MD80 DEP FROM BOS DISPUTES TWR CTLR'S APPLICATION OF WAKE TURB SEPARATION FROM PRECEDING B757.

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IN TKOF POS BEHIND B757 DEPARTING. B757 TURNED L TO 140 DEGS WHICH IS ARCING 2.8 DME ARC ABOUT 20-30 DEGS TO L FROM ME. TWR CLRED ME FOR TKOF WITH LESS THAN 4 MI AND LESS THAN 2 MINS. I DELAYED A FEW SECONDS TO GET SPACING. TWR SAID; 'START YOUR TKOF ROLL OR I WILL CANCEL YOUR TKOF CLRNC...STATE INTENTIONS.' I SAW 6-8 ACFT HOLDING FOR TKOF. I SAID 'THERE IS A B757 AHEAD OF ME AND PUT THAT ON THE TAPE.' TWR SAID 'I NEED 4 MI AND THERE IS 8 AND LET'S PUT THAT ON THE TAPE.' AT THIS POINT; 8 MI WAS AN OUTRIGHT LIE. I DELAYED A FEW SECONDS MORE AND STARTED TKOF ROLL WHEN I FELT THERE WAS ENOUGH TIME AND SPACING. MY CONCERNS ARE: 1) CTLR MISINFO ABOUT THE ACTUAL DISTANCE BEHIND THE B757. PERHAPS HE LIED OR THE EQUIP IS MIS-CALIBRATED OR MY TCASII IS INACCURATE OR HE WAS LIBERALLY ANTICIPATING THE 8 MI. 2) WHEN THERE IS AN IMMEDIATE SIGNIFICANT TURN AFTER TKOF; DIFFERENT PERFORMANCE CHARACTERISTICS OF DIFFERENT ACFT COULD CAUSE THE FOLLOWING ACFT TO TURN INSIDE THE LEADER AND CLOSE THE DISTANCE SIGNIFICANTLY (TURNING REJOIN). 3) AS PIC; I HAVE FINAL AUTH TO DECIDE WHETHER IT'S SAFE TO TAKE OFF. BEING THREATENED TO BE PUT BACK INTO LINE BECAUSE I CHOOSE TO USE THE FULL 2 MINS AND/OR 5 MI IS UNACCEPTABLE. IT IS HARASSMENT THAT COULD INFLUENCE PLTS TO MAKE BAD DECISIONS. THE CTLR'S CONCEPT OF HOW HE WANTS THE PATTERN TO WORK IS NOT THE DEFINITIVE PARAMETER. I WAITED IN LINE; I HAD THE RWY; AND IT MAY NOT EVEN BE LEGAL FOR THE CTLR TO TAKE THE RWY AWAY FROM ME; ESPECIALLY NOT FOR THE 20 SECONDS NEEDED.