I could see the old lawn mower engine melting down long before a slant six engine. And seeing it's on its last legs and worth no more than $20 it might be an option. Would take an entire season to use up that nitro mix even if diluted 3-1. It would be an interesting experiment. The only downside is I leave these inexpensive old push mowers by the side of my driveway when I'm done with them. Someone always seems to have use for serviceable engines. This engine probably won't be so serviceable after a summer's worth of nitro. And not likely I'd put the nitro into my 15,000 mile '99 Camaro SS.