Narrative:

Aircraft had just come from the hangar after a number 1 engine change. Because of windshear; we'd planned a max takeoff and briefed windshear procedures. Winds were a quartering headwind gusting to 32 knots. The first officer was performing the takeoff and pushed up the power; hit to/GA and asked for takeoff thrust. The thrust levers came up and the number 1 lever lagged slightly with the N1 slightly behind number 2. I began to push number 1 up; noticed it was slightly behind number 2 but still increasing. With the headwind and max thrust takeoff; I looked down and we were approaching 90 knots. I called that; fully expecting to get full takeoff thrust on number 1. I hit the firewall shortly thereafter. The thrust was approximately 4 percent less than number 2 and I considered rejecting the takeoff. But as we were at approximately 125 to 130 knots; I elected to continue as this was not a reason to reject above 80 knots. The aircraft was accelerating very rapidly; and more harm than good would happen if we rejected at this time. The N1 was normal the rest of the leg. I called dispatch and maintenance on the way to XXX; notified them of the problem and wrote the issue up. I could've made the decision to reject sooner; but because of the max takeoff and the 32 knots of wind; the airspeed rose very rapidly. By the time I assessed that the engine would not fully make max takeoff thrust; we were in an airspeed regime where I thought it was safer to continue than reject.

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Original NASA ASRS Text

Title: B737-800 Captain reported that after an engine change the engine never fully reached max takeoff thrust.

Narrative: Aircraft had just come from the hangar after a number 1 engine change. Because of windshear; we'd planned a max takeoff and briefed windshear procedures. Winds were a quartering headwind gusting to 32 knots. The FO was performing the takeoff and pushed up the power; hit TO/GA and asked for takeoff thrust. The thrust levers came up and the number 1 lever lagged slightly with the N1 slightly behind number 2. I began to push number 1 up; noticed it was slightly behind number 2 but still increasing. With the headwind and Max thrust takeoff; I looked down and we were approaching 90 knots. I called that; fully expecting to get full takeoff thrust on number 1. I hit the firewall shortly thereafter. The thrust was approximately 4 percent less than number 2 and I considered rejecting the takeoff. But as we were at approximately 125 to 130 knots; I elected to continue as this was not a reason to reject above 80 knots. The aircraft was accelerating very rapidly; and more harm than good would happen if we rejected at this time. The N1 was normal the rest of the leg. I called Dispatch and Maintenance on the way to XXX; notified them of the problem and wrote the issue up. I could've made the decision to reject sooner; but because of the max takeoff and the 32 knots of wind; the airspeed rose very rapidly. By the time I assessed that the engine would not fully make max takeoff thrust; we were in an airspeed regime where I thought it was safer to continue than reject.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.