Specifications for the Seca 650 Turbo (XJ650LJ)
Performance (Cycle Magazine)
Standing 1/4 mile	12.49 sec. @ 105.63 mph
Engine rpm @ 60 mph, top gear	4446
Average fuel consumption	42.2 mpg
Load capacity (GVWR less curb weight)	348 lbs.
Maximum speed in gears @ redline	(1) 48 (2) 69 (3) 90 (4) 112 (5) 128
Engine
Bore and Stroke	63.0 x 52.4 mm (2.48 x 2.06 in.)
Piston displacement	653cc (39.8 cu. in.)
Compression ratio	8.2:1
Carburetion	(4) Mikuni 30mm constant vacuum
Oil capacity	3.7 qts. (3.5 L)
Transmission
Type	Five-speed, constant-mesh, wet-clutch
Primary drive	Straight-cut gear; 97/58 sprockets; 1.67
Final drive	Shaft and bevel gears; 49/36, 19/18, 32/11; 4.18
Gear ratios (transmission)	(1) 2.19 (2) 1.50 (3) 1.15 (4) 0.93 (5) 0.81
Gear ratios (overall)	(1) 15.29 (2) 10.47 (3) 8.05 (4) 6.51 (5) 5.67
Chassis
Wheelbase	56.7 in. (1440 mm)
Wheel, front/rear	Cast, 1.85 x 19 / Cast, 2.15 x 18
Seat height	31.3 in. (795 mm)
Ground clearance	6.1 in. (155 mm)
Curb weight, full tank	567.0 lbs. (257.2 kg)
Speedometer error	30 mph indicated, actual..28.30 mph 60 mph indicated, actual..55.21 mph

The turbocharger normally operates at speeds up to 170,000 rpm, and can safely spin up to a maximum of 210,000 rpm. The Mitsubishi turbocharger's output is limited to 7.7 psi of boost.

The following is a dyno run for Mark Yager's 1982 Seca 650 Turbo with factory boost kit. Other than the boost kit, it is completely stock and unmodified.  This run was done just after a tune up at the 70,000km mark.  As you can see it makes 87 horsepower, quite healthy for an XJ!