6.4 HEMI throttle body BBK
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6.4 HEMI Throttle Body Upgrade Guide

Chandler Stark

Meet Chandler

Chandler is an automotive expert with over a decade of experience working on and modifying cars. A couple of his favorites were his heavily modded 2016 Subaru WRX and his current 2020 VW Golf GTI. He’s also a big fan of American Muscle and automotive history. Chandler’s passion and knowledge of the automotive industry help him deliver high-quality, insightful content to TuningPro readers.

One of the most popular 6.4 HEMI bolt-ons is a throttle body upgrade. A throttle body upgrade offers impressive performance gains at a cheap price point – relative to other upgrades. It’s a simple upgrade that’s essential for pushing the engine to the next level. In this guide, I discuss 6.4 HEMI throttle body upgrades, benefits, and the best options available.

6.4 HEMI Throttle Body Basics

Before we talk about 6.4 HEMI throttle body upgrades, first let’s go over what a throttle body does on an engine. Throttle bodies are part of the intake system and connect the air intake to the intake manifold. They are bolted to the intake manifold, and the 392 HEMIs have an 80mm OEM throttle body with a 4-bolt pattern. It’s one of the most basic systems on the car and a part of nearly every production engine. 

Throttle bodies are essentially hollow cylinders that have a butterfly valve at the bottom. The valve swings open to allow air in, and shuts closed to stop air from coming in. These valves are controlled by what is called a throttle blade, which determines when and how much they should open. On the 6.4 HEMI, the throttle blade is controlled electronically and its position is dependent on how much throttle is given. More throttle means more air is needed so the valve opens, and the less throttle means less air so it starts to close. 

Why Upgrade Your Throttle Body?

It’s probably pretty obvious, but the reason to upgrade your 6.4 HEMI throttle body is to increase its diameter. A larger diameter throttle body will allow more air to enter the intake manifold, and thus the engine. More air means more oxygen, which creates more horsepower and torque during combustion. 

While many naturally aspirated builds will continue to use the stock throttle body, if you are considering adding a HEMI centrifugal supercharger or turbocharger, upgrading the throttle body is almost required. You will find it to be too much of a restriction if you start to run boost, and you will want something larger. In addition, if you are upgrading your 6.4 HEMI intake manifold, you should also consider a bigger throttle body. 

Even if your build is naturally aspirated, you can still upgrade the 6.4 HEMI throttle body and see some gains. On the 6.4 HEMI, larger throttle bodies have been shown to produce increases of as much as 15 horsepower and 15 lb-ft of torque, even without boost.  

Ported Throttle Bodies

You may have heard of porting throttle bodies instead of upgrading them, and for some engines that’s a viable option. Porting involves honing and smoothing the inside of the throttle body to allow for better airflow. It does not appreciably increase the diameter of the throttle body, but gets rid of imperfections and bumps that create too much turbulence and restrict smooth-flow. However, most dyno runs have shown that porting the stock 392 HEMI throttle body is practically useless. It does not offer any real gains and is not worth the cost.

6.4 HEMI Throttle Body Spacers

Another term you might have heard thrown around with throttle bodies are throttle body spacers. Spacers sit between the intake manifold and throttle body and are designed to increase airflow into the engine. The benefits of these are very hotly debated, with some people claiming they are amazing and others saying the opposite. For the 6.4 HEMI, we suggest staying away from spacers and buying a larger throttle body. 

Throttle Body Sizing

The OEM 6.4 HEMI throttle body measures 80mm in diameter. Upgraded 392 HEMI throttle bodies typically range from 84–95mm, though a few are available that are larger. For the most part, 84mm throttle bodies will be sufficient for most builds, but those running forced induction probably want to consider 90mm or above. 

392 HEMI Throttle Body Upgrade Benefits

The main benefits of an upgraded 6.4 HEMI throttle body are:

  • +5-15 horsepower
  • +5-15 lb-ft of torque
  • Increased airflow over stock
  • Improved throttle response
  • Larger power band

The most significant benefits from upgrading the 392/6.4 HEMI throttle body are the power gains. Dyno runs have shown that upgrading to a larger throttle body will net peak gains of 5-15 horsepower and 5-15 lb-ft of torque. This is due to the increased volume and flow of air entering the intake manifold and engine. 

In addition to peak gains, you’ll also notice a larger overall power band and a more responsible throttle pedal. The gains aren’t going to be drastic, like installing a blower, but most people notice a little bit more zip taking off from a start and at the top end. If you are running forced induction like a centrifugal supercharger or a turbocharger, a larger throttle body will net even more gains by decreasing airflow restriction. 

Top 6.4 HEMI Throttle Body Upgrades

The 5 best 6.4 HEMI Throttle Body Upgrades are:

  • Hellcat Throttle Body Upgrade
  • Fastman Throttle Bodies
  • Modern Muscle Throttle Bodies
  • BBK Performance
  • Moe’s Performance

There are a lot of throttle bodies on the market for the 392 HEMI, and these are the top 5. We have balanced performance with price and quality control to hone-in on the top available options. Keep in mind, brands have different sized throttle bodies, which will impact performance. Make sure to confirm all fitments and models before ordering. 

1) Upgraded Hellcat Throttle Body

6.4 HEMI throttle body
Credit: Jannety Racing (Hellcat Throttle Body)

First up on our list is upgrading the 6.4 HEMI to the Hellcat’s stock throttle body. The 6.4 HEMI throttle body is 80mm, but the stock Hellcat throttle body is 15mm larger at 90mm, despite the engine having less displacement. Simply swapping the larger Hellcat throttle body will net gains of 10-15 horsepower even on otherwise stock cars. 

Importantly, the stock Hellcat throttle body is not a direct bolt-on replacement for the 6.4 HEMI. To make it fit an adapter is required, and unfortunately they are a bit expensive. However, the 95mm Hellcat throttle body is larger than most other aftermarket options, so it is an especially attractive option for those running boost through forced induction. 

2) Fastman Throttle Bodies

Next up are the Fastman modified 6.4 HEMI throttle bodies. Within the HEMI community, the Fastman modified throttle bodies are some of the most popular TB upgrades available. They take standard HEMI units and modify them to increase airflow and size. Both 82mm or 84mm options are available, but it’s worth noting that the Fastman units actually flow better while at wide open throttle. This is due to modifications to the factory shaft, which allow for an extra 4-mm of opening at WOT. This effectively makes them 86mm and 88mm units. 

Dyno runs have shown the Fastman to be one of the most powerful upgraded throttle bodies for the HEMI. Fastman uses OEM throttle bodies and bores them out and then makes the other modifications. When ordering from Fastman, you can either get a brand new unit from them or send in your stock unit for them to modify. 

Fastman might not have the brand-recognition of larger companies, but they deliver quality products and have great customer service. There is a reason that even a small shop has such a great reputation among the community, and it is well deserved. 

3) Modern Muscle Xtreme TB

Third on our list are the Modern Muscle Xtreme ported 85mm and 87mm throttle bodies. These are slightly smaller than the Fastman units at WOT, but they still deliver solid performance. There is no tapering on the MMX like the Fastman, and there is also no difference between regular and WOT operation on the MMX. 

MMX’s TBs are CNC ported to make sure they have the most optimal flow characteristics possible. They definitely outflow the stock units and have been shown to really improve throttle response. They have a venturi-like design and are direct bolt-on replacements for the stock unit. MMX has been a leading producer of HEMI products for several years, and their throttle bodies are very well regarded. 

4) BBK Performance TB Upgrade

Fourth on our list are BBK Performance’s 85mm and 90mm throttle bodies. Both of these units provide better airflow than stock, and the 90mm unit is one of the biggest available for the 6.4 HEMI. Like the MMX TBs, BBK’s are CNC-ported to decrease any potential turbulence or restriction of the air. 

BBK claims gains of 10-12 horsepower with the 85mm TB, and 12-15 horsepower for the larger 90mm TB. In addition, what helps the BBK stand out is they got their throttle bodies CARB approved. They have a specific EO number, so they are legal in all 50 states. This makes the BBK a great option if you live in a strict emissions state, like California, and can only use CARB approved parts. 

Chances are, if you’ve researched throttle bodies before, BBK likely came up at some point. They make TBs for a huge variety of engines and vehicles, and most of them are very well reviewed. They have solid quality control and are known for making decent power. 

5) Moe’s Performance Throttle Body

The final recommendation we have are Moe’s Performance’s 392 HEMI 87mm throttle body. Moe’s Performance only offers 87mm options for the 6.4 HEMI, as their others only fit the 5.7 HEMI. Their throttle body is CNC-ported and a direct-bolt on replacement. They also use a venturi-like design for the best possible airflow, similar to MMX. 

Moe’s claims gains of 12-15 horsepower with their unit, which is pretty similar with other manufacturers. Again, like Fastman, Moe’s Performance isn’t a huge name in the industry, but they are known for producing quality parts. Customers have reviewed their TBs very well, and they have solid quality control. 

6.4 HEMI Throttle Body Upgrade FAQ

Should I upgrade my 6.4 HEMI throttle body?

Upgrading your 6.4 HEMI throttle body will allow for more air to reach the engine quicker. This will produce increases of 10-15 horsepower and 10-15 lb-ft of torque. It is a very popular and easy to do modification.

What size is the 6.4 HEMI throttle body?

The stock 6.4 HEMI throttle body has a diameter of 80 mm.

Can you put a Hellcat throttle body on a Scat Pack?

Yes, the Hellcat throttle body will fit the smaller 6.4 HEMI engine, but not without an adapter. An adapter is required for proper fitment.

What is the best 6.4 HEMI throttle body?

The Fastman modified throttle bodies are the best 6.4 HEMI throttle body upgrades.

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