After owning a GSX1100EF (known as GS1150 in the U.S.) for nearly 30 years, there's one question I've never found an answer to - wasn't much of an issue until recently, when I rebuilt the bike and installed earlier engines from bikes I bought in Switzerland.
It appears that the initial engines from 1984/85 has a performance of "only" 114 HP (maxing at 8,700 rpm), whereas the latter engines puts out 124 HP and maxes lower, namely at 8,500 rpm. I think the torque maxes lower as well on the latter engines.
I was thinking it could be the camshaft height, but according to my Haynes Workshop Manual, they all seem to have identical cam heights (no mentioning of any differences, anyway).
Does any of you guys know what causes the difference? Same bore and stroke, same carburettors, apparently same camshafts, etc... but still 10 HP less?

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