I saw somewhere a chart on the difference in exhaust temps post and pre turbo. i thought it was about 200 degrees difference. i installed mine pre turbo and a friend said i was wasting my time that the post turbo was just as accurate and easier to install. if anyone knows of a chart that to comparisons were listed could you post the link. thanks.---pete

 

It is at least 300 degrees difference. Tell your friend that his set-up is a losing proposition. You did right by putting it pre-turbo. You have no worries.

 

Yes, at least 300 degrees difference.

We are monitoring exhaust temps to prevent melting of pistons.
(and have a reading for shutdown to prevent coking of the turbo bearings)

As they melt at sustained temps of 1350 degrees (read, sustained),
we want to measure as close to the pistons as possible.
Closest point would be the exhaust manifold.


phox

 

thanks for the replies. the chart i saw showed testing from different models with the pre and post temps. i sure would like to see it so i could copy and paste it in an e-mail. thanks again.--pete

 

Pre-turbo install tells you what is coming out of your cylinders (very important for melt downs) and post-turbo tells you what is coming out of the turbo.

 

I would also like to find this chart. I find this hard to believe. Granted, I am no physisist(or expert in spelling) , but if the very fast moving exhaust gas can lose 300 degrees in 5-8 inches of pipe, then it should be at least 300 degrees cooler at the tail pipe(right)? But I know this is not the case. I installed my EGT post turbo. When cruising at 70(2050 rpm's, no load, 5 psi boost) , I am seeing about 600 degrees on the EGT. Does this mean when I let it cool to 250 before shutting down, is my turbo actually around 450? When towing my 4000# boat, and full throttle up to cruising speed, I can sometimes see the EGT gauge go to 850 degrees. So that means preturbo EGT is 1150. This is on a stock truck. Doesn't leave me much room to increase fueling as I planned.

 

gamiller31:

As long as you stay within reason and increase boost when you increase your fueling, your EGT's will be o.k. Prior to adding my EZ, I hit 1200degrees easily while towing my 5th wheel. After the EZ (with disabled wastegate=more boost), I have a very hard time getting anywhere near 1200 degrees and I have ALOT more towing power.

 

How do you disable the wastgate?

 

I had a pre and post turbo set up on my truck for a while. I noticed that on average, while crusing at 70, temps were about 200* different. At WOT, I saw a difference of 500* once. Average was 350-400. Normal around town driving and idling to cool down was maybe 25-50* different.

 

OK, that means the wastegate is in the equation, right. If the wastegate is allowing most of exhaust to bypass the turbo, the temp pre and post turbo is within 75* of each other. So this means the turbo is a major restrictin in air flow, which is understandable, so if I disable the wastegate(all exhaust pushing the turbo) then the egt pre and post turbo should be quite different all the time.

BigBlue
What kind of mods on your truck? I don't imagine I am pushing anywhere close to the same amount of fuel as you are, so I don't imagine my egt will be so different pre and post turbo as what you saw.

When I installed my gauges, I did not really like my location options pre turbo, so I just put it post turbo expecting to mentally add 100* to the reading. Anybody have pictures of pre turbo pyrometer location on stock manifold?

 

There IS no chart for the difference between pre and post because it's always changing.

If you're coasting down after a hard run, the post temps can actually be HIGHER than the pre temps!

I also saw as much as 500 degree difference between pre and post.

If you are monitoring EGTs, the Pre-turbo is *THE* proper location Otherwise you're not monitoring EGT, your monitoring TOT (turbine outlet temp)

Justin

 

The hot end of the turbocharger is an energy extraction turbine. The more energy it extracts to drive the compressor impeller, the greater the temperature differential will be between the turbine inlet (pre-turbo EGT) and turbine outlet (post-turbo EGT). Over the entire operating range of the engine, this differential ain't gonna be a constant as Justin and others have pointed out with actual data!!

As a rule, the industrial engines (diesel, gas/diesel and natural gas fueled) our company has built have been supplied with individual cylinder exhaust thermocouples and a pre-turbo thermocouple. Unless a customer is doing thumbnail turbocharger performance calculations or has a temperature-critical device installed downstream of the turbocharger (e.g., a waste heat boiler or catalytic converter), the post-turbo EGT is really of no interest.

Justin, let's not get into the acronym for Turbine Inlet Temperature!

Rusty

 

The turbo is one big heat sink, and the more boost you make, the more heat it wil eat up.

at 5PSI, you might see a 200* difference.
at 35PSI you may see as much as 500*

There is NO WAY of telling you what the temp difference will be.

Post turbo monitering is to moniter turbo cool down. You don't want the turbo to be over 350-300 * on shut down. Thaqt's usually 250* pre-turbo,, but after a long hard pull, sustaining 1,100 1,200*, you could idle at 300* pre turbo, and 500* post turbo.

You can easily be melting your motor down with 800-900 post turbo temperatures.


The pre-turbo scare of,, "The thermocouple will break and go into the turbo" is a moot point. Many, MANY manufacturers in Heavy Duty Diesel, and Jet applications equip there motors from factory with a thermocouple pre-turbo. Jet motors even have a thermocouple in the center of their turbine.

If your t-coupl does break,, you have alot more things to worry about than just a broken t-couple, and bent turbo blades.

If the t-couple melts off, you had to be exceeding 2,000*EGT, and pistons are known to melt at 1,600. (Sustained)

Merrick

 

QUOTE[[There IS no chart for the difference between pre and post because it's always changing.

If you're coasting down after a hard run, the post temps can actually be HIGHER than the pre temps!]]QUOTE


i realize what you are saying. the chart i saw was a direct comparison with a pre and post pyrometers. it showed at various conditions the comparison temps. i wish i would of saved the link. thats why i posted hopefully someone else saw it.

 

[QUOTE]Originally posted by gamiller31
I would also like to find this chart. I find this hard to believe. Granted, I am no physisist(or expert in spelling) , but if the very fast moving exhaust gas can lose 300 degrees in 5-8 inches of pipe, then it should be at least 300 degrees cooler at the tail pipe(right)? But I know this is not the case. I installed my EGT post turbo. When cruising at 70(2050 rpm's, no load, 5 psi boost) , I am seeing about 600 degrees on the EGT. Does this mean when I let it cool to 250 before shutting down, is my turbo actually around 450? When towing my 4000# boat, and full throttle up to cruising speed, I can sometimes see the EGT gauge go to 850 degrees. So that means preturbo EGT is 1150. This is on a stock truck. Doesn't leave me much room to increase fueling as I planned. [/QUOTE

When you add a timing box it can actually lower total EGT's. Adding more fuel increases EGT's but thats why you need to open the exhaust and open the intake. Then if thats not enough then a bigger turbo is in need. By the way, if you totally modify your truck it might not make a good towing vehicle.
And the reason you see lower temps post turbo is turbos need heat to produce boost. They dont actually run off air flow. Try mashing the throttle in N and you might see 2-5 psi boost. Why? No heat. Fuel is heat, heat is boost. Boost is needed to keep EGT's in control.