Not getting full power

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JeffFranks

Filing Flight Plan
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Jeff F
I've had a 172H for about 5 years and have always assumed that the 145 horse Continental was just a bit smaller than the 160hp Lycoming I had gotten used to, so the lack of power wasnt concerning. But now I'm not so sure.

I just had my annual completed and the engine checked out great. Even had the cam lobes checked to be sure the valves we lifting properly. All is good. But when I mentioned that we average about 6.5 to 7.0 gph, the A&P looked at us funny and said he's had planes with this same engine and none got less than 8 gph.

After talking further, there are several other numbers that don't sound right. When sitting at the end of the rwy, static full power maxes out at 2200rpm. In flight in straight and level, full power is 2600 @ 115 mph. I'm being told that 65% power is 2450. Heck, I seldom cruise above 2350!

So the question is, what could be causing this? Are we getting full power? At first I thought it could be the tach, but the fuel flow matches. Could the throttle cable be getting stopped/too short?

Thoughts?
 
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I flew a C172H that was owned by another member of this board for about a year. I could regularly get fuel burn to be 7 gph - 7.5 GPH. Check the TCDS, but full static runup at the end of the runway is 2250 with the standard cruise prop.

For me, Full power climbout, and leveling off at 3000, rpms would come up to about 2350-2400, and about 110 mph. At 5000 feet, 2500 rpms-2550 rpms. At 6500 feet, I'd hit the redline of 2700 rpms if I didn't pull back.

Check the POH tables, but the 65% you mentioned is probably on a chart where cruising is above 5000 feet. Of course, this is all leaning the mixture properly.

Sounds like you are experiencing the typical O-300D performance that I had.
 
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JeffFranks said:
I've had a 172H for about 5 years and have always assumed that the 145 horse Continental was just a bit smaller than the 160hp Lycoming I had gotten used to, so the lack of power wasnt concerning. But now I'm not so sure.

I just had my annual completed and the engine checked out great. Even had the cam lobes checked to be sure the valves we lifting properly. All is good. But when I mentioned that we average about 6.5 to 7.0 gph, the A&P looked at us funny and said he's had several planes with this same engine and none got less than 8 gph.

After talking further, there are several other numbers that don't sound right. When sitting at the end of the rwy, static full power maxes out at 2200rpm. In flight in straight and level, full power is 2600 @ 115 mph. I'm being told that 65% power is 2450. Heck, I seldom cruise above 2350!

So the question is, what could be causing this? Are we getting full power? At first I thought it could be the tach, but the fuel flow matches. Could the throttle cable be getting stopped/too short?

Thoughts?
Click to expand...

Your numbers are right by the book, you use 2350, that is why you get low fuel consumption, because you are way below advised cruise power of 2450.

DO NOT LUG that engine it is more harmful to run low RPM than to run it WOT

I run the 0-300 at 2450-2500 all day, and get about 8 GPH.

There is nothing wrong with your engine, and remember Precision Airmotive has altered the basic design of the MA 3 SPA, and it now burns more fuel per hour than the early carbs, AS operators find out the later carbs run rich, the price of the older unmodified carb, have increased to near, 250 for a old core.

never have an older carb rebuilt, they destroy it when they do. KELLY Aerospace now owns the production certificate, but they have always manufactured the parts for it. Keep our old carb, and find an old mech to repair it, the float never wears out but Kelly will replace it with a plastic one, the needle valve in the old carbs was a solid brass or stainless one, they never wear out by Kelly will replace it with a rubber tipped one.

The Kelly carbs will not run auto, the older ones will with no problems.
The only wear issues with the MA 3 is, the throttle shaft bushings and mixture valve, both parts can be bought under 100 bucks. a new or rebuilt carb is now over $900.

MY best advice for 0-200 & 0-300 operators is simple, run as lean as it will run smooth, at all altitudes, and all power settings.
 
JeffFranks said:
I've had a 172H for about 5 years and have always assumed that the 145 horse Continental was just a bit smaller than the 160hp Lycoming I had gotten used to, so the lack of power wasnt concerning. But now I'm not so sure.

I just had my annual completed and the engine checked out great. Even had the cam lobes checked to be sure the valves we lifting properly. All is good. But when I mentioned that we average about 6.5 to 7.0 gph, the A&P looked at us funny and said he's had several planes with this same engine and none got less than 8 gph.

After talking further, there are several other numbers that don't sound right. When sitting at the end of the rwy, static full power maxes out at 2200rpm. In flight in straight and level, full power is 2600 @ 115 mph. I'm being told that 65% power is 2450. Heck, I seldom cruise above 2350!

So the question is, what could be causing this? Are we getting full power? At first I thought it could be the tach, but the fuel flow matches. Could the throttle cable be getting stopped/too short?

Thoughts?
Click to expand...


I don't see a thing wrong with your performance or fuel consumption numbers.
 
There is nothing wrong with your engine. I regularly got under 8 gph with a 180 hp 172. Your numbers are book.
 
Depending on the pitch of the prop 2200 static is low and 2600 WOT in level flight is a bit low. Hve the hydraulic units checked. "Soggy" hydraulics will do that to an O-300. Charlie Melot Zephyr Engines
 
JeffFranks said:
After talking further, there are several other numbers that don't sound right. When sitting at the end of the rwy, static full power maxes out at 2200rpm.
Click to expand...
Which prop do you have? If it's the "usual" 76x52/53, min static RPM is 2230, so either your tach is reading low or your engine isn't putting out the power it should. (The 80-inch prop lower limit is 2380, and static RPM of 2200 in that case would be worse).

In flight in straight and level, full power is 2600 @ 115 mph. I'm being told that 65% power is 2450. Heck, I seldom cruise above 2350!
Click to expand...
RPM and %power vary with altitude. What altitude are you at to get 2600 RPM and 115 mph (and is that indicated or true airspeed)?

BTW, getting a proper handbook for the plane with the correct cruise performance tables for your engine/prop might give you a better idea of what to expect and whether or not you're getting it.
 
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Tom-D said:
never have an older carb rebuilt, they destroy it when they do. KELLY Aerospace now owns the production certificate, but they have always manufactured the parts for it. Keep our old carb, and find an old mech to repair it, the float never wears out but Kelly will replace it with a plastic one, the needle valve in the old carbs was a solid brass or stainless one, they never wear out by Kelly will replace it with a rubber tipped one.

The Kelly carbs will not run auto, the older ones will with no problems.
The only wear issues with the MA 3 is, the throttle shaft bushings and mixture valve, both parts can be bought under 100 bucks. a new or rebuilt carb is now over $900.
Click to expand...

Kelly might be rebuilding them (yuck!) but the Type Certificate was bought up by Tempest. They call their line Volare carbs. I hope they can get back the old quality, but those hopes aren't too strong.

http://www.tempestplus.com/home.htm

Dan
 
Dan Thomas said:
Kelly might be rebuilding them (yuck!) but the Type Certificate was bought up by Tempest. They call their line Volare carbs. I hope they can get back the old quality, but those hopes aren't too strong.

http://www.tempestplus.com/home.htm

Dan
Click to expand...

How do you keep the liability of a carb from effecting the other production certificates you own?
 
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