If you're looking to squeeze more power out of your 4G63, the evo 8 cylinder head is basically the heart of the whole operation. It's one of those pieces of engineering that enthusiasts have spent decades obsessing over, and for good reason. While the bottom end of the engine gets all the credit for being "bulletproof," the head is where the actual magic—and the airflow—happens. If the head isn't right, it doesn't matter how much boost you throw at it; you're just going to be hitting a wall.
What Makes the Evo 8 Head Special?
The Evo 8 head is a bit of a legend in the tuning world. Unlike the later Evo 9, which introduced MIVEC (Mitsubishi's version of variable valve timing), the evo 8 cylinder head is a "dumb" head in the best way possible. It's simple, robust, and very predictable. For guys who are building dedicated drag cars or high-horsepower street builds, sometimes that simplicity is exactly what you want. There are fewer moving parts to fail and fewer sensors to go haywire when you're pushing 30 or 40 pounds of boost.
The casting itself is pretty impressive for a factory part. Mitsubishi designed it with a dual-overhead-cam (DOHC) setup that flows remarkably well right out of the box. However, it's not perfect. If you look at a bone-stock casting, you'll see some rough edges, especially around the valve seats and the intake runners. These little imperfections are exactly where you find those extra hidden ponies when you start talking about porting and polishing.
Dealing With High Mileage and Heat
Let's be real: most Evo 8s have lived a hard life. They weren't bought to be driven to church on Sundays. Because of that, a used evo 8 cylinder head usually needs some love before it's ready for a big-power build. One of the most common issues you'll run into is heat-related warping. The 4G63 runs hot, and if a previous owner had a cooling issue or pushed the car too hard on a bad tune, the head might not be perfectly flat anymore.
Whenever you take the head off, the first thing you should do is get it pressure tested and checked for straightness. If it's warped, a machine shop can "deck" it—which just means shaving off a tiny layer of aluminum to make it perfectly flat again. Just don't go too crazy; if you shave too much off, you start messing with the compression ratio and the timing belt tension. It's a delicate balance.
Cracked Castings and Other Nightmares
Another thing to watch out for is cracking, especially around the spark plug holes or between the valves. It's not super common on stock setups, but once you start running massive turbos and E85, the cylinder pressures go through the roof. If you find a crack, it's often cheaper to find a new core than to try and weld and re-machine the old one. It's just one of those "it is what it is" parts of car life.
The Best Upgrades for Your Head
If you've got the head off the car, you'd be crazy not to upgrade the internals. The factory valvetrain is fine for stock boost, but if you're planning on revving past 7,500 RPM, you need to make some changes.
Cams: The Biggest Bang for Your Buck
Upgrading the camshafts is probably the single best thing you can do for an evo 8 cylinder head. Stock cams are designed for a balance of emissions, fuel economy, and a smooth idle. But we aren't here for fuel economy, right? Swapping in a set of GSC S2s or Kelford 272s completely changes the personality of the car. It makes the engine "breathe" better at high RPMs, which is where the 4G63 loves to live. Just be prepared for that signature lopey idle that makes it sound like a small-block V8.
Springs and Retainers
If you're doing cams, you have to do valve springs. The stock springs are pretty weak, and "valve float" is a real thing. Valve float happens when the spring isn't strong enough to close the valve fast enough at high RPMs, and the piston almost wins a game of tag with the valve. That's a game you don't want to play. Titanium retainers are also a nice touch because they're lighter, which reduces the overall mass the spring has to move.
Porting: Is it Worth It?
This is where things get expensive. A professional port and polish job on an evo 8 cylinder head can cost as much as the car did ten years ago. For a street car, a "pocket port"—where they just clean up the area around the valve seats—is usually plenty. If you're building a 800-horsepower monster, then yeah, full CNC porting is the way to go. It smooths out the airflow and increases the volume of air the head can move.
Evo 8 vs. Evo 9 Heads
The debate between the 8 and 9 heads is never-ending. The Evo 9 head has MIVEC, which helps with spool-up and low-end torque. But the evo 8 cylinder head is often preferred by the "old school" crowd. Why? Because it's easier to work on and easier to time. You don't have to deal with the MIVEC oil feed lines or the variable cam gear.
Plus, there's a certain mechanical simplicity to the 8. If you're swapping a 4G63 into another chassis, like a 2G DSM or even an old Colt, the Evo 8 head is a much easier fit. You just bolt it on, set your mechanical timing, and you're good to go.
Maintenance Tips for Longevity
Don't ignore the small stuff. The hydraulic lifters in the evo 8 cylinder head are notorious for "ticking." If your Evo sounds like a sewing machine when you start it up in the morning, your lifters are probably gummed up or worn out. You can try cleaning them, but honestly, just buying a set of "revised" lifters with the larger oil holes is the better move. It'll quiet down the valvetrain and ensure everything is getting the lubrication it needs.
Also, please, for the love of all things fast, use a high-quality head gasket. The OEM Mitsubishi multi-layer steel (MLS) gasket is actually fantastic, but if you're going for big power, a lot of guys swear by Cometic or Athena. Pair that with some ARP head studs, and you won't have to worry about the head lifting under boost.
Finding a Machine Shop You Trust
Not all machine shops are created equal. You want a shop that has experience with Japanese imports, specifically the 4G63. The tolerances on an evo 8 cylinder head are pretty tight, and if someone treats it like an old Chevy tractor engine, they're going to mess it up.
Ask them about their cleaning process. You want it ultra-sonic cleaned or hot-tanked so every oil passage is spotless. There's nothing worse than finishing a build and having a tiny piece of leftover grit ruin your brand-new cams.
Final Thoughts on the Build
At the end of the day, the evo 8 cylinder head is a piece of kit that rewards you for doing things right. You don't necessarily have to spend $5,000 to make it great. A good set of cams, some stiff springs, and a fresh surface job will get you incredibly far.
Whether you're just trying to freshen up a high-mileage daily driver or you're aiming for a 9-second quarter-mile, treat the head with respect. It's the lungs of your engine, and if it can't breathe, you aren't going anywhere fast. Take your time, do the research, and don't cheap out on the parts that matter. Your turbo will thank you later when it finally has a clear path to shove all that air into the combustion chamber.