ATK High Performance GM 350 Stage 1 Long Block: 345 HP

Turn-Key Street Performance with Proven Vortec Head Technology

Introduction

At Hammer Engines, we’ve built everything from stump-pullers to high-RPM race engines, and we understand that most enthusiasts want a significant power bump without diving into the deep end of custom fabrication and tuning. The ATK HP98 Stage 1 Long Block hits that sweet spot with authority. This isn’t a dressed-up stock rebuild; it’s a thoughtfully engineered performance package that delivers proven, reliable horsepower right out of the box, a philosophy we fully endorse for street-driven projects.

This 345 horsepower long block is the ideal solution for the enthusiast or professional builder looking to repower a classic muscle car, hot rod, or light truck with modern, efficient power. It’s designed for the user who wants a dramatic improvement over a worn-out stock 350 but doesn’t want the complexity, fuel requirements, or tuning hassle of a radical cam or high-compression build. The use of production-based Vortec cylinder heads is the key to its efficiency, offering superior airflow over traditional heads at a realistic price point. For a complete, hassle-free installation, our team offers professional Performance Engine Installation & Dyno Tuning Services.

ATK’s assembly process mirrors the standards we apply in our own shop: all rotating components are precision-balanced, and the block is decked and honed with torque plates to ensure optimal ring seal and longevity. This attention to detail is why we’re confident offering this engine with its industry-leading 5-year/unlimited-mileage warranty. It’s a crate engine you can actually drive every day. To ensure it delivers every ounce of its potential, pair it with our recommended Performance Induction & Exhaust System Package.

Technical Specifications Table

Application & Use-Case Section

The ATK Stage 1 is engineered for real-world street performance, making it a versatile upgrade for a wide array of popular GM platforms.

• Classic Muscle Car & Street Rod Revival: The perfect drop-in performance engine for a 1967-1980s Camaro, Chevelle, Nova, or early hot rod. It delivers a visceral, 100+ horsepower increase over a stock 2-barrel 350, transforming the driving experience while maintaining a stock appearance under the hood.

• Light Truck & SUV Performance Towing: An excellent repower for a classic K5 Blazer, C10 pickup, or square-body Suburban. The strong mid-range torque provides exceptional towing and throttle response, far superior to a tired original engine.

• Budget-Conscious Pro-Touring Foundation: A solid starting point for a builder who plans to add aftermarket fuel injection, headers, and an intake later. The Vortec heads respond exceptionally well to these bolt-ons, allowing power to grow with the project. For guidance on supporting mods, read our blog: Maximizing Your Vortec Headed 350 with Bolt-Ons.

Competitor Comparison Table

Hammer Engines Verdict: The ATK Stage 1 represents the best value in the entry-level performance segment. It significantly outperforms any stock-replacement remanufactured engine for a modestly higher price. Compared to other “performance” 350s, the ATK’s use of modern Vortec heads is a major advantage, providing better airflow and efficiency than older “fuelie” style heads. The standout 5-year warranty is a testament to the quality of components and assembly, offering peace of mind that cheaper competitors simply cannot match.

Pros and Cons Table

Frequently Asked Questions (FAQ)

Q1: What intake manifold do I need for this engine?
You will need an intake manifold designed for *1996-2000 Chevrolet Vortec heads*. These heads have a unique, center-bolt valve cover pattern and a different intake bolt angle than standard small block heads. Both carbureted and EFI versions are widely available from the aftermarket.

Q2: Is this engine compatible with my stock TH350/TH400 transmission?
Yes. This engine uses a standard Chevrolet flywheel/flexplate bolt pattern and crankshaft flange. It will bolt directly to any transmission that bolted to your original small block Chevrolet, including automatics (TH350, TH400, 700R4) and manuals (Muncie, T5, T56).

Q3: What is the break-in procedure for the flat tappet camshaft?
This is critical. You must use a break-in oil with high levels of ZDDP (zinc) or a dedicated additive. Upon first start, immediately bring the engine to 2,000-2,500 RPM and vary it slightly for 20-30 minutes to properly seat the camshaft lobes and lifters. Do not let it idle during this period.

Q4: Will this pass emissions in my state?
As a crate engine without any emissions certification, it is marketed for “off-road use and racing vehicles.” Its legality for use in a street-driven vehicle subject to inspection varies by state and local regulations. It is the purchaser’s responsibility to determine compliance.

Q5: Does it include an oil pan, water pump, and harmonic balancer?
No. This is a long block. It includes the assembled engine block and cylinder heads. You must provide and install the oil pan, front cover, water pump, harmonic balancer, intake manifold, fuel system, and ignition system.

Authority-Building Content Hubs & Next Steps

Deepen Your Knowledge

Building a reliable performance engine requires specific knowledge. Our tech library is built from the dyno and the drag strip.

• The Ultimate Guide to Breaking In a Flat Tappet Camshaft

• Choosing the Right Intake Manifold for Vortec Heads

• From Long Block to Running Engine: Your Complete Parts Checklist

Take the Next Step

Ready to inject 345 horsepower of reliable, streetable performance into your project? Our performance engine specialists are here to help you select the right components and plan your installation.

Contact our performance engine team for technical support and a final quote.