I finally got an ideal day for testing the power output differences for my Standard compression Saito FA180 on glow ignition, the standard compression FA180 W/CDI & the High Compression FA180HC CDI BBC (FA220 Big Bore Carburetor) All testing W/the same 15% Cool Power glow fuel
For those not familiar W/the high compression FA180HC project, an illustrated write up is available HERE.
Since the FA180HC BBC was on the test stand I double checked the ignition timing. The timing was set @ 34* BTDC. That will give 34* BTDC @ WOT when running @ high RPM. I'm not sure what the advance curve is, but the 24* retard @ start would give 10* BTD ignition timing @ start & idle.
The 220 Big Bore carburetor has the same bolt pattern as the 150/180 carburetors, it is 12mm bore (the 180 carb is 11mm. the 150 10mm) I bored the updraft portion of the FA150 manifold I had on hand out to 12mm. The horizontal runner where the manifold interfaces W/the intake port was bored out to the standard FA180 ID to match the 180 intake port.
The aluminum intake gaskets that come W/the FA180 are smaller in I D than either the intake manifold or the port on the cylinder head. It appears to be the same ID as the 150 port/manifold. Since I have not had any issues eliminating these gaskets on any of my 150/180 engines, I chose to eliminate it for a smoother transition from the manifold to the intake port.
After fiddling W/the HSN, the FA180HCCDI BBC spun the Dynathrust 18x8 prop @ a solid 8400 RPM flashing 8500, idle was steady 1100 RPM. @ 8450 RPM that generated 3.44HP W/20.44# Thrust.
The standard compression FA 180CDI had the timing checked & set @ the same 34* BTDC.
After tweaking the HSN, the FA180CDI spun the same 18x8 prop @ 8000 RPM flashing to 8100, idle was a steady 1200 RPM. @ 8050 RPM that generated 2.98HP W/18.55# Thrust
The CDI was unhooked, the sparkplug replaced W/a glow plug. The needle setting were opened up to OEM start up specs & the engine started on glow ignition.
After setting the HSN & LSN, the FA180 on glow ignition spun the 18X8 prop @ a steady 7900 RPM, the idle was a rough 1400 RPM but it was reliable. @ 7900 RPM that generated 2.81HP W/17.86# Thrust.
CDI ignition gave an additional 150 RPM, .17HP & .69# of thrust over glow ignition & reliable idle was was 200 RPM lower.
The compressionn ratio increase to 12.77:1 from the stock 9.56:1 coupled W/the 12mm FA220 Carb really brought on the power.
The increase for the standard compression F180CDI version was an additional 400 RPM, HP increased by .46HP (15% HP gain) W/1.89# additional thrust (10% thrust gain) & another 100 RPM lower idle speed.
Comparing the gains from the standard glow ignition FA180, to the FA180HCCDI BBC, HP went from 2.81 to 3.44, .63HP gain, (22% HP gain) thrust increased from 17.86# to 20.44#, a 2.58# gain (14% thrust gain) W/300 RPM slower dependable idle speed.
This puts the FA180HCCDI BBC squarely in the power output range of the FA220 W/much better fuel economy & less weight in a more compact engine package. I am very pleased W/the results.