LS6 Fast LSXR intake manifold
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LS1 and LS6 Intake Manifold 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.

The third generation of General Motors’ small-block V8 engine was one of the most iconic, with the 5.7 liter LS1 and LS6 engines leading the way. GM and Chevrolet put the LS1 and LS6 inside the Corvette, Firebird, Camaro, and even the Cadillac CTS-V. From the factory, the LS1 makes 305–350 horsepower and 335–365 lb-ft of torque. The LS6 is a bit more powerful, at 385–405 horsepower and 385–400 lb-ft of torque. By now, both engines are over 20 years old and ripe for some enhancements, with LS1 and LS6 intake manifolds leading the way. Read on to find out the best LS1 and LS6 intake manifold upgrades to make the most horsepower and torque. 

How does an LS1 and LS6 Intake Manifold Work?

First, let’s talk about what an intake manifold’s purpose is and how it works. Intake manifolds are part of a car’s intake tract and are the last step before air reaches the engine itself. LS-series intake manifolds sit directly on top of the cylinder heads. They take in air from the throttle body and air intake system. In most cases, the intake manifold also houses the fuel injectors, too.

There are two basic parts of an intake manifold: the plenum and the runners. The plenum is the “top” of the manifold that air initially rushes into. After the plenum is full, the air travels down through the runners, which sit directly on top of the heads. There is one runner per cylinder, so LS-series intake manifolds have eight runners with four on each side (or “bank”). Each runner has its own individual butterfly-valve, that when open allows air to flow through to the engine. 

The purpose of an intake manifold is to quickly and evenly distribute air to all of the engine’s cylinders. Typically, aftermarket intake manifolds will have a larger volume and superior flow characteristics when compared with the stock manifold. Upgrading your intake manifold is one of the best and most cost-effective ways to increase the amount of air that goes into your car’s engine, which is how you create more horsepower and torque. 

What Does a Performance Intake Manifold Do?

You might think that if increasing airflow and air volume is the name of the game, just slapping the biggest intake manifold will net the most gains. But you can be forgiven. While increasing the size of the manifold compared with stock is usually automatic, it still has to be sized correctly. As you’ll see, understanding pulse-reversion is key to understanding intake manifolds. 

Manufacturers design intake manifolds to take advantage of certain flow characteristics, one of these is pulse-reversion, and this is how it works. When air enters the intake manifold, it fills the plenum and then travels down through the runners and into the engine. However, whenever the intake valve on the engine closes it stops the air from coming in.

This creates a problem for the air, and the closing of the valve results in a high pressure wave traveling back up the runners. When the wave hits the top of the runners at the plenum, it creates a new wave that is forced back down. If the intake manifold has been designed correctly, the downward pulse should reach the intake valve while it is open again. This sends an extra surge of air into the engine, almost like a supercharger. 

Manifold Runner Size

That’s why it’s important to have an efficiently designed intake manifold that takes advantage of the pressure waves. Both the size and shape of the plenum and the diameter and size of the runners affect how manifolds work. Longer and narrower runners are good for lower-rpm performance when the air is traveling slower. While shorter and wider runners are better for higher-rpm performance when air is traveling faster. 

However, that’s not always the case. Sometimes, longer intake runners will be good for higher-rpm operation if they are also sufficiently wide enough. Many intake manifolds have variable length runners. These combine different sized runners for better performance across a larger rpm-range.

The Stock LS1 Intake Manifold and the LS6

GM introduced the LS1 in 1997, four years before releasing the LS6. However, both of them use the same cathedral-style intake ports for the cylinder heads. This means that LS6 intake manifolds will fit the LS1, and LS1 intake manifolds will fit the LS6. This also applies to the slightly larger LS2 engine, which also uses the cathedral port design: Making all LS1, LS2, and LS6 manifolds compatible with each other. The LS2 intake uses a slightly larger throttle body, but the LS6 intake still outflows it. 

Of them all, the stock LS6 manifold is by far the highest flowing. In fact, from 2001-on, Chevrolet replaced the stock LS1 intake manifold with the stock LS6 intake manifold because it was so much better. That makes the stock LS6 a great upgrade for 1997–2000 LS1 engines, which we’ll get into more about below. 

LS1 and LS6 Intake Manifold Upgrade Benefits

The top benefits to an LS1 intake manifold upgrade and an LS6 intake manifold upgrade are:

  • ~10-30 horsepower and torque
  • Increased air flow over stock manifold
  • Increased engine volume/noise
  • Visual appeal

The biggest benefit to an LS1 intake manifold upgrade or LS6 intake manifold upgrade is the increase of horsepower and torque. By better harnessing the pulse-reversion phenomenon we talked about above, aftermarket intake manifolds should add anywhere from 10–30 horsepower and torque. The increased air volume also helps to add power.

In addition, you will probably hear your new intake manifold when you are behind the wheel. Similar to installing a performance intake, you can usually audibly hear the new part sucking in air and working. 

Finally, having an aftermarket intake manifold will noticeably change how your entire engine bay looks. Depending on what you buy, you can either get a more sleek look or a more bare-bones manifold, and they will definitely give everything a more race-like feel. 

Porting and Polishing and Bigger Throttle Bodies

Many people will recommend porting and polishing an intake manifold instead of getting an aftermarket unit. Porting and polishing involves smoothing and honing the inside of the manifold to help improve air flow. It is a much cheaper service than buying a new manifold, which is what makes it popular. However, most people have only seen minimal if any gains from doing so on the LS1 or LS6 intake manifolds, and it’s usually not worth the price. 

Another modification that goes right along with an intake manifold is getting a larger LS6 or LS1 throttle body. The throttle body attaches to the plenum of the manifold and feeds it air from the air intake. A larger throttle body will allow for more air into the plenum, but unless you upgrade the plenum size you won’t see much gains. That means if you want to upgrade the throttle body with your intake manifold it can be worthwhile, but by itself it won’t do much. 

Best LS1 and LS6 Intake Manifold Upgrades

LS1 MSD Atomic Airforce Intake

The LS1 and LS6 Intake Manifold Upgrades are:

LS1 Intake Manifold Upgrades:

  • LS6 Intake Manifold Swap to LS1
  • Holley Hi-Ram EFI
  • MSD Atomic Performance
  • Fast LSXR 102 mm

LS6 Intake Manifold Upgrades:

  • Holley Hi-Ram EFI
  • MSD Atomic Performance
  • Fast LSXR 102 mm

LS1 Intake Manifold Upgrades

1) LS6 Swap

Price: $400+

Our first recommendation for an LS1 intake manifold upgrade is to swap out the stock manifold for the superior LS6 stock manifold. This only applies to 1997–2000 LS1 cars. The 2001+ got the LS6 manifold from the factory, which should be pretty indicative of its increase in performance. 

Importantly, if you have an F-Body LS1 (Firebird or Camaro) things are a little more complicated than for the Corvette. For the F-Body to pass emissions with the LS1, GM had to use an EGR system, which was integrated into the manifold/heads. The LS6 (including the F-Body) did not use an EGR system, so the intake manifold does not have one integrated. This means the LS6 manifold will not bolt directly to the F-Body LS1 without modification due to the EGR-heads. The Corvettes have no problem because there is no EGR system in their cylinder heads. 

Still, the LS6 intake manifold vastly outflows the LS1, making it a great upgrade if you can get correct fitment. SLP did make an LS6 manifold with an EGR port for the F-Body conversion, but those are long out of production and difficult to find. With the LS6 intake manifold upgrade swap, you can expect 25 horsepower and torque gains. 

2) Holley Hi-Ram EFI LS1 Intake

Price: $1,031.95

Next on our list for the LS1 intake manifold upgrade is Holley’s Hi-Ram EFI LS1 intake manifold. Holley has been one of the biggest names in the American muscle performance business for many years. Their intake manifolds are widely used and celebrated by enthusiasts from pretty much every make and model of American muscle. 

Holley’s Hi-Ram intake manifold is made from cast aluminum and has a high-riser style (as you might expect). High-riser intakes are best at making horsepower in the upper-rpm range when compared with mid or low-riser intakes. The ideal rpm power band for the Holley Hi-Ram is from 3,500–8,000 rpm. It is good for both naturally aspirated and boosted engines. 

When compared with the stock LS1 intake manifold, the Hi-Ram produced gains of more than 60 horsepower, with most of the gains coming after 5,500 rpm. The Holley LS1 unit is one of the most capable intake manifolds on the market, and you won’t be disappointed.

3) MSD Atomic Performance LS1 Intake Manifold

Price: $1,157.95

Third on our list is the MSD Atomic Performance LS1 intake manifold. For several years the MSD Atomic Performance intake has been one of the most well regarded LS1 intakes out there. It uses polymer construction for reduced weight, and is of a two-piece design. The throttle body bore is substantial at 103 mm, meaning a wide variety of throttle bodies can be used.

Compared with the high-riser Holley, the MSD manifold looks completely different and much closer to the stock unit. It has vastly increased airflow over the stock unit, and is CARB certified with its own EO number. It’s a great option for those in California or other more strict emissions states. 

On the dyno, the MSD intake manifold made almost as much horsepower as the Holley Hi-Ram, and lots more torque. The two were very close, with the MSD showing better gains earlier and the Hi-Ram edging it out at the top of the rpm chart. Either way, both performed incredibly well, with the MSD midrange edge potentially making it better for street builds. 

4) Fast LSXR 102 mm LS1 Intake

Price: $1,150.00

Our final recommendation for the LS1 is the Fast LSXR 102 mm LS1 intake manifold. This manifold has been around for several years and is widely considered to be the best aftermarket LS1 intake manifold. Fast also makes a 92 mm LSX intake, but we suggest the updated LSXR 102 mm. 

The Fast LSXR LS1 intake uses polymer material, like the MSD, and is very close to stock appearance. Racers have used the LSXR with both naturally aspirated and boosted applications, and it does a fantastic job of increasing horsepower and torque. 

On a dyno, the Fast LSXR made nearly 60 horsepower and more than 35 lb-ft of torque over the stock unit. Even better, the LSXR showed gains for the entire power band, meaning that everything is more powerful, not just the top end. Other manifolds, like the Holley and MSD, did not really shine until past 4,500 rpm. The Fast manifold picks up gains everywhere. 

LS6 Intake Manifold Upgrades

1) Holley Hi-Ram EFI LS6 Intake Manifold

Price: $1,031.95

LS6 Holley Hi-Ram EFI intake

For the LS6, we recommend the Holley Hi-Ram EFI LS6 intake manifold upgrade. This is the same unit as we suggest for the LS1, and it also shows good gains for the LS6, too. It should be noted that due to the high-riser style of the intake, it might not fit all hoods that are non-stock. So if you have an LS6/1 swap you might want to make sure there is enough clearance before purchase. 

Like on the LS1, the Hi-Ram does its best work on the LS6 in the higher rev range past 5,000 rpm. It can support boosted or naturally aspirated engines, and is the go to for those looking to make the most horsepower. 

2) MSD Atomic Performance LS6 Intake

Price: $1,157.95

For our next LS6 recommendation, once again we are going with an LS1 favorite, the MSD Atomic performance LS6 intake manifold. Similar to the Holley (and the Fast LSXR), the MSD LS intake performs very well on the LS6, too. Gains will not be as dramatic, due to the better flowing stock manifold, but they are still significant.
On the LS6, the MSD will offer earlier torque and horsepower gains than the Hi-Ram, though the Hi-Ram will ultimately produce more horsepower. The final numbers are relatively close, close enough that we would be happy with either for our build. They do look dramatically different, and the MSD offers better hood clearance, so those may be deciding factors for some. 

3) Fast LSXR 102 mm LS6 Intake

Price: $1,150.00

For our final LS6 recommendation, we are going with the Fast LSXR LS6 intake manifold. This is again the same unit as for the LS1, but it fits the LS6 and works exceptionally well. Once again, enthusiasts widely agree that the Fast LSXR intake is the best for the LS6 hands down. It provides torque and horsepower gains throughout the power band, and is comparable in price with other leading brands. It mimics the stock appearance and hood clearance is never an issue, making it the top choice for most LS6 customers. 

LS1 and LS6 Intake Manifold Upgrade FAQ

What is the best LS1 intake manifold upgrade?

The best LS1 intake manifold is the Fast LSXR intake manifold.

What is the best LS6 intake manifold upgrade?

The best LS6 intake manifold is the Fast LSXR intake manifold.

Does the LS6 intake manifold fit the LS1?

Yes, both the LS6 and LS1 engines use the same style intake manifold.

Is the LS6 intake manifold better than the LS1?

Yes, the LS6 intake manifold is vastly superior to the LS1 intake manifold. It flows better and produces more horsepower and torque.

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