Only 2 things make a difference.
1. The RPM ratio of the machine vs the van. Some are 1 on 1, others speed up the ration. And some of us re-pulley these to get even better
ratios. The higher the ratio, the better the fuel usage
2. The type of engine used. I was always sold on a Chevy Astro van as being a great PTO van, but then most companies quit making them for it. In fact I was about to mount a
Butler in one, but they quit making that van/motor. So what is the mileage of the van otherwise? Some are great, others stink.
Bottom line; no matter who's machine we are told does best, it can be done better if the above two are optimized.
Thx,
Dale