Simply put, an engine is a pump. By increasing its ability to ingest fuel and air, convert it to energy, and evacuate the remains, it will make more horsepower. We set out to show just what you can expect from installing a better-flowing intake manifold on your mildly modded LS1 Pontiac using Chris Kirchner’s ’99 T/A.

If you’re just joining us, here is a little background information. We started off with a lightly modified LS1 that had an old MTI T1 cam (221/221 degrees duration at 0.050 and 0.558/0.558 lift on a 112-degree LSA, versus the 202/210-deg, 0.496/0.496 lift, 116-LSA that came stock), a set of mid-length headers, a Hooker exhaust, and an LS1 Motorsports lid. The mid-length headers were tossed and we picked up some power by going to new BBK 1.75-inch-primary long-tube headers. We converted the car to a 90mm LS2 intake so that we could run a Zex plate nitrous system.

The two engine mods we’ve installed so far have enhanced the performance of our LS1, but now we’re looking to take it a little further by ditching our modified LS2 manifold for the FAST LSXR 102mm intake. For an apples-to-apples comparison, we installed an LS1 intake to establish a new baseline on the Ramsey’s Performance Dynojet.

LS1 and LS6 Intakes

The LS1 intake flowed adequately for a stock LS1 back in the day, but was retired after the ’00 engine model year. It was replaced by the LS6, another 76mm intake, which flowed considerably better.

F-Body LS1 and LS6 intakes are easy to differentiate since the LS1 has an EGR provision behind the inlet and the LS6 does not. However, don’t be fooled. To this day there are still people trying to pass off LS1 intakes as LS6s to make a buck. Corvette LS1 intakes did not come with the EGR provision, so it visually looks identical to the LS6 intake. The only sure way to tell if its an LS6 is to flip it over and see if there is a flat bottom, identifying it as such. See the chart to check your intake manifold. The average price for a legitimate LS6 intake on eBay is around $400-$550, used and new.

LSXR 102

While the LS6 is a good intake, the manifold developed by FAST is even better. The engineers flipped the LS1 market on its head when it came out with the original 78mm and 90mm intakes. Since then, FAST has made dramatic improvements over its previous designs to bring out its ultimate creation, the 102mm LSXR. While the 346ci LS1 doesn’t come close to utilizing this intake’s full potential, it still did well in our test. With a good set of heads or a more aggressive cam, the intake will efficiently deliver even more power.

Not only was the LSXR 102mm intake developed as an upgrade over the previous units, it was also designed to work with four-bolt, popular-sized throttle bodies without a problem. Brian Reese, vice president of product and business development at the Comp Performance Group, discusses the LSXR series manifold.

Brian Reese: “The 78mm manifolds were discontinued years ago because people weren’t buying them. Then, we replaced the 90mm intake with the 92mm, which required making some tooling changes to the original LSX manifold. I figured if we are forced to change the tooling, we might as well improve the manifold and increase the bore, yet still ensure that all FAST and OEM 90mm, four-bolt throttle bodies bolt on.

“Our latest manifold is the 102 LSXR, which also accepts 90 and 92mm four-bolt throttle bodies, so producing a 92mm LSXR is unnecessary. The LSXR replaced the LSX manifold because it offers multiple improvements and value over the LSX—it has both front and rear MAP sensor provisions, handles higher levels of boost, has individual runners and increased plenum volume, and it fits Corvettes without modification.

“There’s a rumor that the larger diameter manifold is too big for stock or small-cubic-inch LS engines. This is 100-percent false. The larger size simply reduces restriction, this is true regardless of engine size or modifications.”

Let’s see how the LS1, LS6, and FAST intakes compare on the dyno.