Is it possible?

[Cyrus747]

To convert a newer 15hp to a 20hp efi model From my understanding the only difference is the computer.

[Moonlighter]

You will need to check the parts list to compare one with the other - injectors, air intake for a start. If those are all identical then possibly it can be done. Look closely at the air intake components on some motors there is a restrictor plate that differs between hp.

But the ecu changeover would likely cost too much to make it worthwhile anyway for just an extra 5 hp.

[Greg Moore]

Also check to see if camshafts are the same part number, heads and pistons.. All manufacturers use the common block for ranges of HP but usually just the block, bolt ons and housing/shaft are exact matches. The extra HP can be gained by higher compression (via different cut in head or higher pistons), longer duration of the cams and larger throttle bodies. In all cases yes, at the very least the computer is always involved. In a smaller motor like yours it may just be the computer or minor parts, on high HP motors it's usually much more involved. You'll typically see the higher HP version of any block also runs at a higher RPM which is usually a dead give away for a different cam, bigger throttle body/intake etc

[Hoosmatroos]

The modern suzuki 9.9, 15 and 20hp engines are in the base the same. But as Greg already said, look at the parts and see what's different.