Exhaust temps... what do they mean?

[Canadian1968]

I had my 440 running tonight and randomly started to check a few of the under hood temps. I Noticed that up at operating temp, a few of my header tubes were running quite a bit different than the others. I was measuring approx. 2 inches from the cylinder head on each tube. Most of them were running around 400ish mark, but I had 2 that were quite a bit different. The cylinder closest to the fire wall on the driver side was 600+ and the second in from the fire wall on passanger side was 500+

The engine seems to be running fine, or just as welll as it always had. THis iss just sitting in the garage idle . The headers are hedman ceramic coated headers if that makes any difference .

JUst curious as to what would cause one exhaust port to be running almost 200 hotter than tht others?>>

 

[Jc cooper]

Good question, sure there’s a answer available , would like to hear this info as well! Mine does same if any consultation !

 

[MoparLeo]

Intake/vacuum leak, valve(s) not closing all the way, Let it cool down and pull the spark plugs. How do they look ?

 

[dadsbee]

Intake runner lengths and fuel atomization and how well it's distributed makes a huge difference. My airplane engine is 4 cylinders, front two have an intake runner about 1/2 as long as the rears. Front exhaust pipes run around 1295F while the backs run 1490F or so.

 

[Jc cooper]

Thanks Dadsbee good info and logical ! I enjoy quality input ,Sir This should satisfy the original op’s quiry as well !

 

[1967coronet]

That is interesting....
The ceramic coated headers run the same basic under hood temps as my plain steel tri ys .

 

[Ironbuilt]

Intake runner lengths and fuel atomization and how well it's distributed makes a huge difference. My airplane engine is 4 cylinders, front two have an intake runner about 1/2 as long as the rears. Front exhaust pipes run around 1295F while the backs run 1490F or so.

That's some pretty impressive exhaust temps. What RPM is that engine running at? Is it an air cooled engine?

 

[dadsbee]

2550 rpm, air cooled.

 

[beanhead]

Fuel distribution is not equal especially with a dual-plane intake manifold. You can do things like stagger the jetting and the idle mixtures but even then you don't really have control over individual cylinders. The good news is, it doesn't matter! As long as you don't have one that reads 150 degrees when the rest are over 400...
FWIW my TTIs (as-puchased, and after being re-CermaKromed) show 200-300 degrees after hard driving on all pipes.
The Heddman's may not have the extra thermal barrier, and may not be coated inside. No big deal but it makes a big difference in underhood temps.
Late ignition timing puts a lot more heat into the exhaust. If your timing and mixtures are good, and you like how it runs, I'd chalk it up to "it is what it is"...

 

[66 Sat]

On my 318 poly there was a distinct difference in exhaust note and flow from one tailpipe to the other (passenger side had more burble/stronger flow). The car ran faultlessly. We checked everything, from a stuck manifold heat control valve (I pulled the manifold off only to find there wasn't even a valve in there, just the parts on the outside), blocked muffler, plugs, wires, compression test, couldn't find an issue.
In the end I put a H pipe in which evened out the sound and forgot about it.
Car is still running great 2 years later, just a quirk I suppose, different shape exhaust manifolds from side to side coupled with the firing order maybe?

 

[BB BELLA]

it may be unequal fuel distribution as mentioned or with pipe shape/length and poor scavenging at low rpm. try increasing rpm and re-measure!

 

[Mark Barnes]

Valve adjustment. I had a 57 Chevy with a solid cam 327 and Hooker headers. Set the valve lash to specs, and one night at dusk, opened the hood and 2 header tubes were glowing dull red. Backed off those 2 exhaust valves and it disappeared. Wasn't much adjustment involved either, just enough to give the valve a little more seat time.

 

[Macdon221]

Dads bee is right on. Unless each cylinder is getting the same proportion of fuel and air...and the same mixture...temps will be different and can be by a lot! Perfect balanced fuel injection into each cylinder is the only thing that will create same EGTs.

 

[BSB67]

Fuel distribution.

What intake manifold do you have?

The two cylinders you describe, #5 and #7 cylinders are next to each other and fire back to back. They generally tend to be a bit different particularly with a single plane manifold, and staggerd jetting on the older style dual planes is also common due to poor fuel distribution.

 

[Jc cooper]

Yes , by now pretty sure he ( op ) and I both have same in Elderbrock performer which I believe to be dual plane ,plugs read ok , my temps aren’t as high as his , always great to get imput from many others to verify! Thanks to all !

 

[MoparLeo]

Also the rear runner that has the vacuum port for the brake booster effects it.

 

[RJRENTON]

I had my 440 running tonight and randomly started to check a few of the under hood temps. I Noticed that up at operating temp, a few of my header tubes were running quite a bit different than the others. I was measuring approx. 2 inches from the cylinder head on each tube. Most of them were running around 400ish mark, but I had 2 that were quite a bit different. The cylinder closest to the fire wall on the driver side was 600+ and the second in from the fire wall on passanger side was 500+

The engine seems to be running fine, or just as welll as it always had. THis iss just sitting in the garage idle . The headers are hedman ceramic coated headers if that makes any difference .

JUst curious as to what would cause one exhaust port to be running almost 200 hotter than tht others?>>

IMO....
It sounds like you are reading temps with an infrared optical device. And you are reading metal temps not the actual temp. The best method is by EGT or Exhaust Gas Temperature using thermocouples installed in each header tube, as close as possible to the mounting flange. When during a dyno run, this will provide the most accurate reading of fuel distribution and mixture ratios. While reading the header metal temps, its subject to radiant heat losses and perhaps infrared heat losses. The thermocouple measurements will be the most responsive, however, this method is not the most easily accomplished as it requires a device to read the thermocouple milli voltage generated and translated to degrees F or C. The actual exhaust temps will be in the 1200° - 1400° range. Just my thoughts....
BOB RENTON

 

[chtampa]

High Exhaust Gas Temperature, or EGT will happen if the throttle is pushed before starting rpm is sufficient. A maladjusted Fuel Control will also do this. If it happens after it has been running for a while, it may just be a bad thermocouple. If it is smoking also, perhaps try to make it stall and reseat the carbon seals.

 

[forphorty]

High Exhaust Gas Temperature, or EGT will happen if the throttle is pushed before starting rpm is sufficient. A maladjusted Fuel Control will also do this. If it happens after it has been running for a while, it may just be a bad thermocouple. If it is smoking also, perhaps try to make it stall and reseat the carbon seals.

Exactly

 

[Wietse]

As per OP his description the cylinders with high temperature are #6 and #7.

The cylinder closest to the fire wall on the driver side was 600+ and the second in from the fire wall on passanger side was 500+

IF he is using a dual plane manifold like a Edelbrock Performance (RPM) those cylinders are on the "Low" "rear" section...the passenger side of the manifold.
So that section probably has a different mixture compared to the rest, probably very lean as that causes a higher temperature.
As they are both on the same "port" of the manifold the likelyhood there is an issue with the valves seems very small.
Maybe check the carb settings and ensure all idle screws are set the same, or a idle circuit port could be blocked with dirt?