The crew has burned through a box of donuts and two pots of coffee, the 6.6-liter is strapped to Brian Tooley Racing’s SuperFlow engine dyno, and now it’s time to party! We are back with the second installment of our latest engine dyno shootout we call “L8T To The Party,” where we take a bone-stock factory 6.6-liter L8T crate engine from Chevrolet Performance and see what kind of power it can make with off-the-shelf performance parts and more.

If you missed our introduction to this series, the 6.6-liter L8T has been offered by GM since the 2020 model year as the base gas engine for its heavy-duty line of pickup trucks. It is part of the direct-injected Gen-V LT engine family and has gained popularity due to its thick-cast factory iron block and forged crank with a 3.858-inch stroke. We teamed up with Chevrolet Performance and the crew at Brian Tooley Racing to throw this big-inch LT on their engine dyno with a long list of performance parts to see if this tame workhorse can actually be modified to haul more than just your race car or boat.

After a brief break in period on the engine dyno, it was time to make the first power pull on this brand new, all-stock crate engine.

Fresh Out Of The Crate – The Baseline Runs

In stock form, the L8T is rated at 401 horsepower at 5,200 rpm and 464 pound-feet of torque at 4,000 rpm. That power level was rated by GM with 87 octane fuel, stock exhaust, accessory drive, and a tune in the factory computer that is very conservative. That allows the engine to live a long life, even with customer abuse and heavy towing.

The L8T uses variable valve timing, direct injection, and a low-octane-friendly 10.8:1 compression ratio, but thankfully does not come with the finicky dynamic fuel management system and it’s failure-prone lifters. With the 6.6-liter strapped down to BTR’s dyno, it does not run an accessory drive, the stock exhaust has been replaced by large-primary dyno headers and open exhaust. It’s also been tuned on fuel rated higher than the cheaper 87-octane gas. Time for a baseline L8T dyno run!

The baseline run on 93-octane pump gas resulted in 476 horsepower at 5,300 rpm and 554 pound-feet of torque at 3,900.

The baseline testing ultimately resulted in 476 horsepower at 5,300 rpm and 554 pound-feet of torque at 3,900 rpm on 93-octane pump gas. A little extra breathing and more timing for the higher octane gasoline really wakes up this big-cube LT! But what if we try E85? A fuel that has proven to offer performance benefits with other engines?

With nothing more than swapping the gas in the fuel cell for E85 and a retune resulted in an astounding 500 horsepower at 5,100 rpm and 580 pound-feet of torque at 3,900 rpm! That’s an increase of 24 extra horses and 26 more pound-feet of grunt over 93 octane at the peak, with similar gains across the entire rev range.

Swapping the gas in the fuel cell for E85 and a retune resulted in 500 horsepower at 5,100 rpm and 580 pound-feet of torque at 3,900 rpm. Impressive for a stock crate engine.

What Are SAE And STP Correction Factors?

You may see on our first L8T dyno run with an increase of 75 horsepower and 90 pound-feet of torque as an impressive jump over the stock rating published by GM. Is the factory rating conservative? Do headers and a 93-octane tune really gain that much power? There are a couple of reasons for this big leap in horsepower and torque, the exhaust and tune being one, but the different correction factors used with engine dynos being the other.

The larger cams tested require BTR’s 0.660 lift valve spring kit, they install on the factory heads with no machine work needed.

When an automotive manufacturer dyno tests their production engines, they use the industry-standard SAE J-1349 correction factor. This is used to correct dyno output figures to conditions of 29.23 inches of mercury, dry air, and 77 degrees Fahrenheit. Since temperature, air pressure, and humidity can play a big role in the measured output of an engine, and can vary not just between locations, but also the time of day, this correction factor brings all manufacturers’ horsepower and torque ratings to a level playing field so we can have an apples-to-apples comparison, regardless of the ambient conditions when testing takes place.

The performance and racing industry also uses a dyno correction factor for these same reasons, but it is called STP J-607 and is another power correction standard. STP stands for ‘standard temperature and pressure’. The STP correction factor is slightly different to reference conditions of 29.92 inches of mercury, dry air, and 60 degrees Fahrenheit. Because these reference conditions include higher air pressure and cooler air than the SAE standard, these corrected power numbers will always be about four percent higher than the SAE power numbers. This difference, along with the large-primary long-tube headers with no exhaust, no accessory drive, and higher octane tune, contributes to the large impressive jump over the stock rating published by GM.

With the stock long block, stock cam, E85, and the BTR Trinity Truck intake manifold resulted in 531 horsepower at 5,200 rpm and 544 pound-feet of torque at 4,400 rpm. An increase of 31 horsepower at peak.

The Trinity Gen V Truck Intake Manifold

The BTR Trinity Gen-V intake manifold was introduced almost three years ago and has been dyno-proven to increase upper-RPM power. The latest truck version of this intake features the same three-piece, cast aluminum design but with eight-inch long runners to allow for more mid-range power and torque compared to the original short-runner manifold. The team at BTR wanted to see what this intake would do on our stock-cam L8T dyno runs.

Sticking with E85, the fuel used for the rest of the dyno runs, the factory plastic intake manifold was swapped for the Trinity truck intake manifold for the next L8T dyno run. The result was 531 horsepower at 5,200 rpm and 544 pound-feet of torque at 4,400 rpm. The intake swap picked up horsepower and torque gains after 5,000 rpm with an extra 31 peak horsepower but at the sacrifice of low-end power and torque. The L8T comes from the factory with the same intake manifold as its 6.2-liter L86 little brother and performs well with the stock cam. We will come back to this intake manifold once we swap in a bigger camshaft.

The 6.6-liter L8T churned out 520 horsepower at 5,400 rpm and 589 pound-feet of torque at 4,000 rpm with the first cam swap. This run had the stock intake reinstalled.

The First Bumpstick Swap

With the stock intake manifold reinstalled, it was time to do the first cam swap. In years past with the LS and LT engine platforms, stock or stock-like cams that have smaller profiles have proven gains. So, just for curiosity’s sake, the BTR team decided to try their L86 DOD-Delete camshaft first. This camshaft has practically the exact same duration and lift as the L86 and LT1 engines, but with a non-DOD lobe profile.

With only an extra seven degrees of duration on the intake and exhaust lobes with a small increase in lift, the L8T churned out 520 horsepower at 5,400 rpm and 589 pound-feet of torque at 4,000 rpm. Over the stock cam, the L8T picked up power and torque across the entire rev range with the biggest gains after 3,500 rpm — 20 horsepower and 9 pound-feet of torque at the peak of the curves. Very impressive for a camshaft that has a stock-like idle quality and drivability and still has the full function of VVT.

The BTR L86 DOD Delete cam is barely bigger than the stock L8T cam, but still offers reasonable gains.

BTR’s All New L8T Torque Cam!

For the next dyno test, the BTR team tested their new L8T Torque Cam for the 6.6-liter that utilizes a lower lift profile, so you can use the less expensive, more durable factory LT1 valve springs. The intake and exhaust lobes are designed to improve power and torque from idle to redline. For this L8T dyno test, as well as the rest of BTR’s cams in this dyno shootout, they installed a 4-degree VVT limiter. VVT is a beneficial system that adjusts cam timing across the rev range, keeping it is best for both torque and horsepower. Our next article in this series will discuss the function of VVT and why you might need to install a limiter or lockout with your cam swap.

The BTR L86 DOD-Delete cam showed respectable gains, but the L8T Torque cam proved to be a large improvement over the entire rev range.

The final result with the new L8T Torque Cam was 536 horsepower at 5,100 rpm and 592 pound-feet of torque at 4,000 rpm. Not only did this cam swap pick up an additional 36 horsepower and 12 pound-feet of torque at the peaks, but it also picked up power and torque across the entire rev range and made over 480 pound-feet of tire-annihilating grunt from 1,800 to 5,800 rpm! Making this camshaft the best all-around pick for your weekend tow pig or hot rod!

I love the L8T engine. When you look at how it responds to the camshaft changes in terms of power gains, it’s very impressive. We were all happily surprised at the performance of the L8T throughout all of the testing. – Brian Tooley

Since the BTR 220 cam and BTR 225 cam have the same lift, the cam swap was quick and easy.

A Big Step Up With The BTR 220 and 225 Cams

The BTR 220 camshaft is the first of the “big” cams in this dyno shootout and it shows with a gain of 88 horsepower and 11 pound-feet over the stock cam. The power band shifted to a higher RPM with a mild loss of power and torque below 3,400 rpm. Still running the stock intake manifold and E85 as in the previous tests, swapping the BTR L8T Torque cam for the BTR 220 cam resulted in 588 horsepower at 5,900 rpm and 591 pound-feet or torque at 4,400 rpm.

This camshaft would be best suited for a high-performance street truck or engine swap application and is also the first of the cams we’ve tested that might require a larger stall converter to match the performance. The experts at BTR will be able to advise you on exactly what you would need depending on your application.

With the stock intake manifold, E85, and the BTR 220 cam resulted in 588 horsepower at 5,900 rpm and 591 pound-feet or torque at 4,400 rpm. A big jump in power and torque in the top end, but a small loss in the low end.

Out with the BTR 220 cam and in with the BTR 225 cam. This cam swap was easier than usual since both cams use the same valve spring kit from BTR. The BTR 225 cam produced the best horsepower and torque numbers so far, while still utilizing the stock intake manifold. 596 horsepower at 5,900 rpm and 593 pound-feet of torque at 4,500 rpm, a gain of 96 horsepower and 13 pound-feet with just headers, E85, and a streetable cam is impressive, especially when you consider this engine was designed by GM to be long-living reliable workhorse, not a performance engine.

The BTR 225 cam produces a very similar power band and power numbers as the BTR 220 cam, which is not surprising, but notice the mild loss of power and torque is only below 3,000 rpm instead of 3,400 rpm with the previous cam. The BTR 225 cam might be the sweet spot for a naturally aspirated L8T street engine that’s only looking for a cam swap.

596 horsepower at 5,900 rpm and 593 pound-feet of torque at 4,500 rpm. A gain of 96 horsepower and 13 pound-feet with just headers, E85, and the BTR 225 cam makes this the highest horsepower run with the stock intake manifold.

The Holy Trinity Of Airflow

For the next step in our “L8T To The Party” dyno shootout, we pulled two BTR trinity intakes off the shelf for testing — the Trinity Truck intake from earlier and the original Trinity intake with the shortest runners. You may think that these two intakes only differ in hood clearance, but runner length can have a drastic effect on an engine’s powerband. A shorter runner will favor the upper RPM range while longer runners will favor lower or mid-range RPM.

Off comes the stock L8T intake and on goes the Trinity Truck Intake from before with its long-runner design with eight-inch long runners. This intake produced hefty horsepower gains with the stock cam but lost some low-end torque, even with the long runners, hinting that this intake wanted more than the puny stock bumpstick with sub-200 degrees of duration. So how did the Trinity Truck intake like the BTR 225 cam? We think 648 horsepower at 6,400 rpm and 586 pound-feet of torque at 5,200 rpm tells the story. This cam and intake combo produced a whopping 148 additional horsepower over baseline, a 52 horsepower increase over the BTR 225 cam only L8T dyno run.

If the Trinity Truck intake did that well, will the short runner do better? Or will it be a case of mismatched parts? On went the Trinity short-runner intake manifold, with a runner length of less than five inches, and after a couple of pulls the results were in. 653 horsepower at 6,700 rpm and 575 pound-feet of torque at 5,200 rpm. With a small gain of five horsepower over the long-runner Trinity Truck intake at the very top of the rev range, the short-runner Trinity intake manifold produced the highest horsepower figure in our “L8T To The Party” dyno shootout but still suffered a small loss of 11 pound-feet of torque at peak.

This is an overlay of the L8T with the BTR 225 cam, E85, and all three intake manifolds. A close look shows the stock intake is still best for lower-rpm grunt while the Trinity intakes prefer a higher rpm powerband.

Is The King Of The Hill Really King?

BTR’s 230 cam is the biggest off-the-shelf offering for the Gen-V LT engine platform, reserved for those looking to make big power naturally aspirated in larger displacement engines or even under boost. Since the previous cam and intake testing showed the short-runner BTR Trinity intake lost a small amount of torque in favor of a few extra horses up top, the BTR crew decided to try the mid-length runner Trinity intake manifold to see if it could be a better fit for this application.

The last cam tested was the BTR 230 cam, their largest offering for this application. On E85 and the BTR Trinity mid-length intake manifold, the L8T pumped out 650 horsepower at 6,800 rpm and 554 pound-feet of torque at 5,400 rpm on the dyno.

The final results were 650 horsepower at 6,800 rpm and 554 pound-feet of torque at 5,400 rpm. This combination made a huge shift in the power band to higher in the rev range with torque loss below 4,800 rpm compared to baseline. Even with a gain of 150 horsepower over stock, a loss of 26 pound-feet shows us that this cam and intake wanted more cubes and compression. The BTR 230 cam might be best reserved for our ported-head testing coming up soon. There, we will try to find the ultimate capabilities of a naturally aspirated L8T with a stock bottom end.

This rundown of camshaft offerings from Brian Tooley Racing helps you visualize the difference in duration, lift, LSA, and fuel lobes.