April 2, 2015

Free Article – X-Dyno Protek RC Samurai 321B

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Written by: Derek Buono

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Time again for a little wailing of the dyno,aggravating the neighbors and filling my garage with a noxious, whitish-blue haze. For this issue, I have the latest from Protek RC (A-Main’s house brand), the Samurai 321B buggy engine. Although it bears an amazing resemblance to the OS Speed 21 XZ-B Spec II, it does have some very important differences; mainly, the bore and stroke are not the same as the current offering from OS Speed but are nearly identical to the short-stroke Speed VZ-B Spec II. Possibly more important, however, is that it costs $100 less.
Protek RC has, in my opinion, made a smart move by offering the short-stroke engine, as the discontinuation of the VZ series engines from OS have left the buggy market with a void just begging to be filled. The power and tune-ability of the short-stroke version of this engine will be welcome in many buggies across the world. And if the dyno is any indication of this, the Samurai 321B is sure to bring back the short-stroke legacy this season.

Protek RC delivers race-quality craftsmanship starting with the outstanding black, hard-coated crankshaft. Knife-edged, scooped, slugged, and filled, it is everything we have come to expect in the highest quality competition components. I especially like the hard coating used on this piece, as it really extends the life of the crank pin—often one of the weaker links in micro-engines because it commonly wears faster than any other component in the engine. The hard coating definitely slows this process dramatically.

I’m detecting a theme here, and I think it’s black. Everything black. The finely cast crankcase is covered with cooling fins and is anodized black. Precision work has been focused on the intake port that leads to the crankshaft inlet window, leaving no stone unturned. One of my only beefs with this engine is the somewhat generic branding of the 321B and Protek RC logo on the sides of the crankcase. Petty, I know, but I would have expected a little more flash here.

Connecting rod:
Seems like every manufacturer makes their connecting rods from the same mold however the quality is definitely there in the Samurai engine, which feature a high-strength aluminum knife-edged conrod with precision brass bushings at each end and lubrication holes drilled in each end to supply the piston pin and crank pins with the necessary lubrication to achieve extremely high rpm.

Piston and sleeve:
I always go on about the importance of the aluminum’s quality and the quantity of silicon infused in the alloy, and I have to hand it to OS. As an engine manufacturer, they have it down to a science; they produce some of the highest quality pistons in the business. The Protek RC 321B engine is no exception, as it displays a traditional OS-quality piston that has been precision machined and ground to a perfect finish.
The Samurai’s ABC cylinder shows equally impressive port machining and quality finish, using a 3-port configuration with an extra-wide exhaust. This configuration lends itself to the high mileage that today’s racers are demanding from their competition engines.

The Samurai has an all-aluminum carburetor body that uses a proven 3-needle design and a nylon isolator base to aid in combating heat soak. Unique to the Samurai are the two included carb insert restrictors, which are elliptical in design and keyed to the carb body. This allows the 321B to further extend the fuel mileage without wasting that valuable commodity: fuel!

Head and head button:
The cooling head of the 321B Samurai engine is a bit of a new take on an iconic design. It appears that Protek RC adopted the XZ cooling head, which sits quite low on the engine due to its being milled on the bottom to conform around the top of the case, thus lowering the whole assembly roughly 8mm. This design is very common on today’s race-type engines and brings the VZ styling up to snuff. To top it off, they went and drilled the bottom eight fins with gobs of lightening holes, further lowering the weight and CG of this engine.
The head button itself is a bit anti-climactic. Though just your traditional run of the mill turbo head button, it is nicely machined and has a dome shape to lend power to the higher rpm range.

Protek RC 321B MAX
Let’s face it: these engines aren’t getting any easier to break in as technology evolves, and the Protek RC 321B is definitely no different. With pinch aplenty, it took some time with the heat gun to get this ready to pop to life. Carb settings were quite a way off on the rich side and took some tweaking to get the mixture to the point where the engine would fire, primarily the low speed, which was about 1½ turns too rich to start with. Once it was running, I idled two tanks of fuel through the engine while also keeping a close eye on the case temps; I never allowed the engine temp to drop below 190˚F. After each tankful, I lowered the piston to bottom dead center and allowed the engine to cool to ambient room temp before starting the process again. The third and fourth tanks were leaned slightly and alternated between long idle periods and soft, smooth run ups in the rpm range to clear the engine of accumulated fuel/oil. During this process, I like to try and keep the engine in the temp range where it will be spending most of its life; in this case, that is approximately 230°F and, again, between each tank I allow the engine to cool to ambient room temp before proceeding.

A couple hours of fiddling later, we were finally ready to start leaning on the needles and making some full-throttle, full-power runs. I immediately noticed that this engine is really smooth and doesn’t have many bad habits, or dips and lulls in the power, either on the front side of the curve or the back. Even when a bit over-rich, the engine still pulled well from the lower rpm all the way up to max revs, and although this may result in slightly lower output figures, it will still be plenty runnable on the track.
After some additional attention to mixtures, this little gem really started to come to life, and what impressed me the most about this engine was the smoothness of the curve on the front side, but more important, the breadth of the power way out into the over-rev range. It simply continued to make power way past its torque peak all the way into the stratosphere of rpm. All said and done, the Protek RC 321B Samurai engine produced an impressive 1.50hp @ 26,000rpm and a peak torque of 59.82 oz.-in. at 25,000rpm. It topped the rev range at around 42,750rpm.
Protek RC 321B timing_wheelchart

Seems as though a ton of engines are on the market these days, some of them ridiculously expensive and others super cheap. With so many choices, it’s difficult to decide which one to spend your hard-earned money on. It’s easy just to look at what everyone else is running at your local track and follow the leader, but sometimes, those just aren’t within your budget. And then along comes the Protek RC from AMain Hobbies, who releases a top-of-the-line engine, rebadged, for $100 bucks less while clearly not giving up anything in the power department. And knowing where this engine comes from, in my opinion, makes the decision a bit easier because you know that the source is a brand you can trust. In this day and age, any time I can save a hundred bucks or more on an engine that runs this well, it has to be a no-brainer! Well done, Protek RC; well done!


Protek RC Samurai 321B 1/8 scale off-road buggy engine
Part #: PTK-2500, Street Price: $349.99

Bore: 16.6mm (0.65 in.)
Stroke: 16mm (0.63 in.)
Displacement: 3.46cc (.21ci)
Carb type: Slide type, aluminum body w/nylon insulator, three-needle
Carb bore: 8mm and 7mm elliptical restrictors
Manufacturer’s recommended carb settings (after break-in): HSN 2.5 turns out from seated, LSN 0.5mm out from flush, and mid-speed needle flush with carb body
Head button: Turbo
Supplied glow plug: P3 Turbo
Ports: 4
Piston/sleeve: ABC
Crankshaft type: 14mm SG
Timing specs:
Exhaust port height: 6.4mm from BDC
Transfer port height: 3.5mm from BDC
Exhaust port timing: 165°
Transfer port timing: 114°
Intake port opening: 15.5° ABDC
Intake port closing: 74.5° ATDC
Intake port duration: 239°
HP: 1.50 @ 26,000rpm (peak corr. hp)
TQ: 59.82 @ 25,000rpm (peak oz.-in. tq)
Peak Dyno RPM: 42,750 (peak rpm measured)
Low Avg HP: 41.17/.64 (oz.-in. tq/corr. hp)
High Avg HP: 53.87/1.07 (oz.-in. tq/corr. hp)

About the Author

Derek Buono
Derek Buono
Derek Buono– Started in the industry as an assistant editor at RC Car Action where he spent 2 years before being recruited by Xtreme RC Cars Magazine. For the past 10 years Derek lead Xtreme RC Cars and helped double the circulation, improved editorial quality and helped lead the market in design and creativity.



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