Egt-how Much Heat Is Too Much ?

[liberatorx2]

I KNOW I READ IT B-4 , BUT WHAT TEMPERATURE IS TOO HOT ? AT WHAT TEMP. DOES ALUMINUM MELT ? I WENT FROM 900-950deg. AT 8900 rpm TO 1200-1250 SAME RPM. WEATHER WAS A LITTLE COOLER WITH 900 READING, BUT COULD AIR TEMP. AND HUMIDITY CAUSE THAT MUCH OF A DIFFERENCE ? ONLY OTHER DIFFERENCE WAS PLUGS. I TOOK OUT B9HS-10 CAUSE THEY WERE STARTING TO TO CARBON UP A BIT AFTER RUNNING IT HARD MEMORIAL WEEKEND. PUT IN THE BUZHW 2 DAYS LATER, WENT TO THE WATER & EGT NOW READS 1200-1250 @ 8900rpm . BRAIN HAS BEEN AT 101% THE WHOLE TIME. COULD THE CHANGE IN PLUGS CAUSE THIS MUCH MORE HEAT ? THANKS FOR ANY HELP.....RICK MOORE

[Markus]

Cooler weather should cause your EGT to run hotter, not cooler.

The spark plug change cannot explain 300 degrees difference - too hot plugs can cause detonation, but you would see the insulators melting.

There is no general rule as to what EGT temperature is the limit. Although thermocouples are very exact, gauges are not, the placement of the probes makes a huge difference, so does the exhaust back-pressure driven by the pipe design, as well as timing, etc.

If you describe your engine, maybe someone else with the exact same engine could describe what EGT readings they get, which would still not isolate the difference in gauges.

300 degrees a big, weird, jump. However, to know whether you are safe or not, you need to read the pistons or the plugs. There is a link to an excellent article about reading plugs by Gordon Jennings on my links page, and how to read pistons has been discussed here numerous times before.

[ken medendorp]

maybe you lost some fuel pressure. for drag racing 1200 deg is fine but for top end running 1150 deg is where you want to be.But you should read piston top's.I had my 2.5 drag out the other day EGT where at 1220 0n a 70 deg day at 101% 9000 RPM

[liberatorx2]

THANKS FOR RESPONSES. MOTA IS 2.5 260 JSRE MODIFIED. FUEL PRESSURE IS CONSTANT 38lbs. CHECKED PLUGS & THEY LOOK GOOD AS FAR AS COLOR. LOOKED AT TOP OF PISTONS THRU PLUG HOLES WITH LITE , AVERAGE CARBON BUILD UP {not bad] PISTONS LOOK JUST LIKE THEY DID 2 WEEKS BACK WHEN I CHANGED OUT TO RUN TIGHTER HEADS FOR A DAY. WILL GET A BETTER LOOK AT PISTONS LATER THIS WEEK WHEN I PUT TIGHT HEADS ON AGAIN. DON'T THINK THERE WAS A DETONATION PROBLEM CAUSE I USUALLY MIX IN A COUPLE GALLONS OF 108-110 TO BE ON SAFE SIDE........NEW TRIP. RAN MOTA AGAIN JUST NOW. AT 8900-9000rpm...1225-1250. AS I CLIMBED FROM 9000 TO 9500rpm TEMP. STARTED DROPPING BACK TO ABOUT 1100-1125. STILL WONDERING ABOUT THE ORIGINAL 300 DEGREE JUMP THOUGH ?WHEN IT RAN 900-950deg. i ran it all day that day & hottest it got was at the high rpm. HELL MY PLANS WERE TO BACK IT UP TO 99% B-CAUSE IT SEEMS RICH AT 101% & TEMPS. WERE LOW. ANY OTHER THOUGHTS ? ..... JAY YOU KNOW THIS MOTA LIKE A FAMILY DR. KNOWS HIS PATIANT. WHAT YA THINK? BTW YOU WERE RITE DEM HEADS IS AWESOME......RICK MOORE

[stvhelm]

if something clogs that tube fitting to the ecu your egt will drop. just a thought:confused: ... maybe it cleared itself up? I know if I disconnect mine it will drop the EGT drastically. 1200 is about the right temp. Ive seen 1400 on the gaffrig egt before and nothing happened.

[Techno]

Exhuast Gas Temperature.
They don't read piston temp or combustion temp so the fact aluminum has melted or has no strength at these temps means nothing.
You need to run at WOT, cut clean and check the piston tops. After that you'll know what your temps mean on your boat.

Possibly you weren't burning all your fuel before so the rich mixture was cooling this exhaust gas. If a rich mixture ignites in the exhaust then the temp can go even higher but is a flame temp on the probes- not the combustion chamber. 2 ways for the things to fool you. Rich and not burning cools, rich but burning now and heats.