Individual header tube temp. Egt. Varies

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Caco2120

Caco2120

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Hi all,

Anyone ever paid any attention to individual egt per each individual tube on a sb?

I bought a cheap infrared temp gun, and all my cylinders range at idle from 180 degrees F clear up to 280. 1,3,7, 2,6 all seem to be 180.
#8 is actually always my hottest. Clear up to 280. Then #5 and 4 are more like 220.

Is the temp on 8 just the typical lean cylinder of the way a sb flows? Or i have more going on?

Single plane holley intake. Cammed 318. Double pumper carb. Running 13.5 AFR at idle. On the passenger bank.

Engine runs ok. Would never even know about this had i not bought the temp gun. Am i making something out of nothing?
Maybe screw out the passenger rear screw on the metering block another 1/2?
Thx!
 
What you have found is normal.
You can correct this with mods to the intake manifold. Ether or both (& probably both) would be to port the intake and add in dams.

Do not make a big deal out of this but do so pay attention to make sure that non of the cylinders are to lean. Enriching the lean cylinder will make the others richer as well. Your in a catch 22. So don’t loose your mind and hair over it.
 
It's hard to get the idle temps equal. Especially when the headers make a sharp turn right out of the port.

I'd double check my idle setting and not look at the AF ratio while doing it. Get the engine to idle it's best and then look at the AF ratio.

I wouldn't get excited about idle exhaust temps. If you really want to lose your mind, check an engine running alcohol. Most guys run them dead rich with slow timing. The exhaust temps go through the roof. So they add more fuel and take out timing and it gets worse. Some never learn.

Also, double check your timing at idle. You may need more initial. If the cam is what you say it is. 18-20 initial may not be enough.
 
At idle, I would not pay much attention.. too many variables as noted. A really cold cylinder could mean a bad plug/wire. The EGT's when the engine is loaded is the key....can't say I have seen that measured on a car, but it is done on higher performance piston aircraft engines, and the injectors are varied to even them out when loaded (in flight).
 
Hmmm to my memory ..when I shot my header tubes years and years ago on a fairly warmed up 340 they were around 500- 600. Lean idle.
You guys run who run out of the box intake manifolds need to realize that none of the runners flow the same ,none of them distribute fuel the same.

Dual planes, center ports...lean.
Just truly get your idle dialed perfect, dial your carburetor in ...or as close as you can get it... then go check those Center plugs...they will be the cleanest or even white
 
A 100°F difference in temp in 1 cylinder would be a big deal for me.
Start checking for vacuumleak in that cylinder.
(You don't have the PCV hooked up in that area of the intake do you?)

My propane fed 360ci has cyl.no 6 idling with 40°F warmer because of a less then perfect valve seat seal.
The other cylinders only vary about 10°F between them.

If you have an automatic you load the engine against the convertor at you chosen rpm and check all the cylinders again and see if the big difference in temp follows along or evens out.
 
BigBlockMopar said:
A 100°F difference in temp in 1 cylinder would be a big deal for me.
Start checking for vacuumleak in that cylinder.
(You don't have the PCV hooked up in that area of the intake do you?)

My propane fed 360ci has cyl.no 6 idling with 40°F warmer because of a less then perfect valve seat seal.
The other cylinders only vary about 10°F between them.

If you have an automatic you load the engine against the convertor at you chosen rpm and check all the cylinders again and see if the big difference in temp follows along or evens out.
Click to expand...
Are you injecting propane as vapor in what is essentially a big 1 BBL carb? Nice idea on the testing.
 
One propane carb (Impco 425) mounted on a 4-bbl Holley-like baseplate.
The Propane is vaporised outside the engine in a vaporiser.
 
Last edited:
Caco2120 said:
I bought a cheap infrared temp gun, and all my cylinders range at idle from 180 degrees F clear up to 280. 1,3,7, 2,6 all seem to be 180.
#8 is actually always my hottest. Clear up to 280. Then #5 and 4 are more like 220.
Click to expand...
I too thought the exhaust tube coloring (indicator of heat) could be a helpful indicator of balance but seems it isn't so.
For meaningful comparisons need to actually the CHT or Exhaust gas temperatures, not the outsides of the tubes. :(

Moparoffial is putting you on the right path. If anything read the plugs. But basically for idle, make adjustments until runs the best. Do it with the engine hot, and if its an automagic, go by best in-gear.
 
Been doing exhaust temps & Dyno work for 40 yrs for the big 3 car company's. Plus or Minus 50° C is fine.
 
BigBlockMopar said:
One propane carb (Impco 425) mounted on a 4-bbl Holley-like baseplate.
The Propane is vaporised outside the engine in a vaporiser.
Click to expand...
OK, that would give a wonderfully uniform fuel-air mix, all in one big throat, not 2-4 of them. Something I had never thought of....

So apples and oranges in that way, when compared to a multi-throat carb.
 
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