According to official sources, only 71 people-lucky owners of two Corvettes and 69 Camaros-were fortunate enough to get their hands on what was arguably the most powerful production car and engine package ever offered to the American public: the '69 all-aluminum big-block Chevy 427ci RPO ZL1. A relative of that era's all-aluminum Can Am road-race Rat motors, the ZL1 was factory-rated at 430 gross horsepower at 5,200 rpm, but the actual output was nearly 600 gross horsepower after tuned headers were installed in place of the restrictive factory cast-iron exhaust manifolds. Although it technically carried the standard GM five-year/50,000 mile warranty of the day, ZL1s-with their 103-octane-guzzling 12.5:1 compression ratio, chokeless 850-cfm Holley double-pumper carb, blocked-off distributor vacuum advance, and huge mechanical-lifter camshaft-were really intended for racing only. They didn't idle, low-end response was nil, you didn't drive them to a family picnic, and you sure as hell didn't sit in rush-hour traffic. But, hey, those were the '60s.
Now it's 2002, and the ZL1 is back for what GM says is a one-time only run of 200 all-aluminum engines, available complete in the crate with custom, consecutively serial-numbered valve covers, blocks, heads, and throttle bodies from your friendly GM Performance vendor (assembly PN not yet available). Based on an improved and strengthened block, the new engines have gone to finishing school, emerging as a civilized high-zoot package that's fit to be seen in polite street-car engine compartments. We're talking about 454 cubic inches, heads and cam tuned for a broad torque curve and midrange driveability, a 10.2:1 compression ratio compatible with today's pump gas, and all-season, no-fuss/no-muss electronic fuel injection (EFI) calibrated by real GM engineers.
GM plans to sell the ZL1s complete with the wiring harness and computer. They'll have a short water pump; an externally balanced, 14-inch, 168-tooth auto-trans flexplate; and an oil pan that fits classic Vettes, fullsize passenger cars, and pickups.
Chevelle/Camaro pans and manual-trans flywheels are available separately from your GM dealer. Exhaust manifolds or headers must be supplied by the customer.
The fuel-injection setup is based on the Ram Jet 502 package. Its long-runner, torque-friendly EFI intake is fed by a 58mm aftermarket rendition of a two-barrel TPI/LT1-style throttle body, which in testing proved the best compromise in terms of performance versus velocity and driveability. A production 48mm throttle-body was too small; a huge 1,300-cfm unit gave up too much midrange while only gaining 4 hp upstairs. Injectors are Rochester Multec 38 lb/hr units batch-fired by the new and improved MEFI-IV all-weather controller.
If you're worried about old-style aluminum blocks' notorious durability problems-including mysterious coolant-passage porosity and cylinder-wall liner instability-don't be. This engine has passed GM's 50-hour durability torture-test, where the engine is continuously run at full throttle, cycling back and forth between peak torque and peak power in 125-rpm, 10-25-millisecond increments.
Speaking of full-throttle, just how well does this new, "civilized" ZL1 run? GM currently uses the conservative SAE net correction factor that's more representative of real-world operating conditions than the old gross-power rating method that was used in the '60s and is still the choice for typical aftermarket performance dyno tests. Dyno-tested with Hooker Chevelle headers (2-inch primaries x 311/42-inch collectors), on 93 premium unleaded fuel, the engine made 492.9 net lb-ft of torque at 4,250 rpm, and 510.3 net hp at 5,750. With the long-runner fuel-injection intake, the broad, flat torque curve generated over 450 lb-ft from 2,750 to 5,750 rpm.
Rating the engine by typical hot rod gross power standards would be worth another 30-40 numbers. Plus the 498-pound (dry) engine shaves nearly 400 pounds compared to an all-iron Rat motor-and every 2 pounds saved is like gaining 1 hp. Of course, pounds/dollar is a whole 'nother issue. Although pricing hadn't been finalized as this is written, we expect turnkey engine list prices in the $20,000 range.
Adventures in Calibration
One perceived virtue of EFI is its supposed ability to virtually dial itself in, eliminating lengthy and complex tuning. That may be true if you only want to go down the racetrack at wide-open throttle, but it turns out that calibrating EFI to GM quality standards-operating seamlessly and transparently under all part-throttle conditions regardless of climate or elevation-is a major undertaking. In fact, GM's requirements for dialing in fuel injection involve about 10 times more work than what's needed with a carburetor. Strict standards must be met in terms of airflow, injector pulse width, injector duty-cycle, and spark timing. Stable idle, spark knock versus timing retard, cold-start, and hot soak behavior are critical.
I discovered this firsthand when GM invited me to ride along while the ZL1's computer got programmed at the General's Arizona Proving Grounds and in an on-highway thrash back-and-forth between Phoenix and Flagstaff. Why Arizona? The drive-route from Phoenix's 120-degree F dry desert heat and near sea-level elevation up to Flagstaff climbs as high as 8,000 feet, and in the process the temperature drops into the 70s. It's one of the best places you can find to program fuel and spark maps and verify driveability.
When I arrived, the '70 Chevelle mule would barely idle; 24 hours later the car was purring like a kitten-despite the raspy roller cam. But the engineers still weren't satisfied and eventually invested 1,000 man-hours to get the calibration spot-on for open-loop operation (there's no O2 feedback on this package). According to GM's Jim Stewart, dialing in for closed-loop operation would take 1,000 hours more!
Tech Specs
All dimensions are in linear inches, except as noted.rated output
Power @ rpm: 510 net hp @ 5,200
Torque @ rpm: 500 lb-ft @ 3,600
Output as tested
Correction Factor: 77 degrees F, 39.31 inch-hg
Max Power @ rpm: 510.3 net hp @ 5,750
Max Torque @ rpm: 492.9 net lb-ft @ 4,250
Short-Block
Displacement: 454 ci
Bore x Stroke: 4.25 x 4.00
Recommended Redline: 6,000 rpm
Fuel Shutoff: 6,375 rpm
Nominal Compression Ratio: 10.2:1
Block: Chevrolet Mark IV aluminum ZL1 (PN 12370850)
Main Caps: 8620 steel, four-bolt, splayed outer holes
Crankshaft: GM forged 1053 steel (PN 3963523)
Rods: GM forged 4340 steel, 71/416 bolts (PN 10198922)
Pistons: Speed-Pro forged with pressed pins (PN L2465F)
Rings: Plasma-moly 51/464 top, 51/464 ductile-iron second, 31/416 standard-tension oil
Balancer: GM 8-inch-od, counterweighted (PN 10216339)
Flexplate: GM 14-inch-od, counterweighted (PN 14001992)
Starter: GM lightweight gear-reduction (PN 9000852)
Oil Pan: GM Corvette trap-door style (PN 14091356)
Oil Pump: GM high-volume, 1.3-inch gears (PN 3969870)
Windage Tray: GM new design, Teflon-coated
Water Pump: GM short aluminum (PN 14058915)
Cam & Valvetrain
Type: Comp Cams mechanical roller tappet
Grind No.: CBVI 4873B/1498S SR114.0 (custom)
Rocker Arms: GM 1.7:1 roller-trunion (PN 12361330)
Theoretical Valve Lift (Zero Lash): 0.640/0.598
Duration at 0.015 Tappet Lift: 273/276 Degrees
Duration at 0.050 Tappet Lift: 236/232 degrees
Lobe Separation: 114 degrees
Lobe Centerlines: 110/118 degrees
Pushrods: Comp Cams one-piece, 31/48 od x 0.080 wall
Timing Chain: GM single-roller (PN 12371053)
Valvesprings: Dual 1.550 od, 205 pounds seat at 1.900
Cylinder Heads
Type: GM aluminum oval port (assembly PN 12363390)
Intake/Exhaust Valves: 2.25/1.88 stainless steel
Intake/Exhaust Runner Volume: 290/110 cc
Combustion Chamber Volume: 110cc semi-open
Head Gasket: PermaTorque, with preflattened copper wire ring (GM PN 12363414), 9.7cc compressed volume
Piston-to-Valve Clearance: 0.100 at running lash
Fuel & Engine Management
Intake: Ram Jet (PN 12464482, bottom; 12464484, top)
Throttle Body: 58mm 2-bbl., 968-cfm @ 28 inches
Injectors: Rochester Multec disc-style, 12.20 ohms
Rated Flow Capacity: 38 lb/hr @ 45 psi
Operating Pressure: 52-55 psi, 90 percent duty-cycle
ECU: Delphi MEFI-IV
Primary Sensors: MAP, TPS, IAC, MAT, knock
Distributor: GM computer-controlled (PN 1104060)
Fluids & Tuneup Specs
Fuel: Premium unleaded, 93-octane preferred
Oil: 5W-30 or 10W-30, 6 quarts (with filter)*
Oil filter: AC PF25 or PF35
Coolant: 100-percent GM Dex-Cool long-life
Operating Temperature: 195 degrees F, 5 degrees
Ignition Timing: 36 degrees total
Spark Plugs: AC R43LTS, 0.045 gap**
Valve Lash: 0.016 intake/0.018 exhaust, "hot"
*Break-in on mineral oil, synthetic oil preferred after break-in.
**Preliminary; subject to revision
