LS1 and LS6 Intake Manifold Upgrade Guide

The third generation of General Motors’ small-block V8 engine was one of the most iconic, with the 5.7L LS1 and LS6 engines leading the way. One of the best ways to improve power and performance on the LS1 and LS6 engines is through an intake manifold upgrade. Aftermarket intake manifolds will have a larger volume and superior flow characteristics when compared with the stock manifold.

Ultimately, a manifold upgrade will net around 25-30 horsepower gains on both the LS1 and LS6 engines. There are a lot of things to consider like manifold runner size, pulse reversion, and throttle bodies so we’ve compiled this guide to teach you everything about manifold upgrades. Additionally, we discuss the popular LS6 to LS1 intake manifold swap.

LS1 and LS6 Intake Manifold Upgrade Benefits

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

The biggest benefit to an LS1 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. 

Manifold Runner Size

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. 

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.

Understanding Pulse Reversion

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. 

Porting, 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 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. 

LS6 to LS1 Intake Manifold Swap

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. But, for earlier model LS1’s this is going to be the best option for upgrading the manifold.

Importantly, if you have an F-Body LS1 it’s a bit trickier. To pass emissions, GM had to use an EGR system, which was integrated into the manifold/heads. The LS6 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. With the LS6 intake manifold swap, you can expect 25 horsepower and torque gains.