Unfortunately, thermocouple response time is much slower than we want to believe.

Read this:http://www.turbodieselregister.com/EGT_EVAL.pdf

As an example, an Isspro pyrometer took 47 seconds to reach its peak voltage!! That's with a torch held to the probe the whole time.

I'd venture to say that a heavily overfueled engine with a tight turbo can increase EGT much faster than the pyro probe can respond.

Suffice it to say, that by the time the gauge reads 1300, you've already reached 1300 and probably passed it. I can envision a scenario where this lag is sufficient to cause engine damage when the driver thought he was perfectly safe, "driving by the pyro."

The fastest responding pyro was the SPA technique. At least you get something for all that $$.

This is the only advantage I can think of to a post-turbo pyro installation. Because temps change so much slower after the turbo, I'd think that pyro lag is almost nil in this case, and you be assured that the post-turbo location is pretty accurate in transition, relative to what the pyro "sees."

Unfortunately, the pyro is flying blind inthe post-charger location.

In the pre-turbo location, the pyro sees more accurate (and useful) temp info, but the driver does NOT, a least during rapid transients, because the pyrometer itself has lag to it. The better the pyro, the less lag it has.

A pyro can only change voltage so fast. No matter how hot you make it. You can hold a 2000º torch to the probe, and still it will quite a few seconds before the guage even reads 1200º.

I post all this just so that we as diesel enthusiasts don't put TOO much faith in the pyro and find ourselves with some expensive engine damage caused by not accounting for the gauge's lag.

Hth.

H

 

On level ground at 1400°F with an (unknown) leaking headgasket it takes about 90 seconds...




brandon.

 

Justin, Seems to me the 47 sec figure is under test conditions...and is misleading.

I remember reading that article, and did not come away with a big concern. After rereading it now, a couple of points are worth looking at...IMO.

1-Quote from article "Time to temperature, within the operating range of the instrument, should be linear throughout the range of the instrument" - Page 3, Paragraph 4.
Since the ISSPRO took 47 sec to go from 100* (test room temp) to 1700*....it should only take 14.7 sec to go from cruise (700*) to 1200*, for example.

2-Also, in the test, they added 5 sec after the probe reached max voltage, to be sure the reading had stabilized.
Page 2, Paragraph 2...Right Side.
So if we deduct 5 sec from the 14.7 sec in the example above.....we are looking at a 9.7 sec delay to read 1200* after actually reaching 1200*.
9.7 sec delay is still considerable but within the allowable time frame for our pistons before damage is likely to occur.

The example above (700* to 1200*) is intended to simulate accelerating while towing or hauling heavy on the highway.
Drag racers going from say 700* (reved up motor) to 1500* would have longer delay to get accurate reading....2.94 sec per 100*...or 23.52 sec. So...something in the test article DOES NOT apply to actually driving conditions.
I say this because my ISSPRO will go from 350* (0 mph, idling in gear) to 1500* (WOT) in 8 sec.

WHERE IS THE DELAY??

RJ

 

I came away with the same conclusions on the article as RJ does.

My old Westach reacted almost instantly to EGTs - at least twice as fast as my current Isspro, which isn't a slouch.

 

So you guys are saying the best place to put the EGT probe is on the front end (pistons 1-3) of the exhaust manifold (circled in the pic below)?

 

Talking with Piers he said your circle is in the right place for a 12 valve, on a 24 the probe should be a couple inches rearward of your location on the other side of the center web (#4-6 cylinders) in the manifold. He also said it makes very little difference which three cylinders are being measured except for people who are pushing lots of power and high egts.

 

I guess for me the real question is how fast can the CTD get super hot EGTs? If it can only increase them as fast as the probe reads, then it's nothing. I agree that the lag may not be significant, but it *IS* present.

I just wanted to point out the data that some people have mined. What conclusions to draw, if any, are hard to say.

I'd think that RJ is right on. I just wanted people to know that there IS pyro lag, and throw out the question of what is the significance?

 

Sorry WCB....we kind of got off the original subject!
If you follow the directions here...but do the front side of the manifold divider (#1,2,3), instead of the rear...you'll be in great shape.
http://www.piersdiesel.com/TechPyroInstall.htm

RJ

 

When putting a EGT pre turbo in the cast manifold, is anybody having a problem with it leaking? Are you welding it in, heard that can be hard? I am getting ready to buy a new manifold and have a probe put in before installing it, just trying to get an idea of best way to secure the probe bung, weld or botl it up?

 

No problem with leaks on my threaded probe adapter. I'm not familiar with the welding rod that is capable of joining cast iron and regular steel together. Not that there isn't any out there, but why not do what hundreds of others have done, with zero leaking troubles I might add, and just thread it in?

 

I guess then it would have been nice if Piers did (or would) add in something about 12V vs. 24V placement.

 

I have found the end all to this discussion. It also takes care of the rest of the gauges and having to watch them all the time.

http://www.buy-ei.com/EI_MVP-50_Glas...tor_Prices.htm

I won't be buying one anytime soon. At least for my truck.
Randy