Duke

Sorry Todd you are wrong. Most people forget that the heat comes in exhaust pulses from each cylinders exhaust stroke.
In the crossover you have the heat from FOUR pulses rather than just one when measuring in a runner.

I've tried to explain this many times on this forum so I was happy when the practical physicist Laust did measurements and posted here some time ago. At continious WOT you will see higher EGT in the crossover.

toddk911

I said he was correct in his example that rich fuel and retarded timing can cause higher EGT's. He did not say he was seeing hotter temps in the crossover vs. the header.

I was saying you will ALWAYS get lower EGT readings the farther away from the header you have your EGT probe. At least, I have yet to see data otherwise.

And seeing flames and or exhaust igniting farther down the exhaust path, does not mean higher temps. A flame starts at about 1,400 degrees and some redhot exhaust headers/manifolds can easily go upwards of 1,700-1,800+

toddk911

You still have his results?

Also, I was refering "in the header" as at the last header, as to get the heat from all four chambers.

Duke

The header design is 4-2-1 and the 2-1 merge is on the crossover pipe so probe in "crossover" = right after all cyl have merged.

Search is your friend for Lausts data

Laust Pedersen

Duke, you beat me to it (correction of Todd’s claims).


Todd,

On a hot engine and above a certain exhaust flow and load (high calorie/second number) the EGT is higher in the X-over pipe than any of the four header pipes.
High cal/sec supply means that the steady cooling of the pipes has less of an influence on the EGT.
As you know, compressing a gas (in this case exhaust) generates heat (increases temperature) and expanding it extracts heat (lowers the temperature). The pulsating exhaust gas in the header runners creates a heat oscillation, which cannot be detected by the slow reacting EGT sensor(s). They detect the temperature averaged over a few seconds. The duration of the high pressure in each runner is much shorter than the low pressure duration, but when they merge after the header, the pressure peaks nicely fill in the valleys, creating a higher average EGT.

Also your recommendation about installing a WBO2 sensor in the X-over pipe is contrary to most other recommendations I have seen, although it is possible when adding a heat sink, which should keep the sensor alive, for its intended life span. However I have not seen data or even comments on the effect of the high exhaust pressure on a WBO2 sensor.

Laust

OZ951

Glad to see that this thread has brought out some good discussion on the subject of EGT. Laust your findings from your comparisons between the EGT near the head vs the x-ver are particularly handy as a reference.

333pg333

So can we get a definitive best place for the sensors and this should tell us if we need to have 4, 2, or 1 probes.

OZ951

It depends on how much information you want. Most wont ever bother with 4 sensors adjacent to the ports. I'm partial to one adjacent to an exhaust port and i'll live with the knowledge gained from lausts investigations that the turbo may be dealing with a higher temp - my main concern being the temp the exhaust valves and ports are dealing with.

74goldtarga

Reviving this thread as I ran on the track yesterday with new engine config and EGT / AFR gauges. Saw 1750 peak egt on 100 octane with M-tune at AFR of about 12.2 full load / boost. Boost was 13.7 peak on the gauge. About 50 - 100 deg less with boost at 10.8 peak. Any thoughts or recent track experience with EGT monitoring. Probe is at crossover, PLX kit.

Rogue_Ant

Having the prob in the crossover tends to read high (as compared to right at the exhaust port), around 100°F high at heavy loads... In-case you missed the post:

https://rennlist.com/forums/3607772-post49.html

So your EGTs are right in-line with what we've typically seen.