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 without breaking the bank, this is a great way to do it.
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 some G35 exhaust modifications like G35 y-pipes, G35 headers or G35 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.
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!
Part Number: 307-07-0400
Installation: Minor Fabrication Needed
Construction: Thermal Polymer
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.
Manufacturer: Blox Racing
Part Number: BXIM-40201
Construction: Thermal Polymer
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 very precise inch pound 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.
Part Number: MD-516″B
Construction: 6061 Aluminium
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.
Manufacturer: AAM Competition
Part Number: AAM35I-APS
Construction: 6061 Aluminium
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 upgrading 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? Stuck using octane booster with pump gas to avoid pinging and thinking about fixing the problem for good?
Let us know by leaving a comment below!
I went the cheap route with a Blox ⁵/¹⁶ spacer. Picked one up for $82! It came with a sticker, instructions and all new hardware. It was a pain at first keeping the 6 little metal spacers lined up that go in the middle of the plenum. They used to be plastic but are aluminum alloy, or at least the kit I had came with them. They kept sliding out of place whenever I’d get the plenum put together. You have to pay close attention that these spacers line up. If one gets loose it’ll get sucked into the intake manifold and goodbye valves. You can look down the holes where the 6 center bolts go and easily be able to see if they are lined up where they need to be.
I solved my problem by applying a bit of RTV to these spacer and placed them accordingly on the gasket that lays upon the runners. This helped from keeping them from sliding out of position whenever you connect the upper and lower plenum. I also kept the stock OEM plenum gasket and used RTV to seal them together, then more RTV to seal the plenum spacer onto the plenum. You won’t need much just a thin bead that goes all the way around the plenum, much as you would use RTV for the oil pan, etc.
While you have everything apart, it’s a good idea to clean the inside of the plenum, runners, as well as the upper and lower intake manifolds. Mine surprisingly didn’t have too much built up oil residue but it was dirty and full of carbon. I seafoamed it through the vacuum before I did this, then used brake cleaner to clean the inside really well. Don’t forget to clean the butterfly to the throttle body as well, you can also add a throttle body spacer on as I did.
I also went ahead and by passed the coolant lines that go into the throttle body and plenum. You can either cap them off, install a hose connecter or a by pass valve of some sort. This will prevent the hot coolant from getting into these areas, helping keeping overall temps down. I also painted my plenum a high temp paint color. Before these mods you could barely touch the plenum without getting burnt. Now with these mods, plus a CAI set up. I can drive it for 4 hrs straight and it’s barely warm to the touch! It’s definitely a mod worth doing, it makes a huge difference.
I also changed my valve covers and gaskets, since I already had everything apart. I painted the new valve covers as well. I just used some cheap covers which I paid like $55 for. It came with the new valve covers, gaskets and hardware. I also went ahead and installed 6 NGK Platinum spark plugs for $22 bucks and a set of Denso coil packs for $38! I then capped off the inlet to the PCV system vacuum from bank 2 that goes to the intake tube. Rerouted a longer 3/8 hose behind the engine to the passenger side to an Oil Catch Can. Then connected the PCV hose with another 3/8 hose to the OCC. It has an outlet that I used another hose going to the lower plenum vacuum line. It’s a baffled can and it does a great job at catching all of the nasty blow by. I empty maybe an oz or so of build up per month. Since it’s baffled, I made it a closed system. So the PCV system is essentially still like the stock set up. Just eliminating the bank 2 side from venting into the intake tube.
Both banks are just routed to the OCC instead catching any blowby. Helping keeping the intake much cleaner in the process. Which keeps the combustion chamber from being polluted creating a much cleaner all around cycle. It’s a must have for these cars. A G35 CAI, a plenum spacer, and an OCC. That along with a much needed cleaning and tune up turned my car around. I had just purchased it at 199k. I’ve put 10k on it in 6 months, I’m amazed in how nice it runs for a 16yr old car with 209k miles!
The engine sits at perfect 650 idle, it runs quiet and smooth. No ticking noises, no knocking and pinging, just smooth V6 sounds. Maintenance is often overlooked and I do this every time I get an used car. The old spark plugs were so toasted and I had two coil packs break apart on me while I took them off. Since I also have a X AWD model I changed the ATF and transfer case fluids, as well as the front and rear diff fluids. That also made a huge difference in the overall feel and performance of the vehicle. It just grips the road now in confidence, I let a few ppl drive it and they too were very impressed with it. They couldn’t believe it was even a 16yr old car with such high mileage!
Dude the hose off of the back of bank 2 valve cover is crucial and will need to be put back to original location up by the filter!!! You’ll end up messing something up if you leave it as you have it now, that is unless the damage HAS ALREADY BEEN DONE while driving the car this way. Before I tell you this I want you to think about your POV system as it sits right now, and tell me where the hell is the air that you are so hastily trying to vent from your crankcase coming from?????🤷🏻♂️🤦🏻♂️🤦🏻♂️ EXACTLY!!! Surely not from inside of the sealed OCC you installed! See the problem yet???
• you basically have a snorkel in your mouth right now trying to breathe, well by removing the line up by air filter and connecting to sealed OCC, you have essentially placed both ends of the snorkel in your mouth and sealed your lips around those two ends airtight! Good luck breathing!!! So if you’re not dead already from lack of fresh air to your lungs, you can thank me in a min. K
•the hose connection up at the air filter is prob the MOST IMPORTANT of all connections in your occ system! It’s highly critical because that is where the bottom half of your motor inhales from, the air it is taking in enters at the back of The bank one valve cover then flows down through passages and enters the lower half of your motor and then leaves the number to bank via small port at the front side of that valve cover Which has a short piece of let’s call it jumper hose which delivers that air over to bank one intake port which is located approximately the same area as bank ones port that it’s coming out of it once it enters bank one it flows around and down back into the bottom half of your Engine block then rises up through the passageways and enters the valve cover again where it sits and waits for your PCV valve to open so that it can escape and enter through your PCV hose that connects to your intake manifold which in a naturally aspirated car like yours is always under a vacuum while the engine is running.
• put that hose back up to the connection you capped off up by the air filter, and cap off that 3rd (now unused) port on your OCC. Thank You Daniel Son!!! You are welcome! Next time ask for some installation instructions when you buy stuff! 😉😉👍🏼