Both the 4 valve and the Endrigo can generate a substantial gain in horse power. The gain in either is achieved by creating a larger volume of flow. In a 4 valve this is done by simply increasing the area of the flow tract, more valves =more flow area. Flow in the Endrigo is accomplished by altering the flow tract for maximum efficiency.
Neither is a "plug & play" item. In order to achieve maximum performance you will need a intake and carb with enough flow volume to fill the cylinder. You will also need a exhaust capable of extracting the increased volume as well. Correct jetting/tuning plays a big part. Without the matching intake/carb and exhaust you won't see any real gains. Using the correct sized components is extremely important.
Both have advantage and disadvantage. The 4 valve is a little more forgiving, It relies simply on sheer size of the head to accomplish the goal, so it will give some performance across across the rpm range. The endrigo as with most port jobs relies on correct velocity as well as volume so it only meets optimum performance in a much tighter rpm range where maximum velocity is achieved. IMO, the hp produced in that narrow band exceeds the 4 valve, Outside of that narrow band I believe the 4 valve may perform a little better,
The 4 valve needs component specific parts, cam chain, piston, cylinder studs, valve cover, cam and a unit specific exhaust pipe while the Endrigo uses common gy6 items.
The four valve isn't forgiving with extended top rpms. The Endrigo, based on the stock configuration is more rpm tolerant and prone to be more dependable.
Either way both will produce gains when set up correctly.
On a side note: Though it's really insignificant but most all hot rodders do take into consideration is the sound. That four valve has a very distinctive exhaust note. It sings "this ain't no stocker"! Personally, I do enjoy the tune that 4 valve plays! While with the Endrigo they won't know what you got until you blow'em away!
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