O.S. Engines 12TG(P) .12 Off-Road Engine
Text by Eric Miller
O.S. has a rich history in the nitro engine game. The company is known for building well-performing, reliable engines for all different types of vehicles. It doesn’t matter whether you’re a hardcore racer, a budget racer, or a pure basher, O.S. has an engine to meet your needs. I recently came across the 12TG series engine (this sample has a pilot shaft and rotary carb), a perfect addition for my GT2! I decided to ditch the stock .15 for something not only ROAR legal but also more efficient overall. Let’s give it a once- over to see how it does.
The engine starts with an ABL cylinder. What is ABL you ask? ABL stands for “Advanced Bi-Metallic Liner.” Basically this method uses two layers of the plating material on the cylinder walls as opposed to a single, thicker layer as with other models. It creates an improved bond to the cylinder and makes a more durable product. Also, the fit between the piston and sleeve is tighter and more consistent. The benefit is consistent performance over a longer period of time. Who can say no to that?
Since this version of the engine has the 12E rotary carb and pilot (SG) shaft, trucks such as my GT2, the DuraTrax Nitro Evader and HPI’s Firestorm will easily accept it as a replacement. It actually drops right in and fits perfectly. Guys running the RTR version of the GT2 will need a rear exhaust header, non-pull- start engine mounts and flywheel as well as a starter box. After bolting it down and adjusting linkages, the truck was ready to go and looks sweet with the tall blue head proudly standing above the chassis.
Time to get to what you came here for—performance testing. I wasn’t surprised by how easy the engine sprung to life. My past experiences with O.S. Products have all been positive with easy-to-start engines. I took my time and broke in the engine over six tanks, slowly leaning it out from tank to tank. Before long, I had the truck screaming past me at full clip. The truck felt strong, and power came on in a linear fashion. The power band was nice and broad, with peak hp arriving near the top of the range. Feel free to try a few different gear ratios with this engine; it can certainly handle them.
As is the case with other .12-size engines, this one wasn’t a real torque-monster. This is actually a good thing. Many guys are race-tuning their overly powerful engines with carb inserts anyway. Think of it this way, limited torque means greater traction, which is essential when you’re only driving two wheels. This made it easier to get on the gas a little earlier coming out of turns and helped reach higher top speeds at the end of the straights, not to mention it was pretty easy to drive without loosening the slipper.
Throughout my testing I noticed one thing. It seemed I could run at length without the need to constantly refill the tank. O.S. claims you can run 14 minutes on a single tank of fuel with this engine, and while I didn’t have a stop watch with me, I wouldn’t try to dispute them. This only made running the engine more fun.
If you are in the market for a ROAR-legal .12 with good overall power and plenty of run time, I say get yourself a 12TG. It’s a great budget-friendly mill that can help you reach the podium or just have fun doing donuts in a local field.
Part no.: OSMG1985
Carb: 12E Rotary
Displacement: 0.128 cu. in. (2.1cc)
Bore: .543 in. (13.8mm)
Stroke: .551 in. (14mm)
Weight: 7.45 oz. (211.3g)
Power output (HP @ rpm): 0.7 @ 28,000
Practical rpm range: 5,000-30,000