a T.I.T of 500-F it's about 190 to 210-f
At a T.I.T of 1000-F it's about 350 to 400-f

This depends a-lot on the turbo itself...i believe the greater the backpressure,the greater the spread...but i could be dead wrong.any way you look at it,it's far more accurate to have the pyro in front of the turbo.
Or you could put two in...one in front and one behind and answer the question for everybody.putting the pyro in front eliminates the guessing as to the turbine inlet temp...far safer.

 

[houdel]

RE: egt spread...

And of what significance, if any, is a pyro read after the turbo? Only thing I can think of is to see if your turbo has cooled enough to shut down the engine; if you idle the engine for about 5 minutes after a run it is assumed to be cooled off enough anyhow so why spend an extra $125 or more just to install a post turbo pyro?

 

[SasquatchSanta]

RE: egt spread...

Hello Lee,

I agree with that you say. It's just that I made a mistake when I installed the thermocouple and am trying to be lazy by factoring in the temp spread.

 

[Ambulancechser]

egt spread...

The only point is to answer the quiestion...what is the actual egt spread pre and post turbo?
You don't have to get a second probe.just keep the mounting post turbo...then load the truck up and take it for a hard run,recording the egt at 100 rpm increments.
then remount the pyro to a pre turbo location,taking the same run and recording the temps at the same rpm readings.then compare the two.
This provides a rule of thumb for other deuce owners who may be in the same boat...where to put the pyro?

 

[houdel]

RE: egt spread...

Ernie - I was not being critical of your remarks. Actually, in my search for a pyro, I found several advertised as "pre-turbo" and several advertised as "post-turbo". I am just wondering what is the value/use of a post turbo pyrometer.

 

[Ambulancechser]

post turbo?

The only thing i can think off that a post turbo pyro could be useful for , is on a computer controlled diesel with EGR.and perhaps those with particulate filters (the self cleaning kind).
without the affore mentioned testing,the post turbo pyro can't be calibrated to account for the temp drop accross the turbo...making it rather useless in finding a true T.I.T
Companies deliberately selling "post turbo pyros" likely sell turbos too...

 

[DrFoster]

RE: post turbo?

There are two locations that are most common, and three setups that can be used:

Easy: Within and not further than 2" from the exhaust housing (most common by far and only gives you about 100 degree difference on the egt)
Not so easy: on the exhaust manifold right at the collecter
Best way if you're an accuracy freak: One in front and one behind.

 

[DrFoster]

Re: RE: post turbo?

Note: guys that have put them in front on vehicles that are going to always be close to the max egt are going to eventually suck that probe into the turbo, unless you're VERY careful about the temps and ratios. That's why the after turbo is the best spot, or most popular spot, then simply add in 100 degrees to your data reading.

 

[jimk]

RE: Re: RE: post turbo?

I thought cast iron was the only metal that didn't need cutting lube .Something about the graphite in it.That was from High School metal shop 25 years ago, i think, so you might want to research and if necessary correct me.JimK

 

[jimk]

RE: Re: RE: post turbo?

I found a cutting fluid table.

http://www.natool.com/engdata/data15.php

Probe at end of manifold will give temp of one cylinder.That info is better than no info.Best to get a overall reading near turbo.That way you will avoid getting misled if an injector acts up.I seen pics of dyno engines with one on each header tube(.With a switch you could use multi probes with one gage.I may to put mine just past turbine.While probes are ment to take that heat sometimes things just break.A failure before will surely destroy a turbine.Commercail Mack used to have them,just after too, i think.What I hear here will help me make that decision.

The only time those Macks EGTwould get hot was on hills.High load at bottom of operating range(1000rpm) made it hot, but I never saw it get to 1200*F.Downshifing a gear(1600rpm) would drop the temp fast.Perhaps at lower rpm the compressor is blowing unburned fuel into the exhaust??.If it burns in the exhaust system it just makes heat.If it burns in the engine it makes power and/or heats the coolant.

Use anti-seize on the probe.

JimK