6.1 HEMI Intake Manifold Upgrade Guide
Recently, we looked at the 6.1 HEMI engine that lasted from 2005–2010 inside various SRT8 badged vehicles. Depending on the model, they make between 420–425 horsepower and 420 lb-ft of torque. Still, some people consider them to be underpowered from the factory, especially considering their massive 6.1 liters of displacement. Previously, we talked about upgrading to a supercharger for the 6.1 HEMI, and now we’re looking at 6.1 HEMI intake manifold upgrades.
This article will cover everything you need to know about upgrading the intake manifold on your 6.1 HEMI powered SRT8. We’ll explain how intake manifolds work, the benefits of upgrading, and why you might want to look at upgrading your throttle body at the same time. Finally, we’ll give you our top recommendations for 6.1 HEMI intake manifolds on the market today.
How does a 6.1 HEMI Intake Manifold Work?
Let’s start with the basics: what is an intake manifold and how do they work? Intake manifolds are responsible for supplying fuel and air to an engine. They sit between the throttle body and cylinder head(s), and get their air supply from the air intake connected to the throttle body. Fuel is supplied from fuel injectors that sit in the intake manifold itself.
There are two main parts to an intake manifold: the plenum and the runners. The plenum is the top part of the intake manifold and usually looks like a large cylinder or box. The runners are small tubes connected to the plenum that bolt on to the cylinder head. Typically, there is one runner per cylinder on most manifold designs, making eight runners on the 6.1 HEMI.
The purpose of an intake manifold is to evenly and quickly distribute air and fuel into all of the cylinders. Air is drawn through the throttle body and into the plenum, where it then travels down the individual runners and through the cylinder head(s) into the combustion chamber. On its way into the combustion chamber, it mixes with fuel supplied by fuel injectors.
To regulate air exiting the runners of the intake manifold, each runner has its own butterfly valve. These open to allow air through, and close to stop air from coming through.
What are HEMI Intake Manifolds Made From?
When looking at Gen III HEMI intake manifolds, there are a few basic materials available. Manifolds are usually made of either cast iron, cast aluminum, billet aluminum, or composite plastic. Each of them have advantages and disadvantages.
Cast iron manifolds are very cheap and durable, but they are also heavy and flow poorly. Cast aluminum is lighter than cast iron and flows better, but is less durable. Billet aluminum (sheet metal) flows slightly better than cast aluminum, but is more expensive. Composite plastic is lighter weight and costs less than aluminum, but is not as durable.
The stock 6.1 HEMI intake manifold is made from cast aluminum. Most aftermarket 6.1 HEMI intake manifolds will be made of either cast or billet aluminum, or possibly composite plastic. Billet aluminum manifolds, also seen as sheet metal manifolds, have been gaining popularity in recent years due to cost, and they flow very well.
Different HEMI Intake Manifold Styles
Besides material, another thing to consider in terms of intake manifolds is runner length and plenum volume. Many people think that just slapping on the biggest plenum with the longest and widest runners will have the best air flow, but that’s horribly wrong. In reality, you want to have a plenum and runners that work together to have the best possible pulse reversion control.
Pulse-reversion, without getting too technical, is a phenomenon of any intake manifold. When the butterfly valve on the intake manifold runner opens it allows air into the engine. But, when the valve closes, the air has nowhere to go and ends up piling on top of itself. This creates a wave of high pressure, which then travels back up through the runners and towards the plenum.
Once the high pressure wave hits the plenum, it is forced back down the runner, again. Ideally, if the intake manifold runners and plenum are correctly sized, the wave of high pressure will be sucked into the combustion chamber before the butterfly valve closes again. This also has the effect of pushing more than normal into the engine, since the high pressure wave hits at the exact right time. If it doesn’t, then you have multiple waves of high pressure stacking up, leading to air turbulence and poor flow.
Other considerations with runner length are related to the power curve. Typically, longer and more narrow runners will make better power on the low-end, while shorter and more wide runners will allow for better top-end performance.
Which Intake Manifold is right for me?
Your power goals and intentions (street use, autocross, track use, drag racing, etc) will determine the type of manifold you want. Something longer and narrower might be more fun on the street and track, while wider and shorter runners would be suited well for drag racing.
6.1 HEMI Intake Manifold Upgrade Benefits
The top benefits to upgrading the 6.1 HEMI Intake Manifold are:
- ~5–20 wheel horsepower and wheel torque
- Decreased weight over stock manifold
- Increased air flow over stock manifold
- Increased engine volume/noise
- Visual appeal
There are several benefits to upgrading your 6.1 HEMI intake manifold. The first and most prominent is going to be power increases of about 5–20 wheel horsepower and wheel torque. This will come from the improved airflow and plenum volume of an aftermarket manifold. If you have other supporting mods, like a cold air intake, throttle body, and long-tube headers, you will see more gains than on an otherwise stock engine.
Other benefits include decreased weight, increased engine noise/volume, and visual appeal. The stock 6.1 HEMI intake manifold is made from cast aluminum, and weighs about 65 pounds. Aftermarket manifolds usually weigh less than stock, especially sheet metal aluminum, which can decrease weight by as much as half.
You’ll also definitely hear your engine more loudly after installing an intake manifold. Similar to a larger intake or throttle body, the increased air and lack of insulation will make it much more prominent. Finally, your engine bay will undoubtedly look cleaner with a nice aftermarket intake manifold than the stock one.
Upgrading the Throttle Body
For many people, when they upgrade their intake manifold they also upgrade to a larger throttle body. This is not necessary, but does have benefits. Having a larger throttle body will allow more air to enter into the engine, meaning more power. However, for most applications, the stock unit will work fine. Keep in mind, however, that some intake manifolds require use of a larger throttle body, which also means you will need a new air intake.
The stock throttle body is 80mm, and there are aftermarket versions available up to nearly 100mm. If you are considering adding boost to your 6.1 HEMI, either with a turbocharger(s) or centrifugal supercharger, upgrading the throttle body is usually a good idea to accommodate the increased airflow. If you are staying naturally aspirated and below 700 horsepower, the stock unit will be fine (if it fits).
Upgrading to the 6.4 HEMI Intake Manifold
Instead of going aftermarket, another option some 6.1 HEMI users have done is to swap out for the larger 6.4 HEMI’s intake manifold. The 6.4 HEMI intake manifold uses composite plastic instead of aluminum, and also has dual active runners. This allows the manifold to use different runner lengths to variously optimize torque and horsepower through the power band.
However, on the 6.4 HEMI, the active runners switch from long to short at about 4,800 RPM. If you swap the 6.4 intake manifold over, you will need to find a way to activate the switch to get the full benefit of the manifold. Since buying a used 392 HEMI intake manifold is cheaper than a new aftermarket 6.1 intake manifold, many people have chosen to go this route. Still, a properly sized 6.1 aftermarket manifold will likely be superior.
Best 6.1 HEMI Intake Manifold Upgrades
The top four 6.1 HEMI Intake Manifold Upgrades are:
- Ported stock manifold
- Holley Hi-Ram EFI
- Holley Sniper EFI Sheet Metal
- Edelbrock Victor EFI
These are the top 4 options for upgrading the intake manifold on your 6.1 HEMI. The aftermarket for the 6.1 HEMI intake manifold is relatively thin, leaving your choices to be either porting the stock unit, Holley, or Edelbrock. Still, these are all good units that have their own unique benefits, which we’ll get into below.
1) Ported Stock 6.1 HEMI Intake Manifold
The first recommendation we have is to port the stock 6.1 HEMI intake manifold. Porting is a good option for a number of different reasons. One, it is by far the cheapest way to go. While you can send it out to Modern Muscle for them to port the manifold, that’s the most expensive way to do it at $649.00. Local performance and machining shops should be able to port your intake manifold for around $300 depending on your location and local market.
Porting is essentially smoothing and honing the inside of the throttle body to get rid of any roughness, imperfections, or restrictions, that might impede airflow or create too much air turbulence. It’s a relatively simple process that will still give you power gains of roughly 5-15 wheel horsepower on its own.
Porting is such a popular option not just because of its low cost and power gains, but because most aftermarket units won’t make much more horsepower. Getting 5–15 wheel horsepower out of a manifold is a pretty good change, and most aftermarket units will yield maybe ~5 wheel horsepower more at the most.
Unless you plan on running forced induction and boost through either a turbocharger(s) or centrifugal supercharger, porting the stock unit is probably your best bet. It retains stock fitment and will net similar power gains and a much lower price. It will, however, still weigh more than an aftermarket manifold.
2) Holley Hi-Ram EFI Intake Manifold for SRT8
Next on our list is the Holley Hi-Ram EFI intake manifold for the 6.1 HEMI. Holley has been one of the top names in HEMI performance for a long time, and their intake manifolds are highly reviewed and recommended.
The Hi-Ram EFI intake manifold is made from cast aluminum and has long runners. It will be good for making low-end power, and has pads to install nitrous nozzles. The manifold sits pretty high in the engine bay, hence the name, but looks very clean. It can be used for both naturally aspirated and forced induction applications.
The inlet for the throttle body is 95 mm, which is considerably larger than the stock 80 mm. Importantly, some hoods might have clearance issues with this intake manifold, so it is best for those utilizing a HEMI swap. Stock hoods will likely require modification.
3) Holley Sniper EFI Sheet Metal Intake Manifold for SRT8
Third on our list is another option from Holley, the Holley Sniper EFI Sheet Metal 6.1 HEMI Intake Manifold. The Sniper line of intake manifolds are immensely popular on many applications, not just HEMI, and are very well reviewed.
Compared with the Hi-Ram, the Sniper is much lower profile and has shorter and wider runners. It is also a sheet metal intake, so it will weigh less than the Hi-Ram and stock units, too. The sniper uses thick aluminum for maximum durability, and the runners use tapered tops to increase air velocity and distribution.
The throttle bore is 90 mm on the Holley Sniper, making it 5 mm smaller than the Hi-Ram. Like the Hi-Ram, the stock 80 mm throttle body will not fit without modification. The Holley Sniper should fit under stock hoods without issue, and will give similar 5–20 wheel horsepower gains like the Hi-Ram.
4) Edelbrock Victor EFI Intake Manifold for SRT8
The final recommendation we have is the Edelbrock Victor 6.1 HEMI intake manifold. Edelbrock is one of the most reputable companies in the performance industry, and have been making parts for muscle cars literally since they were first created in the 1950s and 1960s. They have been widely known for their carburetors and intake manifolds for decades.
The Edelbrock Victor EFI intake manifold looks similar to stock but flows much better. It has longer flowing runners and relocates the fuel injector bosses for the best flow possible. Unlike the Holley options, the Edelbrock can use the stock 80 mm throttle body without any modifications.
The manifold is made from cast aluminum, and comes with a black powder coated finish. The Edelbrock will clear factory hoods without a problem, but does need a fuel rail kit installed alongside it, due to the relocation of the injectors. It is a little pricey, but the Edelbrock is probably the best bet for those with factory 6.1 HEMIs looking to add forced induction.
6.1 HEMI Intake Manifold Summary
If you’re looking at upgrading the intake manifold on your 6.1 HEMI, you have a lot of good options. Upgrading (or porting) your intake manifold will add horsepower and torque, shed unnecessary weight, increase airflow, increase engine volume, and add a nice visual appeal to your engine bay. Intake manifolds won’t gain insane amounts of power, but it will definitely be noticeable.
For most people, porting their stock intake manifold will probably be the best option. It will give you similar gains as an aftermarket unit, while still retaining stock fitment and throttle body. If you plan on boosting your 6.1 HEMI powered SRT8 with either a turbocharger or centrifugal supercharger, the Edelbrock Victor manifold is a great option. It has longer runners than stock and can use a larger throttle body.
If you have a HEMI swap, you will probably be looking at either of the Holley options, the Hi-Ram or Sniper. Both of them are good options, with the Sniper costing more and being lower profile than the Hi-Ram.
Which intake manifold are you leaning towards on your 6.1 HEMI? Let us know in the comments below!