The whole supercharged lawnmower thing was a lame proof-of-concept idea. I had toyed around with the idea of using a gas-powered leaf blower to supercharge a car. There was something comically appealing about pulling alongside some beefed-up muscle car in my POS Honda, and, while he's revving his engine, I'd just yank the pull-starter cord on the dash and start revving my leaf blower. The thought of whooping somebody with a rusty Honda and a leaf blower was enough to inspire me to at least give it a shot.
I built a primitive pressure tank around the carburetor and gas tank of an old lawnmower (because they're attached together and fairly small) and then literally duct-taped an electric leaf blower to the assembly. I replaced the mower blade with a 25-pound barbell weight and used a heavy leather welding glove and my bare hands to measure torque. Normally aspirated, it was possible for me to roll on the throttle and still stop the spinning barbell with a fair bit of effort. It wasn't easy to stop. I'm pretty sure that with only slightly more power it would have been nearly impossible to manage, so that seemed like a pretty good test to me, even if it's not exactly scientific. If I thought I was having some degree of success I was planning on building an actual band brake and using a fishing scale to measure the braking effort required to control RPM at WOT. ...but it never came to that.
Anyway, by the time I was content that the whole thing was a waste of time, I'd played with the fuel mixture, removed the flywheel key to advance the spark timing, and even with three leaf blowers I didn't notice any real difference other than that it idled a little smoother, but not any faster. The contraption was primarily constructed of duct tape and vacuum cleaner hose.
I measured the pressure by placing a small piece of hardboard over the opening of the vacuum cleaner hose. I added and removed weight until the pressure from the blowers was just barely able to lift the hardboard. Using the area of the opening of the hose and the weight of the hardboard and weights, it's possible to get a reasonably accurate calculation of pressure. ...which wasn't very much. I don't remember exactly how much it was, but it was less than a pound. My leaf blowers were all electric, so it's likely that gas leaf blowers are more powerful, but I don't think it'd be enough to make a substantial difference.
In theory, there must have been a slight increase in power or I somehow failed to get the fuel mixture quite right. I think there was an increase, but it was so small that it was simply imperceptible. I think those motors have either a 7.5:1 or 8:1 compression ratio. (I used to know.) It's pretty low, whatever it is. Perhaps that low ratio is why a small increase wouldn't be noticeable.
Sorry, no pictures. If it had worked, there probably would have been.
The "super sucker" idea isn't exactly a new one, but it doesn't make much difference in most engines. There's a similar idea that actually does make a difference though. Off the top of my head I don't remember what it's called, but it's basically a crankcase vacuum pump. (That might be what it's called.) People often knife-edge the crankshaft counterweights and other parts to reduce drag. Another way to reduce drag inside the engine is to remove all the air. It's horribly turbulent inside there, and by removing the air it's supposed to be possible to gain five to twenty horsepower, depending on the engine. The vacuum pumps draw relatively little power, and the power you get by reducing drag is free power. The downside is that the pumps need to be cleaned very often and also suck a lot of oil out of your crankcase too. I would think that perhaps some sort of oil trap and recirculation sump might be able to recover the oil. I think they use some sort of positive displacement gear pump and that's why they need constant cleaning, but I haven't looked into it much, so I don't really know. It's good for drag racing, but not much else.