Bolt-on power gains on GM’s venerable LT1 motor

It wasn’t too long ago that GM’s LT1 engine found its way under the hood of nearly everything that had a performance flavor to it.

Most commonly, the LT1 5.7L was in Chevy Corvettes, Camaros, Pontiac Firebirds, Trans-Ams, and even Impala SS models. The LT1 proved hugely popular and was the hot ticket. That is, until GM introduced the LS1 motor, which offered superior performance and more potential than the LT1. Suddenly, GM enthusiasts had all but forgotten about the LT1 mill. Well, we are here to help preserve the legacy that the LT1 so rightfully deserves and show you some quick and budget-friendly ways to get more from your LT1.

We teamed up with GTR High Performance (Rancho Cucamonga, California) to try some old-school tricks on an old-school motor. Finding a stock LT1 equipped car proved more challenging than expected, but eventually we located Chris Jocson’s 1997 Pontiac Trans Am outfitted with an automatic transmission. GTR wasted no time in strapping the car onto their DynoJet chassis dyno to establish a baseline. As delivered, it put down 235 rear wheel horsepower (rwhp) and 270 lbs-ft. rear wheel torque (rwtq). Not bad considering the automatic transmission and mileage on the car.

Knowing that our tester would be subject to countless dyno runs, GTR began with basic maintenance courtesy of Royal Purple. The entire Royal Purple synthetic treatment was given to our high mileage warrior: Royal Purple motor oil and oil filter, automatic transmission fluid, power steering fluid and differential gear oil. Do-it-yourselfers can expect to pay about $197 for all the Royal Purple products we used, which is a small price to pay for reliability.

Having used Royal Purple on other projects, we knew it offered unsurpassed protection and performance. With newfound peace of mind, GTR put the Trans Am through its dyno paces and we were pleasantly surprised to discover an extra three rwhp and four rwtq. Extra power is always nice, but when you can get more power with better protection and durability, that seems like a win-win to us.

Next, we wanted to see how the LT1 would react to improved airflow provided by SLP’s Throttle Body Flow Booster. Installation was a snap, requiring only basic tools and about 30 minutes. SLP’s Throttle Body Booster handily won the “best-bang-for-the buck” award, yielding an extra seven rwhp and nine rwtq. The extra power was available throughout the entire rpm range, from the moment GTR buried the pedal until redline. Best of all, the Throttle Body Booster will only set you back $36. No, that’s not a misprint! Working out to $5 per horsepower and $4 per lbs-ft torque it was an absolute steal. Skip lunch for a few days and buy yourself SLP’s Throttle Body Booster; your LT1 will be grateful.

The LT1 reacted favorably to extra airflow, so we figured if some was good, more had to be better. Next on the agenda was Trick Flow Specialties’ cold air induction kit. More upgrades were soon to come, so we needed a good foundation to keep building power and without a well-designed air induction system, our results would be limited. Trick Flow’s kit gave us a 50-state legal upgrade that lends a handsome, understated finish under the hood. Installation is simple and should be within the scope of most auto enthusiasts.

Our tester also received TFS’s cast aluminum inlet elbow, which not only helps flow a bit more air, but also completes the look. All told, the entire TFS kit set us back $315. Solid gains through the entire dyno test rpm range were realized. Overall, we gained an extra four rwhp and four rwtq by letting the LT1 breathe deeper.

Having finished the air induction upgrades, GTR focused on trying to keep the LT1 cool. Through the course of our dyno testing and from previous experience with other LT1 cars, we knew these engines had a tendency to run warm, especially when driven hard. SLP supplied us with a lower temperature 160° thermostat to promote cooler engine temperatures. All engines create more power if the coolant temperatures are kept to a minimum and the LT1 is no exception. The car’s computer monitors engine coolant temperature and once it exceeds a certain temperature, the computer will retard ignition timing, which lowers power output. We gave our LT1 a shot of Royal Purple’s Purple Ice cooling additive which promotes better heat dissipation to complement SLP’s thermostat.

Out of all the parts we tested, this step was the easiest and cheapest at about 25 minutes and $25, respectively. Back on the dyno rollers, the LT1’s power output continued to climb with an extra two rwhp and one rwtq. It now rested at 251 rwhp and 288 rwtq. Although not a huge power increase, this is one of those simple “no-brainer” upgrades that should be at the top of everyone’s list. It’s easy and cheap insurance for your engine’s cooling system.

It was finally time to open up the exhaust side with Magnaflow’s cat-back kit and allow the LT1 to exhale. Our test vehicle was already outfitted with an aftermarket, chambered type muffler that made a lot of noise and not much else. We were glad to ditch the “backyard mechanic” exhaust that was on our test car in favor the stainless steel and mandrel bent work of art from Magnaflow. The exhaust note was so much more pleasing to the senses. No more angry snarls and backfires when the throttle was cracked open, but rather a smooth, powerful tone that spoke fluent muscle car. Interior noise levels were controlled with no drone, making a conversation with passengers possible.

Priced at $445, the Magnaflow cat-back was the most expensive upgrade tested, but considering that it’s constructed from stainless steel and the sheer size of the exhaust, that is to be expected. Regardless of price, it’s worth every cent as the look and sound that the Magnaflow gave the Trans Am was just right.

We expected more power from the Magnaflow system, but were pleasantly surprised to see an extra nine rwhp and six rwtq over the other aftermarket muffler. No doubt the gains would have been larger had we compared it to a factory-stock muffler. Once again, we saw extra power and torque through the entire rpm range, which points to Magnaflow’s high-flow design. Furthermore, close evaluation of the dyno-data showed that until the Magnaflow system was installed, the horsepower output would peak at or below 4,700 rpm, which indicates that the exhaust was restricted. With the Magaflow exhaust installed, power climbed eagerly all the way to 5,000 rpm, thereby extending the usable rpm range. We rested comfortably at 260 rwhp and 294 rwtq, but knew something was missing (literally).

Towards the end of our dyno test session, we had noticed that the motor had developed a high-rpm misfire that got progressively worse as the power continued to climb. A conversation with the vehicle owner revealed that the spark plugs were well overdue. In addition, the LT1 had been chugging down performance-killing 87-octane all along! Both factors were holding us back from achieving our full potential. Running short on time, GTR decided to siphon the watered-down 87-octane and pour in California’s finest 91-octane. There simply was no time to replace the spark plugs, so we had to make do.

With a few gallons of 91-octane fuel, the engine’s sensitive knock sensors weren’t retarding timing anymore, which revealed extra hidden power. By feeding the LT1 91-octane fuel, which should be mandatory, power increased by eight rwhp and seven rwtq! It was done by using the proper fuel that it should have had to begin with! Talk about cheap power; these gains came at a cost of an extra 20 cents per gallon over 87-octane. Lesson learned: never underestimate the importance of basic maintenance and proper fuel!

In summary, we took a stock LT1 Trans Am that rolled in with 235 rwhp and 270 rwtq and pumped it up to a respectable 268 rwhp and 301 rwtq. Peak-to-peak gains of 33 rwhp and 31 rwtq were realized, but even more impressive were the overall largest gains of 34 rwhp and 37 rwtq achieved at 4,800 rpm. Studying the dyno results also reveals an extra 20 rwhp and 27 rwtq as early as 3,900 rpm.

The end result is a strong street-performer that drives better than the above numbers would indicate. All told, the LT1 formula will cost around $1,018 in parts for you to duplicate our results, which is a relative bargain in the world of high–performance auto parts. Dissecting it further, this translates to $31 per rwhp gained and $33 per rwtq gained, which is as cheap as it gets.

Have a stock LT1 powered car and not sure where to begin? Just follow our performance-enhancing recipe for excellent results that won’t break the bank. Just don’t overlook the small stuff.