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Converting a Fourth-Gen V-6 to an LS Engine

The Big Swap


Those of you longtime readers may remember our good friend and fellow SIM Editor, Mr. Jay Heath, the former owner of our '99 LS1 Trans Am project that raucously pounced Englishtown Raceway Park with such proficiency using mere bolt-ons until its final days when it received a ProCharger. Jay has owned several Firebirds over the years, and once again decided to return to the Big Chief. But the problem he faced was one that no doubt many of you have, if you were in the market for a fourth-gen recently. He wasn't willing to pay C5 money for a fourth-gen LS1, and there wasn't much in that price range that didn't need significant work (if it was salvageable in the first place). Thus came the nearly regrettable thought of purchasing a V-6 Firebird and using the leftover money to convert it. Now for a gutted racecar, using a V-6 car is a no-brainer. But if you actually want functioning OEM gauges, creature comforts, and reliability suitable for a daily driver – that is going to take time, effort, and some real craftiness.

And of course, if you are looking for craftiness, AntiVenom is the shop to call. Owner Greg Lovell is a wellspring of craftiness, and he was able to make the impossible possible. Having built, stripped, and parted out more fourth-gens than almost any human on the planet he happened to have possession of nearly every part needed to complete the swap. For those of you attempting this at home, I suggest you start gathering the parts you see in this story over the course of the next year. If you don't already have a head start, it is going to take some time or a full parts car. In case you are wondering, Greg said wrecked LS1 fourth-gens cost on average around $1,800 (though as little as $750). And the faded black '99 Firebird (here-to-forth known as Ashy Larry) that Mr. Heath purchased cost a scant $1,400. Doing quick math, you can recreate this swap at home for $3,200 total, including the price of the car.

But as you might suspect from GMHTP, we had no intention of using a bunch of stock parts that would prevent this Firebird from keeping up with all the modern muscle we encounter on the streets today. We made a few key upgrades to enhance the performance. Instead of using a stock LS1, we sourced AntiVenom for a 6.2L L92 from a low-mile Escalade that had a few bent valves that were replaced. To make it compatible with an LS1 PCM the VVT phaser and camshaft along with the DOD lifters were replaced by LS3 lifters, timing set, cover, and an LS9 cam (for more on this popular swap stay tuned for a later issue of GMHTP). Out the door the total cost for this setup is $3,200, which does not include an LS3 manifold (leftover from a previous project) and 90mm cable throttle body from AntiVenom. To rectify the compatibility issue with the 58x reluctor wheel, Jay also picked up the Lingenfelter Crank Sensor Trigger Conversion Module.

To complement the 6.2L we made sure to pick up some high-flowing intake and exhaust components as well as a well-built transmission. The folks at Hooker Headers had a brand-new set of Super Comp 1 7/8-inch ceramic coated headers and 3-inch mandrel-bent exhaust with an Aerochamber muffler ready to ship out when we called them, so the process couldn't have been any easier. If you haven't installed a set of Hookers in a while, these long-tubes are worth giving a look. The larger primary tubes, 3/8-inch flanges, and the Power Spear in the 3-inch, 4-into-1 collectors (to aid scavenging) really ups the ante. An air intake was sourced from K&N Filters, the 50-state legal FIPK, though we later found out that the V-6 and V-8 models use the same upper radiator support, so a stock style air lid will also work. Regardless of which route you go, the key is to not use a stock piece here if you want to make power. Last but not least, we called Performabuilt transmissions for one of its 4L60E Level 2 packages with a billet 9-inch converter. This stout piece comes complete with upgraded clutches, bands, and a full two-year warranty.

With parts in hand and our Ashy Larry project on the ready, we headed off to AntiVenom in Seffner, Florida to commence the 48-hour overhaul. Follow along for the details.


After making a few tweaks, Larry belted out a whopping 405hp and 385.9 lb-ft of torque on AntiVenom’s Dynojet. Not bad for a factory cam with bolt-ons! Since the dyno session the Firebird has been daily driven with no issues to date, and the owner loves his newfound power and reliability.


Hooker Headers
Aberdeen, MS 39730
Seffner, FL 33584
PerformaBuilt Transmissions
Sugarloaf, AK 18249

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