Legendary 706 Heads - Chevrolet's Big Block Powerhouse Castings

Introducing the Legendary 706 Heads

In the world of high performance Chevrolet engines, one set of cylinder heads stands out from all the rest - the legendary 706 heads. First introduced in the 1960s as part of Chevrolet's Mark IV big-block engine package, the 706 heads earned a reputation for tremendous airflow and power capabilities.

Background on the Mark IV Big Block

The Mark IV engine was a significant redesign of Chevrolet's big block V8 in the mid-1960s. It featured a taller deck height, larger bore centers, and canted valves compared to previous big block designs. The heads utilized on the Mark IV, commonly called 706 heads, were developed with massive intake and exhaust ports enabling exceptional breathing capabilities for high horsepower output.

Several variants of the 706 cylinder heads exist, but the most legendary is the 454 variant which was used on the LS6 454 engine. This engine churned out a staggering 450 horsepower from the factory - a figure that was simply incredible for a production car at the time.

Benefits of 706 Heads Today

Thanks to their superior flow characteristics right out of the box, 706 heads quickly became a favorite for engine builders and racers. Even now, over 50 years later, the 706 head design still offers significant advantages over many options:

• Huge intake and exhaust ports feed high horsepower potential
• Raised intake ports improve line of sight to intake valves
• Compatibility with modern high lift cams and valvetrains
• Strong fully machined castings

These benefits make the 706 one of the best cast iron heads ever produced by Chevrolet for serious big block engine builds targeting high power outputs.

Finding 706 Heads for Your Chevrolet

With their legendary flow characteristics, it's no surprise 706 heads remain popular for Chevrolet engine builders even now. However, finding them available for sale can be difficult given their age and cast iron construction making intact cores hard to come by. Here are some tips on locating a set of 706 heads for your project:

Check Major Engine Builders Networks

Major Chevrolet engine builders will sometimes sell off select take-off cylinder heads when doing builds for customers. This can include 706 heads pulled from old core engines at times. Builder networks to check include places like:

• Wegner Motorsports
• CNC Motorsports
• Pat Musi Performance

Contact them to ask if any 706 castings happen to be available. These will cost more but likely need less work being from reputable builders.

Browse Online Marketplaces

Online marketplaces frequented by automotive enthusiasts and racers can turn up 706 head listings, often being sold off old project cars and garage finds. Marketplaces to browse include:

• RacingJunk Classifieds
• LS1Tech Forums
• ChevyTrucks Forum
• eBay Motors Parts & Accessories

Listings may not come up often but persistence could pay off finding that golden set of original 706 heads for your Chevrolet at a reasonable price.

Check Local Machine Shops

With the 706 being an older head design, some specimens have likely made their way to local machine shops over the decades. It’s worth giving some shops in your area a call to ask if they happen to have any laying around. The chances are hit or miss but you could get lucky.

Get the Most from 706 Heads

While the 706 head castings themselves provide exceptional airflow potential right from the factory, engine builders wanting to maximize their performance on a high horsepower build will still perform key upgrades when assembling them including:

• Back cut intake valves
• Replace press-in studs
• Upgrade valve springs and retainers
• Install bronze valve guides
• Port match intake/exhaust

With strategic upgrades combined with a stout lower end and a large aggressive camshaft profile, 706 heads can support incredible high-RPM horsepower numbers over 1,000 HP in extreme builds.

So for those chasing big power from their Chevrolet V8, the legendary 706 heads remain go-to castings even now thanks to their incredible airflow. With some searching and strategic upgrades, they can enable record-setting horsepower decades after their initial release.

FAQs

What is special about the 706 cylinder heads?

The 706 heads feature exceptionally large intake and exhaust ports that enable incredible airflow. This makes them capable of supporting very high horsepower numbers from large displacement, high performance Chevrolet big block engines.

What cars did the 706 heads originally come on?

The most famous application was the LS6 454 engine option available in the Chevy Chevelle and Corvette models producing 450 HP with 706 heads. Some variants also saw use on Mark IV big blocks powering trucks and other vehicles.

How much power can I make with 706 heads?

With a properly built lower end and supporting mods like a large camshaft, 706 heads can support over 1,000 horsepower in extreme builds while more streetable builds may still produce 600+ HP.

Will 706 heads bolt on my engine?

The 706 heads were designed specifically for the Mark IV big block Chevrolet engines originally, so they directly bolt on those variants. However, some modifications may be required to fit them on other Chevrolet V8s.

Where can I buy 706 cylinder heads?

Options include checking with major engine builders, browsing online marketplaces and forums, or contacting local machine shops. Availability is somewhat limited but they can still be found on occasion.