0-200 gallons per hour....

[8413]

David,
Those spark plug pics look great, nice and even for all 4. I assume 2 were front and 2 from back cylinders? Were you running 100LL when you took those pics or mogas? My rear two cylinders run richer than the front two as they are darker than the front 2.
Josh

[edidin]

Generally the O200 does make its power at a higher rpm. Here is the comparison from the operator's manual.

O200 vs C85 Power Curves.pdf

(661.23 KiB) Downloaded 14 times

[6643]

I do have a manifold pressure gauge, why it was installed years ago is a mystery.

Do the logs show it ever had a Beech-Roby prop installed?

Planes with adjustable pitch props will have a manifold pressure/RPM chart to use to calculate power and fuel flow. The RPM/prop load chart we have assumes full throttle operation. There are a lot of variables that affect fuel flow besides RPM. We don't know which ones they speced to get the numbers on the chart.

Check your MAP gauge. It should read ambient barometric pressure with the engine off. At full throttle (engine running) you should see about 2 inches less than baro. Any reading less than that is going to result in lower fuel flow than the chart shows. Any conditions less than standard (29.92") is also going to result in lower fuel flow, including at altitude.

If you can find a copy of the Continental Engine Operator Manual for the O200 it will give you some typical figures for partial power operation.

Here's a chart I found on the 'net. Trust but verify...
.

O200 partial power chart.jpg (84.01 KiB) Viewed 295 times

[6643]

I was thinking over what I said about propeller load meaning full throttle and enough load to bring the RPM down to 2450, or whatever. This is not correct. What it means is enough throttle to turn the prop to the specified RPM. The problem is, it doesn't take into account things like prop pitch, density altitude, climbing, level or descending, draggy biplane or modern, slippery carbon fiber homebuilt, etc.

You can be certain that it takes more throttle to turn the prop 2450 on an engine on a test stand than it does on a plane that is designed for low drag.

So, again, we have too many variables to make a valid comparison.

[V529]

Ok, I'll weigh in:

0-200 with the standard 69/48 prop for a C-150.

I run regularly at 2500 to 2550 RPM. the only reason is that is the "smoothest" RPM. (I try to keep my engine........smooth)

I see anywhere from 5.9 to 6.3 gallons per hour. The longer flights at higher altitude I can typically get down around 6 gallons per hour.

I get about 108mph at that power setting consistantly.

I do know engines are more efficient at lower RPM and higher manifold (less restriction at the throttle plate).
Fabric wings, empty weight of 950. I usually fly by myself and on trips I top off.
The engine is mid time. Slick mags set at 28 degrees with 21 year old Superior Millenium cylinders. (so "not" the current company Superior but the old one)

Your numbers seem light on fuel usage...........good for you though!