Muscle Mustangs & Fast Fords
Boost Pressure on 5.0L Applications - Big Bad Boost
Effect of boost pressure on different 5.0L applications.
The single kit comes with a 72mm turbo standard, but upgrades are available up to 76mm. Looking to test the kit on stock and modified 5.0L motors, we stepped right up to the 76mm turbo. Since boosted motors generally require additional cooling, CX Racing also developed a bolt-in aluminum radiator upgrade for the 5.0L applications.
Adding the turbo kit to the stock 5.0L required drilling and welding a drain hole in the stock oil pan. After bolting on the exhaust manifolds in place of the header, we ran a oil feed line to the 76mm turbo. The kit included the necessary stainless steel V-band clamps and silicone couplers to connect all the tubing from the turbo to the intercooler and then to the throttle body. We mounted a fan in front of the intercooler to supply a cold-air source while dyno testing.
With the supplied wastegate spring set for 7 psi, we tuned the Holley EFI system to provide safe air/fuel (11.8:1) and timing curves (22 degrees). The peak power number was up to 391 hp, while torque jumped to 471 lb-ft. Using a manual boost controller from Turbo Smart, we stepped boost to 10 psi, which brought 429 hp and 542 lb-ft of torque, while 14 psi took us just over 500 hp with 615 lb-ft of torque.
Though turbo response was artificially enhanced on the engine dyno (stationary loads help spool up), this stock 5.0L application would be better served with a smaller 72-, 70-, or even 60-series turbo. It is at this torque output that you worry about the strength of the production 5.0L block.
After testing on the stock 5.0L, we moved to the second turbo application. This test was run with a single-turbo system from HP Performance, but utilizing the same 76mm turbo from CX Racing. As with the stock 5.0L, this modified 302 was run both normally aspirated at identical boost levels to the stock 5.0L. The modified 302 also featured a forged reciprocating assembly from SCAT and JE, but further enhanced with CNC-ported aluminum cylinder heads from Procomp Electronics, a Crane hydraulic-roller cam (0.542/0.563 lift, 224/232 duration, and 112 LSA), and Holley SysteMax upper and lower intake.
Run in normally aspirated trim, the modified 302 produced 413 hp and 389 lb-ft of torque. Compared to the stock 5.0L, power production was higher in the rev range, though there was no loss in power as low as 3,000 rpm. The heads, cam, and intake simply offered more power everywhere and allowed the modified motor to make peak power 1,000 rpm higher than the stock combo.
The extra 152 hp offered by the modified motor over the (mostly) stock 5.0L carried over once we added boost. Running the same 7 psi, 11.8:1 air/fuel, and 22 degrees of timing, the turbo combination belted out 601 hp and 570 lb-ft of torque.
Duplicating the testing with the stock 5.0L, we adjusted the boost level supplied by the 76mm turbo to 10 psi, and the modified 302 produced 688 hp and 656 lb-ft of torque. At this point, you might be expecting the results of the modified motor run at 14 psi, but the results would likely be less than stellar for two reasons. First, the 76mm turbo was nearing its limit. Though we have exceeded 750 hp on one occasion, calculations told us that the modified 302 combination might exceed 800 hp at 14 psi. Second, not only was this beyond the flow limit of the turbo, it was also well beyond the strength limit of the production block. We were taxing the block at just 10 psi (and 656 lb-ft), so we didn't risk stepping up to 14 psi with this combo.
Looking strictly at the math, we see that the extra 152 hp offered in normally aspirated trim by the modified motor translated into 210 hp at 7 psi and 259 hp at 10 psi.
Photo GalleryView Photo Gallery
Since we didn't get a chance to run the modified 302 at 14 psi, we decided to compare it to a test run previously done by MM&FF. Needing the appropriate strength to crank up the boost, test-motor #3 checked in at a full 363 ci. The 302-based stroker featured a 4.125-bore Dart block stuffed with a custom turbo-grind roller cam from Cam Research Corp. Feeding the 363 stroker was a set of CNC-ported 225 heads from Airflow Research and a Box R intake from Trick Flow Specialties.
In normally aspirated trim, the stroker produced 519 hp and 469 lb-ft of torque. Running a larger 76mm turbo from Precision Turbo, it produced 759 hp at 7 psi and 858 hp at 10 psi. Things got serious at 14 psi—the 363 stroker topped the 1,000hp mark with a peak of 1,003 and nearly 900 lb-ft of torque.
If you're keeping score, this 363 stroker produced twice as much power as the stock motor with the same boost level. If you are looking for a powerful 5.0L, make it big and bad before adding boost.