[Editor’s Note: This LH9 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 LH9 Engines
The LH9 came in GM trucks and SUVs in 2010-‘12 and made between 300 horsepower right out of the box.
It’s a Gen. 4 5.3L Aluminum-block engine, so you’re getting the better intake manifold, connecting rods, and ECM. The engine also had 799 or 243 casting heads which are closely related to the LS6. The engine has flex-fuel capability. The engine is close siblings with the LMF which shared many of the same features…except the block material.
For LH9 engine specs, read this:
How to Get More Power From Your LH9
These engines start life in trucks.
The LH9 is gaining popularity for several reasons:
- It’s an aluminum block alternative to older Gen. 3 5.7L engines that are getting more difficult to find. The intake and accessory drive swap over, but a Lingenfelter crank sensor trigger conversion is required.
- General Motors made a bazillion of them which helps keep prices down.
- The flex fuel injectors will support 450+ horsepower at the wheels.
- Generally, the Gen. 4 engines have better rods and intakes.
Do they have a downside? Maybe just one because VVT isn’t for everyone.
Basic Bolt-On Upgrades for LH9
Trucks are the everyday hotrods of the 21st century and you can think of the LH9 as the modern equivalent of the old 327—a long-time favorite of hot rod builders.
For many people, it starts off with a cold air intake and aftermarket exhaust. The problem is that the engine starts to sound REALLY good and owners find themselves wanting to go faster. All these can be done in the garage, but the tune won’t be optimized.
At this point, we recommend talking to your chassis dyno tuner and decide on a computer programmer. Whether you’re towing on low-octane or springing for good fuel, a tuner can dial the ECM and take it to the next level.
The 5.3L 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 more upgrades that will improve the performance of the LH9 engines.
Upgrading the LH9 Camshaft and Valvetrain
The factory cam is TINY, even by truck standards. A cam provides huge bang for your buck, but the first thing to decide is whether you want to maintain VVT.
What are the downsides to VVT?
More serious cams often require 400 lbs. of valve spring open pressure. This makes it hard for the phaser to actuate. In addition, tuning VVT is a little more complex. If you don’t want to deal with that, a VVT delete kit is an option. It opens the door to a wide selection of camshafts.
Generally, 3-bolt cams are more common and just requires the addition of a 3-bolt 4-pole upper gear to convert it over.
So how do you choose a non-VVT cam?
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, manufacturers close the intake valve at about 40 degrees (@.050 in.) 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 5.3L truck cams in the 210-215 @ .050 range if it’s still a daily driver.
|Intake Duration (@ 0.050 in.)
|Horsepower at the wheels after bolt-ons
|Good with auto and stock converter.
|220° - 230°
|Converter recommended. Still can drive daily.
|230° - 240°
|Fly-cutting the pistons may be required. Heads and intake good for another 40+ hp.
If you’re planning to turbocharge your 5.3L, you’ll want a dedicated turbo cam.
They 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.
LH9 Springs and Things
Drop-in .500 in. lift cams are popular, but factory spring pressure is light to keep people from revving the engines to the moon.
The next step are LS6 springs that will allow you to run .550 in. lift and extend the rpm range. Spring life isn’t a problem because trucks generally don’t spend a lot of time at high rpm.
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.
LH9 Power Adders
In general, the LH9 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 4-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 great for melting tires and nothing beats they’re looks.
- 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 the tight piston ring-gap is the limiting factor beyond that. If you’re wanting to get serious, a single plane intake is less prone to break from 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. Although twins are a little more expensive out of the box, you’ll have more room to grow.
Upgrading the LH9 Fuel System and Tuning
We recommend looking at the injector’s part number before taking it to the tuner.
The LH9 injectors were rated at 37 lbs. and won’t support much more than 450 hp. Luckily, you have many options.
If you’re at the limit of the 1.730 in. O-ring centers of the factory injector, the L96 injector bumps capacity to 49 lbs. and bolts in. The shorter 59-lb. LSA/LS9 injector also works, but a spacer will be required to fit the fuel rail.
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. 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 LH9 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 though, it’s commonly done before the heads.
The factory truck-style manifold has long runners for better low-end torque and make better power up to 6500 rpm due to plenum volume. The LH9 had an excellent intake and performs identically to the best factory intake — the Trailblazer SS LS2 intake. Porting the intake is one option and a good value.
When would a single plane intake be a good idea?
- The first is when you’re running serious nitrous. A nitrous backfire can cause the intake to pop and the mixture distribution is a little dicey as well. A single plane is stronger and the cylinder-to-cylinder mixture distribution can be better.
- The second is when you are swapping it into an old car and don’t want to deal 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 looking for more power and torque, the F.A.S.T. LSXRT intake allows a bigger 102 mm+ throttle body. Truck engine bays also accommodate tunnel rams. These trade a little bit of torque down low for more up high—and nothing looks cooler.
|Losses everywhere below 5500 rpm. *Only recommended for nitrous or boost, or when performing a carb swap.
|More low-end and top-end.
|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 will give you a bit more power.
Upgrading LH9 Cylinder Heads
- The stock heads can be CNC ported for more airflow and milled up to .030 in. for more compression. Flow numbers can be as high as 325 cfm at .600 lift. Lightweight hollow stem LS3 valves can be cut to 2.040 in. to fit the seats. Between the light valves and better springs, the engines will pull cleanly past 7000 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 in. intake valves are common. They flow great and the cross-sections are great for boost. When comparing heads, look at .400 lift numbers as a general indicator of how the heads will perform. With a medium-sized cam, 425+ whp naturally aspirated is common even with the heavier truck drivetrain.
Upgrading the LH9 Rotating Assembly
Still looking for more?
As mentioned before, the pistons are a weak point and you probably know a guy that’s popped one. A set of forged pistons should be high on your priority list. They have stronger wristpins, thicker ring lands, and the added valve reliefs allow you to run big cams.
There are exceptions, but Gen. 4 rods start getting dicey around 800 whp and the bolts don’t like much more than 7200 rpm. They are likely to bend before they break when subjected to real track conditions. If you’re getting forged pistons, it’s best to also get forged connecting rods with 7/16 rod bolts.
Note: If you are reusing your Gen. 4 rods, remember the pins are smaller (.943) than the Gen. 3 (.945) and you’ll need to get a piston that matches. If you want to use a .945 pin piston, just take the rods to the machine shop and have them hone the small end to .9458’.
The LH9 cranks were cast but strong. They’ve been known to handle over 1000 whp. The main reason for going with a stroker forged crank is for the added cubic inches. The extra cubes bring boost on quicker which means you can use bigger turbos.
|Piston Comp. Height
|LH9 5.3L (Stock)
|5.3L to 5.7L
|5.3L to 5.7L
|5.3L to 6.3L
|5.3L to 6.3L
Upgrading the LH9 Engine Block
There is no replacement for displacement.
If you’re running boost, it’s common to overbore .020 in. to 3.800 in. The blocks can be taken to 3.905 (.007 oversize LS1) if it’s not going to see over 1000 hp. Keep in mind, that’s several boring setups for the machinist though, and they need to charge accordingly.
When combined with a 4.000-inch stroke, this will increase displacement to 383 cubic inches.
Although LS9 gaskets don’t have the optimal bore size, many have used them with success. The problem is the fire ring inside the gasket is actually outside the iron liner. You’re better off going with a properly sized gasket that matches the 799/243 chamber.
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.
If you’re really getting up there in power, there are options like the Dart SHP blocks that are just getting started at 1000 whp.
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.