5.7 HEMI Throttle Body Upgrade Guide
Zach is a founder of 8020 Media and TuningPro. He’s been repairing, upgrading, tuning, and writing about cars & engines for over a decade. Zach has written over 400 automotive articles and continues to be a lead writer for TuningPro. His passion, experience, and deep technical knowledge make him a go-to resource for readers looking to take their car to the next level.
The 5.7 HEMI is a solid engine from the factory, but it’s certainly a little underpowered for its size. However, the 5.7L V8 is a capable engine with some simple mods. In the past, we wrote an article about the 5 best HEMI bolt-on mods to really bring this engine to life. A 5.7 HEMI throttle body upgrade didn’t quite make that list. However, it’s still a great upgrade that can offer decent power gains and benefits. In this article, we discuss 5.7 HEMI TB upgrades, spacers, power gains, benefits, and more.
Holly Sniper EFI 92mm throttle body pictured above (does not work with OEM intake manifolds)
What Is a Throttle Body?
A throttle body (TB) is located between the intake piping and intake manifold. The TB houses a butterfly valve to control the amount of air entering the engine. Sensors on the throttle body then communicate the throttle position, so the engine can adjust other parameters like fuel flow.
There are a number of other details and intricacies with throttle bodies. However, the main goal with TB upgrades is simply to increase the size and allow for greater air-flow. As such, the specific details of throttle body operation and all the sensors aren’t important to this topic.
Ultimately, the 5.7 HEMI throttle body controls the amount of air entering the engine. At WOT the amount of air is limited by the size of the stock TB. Upgrading to a larger throttle body can deliver better response and power gains.
5.7L V8 Throttle Body Spacer
The main focus in this article is actual throttle body upgrades. However, 5.7 HEMI TB spacers are another big topic. A throttle body spacer is a simple mod on the surface; it’s literally just a ~0.5-1.0″ piece of metal that fits between the throttle body and intake manifold. However, many spacers also incorporate grooves to create an air vortex. To explain the design it’s easiest to look back on older engines.
In the past, most car engines used throttle body injection or carburetors. The air and fuel mixed further away from the cylinder head. A throttle body spacer with grooves could be used to create a vortex. In turn, this created better fuel atomization as the whirling effect of a grooved spacer could better mix the air and fuel. This indeed leads to better power and performance.
Many newer engines use multi-port fuel injection, as is the case on the 345 HEMI. Whirling the air before the intake manifold will not help fuel atomization as the intake manifold runners will smooth out the air before it reaches the ports. As such, throttle body spacers aren’t as worthwhile on engines like the 5.7 HEMI when compared with older carbureted engines.
Is a 5.7 HEMI TB Spacer Worth It?
It’s unlikely that a 5.7 HEMI throttle body spacer is worth the cost for most people. Some 5.7L V8’s may pick up 2-5 horsepower from a TB spacer. We would argue equally as many will show no gains or even small power losses. Most gains or losses are likely attributed to natural variances in WOT pulls. There also isn’t any reason to believe a 345 HEMI throttle body spacer will increase MPG.
Throttle body spacers are a popular topic that can often lead to heated debates. Some people believe they increase performance slightly, and for about $100-150 it’s worth the try. Others claim TB spacers are nothing more than a paper weight and a scam. On port injected engines we tend to side with the latter.
Creating a “tornado” or vortex before the intake runners and well before the air-fuel mix shouldn’t really do anything helpful. A slight increase in intake plenum size could have a very minor benefit, though. Adding power on NA engines like the 5.7 HEMI isn’t easy unless you go for big mods like headers, cams, or forced induction. Every little bit helps and we wouldn’t knock those who spend $100 in an effort to squeeze out a couple extra horsepower.
5.7 HEMI Throttle Body Benefits
Benefits of upgrading the 5.7 HEMI throttle body include:
- 5-10 horsepower gains
- Similar torque gains
- Better throttle response
- Cheap, simple mod
The main reason to upgrade the 345 HEMI TB is performance. Power gains generally fall in the 5-10 horsepower ballpark. Nothing spectacular compared to mods like a tune, headers, or cams. However, the 5.7 HEMI throttle body power gains are solid considering it’s a cheap and simple bolt-on upgrade. Better throttle response is also a common benefit of a larger TB.
To expand on horsepower, stock 5.7L V8’s will likely see gains on the lower end of that range. Engines with cams, headers, and/or forced induction will likely see bigger gains. Some may even see 10+ horsepower with the right mods and a properly sized TB.
345 HEMI TB Size
If the idea is to increase air-flow through the throttle body then bigger is better, right? Not quite. Choosing the right throttle body size is important to maximize peak gains without giving up any low-end torque. Once the air-flow needs are met then going bigger simply hurts low-end performance and won’t offer any extra gains up top.
The stock 5.7 HEMI throttle body main bore is 80mm. On mostly stock engines moving to something like The Fastman 82mm TB is about all that’s needed. This TB is really 86mm at WOT due to a modified half shaft that adds an extra 4mm of airflow at full throttle. With headers, cams, or FI you’ll likely want to consider something closer to 88-90mm at WOT.
Larger throttle bodies are generally overkill on the 5.7 HEMI unless you have a built engine with head work. The point here is – don’t go too large with 345 HEMI TB mods. Bigger isn’t always better and sizing should be dictated by your current or planned mods in the near future.
Best 5.7 HEMI Throttle Body Upgrades
With the basics out of the way it’s time to move onto some of the best 5.7 HEMI throttle body upgrades. Please note – this is not an exhaustive list by any means. Plenty of great throttle bodies are out there. Instead of an exhaustive list, we’re focusing on a few 5.7L V8 TB upgrades that offer a great balance of performance, price, and quality.
1) 5.7 HEMI The Fastman TB Upgrade
Buy Here: 5.7L Fastman Throttle Body
The Fastman 5.7 HEMI throttle body is possibly the most highly regarded TB on the market. They’re highly tested and proven and one of few brands that are constantly recommended by others. Fastman uses the stock throttle body and makes a number of modifications that deliver great results. They offer an 82mm and 84mm TB for the 345 Mopar engine. However, the throttle bodies are 86mm and 88mm at full throttle due to a +4mm half shaft mod.
Both throttle body openings are 85mm and taper back to 82mm or 84mm at the main bore (depending on which TB you opt for). Fastman charges $250 for the TB modifications but core charges don’t apply. You either need to buy a new throttle body thru them or you can send in your current one to save some money. However, that will require your 5.7 HEMI being apart for a few weeks.
Ultimately, this is the best 5.7 HEMI throttle body on the market according to many. It’s truly hard to go wrong with Fastman throttle bodies unless you’re extremely heavily modded and need something larger than 86mm or 88mm at full throttle. Even then, you probably don’t need a larger throttle body. Anyway, if you’re looking for the best of the best then Fastman is a great pick.
2) Dodge 345 HEMI BBK Throttle Body
Buy Here: BBK 5.7 HEMI TB Upgrades
BBK is another popular brand for 5.7 HEMI throttle body upgrades. They’re also well known for other 5.7L V8 mods like headers, exhaust, intakes, and more. BBK offers 85mm and 90mm throttle bodies for the 345 Mopar engine. However, they recommend using the 85mm for the 5.7 HEMI while the 90mm is better for the larger 6.4L engine.
We agree with that recommendation especially for basic bolt-on only HEMI’s. However, if you have extensive power mods then the 90mm throttle body might make sense. They’re about the same price as The Fastman so it really just comes down to brand preference. However, the latter is less expensive if you’re willing to send in your throttle body in advance.
It’s hard to go wrong with BBK, too. We believe The Fastman 345 HEMI TB’s are the most respected and liked option. However, BBK throttle bodies are great too so if you’re loyal to BBK then this is a great option.
3) Sniper EFI 92mm Throttle Body
Buy Here: 5.7 HEMI Sniper 92mm Throttle Body
This throttle body is taking us in a totally different direction than the above options. The Sniper EFI 92mm throttle body does not work with the stock intake manifold. Instead, it’s a throttle body upgrade for Sniper EFI manifold. We talked about this product in our article about 5.7 HEMI intake manifold upgrades.
An intake manifold and throttle body upgrade can be a great combination of mods to knock out at the same time. Swapping a 6.4 HEMI manifold is a popular option on the 5.7L V8. In that case, the 5.7 and 6.4 throttle bodies are interchangeable. However, true aftermarket manifolds like the Sniper EFI may require aftermarket throttle bodies.
Again, this is a very different direction but it’s something to consider before upgrading your throttle body. You may want an aluminum manifold if you’re planning to add boost, and those generally aren’t compatible with most TB mods.
5.7 HEMI Throttle Body Upgrade Summary
Throttle body upgrades didn’t quite make our list of the 5 best 5.7L HEMI engine mods. Other upgrades like tuning, headers, intake manifolds, and cams can offer more appealing power gains. However, a throttle body is still an excellent mod to maximize performance on the 5.7L V8 Mopar.
One major topic is 5.7 HEMI throttle body spacers, but there isn’t any compelling proof they offer consistent power gains. They’re more effective upgrades on older throttle body injection engines. Still, for less than $150 it may be worth the chance of squeezing out a couple extra horsepower.
Actual throttle body upgrades are where the real performance benefits may be seen. 5.7 HEMI TB mods can offer 5-10+ horsepower, similar torque, and better throttle response. Solid benefits for a $500 upgrade that’s easy to bolt right up to the intake manifold. The Fastman and BBK offer some of the best throttle bodies for the 345 HEMI. If you’re planning to upgrade your intake manifold then consider holding off on a throttle body. Some manifolds require aftermarket throttle bodies that do not fit the stock manifold.