548chevelle

An infra-red thermometer shows these temperarure readings on the exhaust manifold.
right side- 280, 290, 320, 310
left side- 280, 300, 260, 360
Those 2 cylinders on the left side that read 260 & 360 seem to be way out of whack. Could this be injectors not flowing correctly? Or something else.
I've seen dyno tuned engines produce X horsepower. But when EGTs for each cylinder were used and air-fuel ratios for each cylinder were corrected there was a 5-10% hp gain. Depending on how far off the EGT was.

JwT

Usually a temp this far apart would mean a dead or misfiring cylinder. I'm not sure you can get a correct temp on the stock manifold. You could try investing in plugs and wires and recheck. I would say that if these readings were from headers you have issues.

548chevelle

I'd rather not invest in a shot in the dark and just swap the plugs and wires with other cylinders and see what happens.

Mark2009

You probably shouldn't be using an infrared thermometer to try and check header temps. You certainly shouldn't be 'repairing' your engine based on what an infrared thermometer says.

Get a pro to 'read' your plugs if you think you have cylinder issues, which you probably don't. Good luck on finding one.

If you are determined to measure EGT, put a probe in each exhaust tube and get a real number. And don't pay too much attention to the idle temps (you're checking your 'headers' at idle, right?).

Best advice of all: get rid of the infrared thermometer. Mine also has a laser pointer, making it useful to measure the cat's body temp as he chases it along the wall

double06

Though your readings are a little off if something were very wrong the tempature would be way off like mine was and the tempature was like 150 and it turned out to be a broken valve spring. The reading on number 7 is tough as it is hidden behind a bunch of hoses.

dcamick

Very Good!

Vito.A

I assume these readings are at idle? It's difficult to diagnose an engine with cast iron manifolds as they are not as responsive as stainless tubing.
Check the temps again at 2000prm. The trick is holding the RPM as steady as possible.

erikszr1

Although not the end all to a diagnosis, not a bad idea to use that info in conjunction with other testing. Easy too! A bunch easier than installing an egt in every port! Lol

Just Enough

I don't mean to get technical on you, but an infrared thermometer's reading is based on the emissivity of the surface you are pointing it at. Emissivity is dependent on color and surface finish. The stainless LS7 manifolds are not usually uniform in color when they are used a while and they are also double walled with stainless mesh insulation between the layers, all of which would give a very ball park temperature reading. Meaningful EGT is typically measured directly in the exiting gas stream with a manifold mounted thermocouple probe with it's measuring tip centered in the hot gas.

erikszr1

I agree

Mark2009

No, you didn't.

Bill Dearborn

Isn't checking the temp at 2K only incrementally better than checking it at idle? Running at 2K in neutral the engine is only producing enough power to over come internal engine friction that occurs at that rpm which is probably less than 10HP. Same goes for running at 5 or 7K in neutral. EGTs probably don't mean much unless the engine is under load and the throttle is wide open thus producing max HP for that rpm.


Bill