Since its inception in 1997, the LS1 has become the darling of the aftermarket automobile world. Capable of outstanding power straight from the factory, the engine was first transplanted into our beloved Firebirds in 1998, with horsepower and torque ratings of 305 and 335, respectively. WS6 and Firehawk owners received a few more ponies courtesy of the changes to these factory wonders by ASC and SLP, and put out 320 hp and 345 lb-ft of torque.
It wasn't until the '01 model year that the GM engineers made some significant tweaks to the engine. The LS6 intake manifold that debuted on the Corvette Z06 became the standard intake on the LS1, while the EGR valve was eliminated. Exhaust flow was increased with a less restrictive set of catalytic converters, and the camshaft offered a different ramp profile on the same 116 LSA, with less overall duration and lift than the '98-'00 F-body camshaft. All told, these changes added up to an increase of 5 hp and 5 lb-ft of torque, giving owners of the standard Formula or T/A 310/340, while WS6, CE, and Firehawk owners received 325/350.
It didn't take long for the owners of the LS1-equipped Birds to start searching for additional power. With this quest came a whole genre of engine and induction modifications commonly known as the "Free Mods." Technically, not all of them were free, but we will categorize them that way and then list the most popular "cost effective" engine and induction mods as well.
Owners can shop from the buffet of free and cost-effective mods provided here, and in an afternoon of work easily gain between 10 and 30 rwhp. Higher gains can be achieved on cars that have significant modifications to the exhaust and those with higher lift camshafts and/or additional cylinder head work.
According to Brian Lohse, co-owner of Real Performance Motorsports, "The LS1 to LS6 intake swap for '98-'00 Birds is one of the most popular bolt-on modifications for the LS1. The additional airflow capabilities of the LS6 intake allow it to consistently add from 10-15 rwhp over the LS1 intake on a stock-bore, 346ci engine. We see increases across the entire power range due in part to the increase in plenum volume from 5.06 liters to 5.19 liters, without a change to the overall runner length. Not only were the runner shapes redesigned, but the EGR tube that protruded into the top front of the LS1 manifold and disturbed airflow was eliminated.
"To further enhance the power of the LS1, we like to utilize an aftermarket lid to both smooth and increase the amount of airflow into the engine. The factory airbox is restrictive in that the air baffles located on the left and right sides of the lid disrupt the flow of air through the assembly, while the oblong-shaped airbox assembly exit reduces and disrupts the flow of air to the engine.
"Additional power can be gained by taking the excellent factory 75mm throttle body and having it either ported and polished or by replacing it with an aftermarket piece. By increasing the airflow into the motor and then utilizing the enhanced flow capabilities of the LS6 intake, gains of 20-25 rwhp are easily obtainable, with no loss in driveability.
"For horsepower-to-dollars spent, the lid, intake, and throttle-body modifications are hard to beat. Should the owner later want to further increase the power with headers and a head/cam swap, the changes made on the induction side will support additional modifications without any fear of having to spend more money changing out what has already been done. The LS6 intake manifold support upward of 500 rwhp and is the best factory manifold available to feed a stock-cubic-inch LS1. For the purist looking for additional power, all that is required to go back to 'stock appearing' is to put the factory airbox back on."
Follow along as we install an LS6 intake manifold on a '99 Trans Am and then supplement the manifold swap with an aftermarket lid and ported throttle body. Don't worry, as all of the free and low-buck modifications will be performed, with the exception of the airbox mod. Since the airbox mod modifies the airdam and the lower airbox, it is best intended for those drivers whose vehicles will never see the elements, specifically rain.
In Part II, before-and-after dyno pulls will be completed to document the stock car and the impact the LS6 intake, aftermarket lid, and ported throttle body provide to the overall power increases. With a lofty goal of a minimum of 20 rwhp, we have our work cut out for us.
The '99 T/A is owned by Kadin Betts, a graphic designer from Carrollton, Texas, who uses the car as his daily driver. This black, six-speed beauty was picked up used in 2004 for under $9,000 and has racked up only 57,000 miles.
Installation and testing of the modifications were done at Real Performance Motorsports in Lewisville, Texas. Real Performance Motorsports specializes in late-model General Motors performance, and can take care of all of your Firebird, GTO, and Grand Prix needs.
Free Mods (And Low-Buck)
Cost-Effective Mods
Recommended Tools
Recommended Parts And Supplies
Stay tuned for Part II, where we will complete the bolt-on installations and dyno test the T/A.
