The Holley Stealth Ram intake...
The Holley Stealth Ram intake manifold shares a traditional EFI appearance and will fit under the hood of most applications without modification.
The ECU
Recognizing that each induction system needs to be tuned to produce the most power, a FAST XFI programmable ECU is used instead of a GM ECM.
The XFI allows for quick and easily implemented tuning decisions. It removes the tedious process required with GM electronics that doesn't allow on-the-fly tuning unless a Moates Ostrich emulator (www.moates.net) is employed. With GM engine management, every tuning decision requires a download into the memory. This is be extremely burdensome in a test with as many variables as the one we are performing.
The Injectors
Due to the higher rpm capability of the shorter-runner manifolds and matching cam profile, 30-lb/hr fuel injectors are used. As engine speed increases, intake-valve open time in milliseconds goes down. With the long-runner TPI, a 24-lb/hr injector is more than sufficient due to the low speed that peak horsepower occurs. With the other manifolds, 6,200 rpm is possible compared to the TPI's 5,000 rpm. We want to make sure the duty cycle of the injector doesn't reach static during the test, so a comfortable margin is created with the larger injector. Fuel pressure is set at 45 psi at atmosphere, and all fueling changes are accomplished through modification to the injector pulse width.
The GM Ram Jet appears to...
The GM Ram Jet appears to have less plenum volume than the Holley Stealth Ram. If this is true, it should offer better idle quality with an aggressive cam.
The Results
As expected, the intake mainfold/cam combination changed the characteristics of the engine dramaically. For example, peak torque with the TPI was developed at 4,000 rpm, but more important, the engine had more than 400 lb-ft from 2,300 rpm on up with a diesel-like peak of 486.6 lb-ft. A Firebird with this combination will drive as if it has a high torque electric motor and pull like a jet plane on take off. It will offer great fuel economy and throttle response, while enjoying a numerically low rear-axle ratio and tight torque converter.
In contrast, the highest horsepower was produced with the Holley Stealth Ram manifold. The dyno read a staggering 485 ponies from a 355ci engine. This is modified Ram Air IV territory with a corporate small-block that is 100 inches smaller and on 92-octane fuel. Please reference the dyno charts for the exact results for each combination.
The Conclusion
If you want your Firebird to appear stock under the hood, then the long-runner TPI with nearly 417 hp and 486 lb-ft of torque will certainly surprise more than a few competitors. The idle quality with this package is very smooth and slow (650 rpm), with 17 inches of engine vacuum. With this engine, the Pontiac will drive like a stocker until the go pedal is smashed.
If your desire is more toward a traditional street/strip entry with a loose torque converter and 4.11:1 rear gears, then the single-plane or Stealth Ram are excellent choices. With nearly 500 hp from 355 ci, no excuses need to be made.
The Ram Jet produced results close enough to the rest to be called a tie, thereby providing another great choice for a street/strip Firebird that can exploit the attributes of a higher-than-stock stall converter and numerically steeper rear gears. With the Ram Jet, there's the added enticement of keeping your Pontiac all GM.
Though each induction design worked extremely well, this exercise has proven that the best results come with a systems approach. The same was true in the old days and it hasn't changed. The decision of which system to use depends on your plan for your Pontiac.