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How to Get 384 HP Out of a 4.8L Engine - Mini Mouse, Part 1

Squeezing 384 horsepower from 4.8 liters

Richard Holdener Mar 23, 2015
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Some time ago we introduced our Modern Mouse series that covered a whole slew of performance parts applied to a 5.3L LM7 truck engine. Given the popularity of the LS platform in modern machinery, muscle car swaps, and even trick trucks, Modern Mouse seemed like a natural. Toss in the availability and affordability and you have the makings of the next go-to small-block. As popular as the 5.3L is, there was another interesting offering that is equally available and affordable. Say hello to the 4.8L LR4 (or Gen IV LY2). The 4.8L and 5.3L share the same block and bore size, 3.78 inches. The difference in displacement comes from a change in stroke length. The 5.3L sports the common LS length of 3.622 inches but the smaller 4.8L spins a shorter stroke of 3.267 inches. Since the pistons are interchangeable between the 4.8L and the 5.3L (they share the same compression height), the difference between the stroke lengths is made up for by an increase in the connecting rod length (6.098 vs. 6.275).

Essentially, the 4.8L is a destroked 5.3L, much like the original 327 was a destroked 350 and the 302 was a destroked 327. In terms of displacement, the 4.8L checks in a 293 cubic inches and while down on displacement to the larger 5.3L and 6.0L, the short-stroke 4.8L is an interesting departure from the run-of-the-mill 5.3L. Given the minimal displacement of the 4.8L, we couldn’t help but call this project Mini Mouse. Like the Modern Mouse series on the 5.3L, the goal here is to demonstrate just how well the 4.8L responds to a vast array of performance upgrades. Naturally, there will be cam, head, and intake swaps, along with nitrous, forced-induction, and even displacement changes. We don’t want to duplicate the Modern Mouse series, so we will try to cover different upgrades on the 4.8L. There are plenty of 4.8L fans out there and who knows, after this series there may be many more. Know that at some point we plan on taking full advantage of the rpm ability offered by the short-stroke, but that is jumping WAY ahead, so let’s crank up the dyno and get down to business.

Obviously, we needed a starting point and the best resource for a test mule is always the wrecking yard. We found a company that specializes in cores so we picked up a 4.8L. Our original intention was to purchase a high-mileage unit, plop it on the dyno, and start making some serious power. The 4.8L looked OK from the outside, but inside things were far from acceptable. Rust in the bores meant a rebuild was in order. That gave us an opportunity to start fresh with Mini Mouse. The block was cleaned and bored 0.010-over to receive a set of SPR Professional-series pistons from JE. In addition to the strength, the forged slugs offered generous valve reliefs for future cam upgrades and a slight (7.2cc) dome to increase the static compression. This would really come in handy once we performed a head swap, which almost always increases the combustion chamber size. We also surfaced the block and heads along with a quickie valve job. When all was said and done we had a factory fresh 4.8L, albeit with a slight compression increase.

Our first order of business was to establish a baseline so we assembled the freshly machined engine and headed to Westech Performance in Mira Loma, California. Mini Mouse was configured for dyno use with an Accufab manual throttle body, Meziere electric water pump, and Holley HP EFI management system. Also present was a set of 36-lb/hr FAST injectors, 1 3/4-inch long-tube headers, and a Corvette damper. After a pair of break-in cycles, we changed the Lucas 5W-30 oil and were ready to test. After dialing in the air/fuel ratio and timing curves, Mini Mouse generated peak numbers of 336 hp at 5,900 rpm and 347 lb-ft of torque at 4,900 rpm. The stock heads and intake had more power to give but the stock cam leveled off around 5,000 rpm then took off on a downward spiral after 5,900 rpm. We knew there was more power to be had from this combination so we decided the first step was to swap in a better cam.

If you are an LS owner (of any displacement) and are considering your first upgrade, know that you should be thinking of nothing else but a camshaft. All LS engines are blessed with sufficient intake and head flow but where they are generally lacking is in cam timing. The factory cam is designed not with peak power in mind, so the engineers left plenty of power on the table. Though a vast array okf cam profiles exist for the LS engine family, we decided to start with a mild cam, working our way up to wild in later later installments. We wanted to choose a cam that would work well as a performance upgrade for a daily driver. To that end we selected a Crane profile that offered 0.551-inch lift, a 210/218-degree duration split, and a 116-degree LSA. This cam offered almost 19 inches of idle vacuum yet it increased the power output of the 4.8L from 336 hp and 347 lb-ft to 384 hp and 361 lb-ft of torque. Measured peak to peak, the Crane cam swap added nearly 50 hp, but the difference was an amazing 80 hp out at 6,500 rpm (remember, the 4.8L loves to rev).

After the success of the cam swap, we decided to shift gears and tailor the next test to the carb contingent. Like the LM7 5.3L, the 4.8L is a popular swap candidate for muscle and import vehicles. Not everyone has the budget or technical skills to include injection in the swap so there are a great many LS swaps running around with carburetion. For this last test in part 1 of the Mini Mouse series, we decided the age-old battle between single- and dual-plane intakes deserved a yet another look. For the uninitiated, dual-plane manifolds offer better low-speed torque while the single-plane design is tuned for higher engine speeds. In her current configuration, Mini Mouse was admittedly mild but the test was interesting even if only to show what not to run on a particular combination. How many of us are tempted by the promise of big top-end power only to be reminded that our engine spends most of its time well below the power peak?

Anxious to discover the “plane” truth, we removed the factory truck manifold and EFI components and installed an Edelbrock dual-plane Performer RPM manifold, Holley 650 HP carb, and MSD ignition controller. The Performer RPM seemed like an ideal choice for the mild 4.8L, as displacement plays a part in intake selection as well. The smaller the engine, the better it will most likely respond to a dual-plane. The MSD controller was a plug-and-play unit and allowed us to dial in the timing curve of our choice. After jetting and timing sweeps, we were rewarded with peak numbers of 377 hp and 342 lb-ft of torque. The dual-plane intake offered a flat torque curve that exceeded 325 lb-ft all the way out to 5,700 rpm. After swapping on a Victor Jr. single-plane we immediately recognized that the dual-plane was the better choice on this mild 4.8L. Although the Victor Jr. offered acceptable peak numbers of 377 hp and 336 lb-ft of torque, torque production was down considerably compared to the Performer RPM up to 5,700 rpm. If you have a mild combo, the Performer RPM is a better choice. But fear not, as we are just getting started with Mini Mouse, look for even more power next installment.


1. Is there power hiding somewhere under that LR4 truck manifold? Project Mini Mouse has officially begun.


2. Our original intention for Mini Mouse was to start with a high-mileage 4.8L right from the wrecking yard. Unfortunately, our selection turned out to need some work before subjecting it to the dyno. After decking the block, we bored the cylinders 0.010-over and installed a set of SRP Professional forged pistons from JE Pistons. The forged pistons (PN 315551) featured a 7.2cc dome (10.5:1), generous valve reliefs for future cam upgrades, and were designed to work with the 4.8L stock rod and crank.


3. To establish our baseline, the 4.8L received the factory LR4/LM7 camshaft. Mildest of the LS family, this cam was wimpy, even for a 4.8L.


4. The stock 706 heads were given a surface and a valve job before the installation of a set of valvesprings (PN 26918) from Comp Cams. We knew cam swaps were in the cards so we started off with valvesprings capable of supporting these early cam tests.


5. Mini Mouse was run on the engine dyno with an Accufab manual throttle body, a Meziere electric water pump, and a set of 1 3/4-inch long-tube headers. Tuning for the 36-lb/hr FAST injectors came from a Holley HP EFI management system. Equipped with the stock heads, cam, and truck intake, the 4.8L produced 336 hp at 5,900 rpm and 347 lb-ft of torque at 4,900 rpm. Torque production exceeded 300 lb-ft from 3,200 rpm (the start of the test) to 5,800 rpm. Owners of the original 283 small-block will envy this type of torque curve.


6. It should come as no surprise that a cam swap was first on the list for our little LS. For part 1, we decided to start small. Crane supplied a small but powerful hydraulic roller profile that offered 0.551-inch lift, a 210/218-degree duration split, and 116-degree LSA.


7. Swapping the cam required the removal of the coil packs and valve covers to allow access to the stock rocker arms. The rocker arms were removed to eliminate spring load and lifter contact on the cam. We should note that during the valvetrain reinstall we upgraded the pushrods to hardened units from Crane Cams.


8. With our rockers and pushrods removed, off cam the Meziere electric water pump.


9. Next came the LS damper. Eagle-eyed readers will recognize this as a Corvette damper. Unfortunately, the factory truck damper was damaged on our salvaged engine so we installed this Vette unit we had on hand. Using a three-jaw puller designed specifically for the LS application, we removed the retaining bolt followed by the press-fit damper.


10. With the damper out of the way, we unbolted the front cover to gain access to the three bolts securing the timing chain and cam gear. We made sure to rotate the engine (with the spark plugs removed) to push all the lifters up into their respective lifter trays then position the engine at TDC before attempting to remove the cam gear.


11. With the cam gear removed, next came the four bolts holding the cam retaining plate.


12. Out came the factory cam and in went the Crane 210 stick. Cam swaps are a breeze on the engine dyno, but care must be taken not to damage the cam bearings.


13. After installation of the Crane cam, we installed the cam retaining plate followed by the cam sprocket and timing chain. With the engine at TDC, the timing mark on the bottom of the cam gear should point at the timing mark on the top of the crank gear.


14. Despite the relatively mild profile, the Crane cam offered a significant jump in power. The cam swap increased the peak power numbers from 336 hp and 347 lb-ft of torque to 384 hp and 361 lb-ft of torque, gains of 48 hp and 14 lb-ft. Measured out at 6,500 rpm, the cam swap netted a gain of 80 hp!


15. Since the 4.8L is such a popular swap candidate for early muscle cars, we decided to try out a couple of carbureted intakes on Mini Mouse. First up was the dual-plane Performer RPM from Edelbrock. Intake swaps on the LS are made simple by the fact that they don’t disturb any water passages, unlike a conventional small-block.


16. The dual-plane was installed on the awaiting LR4, and yes we know it is backward. We also ran a test to see if the direction made any difference in the power and/or air/fuel ratio (it did).


17. Naturally, we needed a carburetor for this test so Mini Mouse received a shiny, new Holley 650 HP.


18. Run with the dual-plane Performer RPM and Holley carb, the 4.8L produced 377 hp and 342 lb-ft of torque.


19. The final test involved running a single-plane Victor Jr. from Edelbrock. This test was performed more to illustrate that this mild 4.8L combination was not the right choice for a high-rpm, single-plane design. Looking just at the peak numbers (377 hp and 336 lb-ft) tells only part of the story. Check out the graph to see that the single-plane lost out to the dual-plane through most of the power curve, and the limited displacement, mild cam, and stock heads never allowed it to rev high enough to take advantage of what the Victor Jr. had to offer. The Victor Jr. is a powerful intake, just not for this application.


20. Swapping over to the Crane cam netted some impressive power gains. Every bit as important as the increase from 336 hp and 347 lb-ft of torque to 384 hp and 361 lb-ft of torque was the fact that the cam swap improved the power output across the entire rev range. Having more top-end power is good; having more power everywhere is even better.


21. This graph illustrates clearly that our mild 4.8L was no place for a single-plane Victor Jr. intake. The dual-plane Performer RPM offered more power than the single-plane through most of the rev range. Only above 5,700rpm was the Victor Jr. able to match the output of the dual-plane, but just look at the loss in low-speed torque compared to the RPM intake. For a mild application where low and mid-range torque is most important, the dual-plane RPM is the way to go. If you are building a high-rpm screamer, the give the single-plane Victor Jr. a go.


Crane Cams
Daytona Beach, FL 32117
JE Pistons
Huntington Beach, CA 92649
Holley Performance Products
Bowling Green, KY 42101
Memphis, TN 38118
Torrance, CA 90503



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