[Aerkuld]

I was thinking about this and trying to do a quick calculation. These are very rough guesses at best, but please correct me if I’ve done anything really stupid…

Assumptions:
Engine: 2.0 liter 4 cylinder
Peak power @ 6000rpm
Volumetric efficiency of 80% (how much of the cylinder volume is actually filled during the induction stroke)
Leaf blower flow rate: 250cfm

For each revolution of the engine only two cylinders will see an induction stroke. So at 6000rpm the engine would have a theoretical air demand of 6000 liters per minute which is 212 cfm (cubic feet per minute). With a volumetric efficiency of 80% the engine can only actually pull in 80% of this volume, so the actual air demand will be just about 170 cfm. So it does seem as though a leaf blower that can flow 250cfm would provide sufficient air flow to feed a 2.0 liter engine in this situation. Using the same rpm and volumetric efficiency assumptions, that leaf blower should be able to keep up with an engine up to almost 3.0 liters.

There are a few problems that I can see though.
1. The leaf blower is probably designed with significant clearances around the impeller. This is fine for moving a large volume of air but won’t be very good at generating much pressure. This means that the flow rate of the leaf blower will only be true if the inlet and outlet of the blower are unrestricted. Once you start to restrict the outlet by connecting it to the engine then the flow will go down and the ‘boost’ effect wouldn’t be as great as it appears in the calculation.
2. I doubt that the induction system would actually be designed to hold pressure so it probably leaks. This will further reduce the boost effect.
3. Even so, I doubt that a stock engine management system would be able to cope with a significant increase in air pressure. The most likely effect would be that it cannot deliver enough fuel so it will run lean. I doubt it would be able to run like this for any period of time.

Bottom line is that it is does seem possible that you can cram more air into an engine than it could normally consume by using a leaf blower. If you can cram in more air and corresponding amount of fuel into the engine then you will get more energy from the combustion and more power out of the engine. Whether this would work in a practical situation is another matter altogether.