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

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

By Richard Holdener

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.

The first order of business was to run the 4.8L in stock trim to establish a baseline. Though we have factory power ratings, the rated output is not what we see on the engine dyno for a couple of reasons. The major differences between the rated output and the power curve achieved on this engine dyno include lack of accessories, exhaust and induction system. Combine these with an optimized tune (the factory is conservative) and reduced water temperature, and you have the makings of a significant difference in power. For our testing, the difference between rated and as-tested output is irrelevant, as we will use our power numbers for the baseline and the test procedure will remain consistent to illustrate the differences offered by the proposed performance modifications.

Both the 4.8L and 5.3L were run under identical conditions. Up first, the 4.8L was equipped for dyno use with an aftermarket electric water pump, a set of 1-3/4-inch Hooker headers feeding Borla XR1 race mufflers, and a manual Accufab throttle body to replace the drive-by-wire version that came on the test motors when delivered from the wrecking yard.

Run in this trim and tuned to perfection with the Holley EFI system, 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.

With the motor still warm from running in stock trim, we yanked off the stock intake, heads, and out came the wimpy stock cam. These were replaced by a set of CNC-ported (Stage 2) heads from Total Engine Airflow. Full CNC porting, a 2.00/1.54 stainless steel valve package combined with a multi-angle valve job to produce exceptional flow numbers. The heads were combined with a healthy Crane hydraulic roller. The Crane cam offered .590 lift, a 224/232-degree duration split at 0.050 and 115 LSA.

The final upgrade was the LSXRT intake from FAST combined with a 102mm throttle body. Testing on the 4.8L and 5.3L showed that the LSXRT was a little too much manifold for the mild truck motor, as the stock intake offered more power up to 5,500 rpm, with the FAST intake producing an extra 15 hp at the top of the rev range.

For this test, we liked the extra top-end power, as it helped further demonstrate the effect of the displacement. Equipped with these mods, the 4.8L produced peak numbers of 476 hp at a lofty 7,000 rpm and 392 lb-ft of torque at 5,900 rpm. Torque production exceeded 350 lb-ft from 4,500 rpm to 7,000 rpm. Despite what would be a mild performance cam for an LS2 or LS3, these mods transformed the little 4.8L into a high-rpm screamer.

After running the 4.8L, we replaced it on the dyno with the 5.3. Like the 4.8L, the 5.3L was a high-mileage unit from a local wrecking yard. The 5.3L was equipped with the same headers, water pump and throttle body as the 4.8L and first run in stock trim with the Holley EFI system. 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. It is not surprising that the two made similar peak power numbers given the same heads, cam and intake, but note that peak power came 300 rpm sooner with the larger 5.3L.

Torque production was equally skewed, as the smaller motor not only produced less overall torque, but did so at 4,700 rpm compared to 4,300 rpm for the 5.3L. Displacement not only improved power production through the entire rpm band, but lowered the effective operating range.

As with the 4.8L, the 5.3L was subjected to the same heads, cam and intake upgrade. We were thankful to have the Aeromotive fuel system feeding our 42psi injectors. Adequate fuel delivery is critical for maximum performance. After swapping out the heads, cam and intake, we were rewarded with a substantial jump in power, from 344 hp and 379 lb-ft of torque to 484 hp and 424 lb-ft of torque. As with the 4.8L, these mods substantially increased the effective operating speed, upping peak power from 5,100 rpm to 6,800 rpm, and torque from 4,300 rpm to 5,700 rpm.

Though the gains were most prevalent past 4,200 rpm, the modified motor equaled the low-speed power of the stock motor down to 3,000 rpm. It is interesting to note that the relative gains and basic shape of the respective power and torque curves remained constant. The TEA heads, Crane cam and FAST intake improved the power output of the 4.8L by 143 hp and the 5.3L by 140 hp. Peak torque improved by 49 lb-ft on the 4.8L and by 45 lb-ft on the larger 5.3L.

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.

SOURCES
Total Engine Airflow
285 West Avenue
Tallmadge
OH  44278
330-784-4382
www.totalengineairflow.com
Aeromotive
7805 Barton Street
Lenexa
KS  66214
913-647-7300
http://www.aeromotiveinc.com
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By Richard Holdener
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