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Four Dyno-Proven Ways to Add More Power to Your Mild Big-Block Chevy

Unrealized Possibilities: Four dyno-tested ways to add more power to your mild big-block Chevy

Richard Holdener Aug 24, 2016
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A recent trip to the local Pick Your Part wrecking yard revealed row after row of what we like to call possibilities. Under the hood of each and every vehicle in the yard were the makings of a high-performance race engine just begging for a new lease on life. Of course, some would take considerable work to get there while others may never make it. But choose wisely and the rewards can be impressive. When you go looking for power in the yard, it is always best to go big, as in big-block Chevy. In the sea of stock, junkyard engines, bigger certainly means better. Since we planned on running a trio of power-adders on our junkyard “race” engine, we went right for a engine we knew was capable of withstanding both boost and juice. Though earlier Mark IV and Gen V engines are usually available, we zeroed in on the latest and greatest: a Gen VI 454 (7.4L) offered by GM from 1996-’99 (actually into early 2000).

The Gen VI offered a number of desirable features, including the highest rated power output (since the muscle car era). Thanks to small-chamber, standard-size oval-port heads, factory hydraulic roller cam, and increased static compression (compared to the Gen V), the Gen VI was a powerhouse just begging for boost. Of course, the 454 was also sporting a four-bolt main block, a steel crank, and 9.0:1 static compression ratio. Offered by GM with a long-runner, EFI induction system, the late-model 454 was easily converted to carbureted trim using a Speedmaster Eliminator intake, Holley carburetor, and MSD distributor. We made sure to look over our big-block prior to purchase and were rewarded with not only a solid oil-pressure curve but baseline power numbers of 370 hp and 476 lb-ft of torque. Having run no less than five of these junkyard 454s, we can say this was right on par with what we have come to expect with this induction system.

Gen VI 454—NA vs Zex Nitrous (125hp shot)

Big Block Engine Junkyard Dyno Nitrous 2/24

Having established the baseline numbers, it was time to add some power. First on the power-adder list was nitrous oxide, and Zex stepped up with their trick Perimeter Plate nitrous system. The Perimeter Plate system was adjustable, allowing us to dial in the power level using the supplied jetting. For our stock engine (on pump gas) we chose to add 125 horsepower. Thanks to equally spaced injection points, the Perimeter Plate ensured even distribution to all cylinders. After heating the bottle to ensure proper pressure, we ran the Zex system on the 454 with excellent results. The peak numbers jumped to 530 hp and 662 lb-ft of torque, but those readings were taken at the spike (see graph). The power curves illustrate that the Zex nitrous kit improved the power output by at least 125 hp through the tested rev range. How can you go wrong with something that adds 125 extra horsepower at the push of a button?

Gen VI 454—NA vs Comp XR276HR Cam

Big Block Engine Junkyard Dyno Cam 3/24

Having run the 454 with the stock cam and nitrous, we decided it was time to replace the wimpy stock cam and try something a little more powerful. The mild (near-stock) combination and limited piston-to-valve clearance all but dictated a mild cam profile, but we nonetheless wanted something that offered some decent power gains. The Xtreme Energy XR276HR cam seemed like the ideal choice as it offered plenty of performance without a penalty in idle quality, low-speed torque, or driveability. Run with the stock cam (Speedmaster intake, Holley carb, and MSD distributor), the junkyard 454 produced 370 hp and 476 lb-ft of torque. After installation of the Comp XR276HR cam and beehive valvesprings (Comp PN 26120), the peak power numbers jumped to 428 hp and 515 lb-ft of torque. The cam increased the power output by over 60 hp at 5,000 rpm, but bettered the stock cam even down at 2,600 rpm. The cam swap also meant the engine would be making even more power once we added boost.

Gen VI 454—NA vs Vortech (19 psi)

Big Block Engine Junkyard Dyno Blower 4/24

After the success of the cam swap, things really started to get serious. Not wanting to tear into the engine any further to replace the components in the short block or cylinder heads, we decided it was time for boost. Vortech supplied one of their YSi supercharger kits for the big-blocks. The YSi supercharger was capable of supporting 1,200 hp, more than enough for our mild, cam-only 7.4L. The kit included a cog drive pulley system to eliminate any chance of belt slippage. Unlike the nitrous and cam tests, we added race fuel to the mix to eliminate any chance of detonation at the elevated boost levels. We also replaced the standard Holley carb with a dedicated blow-through unit and bonnet from CSU (Carburetor Solutions Unlimited). In retrospect, the boost was probably a tad on the high side for the stock internals, but the 454 shrugged off the extra power like a boss. In the end, the non-intercooled, supercharged combo produced 791 hp at 6,000 rpm and 713 lb-ft of torque at 5,300 rpm. The peak boost registered from the YSi was a healthy 19 psi.

Gen VI 454—NA vs Twin-Turbo (12.3 psi)

Big Block Engine Junkyard Dyno Turbo 5/24

The final test run on the 454 featured a pair of BorgWarner turbos supplied by Lil John’s Motorsports Solutions (LJMS). Originally supplied for a high-horsepower, 6.0L LS application, the turbos were fed through an air-to-water intercooler from CXRacing. Boost from the turbos was controlled by a pair of TurboSmart Hyper-Gate45 wastegates. The turbo system included a set of turbo manifolds feeding 90-degree bends whipped up by JFab. Carried over from the supercharger test, the CSU carburetor and bonnet were employed but the turbo system had the benefit of intercooling. We used race fuel during this test, also, to eliminate the possibility of detonation. We started with low boost then increased it in small increments until reaching a maximum of 12.3 psi. So equipped, the twin-turbo Gen VI BBC produced 832 hp and 866 lb-ft of torque. Each of the BorgWarner turbos was capable of supporting this power level on its own, but having two allowed us to minimize backpressure and maximize power output. Getting a good-running engine from the junkyard is always great, but successfully subjecting one to three different power-adders qualifies as a home run!

Big Block Engine Junkyard Dyno Intake 6/24

01. The factory EFI used on the Gen VI 454 was ditched in favor of a simple, dual-plane Eliminator intake from Speedmaster.

Big Block Engine Holley Carb 7/24

02. The baseline testing was run with this Holley 650 XP carburetor. The 650 was sized perfectly for the power output of the mild 454.

Big Block Engine Msd Distributor 8/24

03. The factory EFI distributor was ditched in favor of this billet distributor from MSD.

Big Block Engine Junkyard Dyno Stock Long Block 9/24

04. Fresh from the yard, the carbureted 454 produced peak numbers of 370 hp at 4,600 rpm and 476 lb-ft of torque at 3,400 rpm.

Big Block Engine Junkyard Dyno Zex Nitrous 10/24

05. The first in our trio of power-adders was a Zex Perimeter Plate nitrous kit.

Big Block Engine Junkyard Dyno Zex Perimeter Plate 11/24

06. The Zex Perimeter Plate featured 12 equally spaced injection ports to ensure even distribution to all cylinders.

Big Block Engine Junkyard Dyno 125 Hp Jet 12/24

07. The kit included adjustable jetting to allow us to dial in the desired power level. We chose 125hp jets for the stock 454.

Big Block Engine Junkyard Dyno Dyno Nitrous 13/24

08. Run with the Zex nitrous kit, the Gen VI 454 produced peak numbers of 530 hp and 662 lb-ft of torque. A review of the graph will show that the Zex kit improved the power output by at least 125 hp through the entire (tested) rev range.

Big Block Engine Junkyard Dyno Comp Cam Swap 14/24

09. Thinking that the big-block might respond to something other than the mild, factory truck cam timing, we installed a Comp XR276HR cam. The 276 offered 0.510-inch lift, a 224/230-degree duration split, and 110-degree LSA.

Big Block Engine Junkyard Dyno Comp Springs 15/24

10. To ensure we could take full advantage of what the new cam had to offer, we also upgraded the valvesprings. The stock spring package was replaced with a set of beehive springs (with new retainers, locators, and keepers). The cam swap improved the power output from 370 hp and 476 lb-ft to 428 hp and 515 lb-ft of torque. The cam swap alone was worth over 60 hp at 5,000 rpm.

Big Block Engine Junkyard Dyno Vortech Blower 16/24

11. After the success of the nitrous and cam testing, it was time for boost. Vortech supplied a YSi supercharger kit capable of supporting over 1,200 hp.

Big Block Engine Junkyard Dyno Blow Through Carb 17/24

12. The Vortech was combined with a CSU blow-through carburetor designed specifically for boosted applications.

Big Block Engine Junkyard Dyno Hat 18/24

13. CSU also supplied a blow-through bonnet for their modified 850 Holley carburetor.

Big Block Engine Junkyard Dyno Cog Supercharger Belt 19/24

14. Run with the cog drive system pumping out a peak boost pressure of 19 psi, the supercharged 454 produced 791 hp and 713 lb-ft of torque. Adding and intercooler would have pushed these numbers up even further.

Big Block Engine Junkyard Dyno Turbo 20/24

15. The final test involved running a pair of BorgWarner turbos on the 454. Though each was capable of supporting over 900 hp, we decided if one is nice, then two must be just right!

Big Block Engine Junkyard Dyno Stainless Turbo Header 21/24

16. The turbos were fed by a set of custom (stainless) turbo headers fabricated by JFab.

Big Block Engine Junkyard Dyno Turbosmark Blow Off 22/24

17. Boost was controlled by a pair of TurboSmart Hyper-Gate45 wastegates.

Big Block Engine Junkyard Dyno Intercooler 23/24

18. Boost from the turbos was fed through this air-to-water intercooler from CXRacing. We ran dyno water through the cooler, but additional power is available with ice water.

0big Block Engine Junkyard Dyno Intercooled Turbo 24/24

19. Running a maximum of 12.3 psi of boost, the twin-turbo 454 produced 832 hp at 5,500 rpm and 866 lb-ft of torque at 4,400 rpm. After the success of these power-adders, we expect to see a lot more BBC enthusiasts hunting through salvage yards to find their budget-friendly race engines.


Comp Cams
Memphis, TN 38118
Memphis, TN 38118
Vortech Superchargers
Oxnard, CA 93033
Bowling Green, KY 42101
Turbo Smart
Rancho Cucamonga, CA 91730
CX Racing
Torrance, CA 90503
El Paso,
CSU Carbs
Fontana, CA 92336
LKQ Pick Your Part
Lil John’s Motorsport Solutions



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