Heeding his advice, we performed the appropriate steps. The next morning we twisted the key and were rewarded with immediate and consistent cold startup. The engine immediately went to high idle (1,000-plus rpm) for several seconds and settled into to our selected idle speed of 850 rpm. The idle was so stable that it was unaffected by gear selection and steering-wheel inputs.
Once up to temperature and on the road, the throttle response was simply amazing. Stepping into the accelerator produced immediate response that propelled the Firebird forward forcefully. Now this is what EFI is all about!
The Power Numbers
We spent hours tinkering with a 800-cfm Quadrajet to get it performing flawlessly at every point under normal driving conditions, and that included several pulls on the chassis dyno to be sure it was dialed in for maximum full-throttle performance. Just before the EFI install, we recorded the 455's output so we might establish a baseline to compare the performance effects EFI might have. After strapping it to the roller drum on the Mustang dyno at H.S. Automotive in Omaha, Nebraska, the 455 recorded a best of 282 hp at 4,800 rpm and 336 lb-ft at 4,100 rpm at the rear tires.
We returned to H.S. Automotive a few weeks later for a follow up dyno session after the EZ-EFI install. We must first preface that a TBI system works much like a carburetor. It still uses traditional throttle blades for air entry, but uses fuel injectors instead of boosters to atomize fuel. Where carburetor jet changes take several minutes and tailoring the air/fuel ratio for a particular engine throughout the entire pull can be tedious, an electronic EFI system can generally be adjusted with a few keystrokes or button pushes, and it can immediately compensate for air temperature and conditions, as well as altitude for maximum possible performance in any condition or location.
The main benefit to an EFI system is its ability to atomize fuel in all conditions and improve driveability in all ranges. We were completely satisfied with what we'd seen from the EZ-EFI system so far and simply hoped to achieve similar peak power numbers from the EZ-EFI. We understood anything more might suggest an issue with the functionality of the Quadrajet we replaced, but anything less may be something we'd have to live with since our intent was improved drivability, and it delivered exactly that.
With the Firebird strapped down, the first pull sounded crisp and clean, but when it commenced, we found the 455 now producing 266 rwhp and 304 rwtq—a loss of about 20 hp and 30 lb-ft. A bit disappointed, dyno operator T.J. Mrsny assured us that the FAST system likely requires a few full throttle pulls for the ECU to adjust accordingly. He suggested a few subsequent pulls and just as he predicted, we saw the numbers climb each time. By the fourth pull we were at 284 rwhp and 337 rwtq—nearly identical to what we saw from the Quadrajet. A few more pulls were made adjusting fuel and timing, but nothing topped the numbers generated with FAST's programmed targets.
14. We had an issue at cold startup where the engine idled suitably, but died whenever a t
15. We were told to adjust the hot-idle IAC count until its between 10 and 20 by adjusting
16. A carburetor uses an accelerator pump to deliver an additional shot of fuel to prevent
17a. We used the Mustang brand chassis dyno at H.S. Automotive in Omaha, Nebraska, to dete
17b. During the baseline test the 455 peaked at 282 hp and 336 lb-ft at the rear tires. Th
18. FAST presets the target air/fuel ratio at full throttle to 12.8:1. It’s easily adjusta
19. The default settings were suitable, but we found our particular 455 idled better with
20. The EZ-EFI throttle body is designed to provide one ported vacuum source. We found on
21. With the Quadrajet in place, we had the distributor’s vacuum-advance unit connected to
The addition of an EZ-EFI fuel injection system has transformed the usability of this particular Firebird. Where it was once difficult to start and drive cold, it now starts immediately and can be driven away within seconds of startup (though we do recommend a minute or two of idle time to allow the fluids to circulate and warm up in cold temps). With as sensitive as the throttle response is, we're certain fuel economy will increase, but we simply couldn't resist stabbing the accelerator to feel the immediate responsiveness the EFI system offers. Best of all, we were able to achieve power numbers nearly identical to the carburetor with minimal tuning effort, and we greatly improved the street manners and overall driveability. That's exactly what the owner was after.
Year/Model: 1967 Firebird 400 convertible
Weight With Driver: Approx 3,750 lb
Engine: 1970 code-YH 455
Cubic Inches Before/After: 455/462
Engine Built By: Willard Auto Machine
Air Cleaner: Open element, 14x2-inch diameter
Fuel Injection: . FAST EZ-EFI throttle body, 1,000+ cfm
Intake Manifold: Performer RPM
Pump: FAST electric fuel pump, 240 lph
Casting: 1974 No. 4X-7H
Head Porting: Mild home porting
Peak Airflow Numbers at 28-inches: 230 cfm
Pistons: TRW forged-aluminum No. L2359F
Rings: Sealed Power replacement
Rods: Stock cast with ARP fasteners
Compression Ratio: Approximately 9.7:1
Crankshaft: Original nodular-iron, 4.21-inch stroke
Rotating Assembly Balanced: Yes
Brand: Nunzi's Automotive hydraulic flat tappet
Duration at 0.050: 232/243-deg
Duration Advertised: 301/313-deg
Lift with Specified Rocker Arms: 0.460/0.470-in
Lobe Separation Angle: 113-deg
Intake Centerline: 109-deg
Rocker Arms: Crower cast-alloy roller, 1.6:1 Ratio
Distributor: Pontiac HEI
Coil: Stock ACDelco
Wires: Taylor 8mm
Spark Plugs: ACDelco No. R45S
Total Timing: 36-deg
RPM Total Timing Is Reached: 3,200
Headers: Dynomax four-tube 1.75-inch primary tubes, 2.5-inch collectors
Exhaust Pipes: 2.25-inch
Muffler: Flowmaster crossflow, No. 42582
Converter: Continental, 2,600 stall
Rear Axle: Original 8.2-in GM 10-bolt
Rear Gear Ratio: 3.55:1