The 5.7 HEMI Throttle Body Upgrade Instructions

The 5.7 HEMI Throttle Body Upgrade Instructions. The 5.7 HEMI is a good engine right out of the box, but it’s obviously underpowered for its size. However, with a few minor modifications, the 5.7L V8 is a formidable powerplant. We previously published an article on the 5 finest HEMI bolt-on mods to truly bring this engine to life. A 5.7 HEMI throttle body improvement was not on the list. However, it is still a fantastic improvement that can provide significant power boosts and benefits. This article discusses 5.7 HEMI TB improvements, spacers, power gains, advantages, and other topics.

Holly Sniper EFI 92mm throttle body (not compatible with OEM intake manifolds)

The 5.7 HEMI Throttle Body Upgrade Instructions

What Exactly Is a Throttle Body?

Between the intake pipe and the intake manifold is a throttle body (TB). The TB contains a butterfly valve that regulates the quantity of air entering the engine. Sensors on the throttle body then convey the throttle position to the engine, allowing the engine to alter other parameters such as fuel flow.

Throttle bodies have a lot of other characteristics and complexities. However, the primary purpose of TB improvements is to simply increase the size and allow for more airflow. As a result, the specifics of throttle body operation and all of the sensors are irrelevant to this topic.

Finally, the 5.7 HEMI throttle body regulates the volume of air that enters the engine. The amount of air available at WOT is restricted by the size of the stock TB. A bigger throttle body can provide improved response and power improvements.

Throttle Body Spacer for 5.7L V8

This page focuses on genuine throttle body improvements. 5.7 HEMI TB spacers, on the other hand, are a hot topic. On the surface, a throttle body spacer is a straightforward mod; it’s essentially just a 0.5-1.0′′ piece of metal that fits between the throttle body and intake manifold. Many spacers, however, include grooves to generate an air vortex. It’s simplest to describe the design by looking at older engines.

Most automotive engines employed throttle body injection or carburetors in the past. Further out from the cylinder head, the air and gasoline mingled. To create a vortex, a throttle body spacer with grooves could be employed. As a result, the spinning effect of a grooved spacer improved fuel atomization by better mixing the air and fuel. This results in increased power and performance.

Many contemporary engines, including the 345 HEMI, utilise multi-port fuel injection. Whirling the air before the intake manifold will not improve fuel atomization since the runners in the intake manifold will smooth out the air before it reaches the ports. As a result, throttle body spacers aren’t as useful on engines like the 5.7 HEMI as they are on previous carbureted engines.

Is a 5.7 HEMI TB Spacer Worth the Money?

Most customers are unlikely to find a 5.7 HEMI throttle body spacer worth the money. A TB spacer can add 2-5 horsepower to some 5.7L V8 engines. We believe that many will exhibit no benefits or even minor power losses. The majority of gains and losses are most likely due to natural variations in WOT pulls. There’s also no reason to suppose that a 345 HEMI throttle body spacer will improve MPG.

Throttle body spacers are a hot topic that frequently sparks heated disputes. Some individuals believe they somewhat improve performance, and for approximately $100-150, it’s worth a go. Others argue that TB spacers are nothing more than a waste of money. On port injection engines, we prefer the latter.

Creating a “tornado” or vortex before the intake runners and much before the air-fuel mix is unlikely to be beneficial. However, a little increase in intake plenum size may have a negligible benefit. Increasing power on NA engines like the 5.7 HEMI is difficult unless you opt for major modifications like headers, cams, or forced induction. Every little bit helps, and we wouldn’t judge individuals who pay $100 to gain a few more horsepower.

Advantages of the 5.7 HEMI Throttle Body

The following are some of the advantages of upgrading the 5.7 HEMI throttle body:

  • Gains of 5-10 horsepower
  • Gains in torque are comparable.
  • improved throttle responsiveness
  • Simple and inexpensive modification

The major reason for upgrading the 345 HEMI TB is for improved performance. Power increases are typically in the 5-10 horsepower range. Nothing exceptional when compared to modifications such as a tune, headers, or cams. However, considering it’s a cheap and simple bolt-on addition, the 5.7 HEMI throttle body power improvements are impressive. Better throttle response is another usual advantage of a larger TB.

To increase horsepower, stock 5.7L V8s will most likely gain on the lower end of that range. Engines equipped with cams, headers, and/or forced induction are likely to realize greater benefits. With the right upgrades and a properly sized TB, some may even reach 10+ horsepower.

345 HEMI TB Dimensions

If the goal is to enhance airflow through the throttle body, isn’t bigger better? Not exactly. It is critical to select the proper throttle body size in order to maximize peak gains without sacrificing low-end torque. Once the air-flow requirements are reached, growing bigger simply degrades low-end performance and provides no additional advantages on top.

The main bore of the factory 5.7 HEMI throttle body is 80mm. On most standard engines, switching to something like The Fastman 82mm TB is all that is required. Because of a modified half shaft that provides 4mm of airflow at full throttle, this TB is actually 86mm at WOT. With headers, cams, or FI, you’ll probably require something closer to 88-90mm at WOT.

Unless you have a constructed engine with head work, larger throttle bodies are usually overkill on the 5.7 HEMI. The point is, don’t go overboard with 345 HEMI TB mods. Bigger isn’t necessarily better, and sizing should be determined by your existing or upcoming mods.

Throttle Body Upgrades for the 5.7 HEMI

After we’ve covered the fundamentals, it’s time to look at some of the best 5.7 HEMI throttle body mods. Please keep in mind that this is by no means an exhaustive list. There are numerous excellent throttle bodies available. Instead of a comprehensive list, we’ll focus on a few 5.7L V8 TB upgrades that provide an excellent blend of performance, price, and quality.

1) 5.7 HEMI Fastman TB Upgrading

Price: $250-547

The 5.7 HEMI Throttle Body Upgrade Instructions

The Fastman 5.7 HEMI throttle body is one of the most well-liked TBs on the market. They’ve been well tried and confirmed, and they’re one of the few brands that are consistently suggested by others. Fastman uses the factory throttle body and modifies it to provide excellent results. For the 345 Mopar engine, they provide an 82mm and an 84mm TB. However, due to a +4mm half shaft mod, the throttle bodies are 86mm and 88mm at full throttle.

Both throttle body apertures are 85mm in diameter and taper down to 82mm or 84mm in diameter at the main bore (depending on which TB you choose). Fastman costs $250 for the TB changes, but there are no core expenses. You can either buy a new throttle body from them or send in your old one to save money. However, this will need the removal of your 5.7 HEMI for a few weeks.

According to many, this is the greatest 5.7 HEMI throttle body on the market. Unless you’re incredibly severely modded and require anything larger than 86mm or 88mm at full throttle, it’s difficult to go wrong with Fastman throttle bodies. Even so, a larger throttle body is unlikely to be required. Anyway, if you want the finest of the greatest, Fastman is a terrific choice.

2) Throttle Body for Dodge 345 HEMI

Price: $500-550

The 5.7 HEMI Throttle Body Upgrade Instructions


Another popular brand for 5.7 HEMI throttle body improvements is BBK. They’re also well-known for various 5.7L V8 mods such as headers, exhaust, and intakes. For the 345 Mopar engine, BBK supplies 85mm and 90mm throttle bodies. However, they recommend the 85mm for the 5.7 HEMI engine and the 90mm for the larger 6.4L engine.

That recommendation is supported by us, especially for basic bolt-on only HEMIs. If you have heavy power mods, the 90mm throttle body may make sense. They’re almost the same price as The Fastman, so it all boils down to personal preference. However, if you’re prepared to send in your throttle body ahead of time, the latter is less expensive.

It’s also difficult to go wrong with BBK. We believe the Fastman 345 HEMI TBs are the most well-known and popular alternative. However, BBK throttle bodies are also excellent, so if you’re a BBK fan, this is an excellent option.

3) Throttle Body Sniper EFI 92mm

Price: $223.95

This throttle body is going us in a completely different way than the ones listed above. The Sniper EFI 92mm throttle body is incompatible with the factory intake manifold. It’s actually a throttle body upgrade for the Sniper EFI manifold. This product was mentioned in our article on 5.7 HEMI intake manifold upgrades.

An intake manifold and throttle body modification might be a terrific pair of changes to do at the same time. On the 5.7L V8, swapping a 6.4 HEMI manifold is a common alternative. The 5.7 and 6.4 throttle bodies are interchangeable in this scenario. True aftermarket manifolds, such as the Sniper EFI, may, however, necessitate aftermarket throttle bodies.

Again, this is a radical departure, but it’s worth considering before upgrading your throttle body. If you intend to add boost, you may want to consider an aluminum manifold, which is normally incompatible with most TB upgrades.

Related : The 5.7L HEMI Lifter Problems: Causes and Solutions

Summary of the 5.7 HEMI Throttle Body Upgrade

Throttle body upgrades did not make our list of the top 5 greatest 5.7L HEMI engine modifications. Other modifications such as tuning, headers, intake manifolds, and camshafts might provide more enticing power improvements. A throttle body, on the other hand, is a good alteration to enhance performance on the 5.7L V8 Mopar.

One hot topic is 5.7 HEMI throttle body spacers, although there’s no convincing evidence that they provide consistent power gains. On older throttle body injection engines, they are more effective modifications. Still, for less than $150, it may be worth the risk of gaining a few additional horsepower.

The actual performance gains can be observed with throttle body changes. 5.7 HEMI TB upgrades can provide 5-10+ horsepower, comparable torque, and improved throttle response. Solid advantages for a $500 modification that bolts directly up to the intake manifold. Some of the greatest throttle bodies for the 345 HEMI are available from Fastman and BBK. If you’re going to upgrade your intake manifold, put off getting a throttle body. Some manifolds necessitate the use of aftermarket throttle bodies, which do not fit the factory manifold.