If you've been scouring swap meets or local classifieds for engine parts, you've probably come across a set of pontiac 46 heads sitting in the grease and dirt. At first glance, they don't look like much—just another heavy piece of cast iron from the 1970s. But in the world of Pontiac enthusiasts, these heads spark a fair bit of debate. Some guys will tell you to leave them right where you found them, while others swear they're the "secret sauce" for a budget-friendly street build that runs on cheap pump gas.
The truth, as it usually does, lies somewhere in the middle. These aren't the high-compression "holy grail" heads from the late 60s, but they aren't boat anchors either. If you're trying to figure out if they belong on your 350, 400, or even a 455 build, you have to look at the specifics of what they are and what they aren't.
The Identity Crisis: What Exactly Are They?
One of the confusing things about the "46" casting is that Pontiac actually used this number for a couple of different applications in the early 1970s. Generally, when people talk about pontiac 46 heads, they're referring to the castings found on 1973 and 1974 engines.
In 1973, you'd find them on the 350 cubic inch V8. These typically had smaller combustion chambers—somewhere around 88cc to 92cc. Fast forward to 1974, and you'll find the "46" casting on the 400 cubic inch engines. These 400-series heads often had larger chambers, sometimes pushing 96cc or even higher depending on the specific casting run.
Why does this matter? Because in the Pontiac world, everything revolves around your compression ratio. By the early 70s, the "Smog Era" was in full swing. Compression ratios were dropping faster than a lead weight so that cars could run on the new low-lead and unleaded fuels. The 46 heads were a big part of that shift.
The "Smog Head" Stigma
For a long time, the 46 heads were ignored. If you weren't running a set of #12, #13, or #62 heads with their tiny 72cc chambers, you weren't building a "real" engine. But let's be real for a second: we don't live in 1969 anymore. The gas we get at the local station today is, frankly, pretty mediocre compared to the high-octane leaded stuff our dads used to buy.
This is where the pontiac 46 heads actually start to make sense. If you put a high-compression head on a modern 400 build, you might end up with a 10.5:1 or 11:1 compression ratio. That sounds cool at the car show, but it's a nightmare to drive on the street. You'll be dealing with pining, detonation, and the constant need for expensive octane boosters.
The 46 heads, with their larger chambers, naturally keep the compression in a "sweet spot" for street use—usually around 8.5:1 or 9:1 depending on your pistons. It's a setup that lets you cruise all day, run the A/C, and fill up at any gas station without worrying about melting a piston.
Valves and Flow: The Technical Bit
If you look at the underside of a set of pontiac 46 heads, you'll notice the valves are a bit smaller than the legendary GTO heads. Most of these came with 1.96-inch intake valves and 1.66-inch exhaust valves.
Now, if you're building a race car, those numbers might make you cringe. You generally want those 2.11/1.77 valves for maximum airflow at high RPMs. However, for a street-driven 350 or 400, the smaller valves aren't necessarily a dealbreaker. They actually help keep the intake velocity high at lower speeds. This means the car feels snappy and responsive when you're pulling away from a stoplight, which is where most of us spend 90% of our driving time anyway.
The port design is classic Pontiac. It's not revolutionary, but it's efficient. With a little bit of "home porting"—just cleaning up the casting flash and smoothing out the bowls—you can make these heads flow surprisingly well. You don't need to be a professional engine builder to make a noticeable difference with a die grinder and some patience.
The Weak Link: Press-in Studs
Every rose has its thorn, and for the pontiac 46 heads, it's the rocker arm studs. Most of these heads came from the factory with press-in studs.
Here's the problem: if you decide to get frisky and install a camshaft with a lot of lift, or if you use heavy-duty valve springs, those press-in studs are going to want to pull right out of the head. There's nothing quite like the sound of a rocker arm coming loose at 4,000 RPM to ruin your weekend.
If you're serious about using 46 heads for anything other than a stone-stock restoration, you have to budget for a trip to the machine shop. You'll want them to pull those press-in studs, tap the holes, and install screw-in studs. It's a standard procedure, and it's not terribly expensive, but it's the difference between a reliable engine and a ticking time bomb. While the heads are there, you might as well have them converted to take standard 7/16" studs so you have more options for rocker arms.
Comparison: 46 vs. 4X vs. 6X
If you're talking about mid-70s Pontiac heads, the 46 is often compared to the 4X and the 6X. The 6X is widely considered the "king" of the smog heads because it's easy to find and has a great chamber design.
But don't count the 46 out. In many ways, the 46 is very similar to the early 4X heads. If you find a set of 46s for a hundred bucks and the guy wants three hundred for a set of 6Xs, take the 46s. The performance difference on a street engine is going to be negligible once you factor in a good valve job and maybe a slightly thinner head gasket to bump the compression just a hair.
Who Should Use These Heads?
So, who are the pontiac 46 heads actually for?
- The Budget Builder: If you're trying to get a Firebird or a LeMans back on the road without taking out a second mortgage, these heads are a fantastic choice. They are often dirt cheap because everyone is chasing the high-performance castings.
- The 350 Pontiac Owner: The 350 is a great little engine that gets a lot of hate. Because it has a smaller bore, putting huge 2.11 valves on it can actually cause shrouding issues. The 1.96 valves on the 46 heads are a perfect match for the 350's dimensions.
- The Daily Driver: If you want an engine that starts every time, idles smoothly, and doesn't overheat in traffic, the lower compression of the 46 heads is your friend.
Final Thoughts on the 46 Casting
At the end of the day, building a Pontiac is about the "total package." You can't just throw a random set of heads on a block and expect magic. But if you've got a set of pontiac 46 heads, you have a solid foundation.
Don't let the "smog era" label scare you off. With a set of screw-in studs, a decent three-angle valve job, and a camshaft that matches your compression ratio, these heads can help produce a surprisingly torquey, reliable engine. They might not be the stars of the drag strip, but for a car that's meant to be driven and enjoyed on the open road, they're a lot better than people give them credit for.
Next time you see a pair of them sitting in a garage corner, don't just walk by. If the price is right and the iron is crack-free, they might be exactly what your project needs to finally get back on the pavement.