Wanting strength and not octane to be the destructive force, we replaced the 91-octane fuel with 118-octane race fuel from Rocket Brand. Truth be told, improper tuning has probably killed more engines than insufficient ring gap, but the two are likely responsible for the majority of boost-related Big Bangs. We kept the total timing on the conservative side (around 18 degrees) and snuck up on boost and power levels. The motor was loaded at 3,000 rpm and allowed to run to 6,300 rpm, though peak power was actually some 300 to 400 rpm higher. Running just 5.5 psi, the twin-turbo 5.3L produced 696 hp and 606 lb-ft of torque. Stepping up to 13.0 psi resulted in 930 hp and 806 lb-ft of torque, while 15.5 psi took us over 1,000 hp to 1,014 hp and 872 lb-ft of torque. Adjusting the manual wastegate controller to a peak of 18.3 psi brought 1,094 hp and 950 lb-ft of torque then 1,174 hp and 1008 lb-ft at 21.0 psi. A few more clicks of the controller upped the power ante to 1,245 hp and 1,056 lb-ft of torque and the highest boosted run of the day recorded an amazing 1,308 hp and 1,109 lb-ft of torque at 24.2 psi before the Big Bang finally came through.

Actually, the Big Bang was more of a little whimper, as the power simply fell off and a check of the dreaded cylinder number seven revealed absolutely no compression. Figuring we killed a piston, connecting rod or both, we called it a day. Before pulling the motor, we decided to check out the internals for a few post-mortem photos. After pulling the turbos, intercooler and valve covers, we discovered the missing compression was not caused by damage to a piston or rod, but rather a broken lifter and pushrod. During testing the higher boost levels, we experienced a misfire that we figured was ignition related. After several attempts to cure it, the power dropped and we thought we had killed the 5.3L. We now suspect the culprit to be valve float, and the hammering of the lifter points in this direction. Before removing the 5.3L, we decided to find out if it was indeed still alive. We replaced the broken lifter and pushrod and ran the motor once again in normally aspirated trim. Though the output was down by roughly 15 hp (excessive blow caused by a combination of 160,000 miles, over .035 ring gap and 70 runs over 1,000 hp), the 1,300hp Big Bang 5.3L was still alive, kicking and ready for more boost (and maybe a new set of rings).

Big Bang 5.3L NA vs. Turbo (5.5 psi) vs. Turbo 15.5 psi vs. Turbo 24.2 psi
NA 5.5 psi 15.5 psi 24.2 psi
RPM HP TQ HP TQ HP TQ HP TQ
3000 209 365 250 438 251 439 224 394
3200 220 362 267 439 271 446 241 395
3400 234 361 290 448 296 457 267 412
3600 248 362 323 471 338 494 317 463
3800 267 369 362 501 393 542 371 512
4000 293 384 404 531 478 628 446 585
4200 313 391 430 537 568 711 549 686
4400 341 407 453 542 629 751 647 773
4600 377 430 495 565 704 804 841 961
4800 401 438 535 585 785 858 984 1077
5000 414 435 559 588 821 863 1056 1109
5200 428 433 576 583 850 858 1089 1100
5400 451 439 601 584 572 858 1122 1091
5600 472 443 636 596 921 864 1168 1096
5800 483 437 669 606 962 872 1212 1098
6000 492 430 689 603 994 870 1254 1098
6200 497 421 695 589 1011 856 1295 1095
6300 499 416 NA NA 1013 845 1308 1091
6600 503 400 NA NA NA NA NA NA