What Do Different Pump Gasolines Really Change in a Two-Stroke Engine?

What do different pump gasolines really change in a two-stroke engine? Rather than relying on opinions, old shop wisdom, or internet debates, I put three common pump fuels through the same controlled series of tests using my custom-built dynamometer and an electronically controlled carbureted Stihl MS261. Every run began under the same cylinder head temperature and was weather-corrected, allowing the fuel itself—not changing conditions or carburetor adjustments—to be the primary variable. Horsepower and torque are only part of the story. Throughout each test I also measured cylinder head temperature, exhaust gas temperature, fuel consumption, fuel efficiency (horsepower produced per gallon consumed), and how each fuel behaved during an extended three-minute full-load test as heat accumulated in the engine. Watching how performance changed as the engine became heat-soaked turned out to be just as interesting as the peak power numbers. Some of the results agreed with conventional wisdom. Others challenged assumptions I've held for years. One fuel actually gained horsepower as the engine heated up, another proved more efficient than many people would expect, and the exhaust temperature data raised some interesting questions about where the engine's energy was really going. Although today's test engine happens to be a chainsaw, the same combustion and thermodynamic principles apply to virtually any carbureted two-stroke engine—from trimmers and leaf blowers to motorcycles, scooters, karts, generators, and countless other small engines. My goal isn't to declare a universal "best" fuel, because the right choice depends on the engine and the job at hand. Instead, I simply measure what happened under controlled conditions, explain what I observed, and let you decide how those results apply to your own equipment. If you enjoy chainsaw porting, two-stroke engine theory, homemade tools, small engine performance, muffler mods, exhaust experiments, dyno testing, or simply settling old shop debates with a little science instead of a shouting match, you’re in the right place. Husqvarna, Stihl, Echo, Poulan, Dolmar, Efco, Farmertec, Neotec, Noker, budget saws, clone saws, and name-brand equipment all end up on this bench sooner or later—and every one of them still has to obey the same laws of physics. Most of what you see here revolves around chainsaws, but the same principles apply to just about any small engine: motorcycles, scooters, mopeds, generators, and all those wildly popular little single-cylinder engines found around the world. Good airflow, combustion efficiency, exhaust tuning, fuel delivery, heat management, and mechanical balance don’t care what color the machine is or what sticker is on the side. A big thanks goes out to Ryan at Wolf Creek Saw Shop for helping support some of the testing and experimentation that happens on this channel. If you’re into chainsaw modifications, quality parts, or just supporting good people in the saw community, be sure to check them out: https://wolfcreeksawshop.com ⚠️ Important Common-Sense Disclaimer: Everything shown on this channel is performed on my own equipment, at my own risk, for entertainment and educational discussion purposes only. I’m simply sharing my own experiments, observations, problem-solving, successes, failures, and curiosity. None of this should be taken as professional instruction, safety training, engineering advice, or encouragement to copy what I do. Chainsaws, heavy equipment, rotating machinery, trees, and modified engines can all hurt you in remarkably efficient ways. Please use good judgment. One of the biggest parts of this channel is testing. I designed and built my own fully custom dynamometer system from the ground up, including the electronics and software. It measures horsepower, torque, cylinder temperature, exhaust gas temperature, fuel consumption, vibration, sound levels, and more. In other words, if a modification claims to make more power, run cooler, use less fuel, or change engine behavior, I’d rather test it than argue about it. If that kind of mildly overcomplicated saw nerd activity sounds interesting, consider subscribing and following along. There’s plenty more coming: chainsaw builds, porting experiments, dyno sessions, fabrication projects, farm fixes, toolmaking, sawmill work, mechanical oddities, and occasional examples of why farmers should probably not be left unsupervised. Questions or comments are always welcome. You can also find me on Facebook at “Everystuff Farming” or reach out by email at [email protected]. Thanks for spending some time with us—I truly appreciate it.