The Neurotoxin arrived in the original box that Zenoah ships their stock engines in. Packaged with the engine are a number of items; the Zenoah owner's service manual, the velocity stack which will not be used, a few machine screws and washers left over after the aluminum isolator block was installed, and a spark-plug socket wrench. The overall appearance of the Neurotoxin isn't that much different from any other Zenoah mod motor, and companies usually personalize an engine with their logo on the pull start cover and sometimes on the top of the water jacket. The Neurotoxin features the TRM skull and crossbones graphic to set it apart from other engines.

Taking a look at the exterior of this engine, we'll first examine the carburetor; I chose the option of a standard Walbro 257 carb. It does not have a choke or primer bulb yet starting is quite easy if you place your finger over the intake and slowly pull the starter until fuel draws up to the carb. The 257 has a high and low speed needle and they are set at 2 turns out on the low and 1 turn out on the high. Attaching your throttle linkage is up to you; I chose a bellcrank that bolts to the motor mount. Behind the carb is the isolator block, used to keep power-robbing heat from soaking the carb. Plastic or delrin blocks can warp and create air leaks so this Neurotoxin was ordered with the optional aluminum iso block. I highly suggest you purchase one when buying your new motor because not only do they keep heat away and eliminate air leaks but they also come with teflon gaskets that will never tear and probally never leak, as long as you keep the carb bolts tight.

As with a majority of modified Zenoah engines, the coil and pullstart are stock parts. The coil works well for the amount of power a modified engine makes up to 18,000+ rpms.

The Neurotoxin's internal modifications are what make it a true race engine; Al has spent countless hours finding a balance between performance and reliability with his motors and this one is no exception. One area that gets attention is the exhaust port; its been raised 2mm to increase timing and widened 2mm to increase volume. Al uses a unique style of widening the exhaust port more on the top than the bottom. Another area that has been modified is the piston; it's been relieved under the wrist pin and the skirt to remove excess material and lighten the piston, freeing up some horses due to less rotating mass. Countless hours have gone into testing to find the perfect amount of material to remove from the piston because there's a fine line between too light and too heavy. But just how much weight is removed is a secret, and TRM has the numbers right-on and removes the exact same amount on each Neurotoxin that goes out the door.

Along with increased compression, the Neurotoxin gets a trued crankshaft, balanced flywheel, and gets made over with stainless steel bolts, flat washers, and lock washers. A stock crank-seal is used instead of a zero-drag seal. Why? Because the minute amount of reduced friction experienced once the engine gets fully run in is not worth the air leak that zero-drag seals create.

Although the motor is ready to bolt in, there are still a few parts you'll need to complete the installation. The first is an exhaust system. This area is really up to your personal preference but I would advise against power-robbing wrap-to-center or wrap-forward headers, as a 90 to 105 degree header is the shortest route to the pipe. Your pipe choice as well as the total length of the exhaust will play a key role in how the engine performs. TRM recommends a 2" band-pipe to give the best overall performance throughout the powerband. The length from the exhaust flange to the center of the band on the pipe should start around 13" and be shortened until there are no more gains in performance noticed. I ended up at 12.5" from the flange to the center of the band which seems to be a good compromise between rpms and torque. A gps and a tachometer are helpful tuning devices and should be utilized to aide in finding a good exhaust length.

Another item you'll need is a pair of Zenoah-style motor mounts. My favorite style are the quick-change mounts which allow you to remove the motor by loosening four nuts. A bellcrank for your throttle is a necessity when it comes to making the throttle hook-up easy. Most bellcranks mount to the rear motor mount and effectively make a 90-degree turn in the linkage. I suggest staying away from a throttle cable that can flex and go with a beefy 4-40 pushrod. Other small items required, assuming you have a boat ready for the engine, are a collet, fuel filter, and plumbing lines for gas and water.

I installed the Neurotoxin in an Aeromanine Avenger Pro for this review. The pipe used was a B.H. Hansen 2" band pipe, the header was a 2" drop, 90-degree Hansen as well. Overall length from the exhaust flange to the center of the band was 12.5". My prop of choice for the Avenger is a 6717x3 piched to 420.

Breaking in any Zenoah engine is the key to a long life-expectancy, and especially so with a full-mod engine. I mixed my gas with 8 ounces to 1 gallon of Amsoil Dominator and ran the engine at a no more than half-throttle for 2 tanks of fuel. During the 3rd tank of fuel, continue varying the throttle, with very brief full-throttle blips. Varying the throttle is crucial in order to get temps up but not for extended periods. The fourth tank should be right on for full throttle running and tuning for optimal performance.

In order to get the best numbers possible from your Neurotoxin, you should expect to put at least 2 gallons through it. Afterwards, your rpm's, mph, and overall torque will increase noticeably. This is due to possible glazing on the ring that gets burned off as the engine runs-in. I experienced almost a 5 mph increase towards the end of the 2nd gallon, doing nothing other than running laps.

Once the engine was run-in and tuned for performance, the real power produced by the Neurotoxin began to show. Even in the heavy offshore-style Avenger, I was consistently putting down mid-to-upper 50s in race trim, which basically is setting the hull up for the rough and choppy water conditions experienced when multiple boats are racing in an oval pattern. The objective is to keep the nose down to avoid blowing over. Overall top speed is reduced some in favor of better handling. Some of the smaller heat-racing style hulls are also running mid-to-upper 50s as well, some pushing into the low 60s in race trim. I had a personal best speed of 57.4 mph in race trim, definitely fast enough to win races. With the Avenger setup a bit more loose, and the hull contacting the water only on the last few inches of the sponsons, I was able to run 63.2 mph with a 6717x3 propeller. Rpm readings were always within 17,500 to 18,200. The Neurotoxin was definitely running strong. Throttle response is absolutely instantaneous with no lag getting on the pipe with my current exhaust configuration and I experience almost zero drop in rpm when turning.

There are a few things to remember when operating a full-mod such as the Neurotoxin. Oil content is crucial for proper lubrication. These engines are operating way outside the limits of a stock Zenoah and must be taken care of accordingly. Mix your gas at around 8:1 and watch your high-speed needle setting; it shouldn't be much below 1-turn from closed. Your spark plug is a window into seeing how your engine is operating. Spend some time with the veterans at your local club and learn to read a plug. Also, if you "dunk" your engine after blowing over or smacking a buoy, make sure to clear the water out of the engine before you attempt to restart. Doing so will prevent catastrophic damage to the con-rod. Once you've removed all you can, run the engine a few laps at a low rpm to burn off any water left behind.

The Neurotoxin is one of a few high performance racing engines that set the pace for the rest of the field. And even though it's a mill made for racing, it's equally at home in any sport boat big enough to handle a Zenoah. I've been running this engine for a few months now and it's held up very well, even with my Avenger liking to fly more than staying on the water; the engine has been dunked over 10 times since I started the review and not one problem has arose. If your in the market for a new engine for your race boat or sport boat, take a look at TRM's Neurotoxin and I promise you wont be disappointed.

Neurotoxin G260
Distributed exclusively by:
Toxic Racing Machines
133 E. 10th St.
Chuluota, FL
32766-8571