[NA]Briggs engine[NA]

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
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Feb 23, 2005
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west Texas
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Dave Taylor
So they have worked through a few problems but now this new 15.5hp 4stroke Briggs and Stratton is not making rated rpm. Apparently it is 150 low, and cannot be adjusted upwards, even with the governor. The dealer called B+S and was told it's the altitude (we are at 5000'). Does this explanation seem plausible assuming the mixture has been correctly leaned for the thinner air? I would not expect that with an a/c engine which is similar. Honestly the rpm loss is not as concerning as 'what else will go wrong with this engine' in the future.
 
Let'sgoflying! said:
So they have worked through a few problems but now this new 15.5hp 4stroke Briggs and Stratton is not making rated rpm. Apparently it is 150 low, and cannot be adjusted upwards, even with the governor. The dealer called B+S and was told it's the altitude (we are at 5000'). Does this explanation seem plausible assuming the mixture has been correctly leaned for the thinner air? I would not expect that with an a/c engine which is similar. Honestly the rpm loss is not as concerning as 'what else will go wrong with this engine' in the future.
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Really? You don't notice a power loss with altitude in a plane? With a C/S prop you won't see it in RPM, but you'll see it in MP. In a fixed pitch plane you will see the loss of power in a drop in RPM. The manufacturers explanation of why you aren't making RPM is most definitely plausible. When you "lean" for the thinner air, you are taking fuel away. If you take fuel away, you take power away. If you want to make rated power at 5000' you'll need some form of air compressor like a turbo charger. Fuel = Power and you need 13.7 pounds of air for every pound of fuel.
 
You don't notice a power loss with altitude in a plane?
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There is a cherokee manual that shows an increase in max available rpm with altitude. Less prop drag, I presume.
 
Let'sgoflying! said:
There is a cherokee manual that shows an increase in max available rpm with altitude. Less prop drag, I presume.
Click to expand...
Correct. I cannot exceed red line in an Archer II at 3000 MSL level, WOT. I can at 8000 AGL level.

So it all depends on what kind of load is on the Briggs in question.

-Skip
 
No load, lack of RPM the governor has to be faulty.
Click to expand...

or..
-inadequate fuel delivery
-inadequate air
-improper cam profile
-valve timing wrong
-valve seating problem
-spark timing problem

Essentially, the altitude suggestion was a brush-off and there is likely more wrong with this new engine. Who wants to guess I will be able to cut my grass by Thanksgiving?
 
Let'sgoflying! said:
There is a cherokee manual that shows an increase in max available rpm with altitude. Less prop drag, I presume.
Click to expand...

That is not the same as as having more available horsepower. You have reduced the drag on the prop more than the power of the engine so the net result is more RPM for less horsepower.
 
Let'sgoflying! said:
or..
-inadequate fuel delivery
-inadequate air
-improper cam profile
-valve timing wrong
-valve seating problem
-spark timing problem
Click to expand...

Yup. I jumped to the assumption that the engine runs normally at sea level. My bad....

-Skip
 
DT what you want to do is drive the engine down the hill and measure rpm at Harlingen.
 
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