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Posted   2/14/2006 by Bruce Smith


SPECS

Engine: Evolution .36NT
Displacement: 354ci
Bore: 0.806 in.
Stroke: 0.695 in.
Carburetor bore: 0.295 in.
Practical rpm: 2,000 to 16,000
Weight w/out muffler: 10.3 oz.
Prop-shaft size: 1/4-in.x28
Price: $79.99

ENGINE HIGHLIGHTS

Excellent performance.
Great packaging.
Tools included.
Comes with 2 muffler gaskets and
2 replacement backplate screws.

COMMENTS

The Evolution .36NT is an ABC 2-stroke with a standard muffler with two gaskets and attachment bolts and a hex wrench; a 2-needle-valve carb with high-speed needle assembly at the backplate; a Hangar 9 glow plug; instruction booklet; and a 2-year warranty.

RECENT ADVANCES IN MODEL ENGINE TECHNOLOGY have enabled designers to capture more performance from less displacement, even when compared with newer engines. Capitalizing on this technological race for the holy grail of power is the new offering from Horizon Hobby—the Evolution .36NT. This engine reestablishes performance boundaries found not only in the .36ci 2-stroke glow-engine class but also in the larger .40 and .46 classes. To further enhance the Evolution .36NT’s performance, I selected a variety of one-piece mufflers and tuned pipes from Macs Products and dialed in the right header size, length and tuned-pipe choice for this very potent, scrappy fighter of an engine.

The Evolution .36NT can be taken apart completely using one Allen wrench. The engine’s quality is obvious throughout.

As does the entire line of Evolution engines, the .36NT possesses all of the user-friendly features that make it extremely easy to start and operate. The “Set Right” needle-valve system is the cornerstone of the Evolution line. From the first flip, my test engine ran and kept on running—a first for any ABC engine that I have run to date. Featuring a dual-ball-bearing- supported crankshaft, anodized propeller thrust washer and needle-assembly parts as well as distinctive cooling-fin styling, the .36NT continues to prove that the manufacturer’s goal of providing a ready-to-mount-and-fly, dependable and well-made product has been irrefutably secured. All Evolution engines so far have provided a no-hassle experience for modelers. The Evolution .36NT comes with a lightweight, reasonably quiet muffler, a Hangar 9 glow plug, a 2-year warranty and a comprehensive instruction booklet.

RUNNING THE .36NT
The .36NT is very easy to start. Attach the fuel line, choke the venturi opening with your finger, and flip the prop several times until fuel fills the line between the remote needle valve and the
carburetor. Open the throttle to about 1¼4 turn, attach the glow driver, and flip the prop again to start. My engine fired up and ran continuously from the very beginning.

I used the recommended 9x6 prop for the first few runs. Evolution engines are promoted as needing no break-in, and this is true; my test engine’s performance was flawless and steady.

The .36NT’s performance is impressive and exceeded my expectations. For my evaluation, I selected a variety of APC propellers and very carefully balanced them all. As the performance tables with the standard muffler suggest, the .36NT cranks up some pretty high revs, and changing to a tuned-pipe system opens the envelope even wider. In addition to testing the engine’s tuned-exhaust performance, I wanted the Macs one-piece mufflers to prove their merit. I used two Macs mufflers of different volumes and dimensions, but they had the same attachment-bolt spacing. The smaller one (item no. 6340) is designed for .21 to .38ci engines, and the larger unit (no. 6650) is suggested for .36 to .46 engines (refer to the Performance Evaluation Tests chart). These mufflers are a great alternative to the stock unit and offer similar performance as well as low noise, lighter weight and economy of design— all wrapped up in a trick matte-black finish.

FINAL THOUGHTS
The .36NT belts out impressive performance numbers with both short and long (low-pitch) propellers, so it’s a great choice for fun-fly, sport, aerobatic and Quickie 500 designs. Run it with the stock exhaust or the tuned-exhaust system, and for the price, I think you’d be hardpressed to find an engine of any displacement that can match the Evolution .36NT. I like the tuned-pipe option, but again, that’s me. You decide!

TUNED-EXHAUST SYSTEMS

TUNED PIPES OFFER ANY 2-STROKE ENGINE a substantial increase in power output. The principle is pretty simple: 2-stroke engines are designed to have a certain amount of time—or overlap—when both the intake and the exhaust ports are open. This occurs during the power stroke, or downstroke, of the piston (after combustion). The overlap is designed to use outgoing exhaust force to draw in the next intake charge before the next combustion event. This is also the reason that 2-stroke glow engines spit out a certain amount of unburned fuel, which also helps to cool the engine.

A tuned-pipe system comprises a header pipe, a silicone-tube coupler and the expansion-chamber muffler. The “tuned” aspect refers to determining the header length that enables the engine to obtain the greatest rpm gain. Tuning an expansion-chamber system requires cutting the header’s length a little at a time and testing the system for an rpm reading at each interval. Typically, shortening the header raises the rpm until you reach a point at which the rpm reading decreases. That’s when you stop cutting.

The performance principle at work with a tuned system is a basic form of supercharging. A tuned-exhaust system creates supercharging by increasing the intake of the engine to a volume greater than it would normally draw in. The “overlap” of the intake and exhaust ports allows this overflow of intake to pass through the engine and partly into the expansion chamber. The sound wave from the previous exhaust stroke travels to the end of the chamber and is then reflected back to the engine, acting like a plunger forcing the overabundance of mixture back into the engine. The net result is a cylinder that’s packed with more combustion mixture than it would obtain if normally “aspirated”— thus, it’s supercharged. The tuning of the system is actually “timing” the moment the pressure wave returns to the exhaust port before the port closes for the next combustion event or power stroke. The increased volume of intake charge makes more power—end of story.

My two favorite publications for additional reading on tuned-exhaust systems are “All About Engines” by Harry Higley and “Basics of Model Marine Engines” by Alan Hobbs—published by Air Age Media.The bottom line on tuned pipes is more power, rpm and fuel consumption.


EVOLUTION .36NT AND THE PIPE

NOT KNOWING HOW THE EVOLUTION .36 would respond to a tuned-exhaust system raised the question of which header/pipe combination to use. As David McAllister of Macs Products pointed out, some engines prefer more backpressure than others. I could find the solution only by testing two individual exhaust systems, the first one being used typically for .21 to .36ci engines (1/2-inch header tube) and the second being typical of larger, .40ci, displacement engines (5/8-inch header tube). Both systems were Macs “muffled” pipes. After a few hours of tinkering with the smaller system without its showing much improvement, I switched to the larger one; it was clear which system worked better and was easier to tune: the .40ci system with lower backpressure (header no. 2650; tuned pipe no. 1230). The optimum header length is with 1/2 inch removed from the header. With significant gains in rpm across the prop chart, the Evolution .36NT responded very well to the higher performance Macs tuned-pipe system. With the increased flow of fuel and air, the high-speed needle valve needs a few more turns richer. Although I didn’t experience any significant air-bleed problems with the needle backed out that far, I’d prefer the manufacturer to add an additional O-ring, as the needle has a fair amount of play and wiggle room. A piece of large-i.d. silicone fuel tubing over the needle-valve stem and sleeve will remedy the loose fit and potential for problems and will also minimize needle vibration. That said, I found that the Macs pipe and the .36NT were a sweet combination!

Provider Name:  Model Airplane News


Issue:  April 2005


Copyright:2005


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