egt monitoring - hottest cylinder

Boost Junkie

(not Boostjunkie94)

 

Registered: Feb 2001

Location: Florida

Posts: 1077

 

I have tested back-to-back with the GReddy EGT probe mounted in the center of the collector just under the turbine entrance, and then with it moved to a position in the DP 1" behind the turbine outlet.

 

With the probe in the collector I would routinely hit 900 C or a little bit more on a pull through 2 or more gears at 28 PSI boost and AFR at 11.5:1. I ran this way for more than 2.5 years, did a compression test, and compression was still 170+ on all cylinders. That means I wasn't melting anything.

 

THEN I moved the probe to the DP position mentioned above. SAME EXACT PROBE, NO OTHER CHANGES. I can make a pull at 32 PSI boost through 4 or 5 gears at 11.5:1 AFR, and I CANNOT get the EGT higher than 720 C, and usually it won't go above about 680. If I only make a pull through 2 gears, the EGTs won't go much beyond 640. That is PROOF to me that the DP position isn't worth much at all. If you don't understand why this means that the DP position is almost completely useless, post a question here and I'll explain it.

 

Also, for the 50th time, #6 is NOT the hottest cylinder in the engine. #1 is hottest, and #3 is 2nd hottest. #2 is the coolest, followed by #6. I used to have a $1700 EGT monitoring system with an EGT probe one each header runner, complete with data-logging, peak/hold, and all sorts of shit. I probably did more EGT monitoring and comparison than anyone on the planet. My conclusion was that EGT monitoring was practically worthless. However, I never burn marginal fuel in my car, so if someone were boosting too much on marginal fuel, and the ECU started pulling a lot of timing, then MAYBE it could be picked up if you had built a good enough profile of what your car's EGTs ought to be, AND you are watching very closely.

 

You can read more about this in the FAQ section of http://www.widebando2.com

 

Steve

 

i came across this on supraforums and just thought id post it here in its enirety and underlined the interesting part.

im not sure where the info came from that no 6 was the hottest, but this quotes its source.

Nice one, good find. Ace as well cos my EGT probe is in #1 runner

And it reinforces the worthlessness of the post-turbo positioning.

Poor guy sounds like he's been trying to get his point across to some people for years

-Ian

Why is it that cyl 5 and 6 always seem to blow past the head gasket or drop a piston? I think 90% of the cars I have heard of have lost cylinder 5 or 6. Is there something else that could cause that problem?

JB

CW also put mine in runner #1 and said that he had tested in the past with a probe in each runner and found that the head flows equally and the temps are the same in each.

Originally posted by Branners

Why is it that cyl 5 and 6 always seem to blow past the head gasket or drop a piston? I think 90% of the cars I have heard of have lost cylinder 5 or 6. Is there something else that could cause that problem?

 

JB

Cylinder 3 went on mine if that helps

Maybe it's just random which one eventually goes?

-Ian

Well, I have been on public record for many years re EGT probe positioning, and it being useless *AFTER* the turbo(s). As to why no 6 is often the failure you will find 90% of coolant problem induced seizures happen at the end farthest from the water pump as that is the forst to suffer reduced coolant flow when things go wrong, water works wise. ideally an EGT probe in all cylinder runners is best (like the Arrows BMW 1.5 litre Megatron engines I was playing with yesterday..), but logistics and costs dictate that most users will have to settle for a single probe, and it's easiest to fit to No1 cylinder. Tests did show no measurable difference when I probed all 6 cylinders on my own engine.