When we last visited our Chevrolet Performance ZZ454 crate engine (PN 19331574) on the dyno, we found a lot to like. Rated at 469 horsepower and 519 lb-ft of torque, this engine is built with all-new parts, beefy forged internals, and is priced to sell, currently at under $7,500 retail from a number of suppliers. Tested with a Holley 850 carb and dyno headers, we found it right in line with the claimed numbers. Looking for more, we stepped the combination up with a Comp XM284 cam, along with their Ultra Pro-Magnum rockers and pushrods, and we had a legitimate 500-horsepower 454. That power level is enough for impressive street performance, but what about if the situation calls for more?
Nitrous has the almost magical quality of substantially boosting power at the touch of a button, while the moderate cost of a system and easy installation make it the shortest path to big power. Our goal with this engine was to hit it with more than a little sniff of nitrous, taking advantage of the inherent beef of the ZZ454 package. Nitrous builds cylinder pressure, and the associated strain means weak components can be subject to failure. Here, we were confident in our beefy Chevrolet Performance four-bolt main block stuffed with forged internals.
Overall, our engine had the right components to swallow a sizable hit of nitrous, but how that gas is deployed requires some consideration. The first decision here is the nitrous system itself. We selected the Nitrous Oxide Systems CrossHair Plate Professional system (PN 02153NOS), which features a unique double spray bar arrangement with both the nitrous and fuel discharged via two separate circuits, clocked 90 degrees apart. Along with the plate, this system features high-capacity solenoids giving a maximum rated boost of 350 horsepower, with output adjustable by jets at the plate. Since the system uses dual injection bars for fuel and nitrous, the plumbing is accomplished with a simple T-fitting and single fuel and nitrous solenoids.
There is power to be had by using a camshaft with specifications favorable to nitrous. Our Gen VI block application uses the specific later-model stepped-nose cam core designed for a cam thrust plate to establish thrust clearance. Here, Westech’s Steve Brule selected a catalog grind, Comp Cam’s XR288HR-14 (PN 01-422-8). This camshaft features 288/294-degrees gross duration, 236/242-degrees duration at 0.050-inch tappet rise, 0.520/0.539-inch lift, and a 114-degree lobe separation angle. Compared to the previous cam, this stick features 6-degrees more duration at 0.050, 2-degrees wider lobe separation, and a small decrease in lift of 0.027-inch intake, and 0.008-inch exhaust. In theory, the wider lobe separation would improve the nitrous performance, while negating much of the increased overlap that would come with the increased duration, maintaining very similar driveability compared to the previous camshaft.
Our final consideration was the intake manifold configuration. Our crate engine came with Chevrolet Performance’s dual-plane intake manifold, which is a nice piece for a mild, torquey street engine. This manifold is actually right on target for the original application. With a serious increase in camshaft timing, plus the prospect of substantial nitrous, an intake manifold change became the next logical step. With nitrous, the open plenum and direct runner routing of a single-plane intake manifold is much more conducive to good cylinder-to-cylinder distribution of the air/fuel/nitrous mixture. We selected a Weiand Track Warrior single-plane intake manifold (PN 7620) to complete our engine package.
The Numbers Please
To get a comprehensive picture of the effects of our engine combination changes we dyno tested in stages, running with each component swap on our way to our final nitrous configuration. The first swap here was our camshaft, and predictably the longer duration and wider lobe separation took a toll on torque lower in the rpm range, while top-end power was noticeably better. Peak torque dropped from 535.7 lb-ft at 3,800 rpm to 530.5 lb-ft at 3,900 rpm, while peak power was modestly up by 4.4 horsepower. Based strictly upon a comparison of the specs of our two cams tested, we would have expected this camshaft to have delivered a bigger advantage at peak, and continue to carry for further gains past peak power rpm. Our suspicion was that the dual-plane intake manifold was limiting top-end power and rpm.
While we suspected the intake was restricting top-end power, it was our plan from the start to switch from the Chevrolet Performance dual-plane manifold to Weiand’s tall Track Warrior single-plane. The Holley 850-cfm XP-Series double-pumper carburetor from our previous test was retained. With a change from a divided plenum, dual-plane intake manifold to a race type single-plane, expect the signal to the carburetor to be reduced. Re-jetting is a requirement for optimized operation with this change of intake manifold configuration. We took the time to carefully dial-in the carburetor tune to work with the intake manifold, and were rewarded with a large increase in top-end horsepower, with 530.6 at 5,900 rpm. On the other end of the scale, torque was down almost 20 lb-ft, peak to peak, with torque loss throughout the lower end of the curve.
Finally, we came to nitrous testing. The NOS CrossHair Plate Professional nitrous kit comes with jetting for 250, 300, or 350 horsepower gains, and we opted for the smallest of these. While an increase of 250 horsepower would put us solidly in the 780 horsepower range, based on our previous baseline power of about 530 peak horsepower, remember that with nitrous, timing has to be pulled back. At this nitrous system jetting, the NOS instructions recommend reducing the total timing by 10 degrees from the optimal naturally aspirated setting. We pulled the total timing back to 25 degrees. At this setting, peak power without nitrous dropped considerably to 486 horsepower. Hitting the nitrous button, however, brought back that lost power and a whole lot more, with the dyno now recording peaks of 760.9 horsepower at 5,500 rpm and torque hitting 733.9 lb-ft at 5,400 rpm. This balance of strong but streetable naturally aspirated power with the hammer-like hit of 760 horsepower at the push of a button gives our ZZ454 a Jekyll and Hyde personality that should be approached with caution.
|SuperFlow 902 Engine Dyno, Tested at Westech Performance Group|
|SuperFlow 902 Engine Dyno, Tested at Westech Performance Group|