4.8L VS 5.3L Engine - Little LS Slugfest

Bru

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This might belong in the GM section, but I think it's a good read regarding displacement and power curves in an NA application. Published last year. I'd love to see the same comparison with BOOST. Excerpts below.

lsxrt-intake-final-upgrade.jpg


4.8L VS 5.3L Engine - Tech - Little LS Slugfest - Super Chevy Magazine - View All Page

Intro:

With 4.8L engines powering countless thousands of trucks on the road, to say nothing of the pricing and availability in wrecking yards, the little 4.8 starts to look attractive. We paid just $250 for ours versus $450 for the 5.3. Down on displacement to be sure, the 4.8L still has everything that makes a Gen 3 or Gen 4 (LQ, LM or LR) small-block great, including cross-bolted mains, high-flow aluminum heads and a combination just begging for the right mods. Rather than just demonstrate what the mods do to the smaller 4.8L, we decided to compare it directly to the more popular 5.3L by performing a back-to-back shootout of sorts. The question we wanted to answer was: How does the smaller 4.8L compare to the 5.3L in stock and modified trim?

The mods:
The idea behind this test was to first run both the 4.8L and 5.3L in stock trim, then subject each to the same top-end upgrade featuring CNC-ported heads (706 castings) from Total Engine Airflow, combined with a streetable (but powerful). Crane cam and the LSXRT intake from FAST. The TEA heads offered significant flow gain (exceeding 300 cfm), while the Crane cam spec'ed out at 0.590 lift, 224/232-degree duration split, and 115 LSA. It was a healthy stick for a daily-driven 4.8L or 5.3L, but we knew it would work well with the ported heads and FAST LSXRT intake.

Stock: 4.8L vs 5.3L
The 4.8L produced peak numbers of 333 hp at 5,400 rpm and 343 lb-ft of torque at 4,700 rpm. Torque production exceeded 320 lb-ft from 3,600 rpm to 5,400 rpm. The larger 5.3L offered only slightly more peak power (344 hp vs. 333 hp), but offered significantly more torque, especially lower in the rev range.With a peak of 379 lb-ft at (a lower) 4,300 rpm, the 5.3L was up 36 lb-ft of torque over the smaller 4.8L, but the largest difference came at 3,700 rpm where the 5.3L offered 47 more lb-ft than the smaller 4.8L.

Given the same heads, cam and intake, it is not surprising that the 4.8L produced nearly as much peak power as the larger 5.3L. What the extra displacement offered by the 5.3L gave you was extra torque, through most of the rev range. Despite the fact that the 4.8L actually produced more power past 5,700 rpm, the additional displacement offered as much as 50 lb-ft lower in the rev range. Even if they make similar horsepower, bigger motors always offer more torque.

Modified: 4.8L vs 5.3L
The difference in the respective power curves continued after the modifications. The larger 5.3 offered more power through most of the curve, but the difference diminished with engine speed. In modified trim, the 5.3 produced 484 hp and 424 lb-ft of torque, while the smaller 4.8L managed 476 hp and 392 lb-ft of torque. The smaller 4.8 nearly equaled the larger 5.3 in peak power, but both peak power and peak torque occurred 200 rpm higher in the rev range. Given the shape of the curves, we suspect the 4.8L had even more power to offer had the heads been set up with even more valve spring pressure to allow for extended rpm up to 7,500 rpm.

Summary
The mods increased the effective engine speed (where each made peak power) by 1,600 rpm on the 4.8L and 1,700 rpm on the 5.3L. Using the exact same components, peak power and torque occurred higher in the rev range on the 4.8L than the 5.3L. As expected, bigger engines indeed make more average power production, but don't count out the little 4.8L when it comes to making power. It just needs a little more engine speed.
 

Yaj Yak

Gladys
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what's tough about building an LS with heads/cam etc... is the money spent could go towards a turbo kit and be right there performance wise all day long on a bone stock engine...

that on3 performance kit is 1900$ with the base stuff... granted you'll need fueling to support it... but why dick around with ported heads and a lumpy cam when you can have turbo goodness.
 

SRT41320

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what's tough about building an LS with heads/cam etc... is the money spent could go towards a turbo kit and be right there performance wise all day long on a bone stock engine...

that on3 performance kit is 1900$ with the base stuff... granted you'll need fueling to support it... but why dick around with ported heads and a lumpy cam when you can have turbo goodness.

This all day long!
 
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