If you're looking to squeeze a bit more juice out of your VQ35DE, starting with the g35 plenum is usually the first thing people talk about. It's one of those modifications that has become almost legendary in the Infiniti community, and for good reason. If you've ever popped the hood of a G35, that big, silver, breadbox-looking thing sitting right on top of the engine is the upper intake plenum. While it looks cool enough from the factory, it's actually hiding one of the biggest bottlenecks in the entire VQ engine design.
Most guys who buy these cars eventually realize that the front two cylinders aren't getting the same amount of love as the back ones. Because of the way the factory plenum slopes down toward the front—mostly to clear the hood—it restricts airflow to cylinders one and two. This creates a bit of an imbalance and leaves quite a bit of power on the table. Fixing this is basically the "G35 101" step for any enthusiast.
Why the Stock Plenum Is a Problem
The VQ35DE is a fantastic engine, but Infiniti had to make some compromises when they designed the engine bay. The hood line on the G35 is relatively low, which meant the intake plenum had to be "pancaked" at the front. When air rushes into that intake, it hits a wall, or rather, it can't move fast enough into the front ports because the ceiling is too low.
This isn't just about losing a few horsepower; it's about how the engine breathes. When some cylinders are getting less air than others, your air-fuel ratios can get a bit wonky across the different cylinders. By addressing the g35 plenum issues, you aren't just adding power; you're actually helping the engine run more efficiently and smoothly across the entire RPM range.
The Most Common Fix: Plenum Spacers
If you aren't looking to spend a fortune, a plenum spacer is the go-to move. It's exactly what it sounds like—a gasket-like spacer that sits between the upper and lower halves of the plenum to lift the top lid. This creates more "volume" inside the plenum, especially at the front where it's needed most.
The 5/16" spacer is generally considered the sweet spot. It's thick enough to provide a massive improvement in airflow but thin enough that you can still close your hood without it rubbing against the underside. You'll see 1/2" spacers out there too, which offer even more volume, but those often require you to mess with the strut tower bar or remove the engine cover entirely.
The beauty of a spacer is that it's a "bolt-on" in the truest sense. You don't need a degree in mechanical engineering to install one. You just take out about eighteen bolts, pop the lid, drop the spacer in, and bolt it back down. Just be careful with the torque. Those plenum bolts are notorious for stripping if you get a little too aggressive with the wrench.
Full Aftermarket Plenums
If you want to go beyond just a spacer, there are full aftermarket versions of the g35 plenum that replace the entire top half. Companies like Motordyne, Crawford, and Kinetix have been making these for years. Some of them are made of cast aluminum, while others use high-tech composites or even plastic to help keep intake temperatures down.
A full plenum replacement usually offers a more optimized internal shape than a factory unit with a spacer. For example, some designs look like a giant bulbous dome. They look a bit strange, but they allow air to tumble into the intake runners with almost zero resistance. If you're planning on going with a forced induction setup later—like a twin-turbo or a supercharger—investing in a high-quality aftermarket plenum early on is a smart move.
The RevUp Engine and the MREV2 Trick
If you own a 2005 to 2007 G35 with a manual transmission, you have what's known as the "RevUp" version of the VQ35DE. Ironically, even though this engine was designed for more top-end power, its lower plenum design actually killed off a lot of the mid-range torque.
The "MREV2" is a popular mod where owners take the lower plenum from a non-RevUp engine, CNC-machine it for better flow, and swap it into their RevUp engine. When you combine this modified lower plenum with a g35 plenum spacer on the top, the gains are actually pretty incredible. It's one of the few mods where you can actually feel the difference in the seat of your pants the first time you pull out of your driveway. You get that low-end grunt back, and the car feels way less sluggish in traffic.
Thermal Gaskets and Heat Soak
While we're talking about the intake system, it's worth mentioning heat soak. Aluminum is great for a lot of things, but it's also really good at soaking up heat from the engine block. After a long drive, your g35 plenum will be hot enough to fry an egg on. Hot air is less dense, which means less power.
Many people choose to install "iso-thermal" gaskets along with their plenum mods. These gaskets are made of materials that don't conduct heat as well as metal does. By isolating the plenum from the hot lower intake manifold, you can keep your intake charge much cooler. It might only give you a few extra horses, but it helps keep your power consistent even on a hot summer day.
What to Expect After the Install
Don't expect your G35 to suddenly turn into a GT-R just from a plenum swap. However, you should expect a much more linear power band. Before the mod, many G35s feel like they "run out of breath" as they approach the redline. With a better g35 plenum setup, the car keeps pulling much harder through the upper RPMs.
You'll also notice a change in the engine note. The VQ is already famous for its "trumpet" exhaust sound, but freeing up the intake side adds a bit of a deeper, throatier growl from the front of the car when you're wide-open throttle. It sounds more purposeful.
Supporting Mods and Tuning
Can you run a plenum spacer or an aftermarket plenum on a bone-stock car? Yeah, absolutely. The factory ECU is smart enough to adjust for the extra air to some extent. But honestly, to get the full benefit, you really should look into a tune (like UPREV or EcuTek).
When you change the way air enters the engine, you're changing the "volumetric efficiency." A tuner can go in and optimize the fuel maps and ignition timing to take full advantage of that extra air. Plus, if you've already added a cold air intake and a cat-back exhaust, the g35 plenum is the piece that ties it all together. Without it, your intake and exhaust are working overtime to move air that's just getting stuck at the plenum anyway.
Is It Worth the Effort?
If you enjoy working on your own car, this is one of the most rewarding weekend projects you can do. It's relatively cheap—especially if you go the spacer route—and the results are backed up by years of dyno data in the community. It fixes a genuine design flaw and makes the car feel more like it should have from the factory.
Just remember to take your time, keep track of those tiny bolts, and maybe replace your spark plugs while you're in there, since you'll have half the engine apart anyway. The g35 plenum might just be a big hunk of metal, but it's the heart of how your engine breathes, and giving it some breathing room is the best favor you can do for your G.