We know motors respond well to basic bolt-ons, like better heads, performance cams, and high-flow intakes, but do they respond the same under boost? Does cam timing, head flow, or intake design even matter when you have positive pressure?
While the premise was simple enough, finding the answer to that question was much more difficult, requiring no less than four distinct engine configurations. To find out if heads, cam and intake make power NA and boosted, we had to first run our near-stock 5.3L test motor in naturally aspirated trim. We then had to follow that up with our single turbo system. After running those two stock configurations, the 5.3L would need to be run again in naturally aspirated trim after the addition of ported heads, a bigger cam, and aftermarket intake. The final test would be to run the modified configuration under boost.
That my friends, is one full dyno day!
Do bolt-ons work the same under boost? We put the question to the test on the dyno.
The 5.3L test motor – on loan from David Freiberger – wasn’t totally stock. It featured forged rods and pistons. For our test, we first configured the 5.3L with the stock LM7 cam, the original 862 heads and an early 5.3L truck intake. For dyno testing, the motor was also equipped with a stock throttle body, a set of 120-pound Holley injectors to suit the modified turbo combination, and 1 7/8-inch, long-tube Hooker headers. To optimize the AF and timing for each combo, we relied on a Holley HP ECU.
After tuning, the first stock configuration resulted in peak numbers of 333 hp at 5,200 rpm and 359 lb-ft of torque at 4,400 rpm. Now it was turbo time. The 5.3L received a custom turbo kit that included Holley turbo manifolds, a single S475 Borg Warner turbo from LJMS and a single 45-mm Turbosmart Wastegate. Not that we would be running excessive boost pressure on this test, but the turbo combo also received an air-to-water intercooler from ProCharger. The wastegate was configured with a 10-pound spring and, after tuning on 91/100 race gas mix, we were rewarded with 532 hp at 5,500 rpm and 555 lb-ft of torque at 4,700 rpm, all at a peak boost reading of 9.6 psi.
The stock 5.3L iron block was equipped with a cast crank, forged (Boostline) rods and dished Wiseco pistons. In preparation for boost, the turbo motor also received ARP head studs.
Now that we’d run the stock combination both naturally aspirated and turbocharged, it was time for some bolt-ons. The stock 862 heads, LM7 cam and truck intake were replaced by units from TFS, Brian Tooley Racing and Holley. For cylinder heads, we chose a set of Gen-X 205 heads from Trick Flow Specialties. The 205 heads were ideally sized for the small, 3.78-inch bore used on the 5.3L, and featured full CNC porting of the ports and chambers, a 2.0/1.575 stainless valve combo and dual valve-spring package.
The Gen-X 205 heads offered sufficient flow to support over 600 hp, or more than the little 5.3L would ever make NA. The stock LM7 cam was ditched in favor of a Stage 2 Turbo cam from Brian Tooley Racing. The Stage 2 offered a .605/.598 lift split, a 226/231-degree duration split and 113 +4 LSA. The final touch was a Holley Sniper Race Series intake manifold, with a 92-mm Sniper throttle body.
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For the first series of tests, the 5.3L was equipped with a set of production 862 heads. The lone modification included a beehive valve spring upgrade.
After installation of the new TFS heads, BTR cam and Holley intake, we ran the motor in naturally aspirated trim. Equipped with the new heads, cam and intake, the modified 5.3L produced peak numbers of 451 hp at 7,000 rpm, and 379 lb-ft of torque at 5,700 rpm. The HCI combination improved the power output of the stock motor by 118 hp.
Now it was time for boost again. After reinstallation of the single turbo kit on the modified motor, we ran the modified motor under boost. Running the same 10-psi wastegate spring, the modified turbo combination produced an impressive 801 hp at 7,000 rpm and 616 lb-ft of torque at 5,600 rpm.
Note that the power and torque peaks on the turbo combination occurred at nearly identical rpms as they did on the NA setup. Note also that the modifications on the turbo motors improved the power output by an impressive 269 hp, though a sizable portion of this can be attributed to the increase in boost from 9.6 psi 11.9 psi on the modified motor.
So what’s the takeaway? Easy, when you make changes to your NA motor, you make those same changes under boost.
To start testing, we installed a factory 5.3L LM7 cam. The mildest of all the factory offerings, the stock 5.3L cam featured a .466/.457 lift split, a 190/191-degree duration split and 116-degree LSA.
To complete the stock package, we installed the stock (early) truck intake manifold, throttle body and fuel rail.
Run on the dyno in naturally aspirated trim, our stock 5.3L produced 333 hp at 5,200 rpm and 359 lb-ft of torque at 4,400 rpm.
After running the motor in NA trim, we installed the Hooker turbo manifolds. This turbo exhaust featured a crossover pipe to join the exhaust from the two turbo manifolds into a common exit.
To provide boost, we selected a T4, billet wheel, Borg Warner S480 turbo and ProCharger ATW intercooler running dyno water.
Boost control was handled by a single HyperGate45 wastegate from Turbosmart.
Turbosmart also stepped up with this blow-off valve, designed to help eliminate the pressure spike that occurs on high rpm/boost, lift-throttle conditions.
To ensure adequate fuel flow for all our combos, we ran these 120-pound Holley injectors.
With the single S480 T4 turbo producing a peak of 9.6 psi of boost (on the wastegate spring), the turbo stock 5.3L produced 532 hp at 5,500 rpm and 555 lb-ft of torque at 4,700 rpm.
Having run the 5.3L NA and boosted in stock trim, we first swapped out the stock LM7 cam for the Stage 2 turbo cam from Brian Tooley Racing.
To enhance flow, we replaced the stock 862 heads with a set of TFS Gen-X 205 heads that featured full CNC-porting.
Further improving the flow and power potential of the Gen-X 205 heads from TFS were CNC-ported chambers and the 2.0/1.575 valve package.
Off came the stock 862 heads and on went the TFS Gen-X 205 heads.
It was necessary to grind down the factory rocker stands as shown for fitment in the TFS heads.
Having it on hand from our previous adventure with the 1,543-hp, Big Bang 6.0L, we opted to install this Holley Sniper Race Series intake. The shorter-than-stock runners would certainly push peak power higher in the rev range on this 5.3L.
Run on the dyno in naturally aspirated trim with the TFS heads, BTR cam, and Holley intake, the modified 5.3L produced 451 hp at 7,000 rpm and 379 lb-ft of torque at 5,700 rpm (a gain of 118 hp).
After running the NA motor in modified trim, we ran it with boost. Run with the same single-turbo set up, the modified turbo motor produced 801 hp at 7,000 rpm and 616 lb-ft of torque at 5,600 rpm. The modifications and extra boost were worth an impressive 269 hp.
Graph 1: NA 5.3L-Stock vs Heads, Cam, and Intake: Is it any real surprise that the LS motor responds well to performance modifications? This 5.3L was equipped with Wiseco forged internals for boosted longevity, but these still allowed us to run the motor with stock LM7 heads, cam and intake. If anything, this motor represented a lower compression LM7. Run in this manner, the 5.3L produced peak numbers of 333 hp at 5,200 rpm and 359 lb-ft of torque at 4,400 rpm. The power curve changed dramatically after installation of the new heads, cam and intake. Equipped with the TFS Gen-X 205 heads, BTR Stage 2 turbo cam and Holley Sniper Race Series intake, the power output jumped to 451 hp at 7,000 rpm and 379 lb-ft of torque at 5,700 rpm. The mods improved the power output of the normally aspirated 5.3L by 118 hp and 20 lb-ft of torque.
Graph 2: Turbo 5.3L-Stock vs Heads, Cam and Intake: Now the question was, would the HCI mods make as much of a difference once we introduced boost from a turbo? Prior to the mods, the 5.3L was run with a single S480 turbo from LJMS using Holley turbo manifolds and a Turbo Smart HypeGate45 waste gate. Run at a peak boost pressure of 9.6 psi, the turbocharged 5.3L produced 532 hp at 5,500 rpm and 555 lb-ft of torque at 4,700 rpm. We then applied the same turbo system (without changing the wastegate setting) to the modified combination. Equipped with the new heads, cam and intake, the turbo 5.3L produced 801 hp at 7,000 rpm and 616 lb-ft of torque at 5,600 rpm. Despite the same wastegate setting, the boost on the modified combination increased to a peak of 11.9 psi. It should be pointed out that each additional psi of boost proved to be worth about 30 additional hp.
