O.S. .21 TM Monster Truck Engine with Revo/Slayer Manifold

The perfect amount of power for the revo. Front wheels have trouble staying down, but so far no drive train damage, even with stock reverse in place. The only thing I don't like about it is the Phillips screws holding on the backplate. They're extremely tight, and you can't remove them without damage very easily. Replace with the 18TZ backplate hex screws and problem solved. Great engine, couldn't recommend more.

Quality, performance, power much better than OE. Easy tune. Does not overpower but enhances and potentiates the overall driving experience on the Revo. Included exhaust manifold and reuse of stock (or aftermarket) clutch assembly make for a easy upgrade. Racing or bashing you can't go wrong with this drop-in engine.

This is the top end motor for Traxxas Revo . An outstanding super heacy duty motor . Easy to adjust and tuned .

just put this in my jato today bought it off ebay and it is really fast has alot more power then the 3.3 and i cant keep it straight down the road i tried 3 different tires and none of them will hook up with this engine

Bought this for the revo. Break in went smooth. Did the adam drake style 4 tanks rich idle 4 tanks 1/4 throttle and 2 tanks full throttle. Still really tight but gets stronger after every tank. Only problem I had was the throttle linkage for the revo was to short at the throttle horn even shorter when I used the os #5 ball link.

*Excellent Quality Engine!!
*Only Produces 1.9 HP.
*Expensive Piston and Sleeve
*Excellent Carburetor
*Runs Better and More HP with 1/8 Muffler
*Fit into my REVO w/ No Mods
*Super Reliable
Highly Recommend This Engine. Pricey but worth it. The 11k Carburetor is Awesome!!!
YOU WILL NOT BE DISAPPOINTED

Sick engine, if you buy one!! It’ll be the coolest highest quality part of your traxxas model haha! Make sure you build your revo 3.3 to match with aluminum shock parts from hot racing and traxxas!!

this is a very beautiful nitro engine and I am awestruck by the high end quality of the materials & craftsmanship that went into it. I'd highly recommend this as an upgrade

This engine is solid so far.

Breaking it in now.. idles solid and carb is very responsive to adjustments.

A heat gun will help the starter turn this thing over and make life easier on the connecting rod during break-in.

I bought this motor and installed it...I broke it in really slowly and easy...then tuned it in and this engine pushes my revo to its limits , over the limits lot of times.. this engine is very quick and fast..once I got it tuned in I have ran it for 3/4 gallons of fuel and haven't (had) to adjust it any..two times I could tell it needed to be leaned a hour cause of the heat outside..it would have still ran good had I not have tuned it in..never ever have to set Lo speed needle or idle again..it holds its tune as well as a few of my hi end Italian engines bb's also... They cost more than the 3.3 but for the ease of tuning and the tremendous amount of power you gain makes it worth it everytime you pull the trigger..you have no chance of goin wrong..

just got this for my revo 3.3 and its awesome!! Lots more power than the 3.3! Great engine!!

A main hobbies is my go-to store for all my RC related parts, engines, upgrades etc. They always send the right part and fast!!

This is my 2nd 21tm now, my experience with this engine has been terrible. The quality of this engine must of took a nose dive after Horizon Hobby acquired OS. This motor didn't survive break-in. I should of fully disassembled this engine before running it. This is due to the fact that the exhaust port wasn't cut properly and left burs that caught the edge of the piston. This caused a chunk to be ripped out of the sleeve and scored the piston. There are numerous cracks in the sleeve at the bottom of the exhaust port next to the chunk that's missing. Now the engine is full of metal debris and completely cooked. For break-in I use the Adam Drake method that he used on his OS .21 racing engines. The procedure involves pre-heating the block to 200f and idling for 4 tanks while maintaining 210-220f. Then running another 4 tanks at 1/4, 1/2, 3/4, then WOT. This is the best break-in method since the manual for this engine is very vague and just asks you to run the engine on the track while slowly leaning it. If I attempted to run this engine this way it would of immediately seized due to the issue with the exhaust port. Finally my 3.3 may not be as powerful and it eats rear bearings every couple of gallons (known issue with 3.3 due to it using the same rear bearing as the 2.5 which is a .15 sized engine), but it has a very nice cleanly cut ports that did not score the piston. Even after 5 gallons of use.





(Old Review from a couple of years ago)I have a gallon through this engine now. I can’t believe how easy this thing holds a tune. Just a couple little quirks when it was new like loose screws and leaky seals around the carb. The fix for me was to just re-seat the seals. After that I’ve had trouble free running ever since and just the slightest adjustment on the H needle every once in a while. Over all it’s a solid purchase and puts the stock motor to shame.

This is a great engine, put it in my revo and have had zero issues. Very easy to tune idles great, screams flat out. Recommend highly.