4.8L VS 5.3L Engine - Tech - Little LS Slugfest

It's 4.8 vs 5.3 in a battle of smaller small-blocks

Richard Holdener Oct 8, 2013 0 Comment(s)
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Let's face it: The little guys never get the love. Case in point, the 4.8L LR-4 or LY2. Everyone wants a 7.0L, 6.2L or at least 6.0L LS engine powering their trucks and muscle cars. Worst case scenario? They grab the medium-sized 5.3L. Enthusiasts pass right by the 4.8Ls in their quest to gobble up all the 5.3L motors in wrecking yards as swap candidates. The reality is that, all things being equal, bigger engines make more power. They certainly make more torque, but the downer is they also use more fuel.

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?

Displacement wise, the 4.8L is to the 5.3L what the original 283 was to the 327 small-block (technically 293 versus 325 ci). Given the bore and stroke of each, a better comparison might be the 327 and larger 350, as the 4.8L and 5.3L share the same bore size of 3.78 inches while the 4.8L makes due with a shorter 3.267-inch stroke (down from the typical LS stroke of 3.622 inches). Since the 4.8L and 5.3L share the same block (externally marked 4.8L/5.3L), not to mention the same heads, intake, and other external features, it is difficult to distinguish between the two. More than one enthusiast has purchased what he thought was a 5.3L, only to receive the smaller 4.8L in its place. Internally there are distinct differences, the most obvious being the use of flat-top pistons in the smaller 4.8L.

It should be mentioned that the (L33) H.O. version of the 5.3L was also offered with flat-top pistons (and floating pins), but the aluminum block is a dead giveaway. The 4.8L flat-top pistons are a common (and inexpensive) upgrade for a 5.3L. Crankshaft and connecting-rod casting numbers are the real key to distinguishing between the two. If you have crank casting numbers ending in 216 and rods ending in 143, then you have a 5.3. If, however, your iron-block motor is sporting a 482 crank and 121 rods, then you have a 4.8. It is thought the rare manual trans 4.8s were also equipped with a 312 crank, but that would definitely be the exception.

In terms of factory power ratings, there is actually not much difference between the 4.8L and larger 5.3L, especially the garden variety LR4 and LM7. Power ratings ranged from 270-290hp net and 285-305 lb-ft for the 4.8L, and 270-305hp net and 315-335 lb-ft for the 5.3L. What should be evident is that the two actually produce similar peak horsepower outputs, but the larger 5.3 will always offer more low-speed grunt. The good news for both 4.8 and 5.3 owners is that they have the ability to extract a significant amount of power from their little V-8s. With proper heads, cam and intake, either can be made to approach or exceed 100 hp per liter (480-530 hp) or 1.63 hp per inch. Of course this kind of specific output will necessitate a high-rpm motor, with cam timing pushing peak power past 7,000 rpm. Such a combination might not be ideal for towing, but would be serious fun in a Camaro, Chevelle or Nova.

As with any LS-based motor, both the 4.8L and 5.3L will respond well to induction upgrades, including heads, cam and intake. The difference when working with the 4.8L is that cam timing usually chosen for a 5.3L (or larger) stroke version will usually be a tad on the aggressive side for the smaller 4.8L. The stock cam timing employed in the 4.8L (shared with the 5.3L) was the mildest of the LS family, checking in with a 0.466/0.457 lift split, a 190/191 duration split (at 0.050) and 114-degree LSA.

Factory cam upgrades for the 4.8L include the 6.0L truck (LQ4 or LQ9) with slightly more lift and 17 degrees more intake duration, the LS6 cam, with 0.060 more lift and 17 degrees more intake duration and 21 degrees more exhaust duration, or the LS7 cam with 21 degrees more intake duration and another 0.040 lift over the LS6 cam. Of course, the higher-lift cams must be accompanied by a valvespring upgrade.

In addition to the cam tested here, Crane Cams also offers Direct-Fit cams for the truck motors designed to work with the stock valvesprings. These Direct Fit LS cams give lots of options and offer significant power gains (as high as 40-plus hp) through the entire rev range (as low as 2,000 rpm) and do so without affecting idle vacuum, drivability or necessitating a spring swap-making them the perfect upgrade to an otherwise stock 4.8L or 5.3L.

Like the cam profiles, head flow and intake design all cater to the smaller displacement of the 4.8L. Head flow that might be insufficient on a larger 6.0L or stroker is likely more than adequate for a smaller 4.8L. Given that even a stock set of 4.8L heads flow enough air to support over 400 hp, there is plenty of power available without resorting to a cylinder head upgrade.

That said, it is also possible to further improve the power output with proper head porting without sacrificing low-speed torque. The last thing you want to do is reduce torque production on your 4.8L.

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.

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