If you've spent any time digging through a pile of small block parts at a swap meet, you've definitely run into 624 chevy heads. They are everywhere. You'll see them sitting on garage floors, listed for fifty bucks on Facebook Marketplace, or still bolted to a crusty 350 engine in a 1978 C10. These things were the workhorse of the mid-to-late 1970s and early 1980s, but they carry a bit of a reputation in the gearhead community—and not always a good one.
Before you decide to dump money into a set or toss them in the scrap bin, it's worth taking a second to look at what they actually are and where they fit into a build. They aren't the "holy grail" double-hump heads from the 60s, but they aren't necessarily paperweights either, depending on what you're trying to achieve.
What Exactly Are the 624 Castings?
The full casting number is usually 333624, and they were one of the most common cylinder heads produced for the 350 Small Block Chevy during the "smog era." If you have a Chevy truck, Camaro, or Nova from the mid-70s, there is a very high probability it came from the factory with these heads.
In terms of specs, they are a 76cc combustion chamber head. Back in the day, Chevy was trying to lower compression to deal with the new emissions standards and the lower octane unleaded fuel that was hitting the pumps. Because of that big 76cc chamber, you're usually looking at a pretty low compression ratio—often somewhere in the 8.2:1 to 8.5:1 range when paired with stock dished pistons.
Most of these came with 1.94-inch intake valves and 1.50-inch exhaust valves. While that's a decent size for a street engine, the port design wasn't exactly meant for high-RPM screaming. They were designed for low-end torque and reliability in heavy cruisers and work trucks.
The "Lightweight" Problem
If you talk to any old-school machinist about 624 chevy heads, the first thing they're going to mention is that they're "thin-wall" castings. This was a big shift for GM. To save weight and improve fuel economy (even by just a tiny bit), they started casting these heads with less iron in certain areas.
While a lighter engine sounds like a win, it came with a major drawback: these heads are notorious for cracking. Because there's less material to soak up heat and handle stress, they tend to develop cracks, especially in the exhaust valve seats or between the center cylinders.
If you're pulling a set off an engine that's overheated even once, you really need to get them pressure-tested or magnafluxed before you spend a dime on them. There's nothing worse than paying for a 3-angle valve job only to find out the head is leaking coolant into the combustion chamber.
How They Perform on the Street
Let's be real—nobody is building a 500-horsepower drag car with stock 624 chevy heads. But for a "budget" street build or a daily driver truck, they actually do okay. They have a decent intake runner volume for what they are, and if you aren't trying to spin the engine past 5,000 RPM, you might not even notice their limitations.
The biggest hurdle is that 76cc chamber. If you're looking for "snap" and throttle response, low compression is your enemy. If you're rebuilding a 350 and you want some real power, you'll usually want a head with a 64cc chamber to bump that compression up into the 9.5:1 range. Using the 624s means you're leaving a lot of "free" horsepower on the table simply because the air-fuel mixture isn't being squeezed hard enough.
Can You Port Them?
You can port anything, but should you port these? Most guys would tell you no. Because the castings are thin, you run a very real risk of hitting a water jacket if you get a little too aggressive with the die grinder. A simple "gasket match" or a light cleanup in the bowls shouldn't hurt, but if you're planning on a full professional port job, you're better off starting with a beefier casting like the old 416s or even the 041s.
The 624 vs. The 882
In the world of smog-era heads, the 624 is often compared to the 333882 casting. They are very similar in terms of performance—both have 76cc chambers and similar flow numbers. However, the 882 is generally considered a "heavy" casting compared to the 624.
If you have a choice between a set of 882s and a set of 624s at a swap meet, most builders will tell you to grab the 882s. They are simply more durable and less prone to warping or cracking under pressure. That said, both will give you roughly the same power output on a stock or mild 350.
Is It Worth Rebuilding Them?
This is the big question. Let's say you have a set of 624 chevy heads and they need a full rebuild—new valves, guides, springs, and a resurface. By the time a machine shop charges you for all that labor and the parts, you could easily be looking at $400 to $600.
In today's market, that's a tough pill to swallow. Why? Because budget aluminum heads have changed the game. For just a few hundred dollars more than a full rebuild on old iron heads, you can buy a brand-new set of aluminum heads that flow 40% better, have smaller combustion chambers for more power, and shave 40 pounds off the front of your car.
However, there are a few scenarios where keeping the 624s makes sense: * The "Period Correct" Build: If you're doing a restoration on a late-70s vehicle and want it to look 100% factory. * The Ultra-Low Budget: If the heads are in good shape, don't need a rebuild, and just need a quick cleaning and some new valve seals, then go ahead and run 'em. * Truck Applications: If you're just building a stump-puller truck engine where you don't care about high-RPM flow, these heads will do the job just fine.
Common Upgrades for 624 Heads
If you do decide to run 624 chevy heads, there are a couple of small things you can do to make them better.
First, consider using a thin "shim" style head gasket. Since these have large 76cc chambers, using a standard .040-inch thick composite gasket is going to kill your compression even further. A .015-inch rubber-coated steel shim gasket can help bring the quench distance down and give you a tiny boost in compression, which helps with efficiency.
Second, check the valve springs. Most factory 624s came with very weak springs designed for low-lift, lazy flat-tappet cams. If you're installing a modern "RV" cam or anything with a bit more lift, those old springs will likely go into coil bind or float the valves early. A simple set of Z28-style springs is a cheap upgrade that adds some insurance.
The Bottom Line
At the end of the day, 624 chevy heads are what they are: a mass-produced, middle-of-the-road cylinder head from an era when performance wasn't a priority for Detroit. They helped millions of Chevys get down the road, and they're still doing it today.
They aren't "junk" in the sense that they won't work, but they are limited. If your goal is a reliable cruiser or a stone-stock truck, they're perfectly adequate. But if you're looking to win races or hear that crisp, high-compression idle, you'll probably find yourself looking for something a bit more substantial pretty quickly.
Just remember: always check for cracks! It's the Achilles' heel of the 624, and no amount of "budget" savings is worth the headache of a cracked head once the engine is already back together.