It doesn’t matter whether it’s a lowly LM7 or a top-of-the-line H.O. sporting higher compression and 243 heads, everyone loves 5.3L truck engines. The 5.3L has quickly become the go-to engine for swaps, performance builds or just about any type of performance use. The reason behind the popularity is that they are both powerful and plentiful, always a good combination. GM produced literally millions of trucks and in many cases the 5.3L was the base engine, meaning it was produced in the greatest numbers. As if that weren’t enough, the smaller 4.8L and larger 6.0L both shared intake manifolds with the 5.3L. What this means is that there are also thousands upon thousands of truck intake manifolds available. As luck would have it, the factory truck intake is a solid performer, bettering both the original LS1 and LS2 for power and nearly matching the much-sought-after LS6. With the original truck intake being so versatile, is it possible to better the factory truck intake? That’s what we are here to find out.
Rather than search the aftermarket for all the available intakes, we decided to keep things simple and focus on “truck manifolds.” Note that the term is in quotes (actually air quotes), and remember that while the tested intakes were originally designed for truck applications, they make excellent induction systems for any performance LS build (hood clearance permitting). In the end, we managed to secure three different truck intakes: one from the early truck, the Trail Blazer SS, and FAST LSXRT (the T standing ostensibly for truck). We hoped to illustrate a few important points with this intake shootout. The first being, is the much-vaunted Trail Blazer SS manifold really better than the original truck intake? We fully expected FAST LSXRT to finish on the top of the truck heap, but would the gains be worth the extra expense over the original or TBSS intakes? Before we could start testing we needed a suitable test engine.
Choosing the test engine was as important as the intakes we planned to run. Compared on a bone-stock engine, the gains offered by the TBSS and LSXRT would be greatly minimized, but running them on an 800hp, big-inch stroker would be equally foolish. The best compromise was to test them on what the majority of enthusiasts are running, so naturally we turned to the 5.3L. Rather than run them on a stock LM7, we upgraded our high-mileage, junkyard engine with ported heads and a cam. The stock 706 heads were swapped out in favor of a set of Trick Flow Specialties (TFS) GenX 205 heads. The GenX 205 heads were designed specifically for the small-bore LS applications (4.8L-5.7L), and offered enough flow to support well north of 550 hp on the right application. The GenX 205 heads were combined with a healthy Comp cam (Grind # 277LrR HR13) that featured a 0.614/0.624-inch lift split, a 227/243-degree duration split, and 113-degree LSA. The spring package supplied on the GenX 205 heads was more than adequate for the hydraulic roller cam lift and rpm potential. Save for new Fel-Pro MLS head gaskets and ARP head studs, the remainder of the LM7 short block was left stock.
For testing, the 5.3L was equipped with Hooker 1 7/8-inch long-tube headers, FAST 46-pound injectors, and a Holley HP EFI management system. The LM7 was run sans accessories and with a manual throttle body swapped in place of the drive-by-wire unit. To start the test, we installed the early truck intake and Accufab throttle body. After dialing in the air/fuel ratio and timing, the 5.3L produced peak numbers of 464 hp at 6,900 rpm and 414 lb-ft of torque at 5,300 rpm with the stock truck intake. Next up, we installed the TBSS intake and 90mm Holley throttle body (the throttle opening on the SS intake was larger). Equipped with the TBSS intake, the power numbers increased to 473 hp at 6,800 rpm and 419 lb-ft at 5,300 rpm. The TBSS intake improved the power output from 4,500-7,000 rpm. As expected, the big winner in our truck trio was the FAST LSXRT intake and FAST 102mm throttle body, which produced 492 hp at 7,100 rpm and 422 lb-ft at 5,800 rpm. The power was up nearly everywhere with the LSXRT, to say nothing of nearly reaching the 500hp mark, but the question remains. Is the extra 20 or so horsepower worth the cost of the FAST manifold? That is something every 5.3L owner will have to decide, but remember, these gains will only increase with wilder and/or larger LS combinations.
1. Which truck intake is the hot setup on your modified LS?
2. Our test engine was a high-mileage 5.3L LM7 augmented with a set of TFS GenX 205 heads.
3. The 5.3L also featured a cam upgrade in the form of a LSR Comp cam (grind # 277LrR HR13). The LSR cam offered a 0.614/0.624-inch lift split, a 227/243-degree duration split, and 113-degree LSA.
4. Equipped with the new Comp cam and TFS heads, the modified 5.3L was ready for the first of our three intakes.
5. First on the list of truck intakes to be tested was this factory (early) truck manifold. The most common of all truck intakes, this is the manifold that accompanied our 5.3L when it was pulled from the wrecking yard.
6. We replaced the factory drive-by-wire throttle body with this manual version from Accufab.
7. We relied on this Holley HP EFI management system to dial in the air/fuel ratio and timing values on all three intakes.
8. Hooker supplied a set of 1 7/8-inch long-tube swap headers for the test. In truth, the 5.3L might work slightly better with smaller 1 3/4-inch headers but there was no shortage of exhaust flow.
9. Run with the early truck intake, the modified 5.3L produced 464 hp at 6,900 rpm and 414 lb-ft of torque at 5,300 rpm.
10. Next up was the Trail Blazer SS intake. Similar in design to the early truck intake, the TBSS manifold nonetheless featured subtle improvements in runner length and cross section designed to improve power production.
11. The TBSS intake was installed using these Fel-Pro cathedral port intake gaskets.
12. The throttle opening on the TBSS was larger than the early truck manifold. We installed a 90mm throttle body from Holley to feed the modified 5.3L.
13. All three of the intakes were run with these FAST 46-pound injectors. We fabricated new mounts to use the FAST fuel rail on the TBSS intake.
14. Run with the TBSS intake, the modified 5.3L produced peak numbers of 473 hp and 419 lb-ft of torque. The TBSS intake improved power production over the early truck manifold from 4,500 rpm to 7,000 rpm.
15. We obviously saved the best for last. The final intake of our truck trio was the FAST LSXRT.
16. The FAST LSXRT required an even larger throttle body than the previous two intakes. The 102mm opening was sized perfectly for the FAST 102mm Big Mouth throttle body.
17. The FAST intake offered substantial power gains over both the early truck and TBSS manifold. Equipped with the LSXRT, the little 5.3L produced 492 hp at 7,100 rpm and 422 lb-ft of torque at 5,800 rpm.
18. The graph illustrates that there is plenty of extra power to be had from the right induction system. Equipped with the early truck intake, the modified 5.3L produced 464 hp and 414 lb-ft of torque. These numbers jumped to 473 hp and 419 lb-ft with the TBSS intake and all the way to 492 hp and 422 lb-ft with the LSXRT. Note that the gains offered by the TBSS manifold over the early truck materialized after 4,500 rpm. By contrast, the LSXRT offered both immediate torque gains to go along with substantial peak power numbers.
Photography by Richard Holdener