Mak Gyver

My Feedback: (1)

New to the gas, came a across Stihl 28cc I converted it to an air plane engine. Need advice on what to do to boost power. Milled flywheel down and made a hub for prop17x8. Have not ran it yet, but been checking up on Sthil web site and it is only rated at 1.01bhp. That is low compared to others like Fuji 24cc rated at 2.2bhp. Can i mill the jug down to increase comp. and how much? any thing need to be done to intake? Wanting to change carb from Zama to Walbro for the high and low speed adjustment. Good or bad? Thanks

rangerfredbob

My Feedback: (13)

get a baseline and go from there. start out with a slightly larger two needle carb (both Zama and Walbro make them, both have the same bolt spacing but the pulse hole is sometims in different places), also gut the stock muffler and give it a couple 1/2" ID outlet tubes. These two changes will imcrease the power from the factory specs, they had it choked down with an air filter and a small carb, along with a tiny exhaust outlet

if that's still not enough for you, take some plumbers solder and put it through the spark plug hole and smash it with the piston at the cylinder wall in the combustion chamber, measure that distance, that will give you how far the cylinder can go down to increase compression, a lot of times it's just enough to fix up by removing the gasket and sealing it with some RTV, from there, print yourself out a degree wheel and check the duration of the intake and exhaust ports, I hear a maximum for the exhaust should be 150*, I don't remember intake off hand.

those are the main power adders unless you jump to a tuned pipe

Flathead

My Feedback: (11)

I don't know much about a Stihl, but I do know that anytime you mill down the jug, you also change the port timing. The ports will open at a different times, and can change things. You may be able to port the engine and improve performance. Check it out. Flathead 4

buck1856

My Feedback: (49)

OK,first of all check both websites and see what RPMS those BHP numbers where compared to.If the fuji was spinning 8000,but the stihl was only spinning 6000,theres a difference.All i know is my stihl 28cc will spin an APC 17x8 at 7400-give or take 100 each way maybe for bad karma.This is a used engine i bought off e_bay,i didnt do anything to it but make a prop hub,install ign,and pitts muffler,WA200 2 needle walbro and run.I have no idea as how much compression it has or how it was run.I dont even remember looking in the exhaust port for scoring.It had compression,so i converted it.
Next,BHP is only good at the 1/4 mile track and on a dyno in my opinion.[Maybe at the tractor pulls].Quite a few dealers post all this info to make there engine look better than anyone elses.I personnaly dont look at any of it.Pick a plane with a decent weight and wing area and then an engine that should fly it great or overpower it a hair.
The stihls and echos are great power plants for the buck and come real close to some of the main frame suppliers.There are also the other homlites,poulans,huskys,redmax.To name a few.Theres a person here in this forum that runs most of his on gas/glow.He has some real screamers in his hanger.Check out[av8tors posts].Check out the thread,[dont forget echo]and [dont forget stihl].