Chevy 383 Stroker Swap

We’re not going to make wild estimations about the flywheel power by claiming a 20 percent or more loss through the drivetrain. This car made nearly 500 hp and a mind-altering 600 lb-ft of torque at the rear wheels on Morgan Motorsports’ Dynojet chassis dyno. That’s enough to put a lot of race cars on the trailer, turn stoplight confrontations into blood baths, and make on-ramps seem like driveways.

Air Flow Research sent a set of 190cc L98-style heads to American Speed for installation. Named for the volume of their intake ports, the heads flow 262 cfm at 0.500-inch lift, and come assembled with 2.02-inch intake and 1.60-inch exhaust valves.

Speed-Pro forged-aluminum “supercharger” pistons with -12cc dishes produced 8.5:1 compression with the AFR heads’ 74cc chambers, an 11.2cc compressed gasket volume, and 0.011-inch deck height. Perfect for lots of boost. The rings are 0.030-over, 1/16-inch ductile iron with barrel-shaped top rings and tapered secondary rings to control boost pressure and improve oil control. The top rings were gapped at 0.024 inch and the second rings at 0.018.

CAT Power Parts provided the 3.75-inch-stroke crankshaft and steel H-beam rods, which didn’t seem like overkill when we turned the nitrous bottle on and pulled the trigger for the first time. Six-hundred lb-ft and 6,000 rpm make you think about how strong the parts are. They are, and for that we’re grateful.

The crankshaft from the car’s original 305 had a smaller hub than the early style 383 crank, so of course it didn’t fit. On top is the stock 305 flywheel that, like the new flywheel, is 10 inches in diameter to fit the clutch and the T5 bellhousing on the Z28. On the right is a standard 11-inch, 168-tooth flywheel. The bigger flywheel was too large to work with the Z28’s clutch, but because it fit on the crank hub, we figured out how to solve the problem: a late-model flywheel with an early-model hub diameter. We could have scrounged a 153-tooth flywheel from a junkyard, but the deadline was closing fast, so instead we bought the last, now-discontinued, McLeod neutral-balance flywheel (lower left) in stock at our local PAW warehouse for $205. To avoid this, make sure to get the late-model small-hub crankshaft and reuse the stock flywheel or buy one used.

The balancer situation was much easier than the flywheel end. The Streetdampr from Vibratech was a no-brainer with its heavy-duty design and superior vibration control.

According to American Speed, late-model, one-piece rear-main-seal cranks are available to build strokers from L98, LT-1, and LT-4 blocks. However, since we ordered ours before we knew that, we ended up with an early style, one-piece-seal crank and an adapter that worked fine (except for the flywheel situation). ARP provided the main studs, head bolts, and rod fasteners.

We wanted a mellow cam that wouldn’t alert the cops and could pass California’s strict emissions laws. Comp Cams had just what we wanted in the Xtreme Marine section of its catalog: a hydraulic roller with 218/224-degree duration at 0.050 and 0.495/0.503-inch lift with a 112-degree LSA. It may seem small, but we attribute the 600 lb-ft of torque to the design of this cam. It’s important to note that this cam is designed for ’87-and-later blocks that were originally equipped with a roller cam; early blocks use a different part number, so check with Comp for the right one.

Along with the cam, Comp suggested using 1.5:1 roller rocker arms and matching pushrods and valvesprings. The dual springs provide 132 pounds of seat pressure at 1.750-inch installed height, and 280 pounds open pressure at 1.250-inch installed height.

With deadlines looming, the ACCEL base manifold required to run the ACCEL SuperRam upper manifold proved tricky to find. We logged on to www.jegs.com and ordered one of the last six manifolds in stock in the country. It came in two days.

Chevy High Performance Editor Jeff Smith gave us the excellent idea of adding studs to the base of the SuperRam plenum to ease installation. Considering that the inside bolts can’t even be seen when the intake is in place, the studs are a good idea. The lower left fitting (arrow) is the new location for the brake booster line, and the sensor in the center takes manifold air temperature (MAT) readings.

The stock manifold is the biggest horsepower cork in a TPI engine, second only to stock exhaust manifolds. Notice the larger ports on the ACCEL base manifold (bottom) compared to the stocker (top).

We put the SuperRam on before dropping the engine in the car. Mistake. It repaid us by crushing the wiper-motor housing on the firewall. Another blunder was not running a heavy bead of silicone across the back of the lifter valley where the block, heads, and manifold meet and around each intake port. The result was a nasty oil leak behind the distributor and a healthy vacuum leak. Fixing the leaks took about 8 hours, with two people thrashing. Despite the hassles, the SuperRam was key to the 600 lb-ft of torque at a low-and-slow 3,100 rpm.

The final trinket was an adjustable Fuel Management Unit from Vortech. This device is simple but critical: It restricts the return line to the fuel tank, thus boosting fuel pressure. Previous issues of Car Craft covered the Vortech and its components in more detail (“Vortech Blower How-To,” April 2000, and “EFI Supercharger Tuning,” May 2000), so we’ll just say that the Camaro was very rich with the 305 and the supercharger, and the adjustable FMU gave us control over the fuel curve.

The first runs on the dyno netted about 425 hp at the wheel, and even though that was enough to shred the Yokohama A520s, we were disappointed. The boost gauge explained why: only 5 pounds of boost. The solution was swapping the original 3.50-inch pulley for a 2.95-inch one. It was worth 3 more pounds of boost and 40 extra horsepower.

With no more pulleys in our bag of tricks, we opened the bottle. Earlier, we’d screwed in a trick NOS annular discharge nozzle and a set of 50hp jets, which required a 1/16 NTP tap to thread it into the aluminum supercharger intake duct. Jeremy White at Westside Performance had the tap on hand and was happy to drill and tap the hole for free (we repaid him by filling our bottle there). The nitrous produced another 34 horses at the wheel and an awesome 80 lb-ft of torque. With 34 degrees of total timing and no boost retard, we hit our target goal of 500/600.

Two weeks from the time the engine showed up in a crate at our doorstep it was running in the Camaro. Slapping a carb and intake on it would have been easier, quicker, and cheaper, but to be legal in California, every emissions device must be present and functioning during a smog test. The parts used in this story have CARB Executive Order numbers, making them 50-state legal. And it still made 500 horses at the wheel. cc

If one power-adder is good, wouldn’t two be better? Seems obvious, and for those who haven’t followed along, Car Craft has tested a Vortech S-Trim supercharger and nitrous oxide separately on a ’91 Camaro Z28, but never at the same time. In order to get these two to work together in the same engine without driving over the crank, we decided that an upgrade from a stock 305 with cast pistons was necessary. During the search for a suitable 350, Gail Trent at American Speed convinced us that the low cost of small-block Chevy stroker cranks makes a 383 hardly more expensive than a similarly built 350, but capable of putting out a ton more torque. We bit.

American Speed’s stroker crate engines include heads that are compatible with factory Tuned Port Injection manifolds and a one-piece rear main-seal block that accepts a roller-style camshaft, like those found in ’87-and-later Camaros and Corvettes. As with all American Speed engines, the 383 was dyno-tested before it was shipped. It made 418 hp on its break-in run with Edelbrock injection.

We’ve got to give a big thanks to the guys at American Speed for helping us through this project. As the parts arrived and the project took shape, Gail had to deal with all the phone calls (two a day for a while) and misdirected mail. We bled, our friends bled, and the swap took a lot longer than anticipated. The engine swap and an unexpected intake-manifold debacle took the entire Fourth of July weekend including at least one overnighter. Some people got coleslaw and dogs; we got Del Taco at 3 a.m. and a phone call or two at the shop from family and friends wondering if we were still alive.

So why do it? The results were more than worth the effort: almost 500 ponies at the rear wheels, and the engine is nowhere near its limits. With only 8 pounds of boost and a measly 50hp shot of nitrous, the power-adders are barely even screwed on. A Vortech T-Trim blower to provide more boost and a little more spray would put 575-600 rear-wheel horsepower within reach. Moreover, it’s mellow, streetable, and inconspicuous. Truth be told, which it is, it was also ungodly expensive. But it still rocks.