Fuji-Imvac BT-50 EI Gas Engine



Weight (bare engine):
Peak RPM:
Rated Horsepower:

3.5 pounds
20x10 CF@ 7400
5.2@ 10,000

fuji50.jpg (30308 bytes)

This is one of the few engines I haven't owned in my 37 years of RC Modeling. So I thought I was past due.

FUJI's Advertisement:
Long known for their power and dependability, Fuji-Imvac engines now come with the many benefits of Electronic Ignition! A sensor on the compact EIS unit measures rpm and adjusts the timing — making starting much easier. The EIS unit reduces vibration and rotating mass on the crankshaft, so engine performance is boosted.

The engine is said to be a high RPM engine, so I attempted to locate bore & stroke information. I haven't found any of this data yet. OK, I can measure this myself, it has a 32.0 mm stroke. It is a short-stroke engine.  Now I can concentrate on other aspects of this engine. If you  are replacing an engine with this one, you may encounter some issues. The muffler & carb location is opposite of most other bigger CC engines. This can cause you to make additional cut-outs in your cowling as well as move your throttle linkage. In a "new" aircraft this won't be an issue. SEE: Rotating the cylinder on a FUJI BT-50 EIS ENGINE! The Fuji BT-50 EI engine is very clean and well designed as the photo depicts. You may also notice this engine uses a Walbro HDA carb. This carb (in my opinion) is the best of the best. Another nice feature is that Fuji offers various lengths of prop hubs. This comes in handy for getting prophub length in the right place without using much in the way standoff's. The Electronic Ignition is a big plus. Not only does it lower the engine weight, it also makes starting easier. In the advertisement, Fuji says it's dynamically balanced. OK, the jury is out on that one. I will just have to see how it does on my bench stand. I can do without the painted light blue jug but if the engine runs good,  I can over-look the color.


fuji_running1.jpg (72621 bytes)

The first start:
I closed the choke, and flipped the engine over 12/15 times. Then turned on the Ignition, it fired up on the 4th flip! I let it idle for about 10 minutes then gave it FULL POWER. The engine didn't need a bit of carb tuning, and it throttled up AGGRESSIVELY! I'm spinning an APC 18x10W prop, and it was AWESOME! The throttle accelleration is the best I have seen on a 46cc engine with this prop. FUJI's claim regarding it being balanced is true. This engine is smoother running than ANY of my other similar sized engines. While it isn't as smooth as a twin cylinder, it comes as close as you will get with a single cylinder engine. It's really surprizingly  smooth! 

The BT-50 EIS seems to be OK smaller diameter props. I will let it run on a tank or two before switching to a 20" prop. All indications "suggest" it will pull a bigger prop without over-heating.

Well, it's clearly obvious that "reverisnig" the cylinder doesn't effect the performance any. This engine really wants to run! The factory muffler has a nice tone and it's not overly loud either.

The Fuji BT-50 EIS is VERY easy to start, it has very aggressive throttle responce, and it's as smooth as glass. The engine weighs 3.5 pounds without the muffler so it's a reasonable weight as compared to similar size engines. That Walbro HDA carb works like a champ, and absolutely no tuning was needed. Reversing the cylinder really made this engine compatable to my airplanes. So I will likely do an engine swap to see how it flies.All in all, I am VERY IMPRESSED with this engine, especially with how smooth it runs!

Here is a photo of the aircraft I am using for the in-flight tests. This is a Great Planes 1/4 scale RV-4. It really ought go! The airplane weighs 14 pounds and the BT-50 makes 19 pounds of thrust.

RV4andFUJI50.jpg (56876 bytes)

The muffler you see is a BENNETT made for a Zenoah G62. It's a perfect match.


Copyright 2007 M. B. Fuess