Anybody have a engine analyzer?

[cfiatzph]

What type of numbers do you get in various areas of flight? Like for instance something that has been concerned is I get a 300+ spread between hotest and cooles EGT on takeoff at full power. In cruise power (leaned) it comes back to about 140 differential between hotest and coolest. IE 1400 for the hotest EGT on takeoff and then 1100 for the coolest. My CHTs run pretty normal the front two run about 260 then the hotest cylinders are like 330 and 360 with the other two around 300.
It is a electronics international analyzer.

Thanks

[cessna170bdriver]

I just bought an EI analyzer and will be installing it when I install the engine I'm currently overhauling. I'm looking forward to the insight it should give me into the engine operation.

A friend of mine has a JPI analyzer on a carbureted O-470 in his C-180. He says that 100-degree plus spread in cruise is not uncommon, and I could see where it might be more at full trottle near sea level. He says that anything at all you do to engine controls sends all the EGT's jumping around to settle out somewhere else. For example, he says he gets less spread in the EGT's with carb heat than without. Go figure.

Miles

[Kim Purcell]

I installed a JPI at my last overhaul and I love it, it's been great for seeing and diagnosing a problem prior to causing damage. I was told not to bother with it since the plane has been running for 50 years without one but it's already saved the cost of a new cylinder. It's also nice to be able to download the data on the computer and look at it.
In cruise leaned at 2450 RPM I usually have 90 - 100 degree spread on my EGTs with a greater difference with takeoff power. I have higher CHT temps, my #2 runs in the high 440 range and my 3 and 4 are in the low 400s. My front two are also running around 300. I have a C145 with the inside cowl and need to do more baffel work to bring the temps down further.

[HA]

Miles, your buddy's carb heat probably helps to even out the atomization between cylinders, since the intake system isn't really a balanced system. that's one reason for the big spreads normally, works the same for lots of engines unless you have tuned intakes and/or fuel injection.

I can see where having one of these would make me tinker endlessly with baffling etc, probably best I don't get one

Hans

[jrenwick]

I have an EI analyzer in my '55 170B (O-300). I asked EI if the EGT spreads I'm seeing are normal, and they said that in a carbureted engine you can expect to see spreads greater than 100 degrees routinely. In my experience, they tend to even out with leaning.

#6 is always the coolest EGT on mine. I suspect this is partly because the #6 exhaust riser is the only one directly exposed to the prop blast. Also, mounting difficulties forced us to place the #6 probe just slightly lower than the others, and I suspect the reading is pretty sensitive to variations in distance from the exhaust valve to the probe.

Best Regards,

John

[GAHorn]

John, I doubt that cooling air-flow to any particular cylinder has much effect on EGT. You're probably on-target about the probe placement. In my harried opinion.
Miles, I've also read that the carb heat probably assists the fuel-vaporization more evenly between cylinders. Droplets/mist don't travel as evenly as the gas/vapors do. It's a shame the carb heat robs manifold pressure as well as air density, or we could lean it out and keep on truckin'.

[cessna170bdriver]

Droplets/mist don't travel as evenly as the gas/vapors do.

So, is the reason fuel injected engines run a closer spread on EGT's that the fuel injectors do a better job of atomizing fuel than the nozzle of a carburetor, or that fuel is being injected into a warmer part of the engine (cylinder intake port vs intake manifold)? I suspect some of each, as well as more balanced induction airflow to start with.

Miles

[GAHorn]

I don't know for sure that they do a better job of atomization, but of course, the injectors are supposedly matched to each other (and to each cylinder in the case of the GAMI injectors) and therefore each cylinder gets a theoretically balanced shot of fuel.