Cylinder Head Temp Variation

[68Formula]

I'm hoping someone will have hard data on this.

For the sake of simplicity, lets assume a layout like the traditional small block Chevy (many other makes are just like this):

• Firing Order 1-8-4-3-6-5-7-2
• Middle two cylinders have adjacent exhaust runners
• Air/fuel ratio identical in all cylinders

What is the typical temperature variance between each cylinder? I would assume the middle two would run hotter due to the pairing of the exhaust runners. Not sure where the rear (firewall) cylinders would end up.

[John S]

I do not think that the pairing of the two center cylinders would cause them to run hotter. I think it would only average any reading you would get. If one was hotter then the other then your indicated reading would be an average of the two. I am actually working on a little experiment right now for a "white paper" on this very subject. I'll post a few pics in the very near future which should help answer your question.

[John S]

Ok, here is a thermal image I took today on my engine. The engine is at operating temperature so the numbers should be pretty stable. I am not going to go into any detail here because I want to ask some questions in a seperate post but I think you can see from the image that temprature varies from tube to tube but the center tubes do not appear to affect each other to any large degree. As far as average temperatures, i think it will take a lot more data then I have to come up with anything definitive but I am sure the information is out there somewhere.

[6'9"Witha69]

That's a whole lotta variation!

[John S]

That's a whole lotta variation!

yes it is, hence my other thread on thermal imaging.

[MonzaRacer]

I dont like thermal imaging for tuning. I saw a guy swap out 7 $300 injectors trying to do that and it wasnt nessesary. We tapped in with thermocouples and tada the imaging wasnt anywhere near the same as it only shows the extrior temps not the actual exhaust temps.
What you will see is greater differences between fans blowing, different shapes having differnt flow variances and the heat rejection there of.
And if the imager isnt getting a perfect shot of the radiated heat ie the imager HAS to get a straight on shot or the readings is not accurate.
But good luck.
And as for the only test I do without is wiping a wet rag on tubes if I have a misfire, the one misfiring will not burn the water off as quick.

[pdq67]

I gotta add this..

It seem's that I've always noticed that my #3 and #5 sparkplugs were always a different color or whatever regardless!!

I figure that it is b/c these two cylinders tended to rob each other b/c of the intake's design and their back to back firing order!!

I may have the cylinder numbers wrong, but still, the two down by the steering gear box!!

Please consider this.. Mybe this is why GM went to the new firing order??

pdq67

[MonzaRacer]

New firing order simply swapped 2 cylinders for a lesser harmonic basicly.
In all honesty I have seen using better cooling system products(coolant included) makes much more even temps.
After seeing some plug color issues in dyno testing I have started selling Evans Cooling NPG-R and NPG+ as it has a better nucleate boiling point, has no water in it and a boiling point of 375deg with no pressure.