If you've been scouring swap meets or old forums looking for a set of mopar 915 heads, you probably already know they're basically the "unicorn" of the big block world. For anyone building a vintage 440 or a hot-rod 383, these heads represent a very specific era where Chrysler was really starting to figure out how to make serious power before the smog era choked everything out. They were only produced for one year—1967—and that's a big part of why they've reached legendary status among Mopar enthusiasts.
It's easy to get lost in the sea of part numbers when you're dealing with B and RB engines. You've got the 906s, the 452s, the 346s, and a dozen others, but the 915 stands out for one primary reason: it was the last high-performance big block head to feature a closed-chamber design. After 1967, everything went to an open-chamber style to help with emissions and lower compression, which left the 915 as the "holy grail" for guys who wanted to build a high-compression street monster without having to spring for expensive aftermarket aluminum heads.
Why the 1967 Casting is Such a Big Deal
Back in the mid-sixties, Mopar was in the middle of a horsepower war. The 440 was the new king on the block, and the engineers needed a cylinder head that could keep up. The 915 casting was the answer. What makes it so special isn't just that it's old; it's the geometry of the combustion chamber.
Because it's a closed-chamber design, it creates a much smaller volume—usually around 73cc to 78cc depending on how much they've been milled over the decades. Compare that to the later 906 or 452 heads, which often sit in the 88cc to 90cc range, and you can see why the 915 is a shortcut to free horsepower. By bolting a set of these onto a standard flat-top piston engine, you're instantly bumping your compression ratio. In the world of old-school iron, compression is king, and the 915 gives it to you in spades.
But it's not just about the squeeze. The 915 heads also featured the better intake port design that Mopar would continue to use for years. It's a bit of a bridge between the older, less efficient designs and the high-flow ports that made the 440 TNT and Magnum engines famous.
Closed Chamber vs. Open Chamber Design
If you're new to the big block Mopar world, you might wonder why everyone makes such a big deal about "closed chambers." Essentially, a closed-chamber head like the 915 has a flat area on the deck surface that hangs over the piston. When the piston comes up to Top Dead Center, it gets very close to that flat part of the head. This creates what engine builders call "quench."
Quench is a beautiful thing. It forces the air-fuel mixture into the center of the chamber with a lot of turbulence, which makes for a more efficient and faster burn. It also helps prevent detonation (that annoying pinging sound) because it keeps the mixture moving and cools the edges of the chamber. When Mopar switched to the open-chamber 906 heads in 1968, they lost that quench area. While the 906s flowed great, you needed a dome-top piston to get the compression back up, and those are heavier and more expensive. With mopar 915 heads, you get the best of both worlds: good flow and high compression with simple, lightweight pistons.
The HP Stamp and Valve Size Confusion
Here is where things get a little tricky. If you're hunting for these at a swap meet, you need to look at more than just the casting number. Not all 915 heads were created equal. Mopar put these on both the high-performance 440s and the more pedestrian 383 two-barrel engines.
The high-performance version, usually found on the 440 Magnum or TNT engines, came with a 2.08-inch intake valve and a 1.74-inch exhaust valve. These are the ones everyone wants. The 383 version, however, often came with a smaller 1.60-inch exhaust valve. The good news is that the castings themselves are identical. If you find a set of small-valve 915s for a good price, any decent machine shop can punch them out to accept the larger 2.08/1.74 combo.
A lot of guys look for the "HP" stamp on the end of the head, but don't panic if it's not there. Over the years, many heads have been surfaced, which can wipe out those stamps. The best way to know what you've got is to flip them over and put a caliper on the valves. Even if they are the small-valve version, they're still worth grabbing because that closed chamber is where the real magic happens.
Prepping Your Heads for Modern Pump Gas
Let's be real for a second—iron heads from 1967 weren't exactly designed for the ethanol-blended, lower-octane fuel we get at the local gas station today. If you're going to run mopar 915 heads on a modern street build, you've got to do a little bit of prep work to make sure they last.
The biggest issue is the exhaust seats. Back in '67, gasoline had lead in it, which acted as a lubricant for the valves and seats. Modern unleaded gas will eat through those soft iron exhaust seats if you're doing a lot of highway cruising or heavy towing. When you take your 915s to the machine shop, it is almost always a good idea to have hardened exhaust seat inserts installed. It costs a bit more, but it saves you from having a valve recede into the head three thousand miles down the road.
While you're at it, you should probably look into a mild port job. The 915s flow well for their time, but they have some "meat" in the ports that can be cleaned up. You don't need to go crazy with a full race port, but cleaning up the casting flash and smoothing out the "bowl" area right under the valves can wake these heads up significantly. A set of well-prepped 915s can easily support 450 to 500 horsepower on a healthy 440.
Are They Still Worth the Hunt Today?
In a world where you can click a button and have a set of brand-new aluminum heads delivered to your door, you might wonder if chasing down a 55-year-old set of iron heads is worth the headache. To me, it depends on what you're building.
If you're building a period-correct muscle car, there is nothing cooler than a set of 915s. They look right, they belong there, and they have a certain "cool factor" that aftermarket parts just can't match. Plus, there's the sleeper aspect. Opening your hood and showing off a factory-looking iron-head engine that runs like a scalded dog is a great feeling.
However, keep in mind that they are heavy. An iron head weighs about twice as much as an aluminum one, and after you pay for the initial purchase, the pressure testing, the cleaning, the hardened seats, the new valves, and the porting, you might actually spend more than you would on a set of budget aluminum heads.
But for the Mopar purist, that doesn't matter. The mopar 915 heads are a piece of history. They represent the peak of the iron-head era before the "dark ages" of the 1970s set in. They provide a level of torque and "grunt" that's hard to replicate, and they just have a soul that modern castings lack.
Final Thoughts on the Hunt
If you do go looking for a set, bring a flashlight and a straightedge. Check for cracks between the valve seats, which is a common failure point if the engine was ever overheated. Also, look at the spark plug threads; these old heads can get pretty beat up after decades of spark plug changes.
Finding a set of mopar 915 heads is like finding a classic vinyl record in a thrift store—it takes some digging, and they might need a little cleaning up, but once you get them on the "player," they produce a sound and a feeling that you just can't get anywhere else. Whether you're building a Charger, a Road Runner, or just a fun street truck, these heads are a legendary way to put some vintage Mopar muscle back on the road.