Not sure what you consider "BIG", but I can tell you about the PowerTech line (the only brand I am familiar with). Last time I was at their place, several years ago, the 10 & 12 KW use a 4 cylinder kubota diesel engine. They were using a turbocharged 4 cylinder on the 17 & 20 KW. The smaller 7 & 8 KW use a 3 cylinder kubota.