I don't know what the differences may be; I don't know that anyone's ever profiled them. However, I am not aware of Toyota ever publishing any information regarding any change in the HP or TQ output from the initial '86.5 model to the later '87-'88 models. There were a number of differences as far as parts go for the '86.5 which had no significantly notable effect on the vehicle's performance.
Of particular interest though is that it appears the same cams which were limited to the USDM '86.5 were used in European MKIII's until the '89 model.
If the change was due to emissions requirements then it was either minor or Toyota did a fine job tuning around it. While there were many ECU revisions the '86.5 had it's own which were not used in later models.
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