I have tried marvel's and sea foam in my 1988 Cherokee and in my 1950 Massey to-20. In the Cherokee the response to rpm, torque, and engine temp all fall into a nice harmony with about a 2.7 improved mpg. (1988 Cherokee, 5.5 inches lift, 31x10.50 tires, and a new process 242 transfer case that is stuck in full time four wheel drive). 12.2 to 14.9 while using the product on the first fill up. After filling up the following times, it will revert to it's normal after about 700 miles on the odometer. My 1989 Dodge D 250 will wield the same results. When I used the sea foam on my Massey or my Jake's I only noticed a cleaner smell from the exhaust. I did notice a very slight improvement in the way that when I was putting the machine under a severe task it did not lag as much., but they did run hotter. I have a 1950 cj_3a and a1960 truck with the 226 super hurricane. At the time they built these motors they were also building one motor for many countries at the same time. Unstable octane levels were present. They installed harder valves and seats to overcome this problem. Pre 1973 dump in what you have, it will not matter. When we ingested into the unleaded era the bottom line of our mowers and tractors did not change much. The most improvement at that time was to take chiseled (I know it is spelled wrong ,but tell a kindle that it can't spell.) and open the office. Treat all of your unleaded fuel products as a semi 2 stroke and add some alternative oil to combat the higher combustion temp that the ethanol creates. Yes we have an unstable fuel but we find our ways. Bless us.