exhaust temp help

[marvstrick]

i have a 502 450 hp chevy only checking exhaust temp on #1 cyl. temp was 1456 is that hi low whats a good number. thanks for any suggestion. marvin strickland 9777 b/cm

[Tom Goldman]

EGT's can vary greatly from car to car ,engine to engine.
1400 degrees on any motor on gas ,without knowing other factors, would be considered lean.
Bottom line is go to basic test mode , jet up several sizes and see if the car picks up.
Dont be suprized if the car slows down and the EGT's go higher, cam profiles , and header design, can have exhaust gasses burning in the pipe,giving false lean conditions.
Probe locations are critical .
I've had engines that ran quickest @ around 1400 ,but I'd want to be sure thats what it really wants.
I think Billy once told me his six cylender runs near 1500 deg.

[marvstrick]

thanks tom i will try that !!

[MOTORSPORTS Innovations]

A couple additions to Tom's suggestions:

1. Make the changes in a couple hour time span at most - preferably make 4 laps in 1 hour trying the various changes. If it's more time then you have to go back to the base jetting. Keep the weather station handy and if DA changes more than 300 feet during testing, go back to you base line.

2. what is your ignition timing? any high speed retards on antyhing?

[Altronics]

It is very important that the starting EGT temperature be consistant as well when trying to determine what "effect" a jet change has made to a tume up. A quarter second more on the two step can cause the inital egt reading to be 50 degrees hotter then the run before with no change in jet or weather. This will level out when approaching peak temp near the end of the run, but you may still see a 10 degree hotter peak temp eventhough you changed nothing.

EGT have there place, but this is where an Air/Fuel sensor proves superior!

[buzzinhalfdozen]

Also check your Ign. timing retarded timing will increase exh. temp. Didn't state whether running gas or alky if alky seems VERY high. Personally I start with Ign. timing start with something safe, then add a few degrees... if EGT goes down keep advancing till it goes back up, when it goes back up go back 2 degrees. Then I work on jetting, just my way of doing it but it works for me. BTW my stuff runs around 1400 at the stripe. Joe

[Tom Goldman]

The AF/R readings from my O2 sensor are far superior to any readings I got from EGT.
First 2 weekends with an O2 sensor helped identify, and helped fix a carb intermediate circuit problem I'd been chasing for months.
I still record the EGT , but just as a backup reference.

[buzzinhalfdozen]

No arguing that Tom with properly working wide band o2's fuel management is greatly simplified. If for nothing less than the increased response time they are a worth while addition to any tuning arsenal. The biggest issue I've seen is racers searching for that "magic AFR" basically there isn't one. Joe

[Chris Hill]

Some other things for EGT from a pure theory standpoint.

Compression goes up, EGT goes down
If starting rich, leaning the A/F ratio will increase EGT, it will peak at stochiometric, then decrease as it gets leaner still
Advancing spark timing increases EGT till ????? (sorry, having a brain fart and can't remember)
EGR (including internal EGR) will decrease EGT
Detonation causes EGT to decrease? (I think this is correct)
Volumetric efficiency causes EGT to ???? (can't remember this also)


EGT trends with peak cylinder temperatures and thus NOx emmisions.

[marvstrick]

engine builder said to get ried off msd timing retard . i am running 40 degrees . when looking at timing with alterator on above 4000 rpm timing keeps going.