The TBSS intake swap is popular among the budget-minded LS crowd. It’s common in the junkyards and dyno proven to be an improvement in both horsepower and torque, as long as you have room under the hood and don’t mind the not-so-pretty looks. But do you also have to do a TBSS throttle body swap along with it? Richard Holdener steps in to give us the answer.

The TBSS intake came on the TrailBlazer SS and became the standard intake on the 2007-2013 model year trucks.

The Test Mule

The engine used for this TBSS throttle body comparison is a regular on Holdener’s YouTube channel: His junkyard L33 5.3-liter LS. The L33 is a limited production odd-duck in the LS world. It is a Gen III 5.3-liter LS that was only available on 2005-2007 extended-cab regular-bed 4WD 1500 Silverados and Sierras, and a majority of those came with the iron block 5.3-liter.

Along with high flowing runners and a larger plenum, the TBSS intake features a larger 90mm opening.

The L33 used the same 3.622-inch-stroke crankshaft and 3.780-inch bore pistons as the other 5.3s, but housed in an aluminum block (think LS1 or LS6 block but with slightly smaller bores). The L33 also was one of the first LS engines to use floating wrist pins in a newer heavy-duty connecting rod that ended up in all Gen IV LSs 5.3 liters and larger.

The pistons were borrowed from the 4.8-liter and the cylinder heads come from its 6.0-liter LS2 big brother. The 4.8 flat-top pistons combined with the 64cc chamber LS2 heads provided a 9.9:1 compression ratio compared to the 9.5:1 compression ratio on other 5.3s. The cylinder heads (either 243 or 799 castings) also flow much more than the other 5.3-liter heads.

The L33 came from the factory with the higher flowing 243 or 799 cylinder heads.

The stock cam for the L33 was slightly bigger than the more common LM7 or L59 5.3s. The 4.8 and 5.3 truck engines used a cam with 191 and 190 degrees of duration on the intake and exhaust lobes with 0.457 and 0.466-inch lift on each with 114 degrees of lobe separation. The L33 cam has 193 degrees of duration on the intake and exhaust lobes with 0.482-inch lift on both and 116 degrees of lobe separation.

Other than headers and an RHP Low Buck Truck Cam, the 5.3 is stock.

All these changes account for a 20-horsepower bump over the standard 5.3s to make 315 horsepower. But no Richard Holdener dyno test is complete without a bigger cam. For this dyno test, Holdener used one of his own cam designs he calls the Low Buck Truck cam. This cam is a healthy jump over the stock unit, but is designed to work with classic swap projects and daily driven late model trucks. This cam features 212 and 22x degrees of duration on the intake and exhaust lobes with 0.552-inch lift on both so you can use LS3-style OEM replacement valve springs with 107 degrees of lobe separation for a healthy amount of chop at idle.

The TBSS Intake Manifold

The L33 came from the factory with the same intake as the rest of the 1999-2007 4.8, 5.3, and 6.0 liter truck engines. These intake manifolds perform well, but MG introduced a better design for the LS2-powered Trailblazer SS (nicknamed TBSS) that featured a new four-bolt mounting pattern for the throttle body allowing for a 90mm throttle body and enough room for aftermarket 92mm throttle bodies. GM also used this intake for the 2007-2013 cathedral-port truck engines.

The low buck truck cam requires a spring upgrade. The dual springs you see here are installed for future cam swap testing.

This intake is a common budget-performance swap for most cathedral port LS builders, especially truck guys or anyone with enough room under the hood to fit the taller truck intakes. The TBSS intake also feature larger runners and a higher volume plenum. Pair those improvements with the larger throttle body opening, and you get a cheap OEM intake manifold that has been dyno proven to outperform the infamous LS6 intake manifold that came on the 2001-2004 LS6-powered Z06 Corvettes.

The ICT Billet throttle body adapter is an inexpensive way to fit a 3-bolt throttle body to a 4-bolt intake manifold.

The only real problem with this intake swap, is the required throttle body change that comes with it. If you have a drive-by-cable throttle body, you have to turn to the aftermarket for a 92mm throttle body to fit, which will cost a few hundred bucks for a good quality one like a Nick Williams or the Accufab one Holdener uses here. If you have a drive-by-wire throttle body, your solution is grab the throttle body off of a 07-plus model year car or truck and use an X-Link to properly convert the signal.

For years enthusiasts have asked if the throttle body swap is necessary and if they could, at a great cost savings for the budget-minded DIY’er, just buy a throttle body adapter like the ICT Billet adapter Richard Holdener is using here to reuse the smaller 87mm throttle body you already have. Now we have that answer.

The AccuFab throttle body requires no throttle body but isn’t as cheap as reusing your smaller throttle body and an adapter.

The Final Numbers

Like all of Richard Holdener’s dyno tests, the throttle bodies were tested back-to-back at Westech’s facility with Holley EFI. With the stock 87mm throttle body, the 5.3-liter L33 produced 426.5 horse power and 411.4 pound-feet of torque. But swapping to the Accufab 92mm throttle body upped the output to 433.8 horse power and 415.8 pound-feet of torque. The increase at peak rpm totals 7.3 horsepower and 4.4 pound-feet of torque, and Holdener points out that the gains are only realized higher in the rev range, above 4,000-4,500 rpm.

With the stock 87mm throttle body, the 5.3-liter L33 produced 426.5 horse power and 411.4 pound-feet of torque. But swapping to the Accufab 92mm throttle body upped the output to 433.8 horse power and 415.8 pound-feet of torque. The increase at peak rpm totals 7.3 horsepower and 4.4 pound-feet of torque, and Holdener points out that the gains are only realized higher in the rev range, above 4,000-4,500 rpm.

The jump in power might not be big, but Holdener reminds us that for a small displacement LS like his L33 dyno mule with a mild truck cam, the results are predictable. A larger displacement LS, like a 6.0-liter with a bigger cam, would yield a bigger power difference as the smaller throttle body would be more restrictive at a higher power level. So if the throttle body swap really required? No. But in the search for more power and torque, every little bit helps.