Does anyone have any experience with reading surface temps on a set of headers?
Why do the temps seem to vary so much between the 4 runners off each cylinder?


In race applications I have seen EGT probes set up about 2 inches away from the head on the headers. I had used a non contact thermometer "harbor freight special" on my H22 and had noticed that the 3rd cylinder away from the distributor was vastly a different temp then the rest of them.. anyone have any ideas?

 

I'm not sure how consistent or reliable trying to read surface temps is going to be. EGT's are meant to read the actual exhaust stream. There are several factors that will determine/affect the exhaust temp, mainly timing and AFR. If they are different, there is likely subtle variation in the aforementioned factors across the cylinders. I know Innovative makes an EGT reader that you can plug 4 sensors into and it will give you realtime readout on a PC; this would be useful for dialing in an EMS that gives you individual cylinder trims on either fuel and/or ignition timing.

 

Ive always heard that #3 will always be a little leaner than the others due to something about manifold design. I've never verified with this with egt sensors or anything though...

How much difference are yo picking up?

 

The #3 runs hotter than the other cylinders because of firing order. It will "see" the heat of the two adjacent cylinders after it fires while the others will only "see" the adjacent heat of one cylinder during a complete cycle.

 

Thank you. Thats very interesting and makes complete sense

 

Alright.. THAT is very interesting. probably trying to tune that out would be kinda worthless based off that idea.

I should post some temps here in the next couple of days off the H22 and or the F22B2 in my accord original ecu not tuned or anything fancy. I had noticed it does this on my dads roadster engine... some big block engine I don't know the specs.. Although if the concept is true, then on a properly running v8 the inner two most cyls on both sides would be slightly warmer then the outer two... since the firing order isn't as often would be the reason why I had mentioned "slightly" warmer...

Hopefully this makes sense.

*Edit -- I have Neptune and it has individual cylinder fuel trim, I don't believe it has individual ignition trim yet.

 

some tuners like to add 1% more fuel across the chart for cylinder #3 in an effort to help control some of the heat.

 

This is a very old principle that's been known for decades. DonF told me he used to use this principle for tuning ITBs. When the EGTs were within a certain range across the board, you know the cylinders are all running "equally."

There's a story about Smokey Yunick having holes drilled in each header runner to test EGT back in the 60s for tuning purposes. Noone had any idea as to WHY the holes were there...and Smokey wouldn't elaborate. The story goes that a bunch of teams went off and drilled matching holes in their headers b/c they figured if Smokey was doing it, it must do something, right? IDK how true that story is (His legend is such that people would believe just about anything about stuff he did).

 

Whenever I can scrap up the funds to make it happen, I plan on putting in the EGT probes to extract what I can. I'll post up what I find, but don't hold your breath, it'll be awhile.