RCU Review: Toxic Racing Machines Neurotoxin G260PUM Full-Mod Race Engine

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    Contributed by: Matt Gunn | Published: April 2008 | Views: 62937 | email icon Email this Article | PDFpdf icon
    Toxic Racing Neurotoxin G260

    Review by: Matt Gunn (webdr)

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


    TRM Neurotoxin powered Avenger in action
    Windows Media 18mb

    High power for sport or race

    Exceptional customer service

    Neurotoxin mods also available for your stock engine

    Optional aluminum iso block


    You can probably count on one hand the number of guys that can take a stock Zenoah 260PUM and, through tried and true methods and years of practice, transform it into a full-blown racing engine capable of pushing a large-scale rc boat to speeds in excess of 70mph, and be reliable. And while there are many people out there milling away at engines, only a few do it for a living; these gentlemen are the leaders in the industry and are sought after for there high-performance modified Zenoah engines.

    One of the aforementioned engine manufacturers on the racing scene is TRM, or Toxic Racing Machines, out of Chuluota, FL. TRM has been modifying gasoline engines since 1990 and working with Zenoah engines since the late '90s, supplying racers and sport boaters alike with some of the best engines available on the market. Owner Alan 'Toxic Al' Gemuendt is the man behind the latest full-mod G260, the Neurotoxin, and it's quality and power are of no exception.

    The Neurotoxin follows a long line of high-performance TRM motors. The original mod-motor was the G230 Chemical Warfare, followed by the G231 Screamin' Demon, then the G260 Venom was introduced, followed by the Neurotoxin. All are race motors and all are race winners.

    So now you know a little about Toxic Racing Machines, let's take a look at Al's latest weapon, the Neurotoxin G260PUM.

    Name: Neurotoxin G260PUM Full-Mod Race Engine
    $500 - motor
    $525 - motor w/ aluminum isolator block
    $550 - motor w/ 257 carburetor and aluminum isolator block
    $225 - Neurotoxin modifications to your stock G260 motor
    Carburetor: Walbro 257
    Height: Lowest point of case to top of water jacket - 5 1/2"
    Spark plug used : NGK CMR7H
    Dry Weight: 3.6 lb
    Needle settings from TRM: High speed = 1, Low speed = 2

    2-stroke oil used: Amsoil Dominator @ 8 oz. per gallon
    Pipe/header used: 90-degree header, 2" band pipe
    Radio equipment: (Included) AM pistol grip, 2 channel receiver, steering servo

    • Zenoah-style motor mounts
    • 2-stroke oil
    • Allen wrenches for working on your motor
    • Header and pipe
    • collet

    Other Helpful items

    • Fuel filter

    Exhaust side
    Pull start and coil pickup
    Intake side
    Drive side
    Walbro 257 carb and aluminum iso block
    Water jacket

    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.

    Installed in an Aeromarine Avenger Pro
    Neurotoxin with 90 degree header and 2" band pipe
    Front view

    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.

    Head with TRM id
    Exhaust port
    Internal head modifications
    Piston mods
    Iso block
    Carb w/ aftermarket throttle arm

    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.

    Neurotoxin-powered Avenger
    Back straight

    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

    Comments on RCU Review: Toxic Racing Machines Neurotoxin G260PUM Full-Mod Race Engine

    Posted by: marineart on 07/04/2008

    Posted by: proz4001 on 10/12/2008

    Posted by: rcgreenhornet on 11/19/2008
    Hey y would you give a AM/radio with a gas engine
    Posted by: rcgreenhornet on 11/19/2008
    Hey y would you give a AM/radio with a gas engine
    Posted by: webdr on 11/19/2008
    ? ?Not sure I know what your trying to say...but a 2.4gig radio was used, not an AM.
    Posted by: webdr on 12/12/2008
    I see what your talking about. I mistakenly put the wrong info under the radio used section. The radio I used was a Futaba 3PK 2.4 gig. Sorry for the mixup.
    Posted by: zalitarique on 08/20/2013
    Can you tell me what size prop you running on the avenger
    Page: 1
    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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