Hot 0-320 cessna 172

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Aaronk25

Pre-takeoff checklist
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Nov 3, 2013
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Aaronk25
Wondering if there is a legal way to increase fuel flow on take off roll. We have a 172 carb in our club and its running 410-430chts and baffles are in perfect shape.

This is only on climb out. The take of fuel flow is about 12.3gph and were thinking it should be about 13.5-14gph.

How do we get the fuel flow there legally.

Thanks,

Aaron
 
Aaronk25 said:
Wondering if there is a legal way to increase fuel flow on take off roll. We have a 172 carb in our club and its running 410-430chts and baffles are in perfect shape.

This is only on climb out. The take of fuel flow is about 12.3gph and were thinking it should be about 13.5-14gph.

How do we get the fuel flow there legally.

Thanks,

Aaron
Click to expand...

Powerflow tuned exhaust is where I would go first, then tune the prop.
 
So your baffles are good and the rubber is not hard?

12.3GPH does seem about right

150hp right?

Stupid pilot tricks

150hp / 2

75lbs hr @ 100%

75lbs / 6lbs per gal for 100LL

12.5GPH at 100%
 
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What is your objective, cool the cylinders? They are not too far out of line, but I'd prefer less than 400. Check your probes for accuracy before you go changing things.
The fuel burn you report doesn't seem low, I beleive it should be right around 12.7. Check the mag timing first, if one or both are advanced that will cause higher temps.
There's no way to increase flow short of the idle mix screw which won't change things much, unless you re jet the carb..or massage it with a wire drill.
Tim
 
If your mags are set right (good EGTs?) and the baffles are really good, maybe there is a louver kit or 337 you could put on.

I target 380 max for climb out.

350 max for cruise.
 
What airspeed are you climbing at that you see the issue? Vx, Vy, cruise climb?
 
The only way I know to increase fuel flow would be to use a properly sized reamer through the main jet. Legal? That's precisely what the TCM rep had my local shop do when my last reman was running too hot. Those of us that have had PPonks for more than 10 years know that not only does PPonk ream the original factory jet but a subsequent service memo about 10 years ago had local shops ream it bigger. It isn't magic. on the other hand, if a normally good-running airplane started seeing the CHTs creep up in high power ops the first place I'd look would be at the muffler. A subtle increase in back pressure will result in a corresponding increase in CHT. Reduce back pressure and CHTs will be reduced and rate of climb will improve even without a recognizable change in static RPM. Ask any Cub guy who's ever changed a stock muffler to a hot rod (STCd) muffler. The hot rod is a legally installed gutted muffler. CHT and ROC improvements are typical. The same is true of the average airplane that gets a new muffler to replace a functional 40 year-old one.

My thoughts on an early morning.
 
What are your outside air temperatures? What is your field elevation? What altitudes are you climbing to and how long does it take to get there?

I see around 420 after about 12 to 15 minutes at full power. I initially climb (C177 w/150hp fixed pitch) around 70 mph to at least 500 AGL then climb around 85-90 mph for better cooling. These are with outside air temperatures around 75 degrees from 1300ish MSL elevation. Fuel flow is right around 12 gallons unless really hot out then down to about 11 at full power.

90mph is about the highest IAS I can climb at full power due to engine RPM limits.

If its really hot outside and I have a big load, I'll climb till about 430 CHT, level out for about 15 minutes then make another push for desired altitude.
 
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Fwiw my engine ran like crap, very rough when leaned and slobbering rich with an old 10-3678-32 which I think had a one piece Venturi AD applied. Don't remember cylinder temps.

The temperatures I described above are with a 10-5217 that was freshly overhauled by Avstar Inc in 2012. This combined with replacing all the intake gaskets was like flipping a switch and the engine ran great and much smoother even when leaned till misfire.
 
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