[Editor’s Note: This LR4 engine upgrade guide is part of a series of LS engine upgrade guides assembled by a team of LS experts at Summit Racing that we are sharing at OnAllCylinders. For a primer on the entire LS engine universe, read LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family.]
Intro to the 4.8L LR4 Engines
The LR4 appeared in model year 1999 in General Motors trucks, vans and SUV until 2006. Being a Gen. 3, it’s the smallest and oldest of all the Gen. 3 truck engines. Not many people had much use for it until the boost revolution, but these engines can still be found for as little as $400.
The LR4 engine led a relatively long life, so be aware that various updates were made along the way.
- The 1999-2000 LR4 with a manual transmission had a crankshaft with a 1.250 in. long rear flange. (Casting #12553312). Automatics and newer LR4 engines had a crankshaft with a 0.857 in. rear flange. (Casting #12553482).
- In 2001, the LR4 was upgraded with MLS gaskets.
- The early LR4 had a return-style fuel injection system. They went returnless in 2004 (except in the Express, Trailblazer, and Envoy).
- The cam bearing housing bore was changed in 2004.
- They went to a full floating pin connecting rod in 2005.
- Head bolt lengths were changed in 2004.
- Drive by wire throttle bodies were phased in starting in 2003.
- 1999 engines had 21.8-lb injectors whereas the later engines had 25-lb. injectors.
For LR4 engine specs, read:
How to Get More Power From Your 4.8L LR4 Engine
The LR4, which began its life in trucks and SUVs, is gaining popularity for several reasons:
- GM made about a bazillion of them, which has helped to keep prices down.
- The engines never had AFM or VVT, so delete kits aren’t required.
- These engines respond well to boost (as with other LS engines) and they’re so cheap that many racers will just swap them out rather than build them up.
Basic Bolt-On Upgrades for LR4
There isn’t exactly a surplus of folks hot-rodding commercial vans, but the engine is often used in engine swaps due to the low price in wrecking yards. If you do want to modify the engine, you can take comfort in knowing it responds the same to mods as the others.
If you own a van, you’re not going to find much in the way of bolt-ons. If you have a truck, you’re in good shape. There are quite a few parts available that also bolt onto the 5.3L variant.
For many people, it starts off with a cold air intake and aftermarket exhaust. The problem—if you can call it one—is that the engine starts to sound REALLY good, and owners often find themselves wanting to go faster. All these modifications can be completed in the garage, but the tune won’t be optimized.
At this point, we recommend talking to your chassis dyno tuner and deciding on a computer programmer. Whether you’re towing on low-octane or springing for good fuel, a tuner can dial in the ECM and take it to the next level.
The 4.8L loves to rev, so raising the rev limit and shift points is common. It also makes it easier to tune with a bigger cam and injectors later on. Before you go, make sure to install a colder thermostat to open up the tuning window.
Below are some additional upgrades that will improve the performance of your LR4 engine.
Upgrading the LR4 Camshaft and Valvetrain
When it comes to bang for your buck, cams top the list.
The price point of a LS3 or LS9 cam is good, but they make the engines pretty soggy up to 5,000 rpm. This is due to the intake valve closing (IVC) point being late and bleeding off a lot of compression down low.
What you want is a dedicated truck cam.
What’s the difference?
To maximize torque in the mid-range, manufactures close the intake valve at about 40 degrees (at .050 inch) after bottom dead center and alter the intake valve opening to set the idle quality. For a good idle and low end, you’ll often see the 4.8L truck cams in the 205-210 at .050 inch range if it’s still a daily driver.
|Intake Duration (@ 0.050 in.)||Horsepower at the wheels after bolt-ons||Idle Quality||Notes|
|191° (Stock)||235 whp||Smooth||Heavy drivetrain.|
|215°||+40 hp||Slightly noticeable||Good with auto and stock converter.|
|220° - 230°||+65 hp||Steady lope||Converter recommended. Still can drive daily.|
|230° - 240°||+90 hp||Lopey||Fly-cutting the pistons may be required. Heads and intake good for another 40+ hp.|
These cams reduce overlap to keep high turbine inlet (backpressure) from flowing back into the cylinder. Generally, supercharger cams and nitrous cams will have slightly more lobe separation and longer exhaust duration. If you’re planning to turbocharge your 4.8L, you’ll want a dedicated turbo cam.
Drop-in .500-inch lift cams are popular, but LS6 springs allow you to run .550 lift cams and extend the rpm range. Spring life isn’t a problem because trucks generally don’t spend a lot of time at high rpm. Beyond that, .575 to .600 inch options aren’t a problem with dual valve springs.
Keep in mind, the intake valve is closer to the deck with the 61cc chamber castings. This can limit cam duration to about 230@ .050. If a larger intake valve is used or the heads are milled, you will need to measure carefully with cams starting around 226@.050 due to the true flat top pistons.
The stock rockers are good to 175 lbs. of seat pressure and 450 lbs. open. You will want to install a trunnion kit for added reliability.
LR4 Power Adders
In general, the LR4 will see boost or nitrous before any serious head work. Before we get into the power adders, there are a couple things to address:
- A four-corner steam kit reduces hot spots that cause the rings to butt and snap the piston’s ring lands.
- Any power-adder will put you well past the limitations of the stock injectors and pump. We’ll address those in the next section.
With that out of the way, let’s get to the fun stuff.
- A roots-style supercharger is dependable and makes great torque in the low- and mid-rpm range. It’s perfect for melting tires.
- A centrifugal-style supercharger is lightweight and makes more power at high rpm. This is partially due to a larger intercooler mounted in front of the radiator.
- A nitrous oxide kit (at low settings) is great for street driving with stock internals. Up to a 200 shot is common. Keep in mind that the tight piston ring-gap is the limiting factor beyond that. If you want to get serious, a single-plane intake is less prone to breakage as a result of a nitrous backfire. A plate system has better distribution than the original intake, but an eight-nozzle fogger system is even better. Running higher octane fuel is advised.
- Truck engine bays make fitting turbos easy. Single turbo systems using turbo exhaust manifolds are an inexpensive way to make big power. If you’re running a single turbo, the T4 hot-side fits well, but the small turbine diameters limit exhaust flow. The 650 whp begins to feel like 400 did in a hurry, so take this into consideration: V-band style exhaust housings open up the turbine options and make plumbing easier. While twins are a little more expensive out of the box, you’ll have more room to grow.
Upgrading the LR4 Fuel System and Tuning
We recommend looking at the injector’s part number before taking it to the tuner. The 2000+ LR4 injectors were rated at 25 lbs. and won’t support much more than 390 hp at the wheels. Luckily, you have many options.
Keep in mind, the best injectors are fully characterized, which helps your tuner maximize idle quality, etc.
When running boost, you can use a water-methanol system to supply extra fuel and lower charge air temps.
The factory pump is good to about 430 whp, but many fuel system upgrade options are available. Drop-in fuel pump modules and external pumps are popular. Other options to maintain or increase pump pressure includes electronic voltage controllers and hotwire kits.
Upgrading the LR4 Intake Manifold and Throttle Body
If you have a power adder, the intake and throttle body can take a backseat for a while longer. If you are naturally aspirated, it’s commonly done before the heads.
The factory truck-style manifold has long runners for better low-end torque. Porting the intake is one option that’s also a good value.
In most cases, a single plane is the wrong way to go; however, it might make sense if you’re running a lot of nitrous since it’s stronger and the cylinder-to-cylinder mixture distribution can be better. It’s a good choice when swapping it into an old car or if you’re not familiar with injection. You can slap your trusty carb on it and run a programmable ignition box that plugs right into the factory coil harness and cam sensor.
If you’re craving a bit more power and torque, the F.A.S.T. LSXRT intake allows for throttle bodies of 102mm and larger. Truck engine bays also accommodate tunnel rams. These trade a little bit of torque down low for more torque up high—and nothing looks cooler.
|Manifold Style||Peak Horsepower||Torque|
|Single Plane||+10 hp||Losses everywhere below 6000 rpm. *Only recommended for nitrous or boost.|
|F.A.S.T. LSXRT||+15 hp||More low-end and top-end.|
|Tunnel Ram||+30 hp||Slightly lower below 3000, equal at 4500, and big gains beyond 5500.|
Ask your tuner about going with a Speed Density tune. Doing so removes the MAF restriction and gives you a bit more power.
Upgrading LR4 Cylinder Heads
Casting number 862 or 706 heads were used and sported a 61cc chamber but had tiny 1.890 intake valves. The stock heads can be CNC-ported for more airflow and milled up to .030 inch for more compression. Flow numbers can be as high as 325 cfm at .600-inch lift. Lightweight, hollow-stem LS3 valves can be cut to 2.040 inches to fit the seats. Between the light valves and better springs, the engines will pull cleanly well past 7,000 rpm.
A better option is aftermarket cathedral port heads. They reduce down time, they’re all new, and you can usually offset the added cost by selling your original heads. Valve angles are typically laid over to 13.5 degrees, and 2.100-inch intake valves are common. They flow great, and the cross-sections are great for boost.
When comparing heads, look at .400-inch lift numbers as a general indicator of how the heads will perform. With a medium-sized cam, 400+ whp naturally aspirated is common, even with the heavier truck drivetrain.
Upgrading the LR4 Rotating Assembly
Still looking for more?
True flat top pistons were used to hit 9.4:1 with the short stroke cranks. The pistons are a weak point—in fact, you probably know someone who has popped one. A set of forged pistons should be high on your priority list. They have stronger wrist pins, thicker ring lands, and added valve reliefs that allow you to run big cams.
Gen. 3 rods weren’t especially strong, but the 2001’s did receive better quality rod bolts. If you’re getting forged pistons, it’s best to also get forged connecting rods with 7/16-inch rod bolts.
The LR4 cranks were cast but strong—they’ve been known to handle over 1,000 whp. The main reason for going with a stroker forged crank is for the added cubic inches. The extra cubes bring quicker boost, meaning you can use bigger turbos.
Performance rotating assemblies are available in many combinations.
|Engine Size||Bore Dia.||Piston Comp. Height||Stroke||Rod Length||Wristpin Dia.|
|LR4 4.8L (Stock)||3.780 in.||1.338 in.||3.267 in.||6.275 in.||0.9431 in.|
|4.8L to 5.3L||3.780 in.||1.338 in.||3.622 in.||6.098 in.||0.943 in.|
|4.8L to 5.7L||3.903 in.||1.304 in.||3.622 in.||6.125 in.||0.927 in.|
|4.8L to 6.3L||3.903 in.||1.110 in.||4.000 in.||6.125 in.||0.927 in.|
Upgrading the LR4 Engine Block
There is no replacement for displacement.
If you’re running boost, it’s common to overbore by .020 to 3.800 inches. The blocks can be taken to 3.905 (.007 oversize LS1) if it’s not going to see a lot of power.
When combined with a 4.000-inch stroke, this will increase displacement to 383 c.i.d.
The blocks have been known to withstand 850+ hp at the wheels with proper machining, racing fuel, and an excellent tune.
Head and main studs are advised if you’re making more than 850 whp. At that point, a set of head studs are a good idea. Though LS9 gaskets don’t benefit from the optimal bore size, many people have used them with success.
The factory main caps aren’t doweled. It’s better to reduce ignition timing and compensate with added boost to reduce the cylinder pressure spikes that lift heads and cause the main caps to dance.
NOTE: You can find engine specs and detailed engine upgrade advice for every LS and LS-based Vortec truck engine in one place: The Definitive Guide to LS Engine Specs and LS Engine Upgrades.