* 12-bolt GM (preferred): This is the most popular and arguably best choice for its strength and readily available parts. You'll want to find one with:
* 3.73-4.11 gear ratio: This range is suitable for street/strip use. Lower ratios (numerically higher) are better for highway cruising, while higher ratios (numerically lower) are better for acceleration. Your choice depends on your intended use.
* Posi-traction (limited-slip differential): Absolutely essential for handling the power and preventing wheel hop.
* Heavy-duty axles: The stock axles in even a strong 12-bolt might not withstand 500+ hp, so upgrading to aftermarket axles is highly recommended. Look for 30-spline axles at a minimum.
* Forged axles: These are even stronger than the more common 30-spline axles.
* Ford 9-inch: Another very strong option, known for its durability and aftermarket support. The downside is it requires more fabrication to fit a '69 Chevelle. Similar considerations regarding gear ratio, posi-traction, and axle strength apply.
* Dana 60: While exceptionally strong, this is overkill for most street/strip applications. It's heavier, more difficult to fit, and parts can be harder to find than the 12-bolt or 9-inch.
Before choosing:
* Consider your budget: A strong 12-bolt with upgrades will be significantly cheaper than a professionally built 9-inch or Dana 60.
* Your driving style: If you're mostly street driving, a slightly lower gear ratio might be preferred. For primarily drag racing, a higher ratio will be better.
* Professional installation: Proper installation of any rear end, including axle setup and pinion angle, is crucial for longevity and performance. Consider having a professional do the work, especially if you're not experienced with rear-end installations.
In short, a properly prepared 12-bolt GM rear end with upgraded axles and a suitable posi-traction unit is the most practical and cost-effective solution for a '69 Chevelle making 500+ horsepower. A Ford 9-inch is a viable alternative if you're comfortable with the extra fabrication involved. The Dana 60 is generally unnecessary unless you're competing in extreme performance events.
