Best G35 Plenum Spacers: Are the Gains Worth It?

We love upgrades that don’t cost much and actually make our cars drive better. If you’re like us and you drive an Infiniti G35, you’ll love the difference a plenum spacer will make to the way your car feels.

Plenum spacers are a great starter mod. If you’re just getting into modifying your Infiniti G35 and want something that works and won’t break your bank, look any further.

The main reason why we recommend installing a plenum spacer is that the VQ35DE engine has a flaw in its plenum design. It cuts off a small amount of air to the intake runners which restricts airflow.

Installing a plenum spacer is the best way to solve this issue and unlock that lost airflow. Doing this will result in a freer throttle response and slightly improved fuel economy. The latter heavily depends on your driving style though.

In this guide, we list the best plenum spacers for G35s and explain how they work. At the end, we’ll show you which one to buy and why.

How and Why Plenum Spacers Work

The stock intake plenum on your VQ35DE engine is notorious for cutting off airflow to the front two intake runners. This happens because the inside top section of the stock plenum is a bit too close to the lower plenum intake runners.

Because of this design flaw, the clearance between the first two inlets and the plenum cover is only 1/8th of an inch! This airflow restriction reduces engine breathing and causes a drop in power output.

Even though there are many solutions to this problem, installing a plenum spacer is by far, the cheapest and easiest way. These spacers are gasket-like metal structures that fit right between the upper and lower part of your plenum.

Installing a plenum spacer increases the air volume capacity in your plenum chamber. By doing this, the volume of air going into the engine increases, causing the airflow to be evenly distributed among all cylinders. This results in a small bump in power.

Reduced intake temperature is an added benefit of increasing the flow of dense air into your engine. The additional cooling effect helps to keep the power delivery intact even under extreme levels of heat. However, if you live in a place where its too hot, this will only help to keep the engine temperature slightly low.

G35 Plenum Spacer HP Gain: Is It Worth It?

There are many ways to upgrade your stock intake plenum. However, plenum spacers are the most popular choice among G35 owners thanks to their simplicity.

Whether G35 plenum spacer gains are worth it or not is a hotly debated topic. Enthusiasts who have installed one of these on their VQ35DE engines have seen mixed results.

If your G35 has the non-RevUp engine, you’ll definitely benefit from this upgrade. If not, the increased power output won’t be very noticeable unless you also install exhaust upgrades.

Truth be told, with just the spacer alone you won’t get noticeable performance gains but it’s a good start. Pair it with a cold air intake and exhaust modifications like y-pipes, headers or test pipes and you’ll definitely see gains close to 15HP.

Considering how much plenum spacers cost, there’s no denying that they’re worth every dime. More advantages of plenum spacers include better sound and smoother throttle response.

Plenum Spacer Sizing

Selecting the right size when purchasing a plenum spacer is very important as it can impact your power output. Thicker spacers allow your plenum chamber to hold a higher volume of air. More air means more power.

However, your size selection also depends on whether or not you have a strut bar (also known as a strut brace). If you do, sizing up too much on the spacer can lead to clearance issues.

G35 plenum spacer and strut brace clearance

Typically, larger spacers are ideal if you have a G35 supercharger kit or turbo on board. Plenum spacer size selection also depends on which RPM range you want that extra power in.

Larger spacers deliver power in a higher rev range, for example:

  • ½” — 5500 to 6000 RPM
  • ⅝” — 4500 to 5500 RPM
  • ⁵⁄₁₆” — 3500 to 4500 RPM (recommended for daily driving)

The Best Plenum Spacers for G35s

All plenum spacers are mechanically similar and more or less do the same thing. However, the most notable differences between the various Infiniti G35 plenum spacers available include size and material.

Aluminum spacers are more durable and last longer while those constructed using thermal polymer tend to degrade faster but do a better job at managing heat.

You can choose the spacer size based on your power output goal and available space in the engine bay. We recommend going with ⁵⁄₁₆” spacers as they’re the safest option out there.

To get the most optimal results, get your engine tuned after installing a plenum spacer. Anyway, let’s take a closer look at your options!


Skunk2 Plenum Spacer for an Infiniti G35

Manufacturer: Skunk2
Part Number: 307-07-0400
Installation: Minor Fabrication Needed
Construction: Thermal Polymer
Thickness: ⅝”
Weight: 2.2 lbs
Buy On: Amazon | Enjuku Racing

When it comes to size selection, if you feel that ⁵⁄₁₆” is too conservative while 1⁄2” is a bit much, the ⅝” Skunk2 spacer is perfect for you. The size is just right and you’ll have the best of both worlds.

From a budget point of view, this is the second least expensive plenum spacer on this list. However, with prices so low, there’s no reason to cheap out on this upgrade.

Unlike the Motordyne and AAM Competition plenum spacers, this one is constructed using thermo-polymer composite which does a great job at insulating heat.

The only downsides to the Skunk2 plenum spacer are the lack of instructions and less than perfect installation hardware. The supplied washers are too small for the bolts, but it’s nothing that a little bit of fabrication with a file or Dremel can’t solve.

Blox Racing

Blox Racing's G35 Plenum Spacer

Manufacturer: Blox Racing
Part Number: BXIM-40201
Installation: Bolt-On
Construction: Thermal Polymer
Thickness: ⁵⁄₁₆”
Weight: 5 lbs
Buy On: Amazon

Plenum Spacers have a simple function and from a manufacturing standpoint, there isn’t really a way to mess them up. Considering that, there’s nothing wrong with buying cheap plenum spacers.

The Blox Racing plenum spacer is one of the cheapest you’ll find and it gets mixed reviews. Some enthusiasts claim that this spacer tends to crack during installation. However, in our experience, we find that this happens because of over-torqued bolts.

If installed correctly with a torque wrench, this plenum spacer holds up just fine and does exactly what its supposed to. The packaging isn’t as great as what you’d get with Motordyne or AAM Competition and like the Skunk2 spacer, it’s missing the instruction manual. But at a price so hard to beat, these things are easy to overlook.


The iconic Motordyne plenum spacer for the Infiniti G35

Manufacturer: Motordyne
Part Number: MD-516″B
Installation: Bolt-On
Construction: 6061 Aluminium
Thickness: ⁵⁄₁₆”
Weight: 3 lbs
Buy On: Amazon

Motordyne makes the most widely used G35 intake plenum spacers on the market. The installation is quick, it fits perfectly and leaves enough room for a strut brace if needed.

This plenum spacer can be purchased in different sizes. If you have a strut brace, we recommend buying it in size ⁵⁄₁₆” for the most ideal clearance. If you don’t have one, we recommend going for the larger ½” spacer for more airflow and power.

Once installed, your engine will sound a lot deeper and your throttle will feel a lot more responsive. Pairing the Motordyne plenum spacer with high flow catalytic converters and cat-back exhausts can net you close to 15 HP.

The packaging of this plenum spacer is extremely clean, with all components labeled and packed individually. Installation instructions are well illustrated and easy to understand.

This is the best plenum spacer for G35 owners who are happy to pay for something tried, tested and proven.

AAM Competition

AAM's Infiniti G35 Plenum Spacer

Manufacturer: AAM Competition
Part Number: AAM35I-APS
Installation: Bolt-On
Construction: 6061 Aluminium
Thickness: ½”
Weight: 3 lbs
Buy On: Enjuku Racing

When it comes to build quality, the AAM Competition plenum spacer is just as good as what Motordyne makes. They’re both constructed using aluminum alloy and they provide similar power gains.

What makes this plenum spacer unique is its angled design. It is thicker towards the front and gets thinner as it tapers towards the rear cylinders.

This design allows the engine cover to sit flush with the hood, leaving enough room for an aftermarket strut brace. Instead of maximizing the airflow for all 6 cylinders at once, it does so only for those that need it the most (front two).

Angled spacers tend to crack if not installed correctly. We recommend using a torque wrench at 8Nm when fitting this AAM Competition angled plenum spacer.

Our Favourite Infiniti G35 Plenum Spacer

Plenum modifications are very underrated. If you’re just getting into modifying your Infiniti G35, they are a great place to start.

Out of all the plenum upgrades out there, spacers are the cheapest and most easily accessible of them all.

In case you’re still unsure and don’t know which plenum spacer to buy, let’s make it simple; get the Motordyne!

The Motordyne plenum spacer ticks all the right boxes. It bolts right on, the installation instructions are easy to understand, all of the components bolt on just as they should, and not a single component feels flimsy.

If you feel like stepping it up a notch and want a thicker ½” spacer, Motordyne makes these in larger sizes as well.


What’s your take on plenum spacers? Do you feel that a G35 plenum spacer is worth it?

Let us know by leaving a comment below!

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