Continental TSIO-360 power rating

[gassed budgie]

I think if the engine develops more power at 12,000ft with a 40 inch differential between inlet manifold & atmosphere than it does at ground level, then something else is at play

There may well be other factors at play, but I would have thought that the extra power available at 12,500' could largely/mostly be attributed to the reduction in back pressure at altitude.
If you think of back pressure as a form of resistance, all engines use up power in overcoming this 'resistance' whether it be, internal friction or driving a mechanical supercharger for example.
The engine uses a certain amount of power pumping exhaust gases overboard, so if that 'resistance' is reduced at altitude because of the lower atmospheric pressure, ultimately more power is delivered to the prop.

[Old Akro]

I'm told the MP gauge reads absolute, not gauge pressure. Therefore at 12,000ft the engine is effectively getting more boost than ground level because the pressure differential between the inlet manifold and ambient atmosphere is greater. If I thought about it, I would realise that since the needles don't always point to the same reading depending on variations in QNH.

The question is why Continental allow it? Although its probably academic because CHT and EGT limitations probably mean you can't sustain that power at 12,000 ft. Since the power charts are expressed as % of rated power, then 75% power at 12,000 ft is still 150 Hp (not 161 Hp). The charts are effectively saying the engine will run above 100% power between about 10,000ft and 14,000, peaking at 107% at 12,000ft.

[Lumps]

Akro, I think your gauge theory is in fact another way of saying that there is reduced backpressure. As far as I know the MP gauge is a closed system, it doesn't know what the ambient pressure is unless the engine stops. So 40" is still 40", but as you say the ambient pressure is less, so while on the induction side the engine is copping 40" of manifold pressure, on the exhaust side it only has to push out against 18"

[Old Akro]

In the automotive world backpressure tends to refer to the pressure losses due to plumbing bends, mufflers, pipe diameter changes. I agree with you, but tripped up in the nomenclature.

[aditya104]

Another incongruity between the POH and the Continental publication is of the critical altitude. This discrepancy can be explained by the variation in setting of bypass orifice.
Seneca III POH- 12,000'
TSIO 360KB Publication- 14,500'

The Continental publication on the engines is no doubt the prime document but pilots are better off following the POH, IMHO.
Also, thanks for Red Sky Ventures Free Aviation Downloads.
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The engine uses a certain amount of power pumping exhaust gases overboard, so if that 'resistance' is reduced at altitude because of the lower atmospheric pressure, ultimately more power is delivered to the prop.

Hate to bring this up, but I discovered some engines in the continental publication posted above which are rated less at critical altitude than at S.L.. Those engines are:

• TSIO-360-A, -AB, -B, -BB
• TSIO-360-C, -CB
• TSIO-360-D, -DB
• TSIO-360-H, -HB
• TSIO-360-JB

Then, to our delight:
Note 4 on Page 8 of the publication writes about the exhaust system max back pressure for the engines listed in there. The above list of engines which are rated to produce less power at critical altitude are limited to a Exhaust system max back pressure of 40"Hg abs.

Where as the other engines which are rated to produce the same or more power at critical altitude are limited to a Exhaust system max back pressure of 48"Hg abs.

This information hints to the differences in design of the exhaust system of different models of the Continental engine responsible for rated power at critical altitude.

[43Inches]

12000' DA is the critical altitude where 40' MAP intercepts full throttle movement. Above manifold px will decrease due to maximum throttle position achieved and below the throttle needs to be closed to remain below maximum MAP.

With the throttle wide open it provides the least impedement of charge into the cylinder offering the highest BMEP and highest HP output.

The higher the critical altitude setting for the TC the greater the HP loss to SL operation.

*forgot to add that this is for a fixed wastegate system, most automatic wastegate systems will be able to operate at full open throttle at any altitude and therefor HP remains constant or decreases. ie the density controllers in the PA31-350 automatically acheive 350 hp at take-off by varying wastegate position at full throttle position.

[Lumps]

Note 4 on Page 8 of the publication writes about the exhaust system max back pressure

Thank you! Finally. So does this mean if you stuck a pressure gauge in the exhaust system before the turbine it would read more than 40" on the 200/215hp EB model?

[43Inches]

Note 4 on Page 8 of the publication writes about the exhaust system max back pressure

The backpressure quotes apply to a number of engines including the TSIO-360 KB which does not have increased HP at altitude. The KB is just an EB with increased rating according to the TCDS. It does have a higher HP rating all round by means of higher RPM 5min limit. The difference between the EB and KB holds the answer...

[baron_beeza]

Note 4 on Page 8 of the publication writes about the exhaust system max back pressure
Thank you! Finally. So does this mean if you stuck a pressure gauge in the exhaust system before the turbine it would read more than 40" on the 200/215hp EB model?

Whoa up, - I gave that info days ago.

You must have read it yourself then ?

[Lumps]

I didn't come across the fine print relating to backpressure. Needed it pointed out it seems. Still, no one is much the wiser - or if they are they've failed to translate it to simpleton pilot speak.