PRODUCT TEST REPORT
by Gordon Banks
CHEERS - Three-year warranty; comes with spark plug, muffler, and engine mounting plates; muffler can be mounted upright or inverted; includes wrench for spark plug and prop bolt; overall good looks; single prop-bolt; Walbro pumper carburetor can be mounted upright or inverted (see Jeers); easy throttle linkage connection; very good instructions; easy to start by hand; good idle; clean and instant acceleration; very impressive peak power (see text).
JEERS - Carburetor adjustment screws point toward prop (but carb can be rotated to prevent this); supplied muffler very loud; narrow mounting plates for such a powerful engine.
This has been one of, if not the most requested engine tests ever! My apologies for taking so long to get to it. I've been a busy, busy boy!
The very first thing I want to say here, is that this is the easiest hand-starting gas engine I have ever messed with! I feel sure that at least part of this is due to the heavy-duty magnets and the built-in Automatic Timing Module, but part of it too is that I've learned quite a bit about big model airplane gas engines from Brian and other resources. But for whatever reasons, I had absolutely no problems starting this engine by hand, time after time after time. I call it a "three-flipper", because it almost always starts on the third flip of the prop. I don't recall it ever starting on just one flip, and the only times it took more than four flips were when the gas line and carb were run dry. Then it took considerably more flips to get gas through the line, through the carburetor, and into the engine again. But when killed with the electrical kill switch, and the gas line still held gas... three flips. (I mention this because of my very poor track record when it comes to getting magneto-ignition gas engines to start easily.)
As you can see from the first photo, there's "some assembly required" when the new engine comes right from the box. The prop hub and muffler have to be bolted into place, and the muffler allows a choice, since it installs and works fine, upright or inverted. The carburetor is already installed, but it too can be removed and installed inverted. When upright (as it comes from the box), the fuel mixture adjustments screws lean toward the propeller, making running adjustments somewhat dicey (as in "slide and dice"), since you'll be very near the spinning prop. When the carb is inverted, however, the adjustment screws lean away from the prop, making fuel mixture adjustments easier and safer.
With the two fuel mixture adjustments set as per the instructions (which are excellent instructions, by the way), I attempted the first start. I was using a black neoprene fuel line, so I couldn't see the fuel moving through the line... or the lack thereof. After a lot of fruitless prop-flipping with the choke closed and the throttle wide open, I'd yet to hear the first indication of the engine trying to run. I yanked the fuel line from the carb to check for fuel flow. Bone dry. At this point I gave up on trying to "draw" fuel to the carburetor, deciding to "force" it there instead. After pinching the gas tank vent line closed, I squeezed the tank itself until gas ran from the fuel line. With fuel flow established, I pushed the line back onto the carb fitting, replaced the gas tank in its holder on the test stand, and began flipping the prop again. I guess it took about four or five flips to work gas through the carb and into the engine before I heard the first "pop". I opened the choke, set the throttle to a guestimated high idle, and three flips later the engine suddenly got loud. And that seemed to set the pattern for the remainder of the break-in runs and prop tests... three flips, unless the gas line ran dry.
With a typical glow engine, I can just give the fuel tank 8-10 oz. of fuel, and let it run dry several times, with cool-down periods in between. With a gas engine, that doesn't work. Some seem to run all day on 10 oz. of gas! Well, not really... but it seems that way when you're standing there waiting for it!
Although the engine ran a bit rough right at first, it began to noticeably smooth out during the first break-in run. I let it run at a high idle for about eight minutes, then let it sit and cool off to the point where I could touch the cylinder heat without discomfort. I did that twice before I began letting it run faster and faster with each eight to ten minute run. Nearing full throttle, I allowed it one extra run during which I frequently cycled the throttle from mid to full, back and forth numerous times, allowing it to run at full throttle a few seconds longer each time. Finally, I allowed it two full-throttle break-in runs, during which it seemed to run smoothly from start to finish.
I tried a few experiments with fine tuning the fuel adjustment needles, and settled on a setting with the low speed adjustment right where the instructions suggest, and the high-speed screw about 1/4 turn leaner than suggested. I also noted that the high-speed adjustment was narrow and sensitive. If turned a half-turn in either direction, the Fuji-Imvac BT-64 ran poorly. And that 1/4 turn... it made a peak difference of approximately 300 RPM! With big props, that's a lot! We never did finish up our thrust tables for 22" and 24" props before Brian left, but on a 20x10" prop, the difference between 7,700 RPM and 8,000 is a whopping 30 oz., nearly two full pounds! A 300 RPM difference with a 22x10" probably exceeds two pounds!
Another huge difference was noted between the 22x10 Zinger and 22x10 Bolly. The Bolly spun an amazing 600 RPM faster! Impressive, to say the least. Or is it? Most Zinger wood props have a narrow but definite flat leading edge across their entire length. While that much flat edge certainly doesn't lend itself to propeller efficiency, it does make a big difference when an absent-minded modeler sticks his hand into the propeller arc. Theoretically, the flat leading edge not only reduces the depth and severity of the resulting cut, but the higher resistance of that flat leading edge lends to the probability that the prop will break before the unlucky modeler's bones! Composite props with sharper leading edges and thinner airfoils are almost always more efficient, and provide better performance. Woods props, however, seem to be a lot more friendly to the poor modeler who gets whacked by one.
While still in the break-in phase, it became loudly apparent that the Fuji-Imvac BT-64's muffler is not going to win any awards for being nice and quiet! With the sound meter 10' away, and the 22x10 Zinger prop at peak RPM, I measured an almost painful 104 dB(A). A simple 6" silicone rubber extension (connecting material for a tuned pipe) cut that down to 102 dB(A). That's about 30% less noise, with no loss of power.
Speaking of peak RPM, I guess the most logical comparison would be with the Zenoah G62, which Brian and I found very difficult to start by hand until a CH Electronics "Jump Start" was added. Some people find the magneto version nearly impossible to start by hand, while others have few problems at all. The Fuji-Imvac BT-64 has built-in ATM (Automatic Timing Module), and doesn't seem to need an aftermarket add-on.
In every comparison, the Fuji-Imvac BT-64 has more:
Power-wise, the 63.1 cc Fuji-Imvac turns the same props at least 300 RPM more.
Weight-wise, the 81.9 oz. Fuji-Imvac, w/o muffler, weighs 3.6 oz. more than the G-62 w/o muffler. The stock Fuji-Imvac muffler weighs 0.5 oz. more than the G-62's 9.3 oz. muffler. The total difference is that the Fuji-Imvac, with muffler, weighs 4.1 oz. more.
Noise-wise, with the stock mufflers, the Fuji-Imvac BT-64 was a whopping 9 dB(A) more than the, by comparison, much quieter G-62.
Personally, I think the Fuji-Imvac BT-64's extra 4 oz. of weight is more than offset by its extra power, and since few people will use the stock muffler on either engine, the muffler's performance is probably equally unimportant. If I was planning on using the stock muffler, though, then all that extra noise would weigh more heavily on my decision.
So there you have it. The Fuji-Imvac BT-64 looks good to me.
R/C REPORT ENGINE TEST REPORT
Manufacturer . . . . . . . . . . . . . . . . . . Fuji Imvac Inc., Japan
Importer/Distributor . . . . . . . . . . .Great Planes Model Distr. Co.
P.O. Box 9021
Champaign, IL 61826-9021
(217)398-3630
www.greatplanes.com
Price. . . . . . . . . . . . . . . . . . . . . $429.99 at Tower Hobbies
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . .Three Years
Muffler Included . . . . . . . . . . . . . . . . . . . . . . . . . .Yes
Spark Plug Included. . . . . . . . . . . . . . . . . . . Champion RCJ6Y
Ignition . . . . . . . . . . . . . . . . . . . . . . . Magneto with ATM
Tools. . . . . . . . . . . . . . . . . . . . . . Combination wrench for
spark plug and prop bolt, one Allen wrench
Accessories. . . . . . . . . . . . . . . Engine mounting plates, engine
mounting template, and gasoline fuel line.
Displacement . . . . . . . . . . . . . . . . . . . . 63.1 cc (3.85 c.i.)
Recommended RPM Range. . . . . . . . . . . . . . . . . . . . 1200-9000
Advertised HP. . . . . . . . . . . . . . . . . . . . . . . . 5.7 @ 9000
Schnuerle-Ported . . . . . . . . . . . . . . . . . . . . . . . . . .Yes
ABC Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . No
Ball Bearings. . . . . . . . . . . . . . . . . . . . Two on crankshaft,
needle bearings on connecting rod
Engine Weight. . . . . . . . . . . . . . . . . . . . . . . . . 81.9 oz.
Muffler Weight . . . . . . . . . . . . . . . . . . . . . . . . 9.8 oz.
Recommended Props. . . . . . . . . . . . . . . . . . . . . 22x10, 22x12
A. Overall Length. . . . . . . . . . . . . . . . . . . . Minimum 7-7/8"
(Actual length depends on prop thickness)
B. Overall Height . . . . . . . . . . . . 8"-7/17" w/spark plug
C. Overall Width at Mount. . . . . . . . . . . . . . . . . . . . . . NA
D. Overall Width at Carb . . . . . . . . . . . . . . 5.58" w/o muffler
E. Firewall to Prop, minimum . . . . . . . . . . . . . . . . . . 5-7/8"
F. Firewall to First Mounting Hole . . . . . . . . . . . . . . . . . NA
G. Crank Center to Outermost Point . . . . . . . . . . . . . . . 6-7/8"
(muffler not included)
H. Mounting Beam Width . . . . . . . . . . . . . . . . . . . . . . . NA
I. Mounting Hole Centers, Side to Side . . . . . . . . . . . . . 2-3/4"
J. Mounting Hole Centers, Front to Rear 2-3/4"
K. Prop Bolt Diameter. . . . . . . . . . . . . . . . . . . 10 mm or .4"
L. Prop Bolt Length. . . . . . . . . . . . . . . . . . . . . . 1-15/16"
Fuel Used. . . . . . . . . . . . . . . . . . . .Texaco 87 octane, mixed
40:1 with Bel Ray MC1 oil
Spark Plug Used. . . . . . . . . . . . . . . . . . . . . Champion RCJ6Y
NOTE: All Test Props are Zinger
wood props unless otherwise noted.
Minimum Reliable Idle
Propeller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .RPM
22x10 Zinger . . . . . . . . . . . . . . . . . . . . . . . . . . .1,500
22x10 Bolly. . . . . . . . . . . . . . . . . . . . . . . . . . . .1,300
Maximum Measured Noise
Propeller. . . . . . . . . . . . . . . . . . . . . . . . . . . . .dB(A)
22x10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104.0
Maximum Measured RPM
Propeller RPM Thrust
20x10 8,000 449
22x8 7,700 395
22x10 6,900 NA
22x10 Bolly 7,500 NA
24x6 7,200 NA
24x8 6,600 NA
(Thrust measured in oz.)
Photos by Gordon Banks. Reprinted with permission.
June 2003 R/C Report
Editor: Gordon Banks
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