[Editor’s Note: This LC8 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 LC8 Engines
The LC8 engine came in Chevy and GMC 2500HD series trucks and commercial vans from 2011-19. Usually in fleet vehicles. It is the longest standing Gen. 4 engine due to its unique ability to run on gas, compressed natural gas (CNG), or liquid propane gas (LPG).
Due to the different fuels, power and torque differs greatly depending on which fuel you’re running.
|Gas||342-360 hp||373-380 ft.-lbs.|
|CNG||282-301 hp||320-333 ft.-lbs.|
|LPG||332 hp||370 ft. lbs.|
If you stumble on one of these engines, that’s a very good thing. The cylinder heads had some high dollar parts inside to increase longevity with CNG/LPG. We’ll get into those changes further into the article.
If you’re considering modifying the engine, you’ll be glad to know that it’s still the same good old rectangle port 6.0 iron block engine at its heart. It’s known for withstanding big boost or nitrous.
The rugged iron block 6.0L came with VVT, but without AFM, which saves you the cost of an AFM delete kit.
You also get the sturdy 4th-gen full-floating connecting rods and a boost-friendly 9.7:1 compression ratio. Most 6.0L truck engines came with cathedral-port heads. The LC8 (along with the LY6, L76 and L96) came with high-flowing LS3-type rectangle port heads.
[Every engine spec you’ll need can be found here: LC8 Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More.]
How to Get More Power From Your LC8
For many people, upgrading an LC8 starts with adding a cold air intake and aftermarket exhaust. This will definitely free up a few horsepower and the V8 burble will make your ride the center of attention at a stop light.
Trucks often come with mechanical fans that sap horsepower. An electric fan kit will free up that power.
These mods can be done in your garage, but the tune won’t be optimized.
We recommend that you talk to your local 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. Raising the factory redline is a big part of this because it allows your vehicle to be in the meat of the powerband longer.
Torque limiting can be completely shut off, shift points can be raised and it makes it easier to tune for a bigger cam and injectors later on. Before beginning the tuning process, we recommend installing a colder thermostat to open up the LC8 tuning window.
Below are some more upgrades you can make to improve the performance of an LC8 engine.
Upgrading the LC8 Camshaft and Valvetrain
At 198° of intake duration and .467 in. lift, the LC8 cam is holding the engine back.
[Read LS Tech: How to Delete Variable Valve Timing (VVT) on an LS Engine for more info and part numbers.]
An LS3 or LS9 cam makes decent power, but not where you want it if you’re using the LC8 engine in a truck. What you need is a cam that delivers a gut-punch right when the converter hits. We recommend a dedicated truck cam.
What’s the difference?
To maximize torque in the mid-range in a truck cam, manufactures close the intake valve at about 35-40 degrees (@.050 in.) after bottom dead center and alter the intake valve opening to set the idle quality.
The 6.0L engine can take a little more cam than a 5.3L and still idle well.
What if you already have a power adder?
Generally, supercharger cams and nitrous cams will have slightly more lobe separation and longer exhaust duration. Turbo cams reduce overlap with less exhaust duration split in relation to the intake.
|Intake Duration (@ 0.050 in.)||Horsepower at the wheels after bolt-ons||Idle Quality||Notes|
|198° (Stock)||300-325 whp||Smooth||Heavy drivetrain.|
|215°||+50 hp||Slightly noticeable||Good with auto and stock converter.|
|220° - 230°||+75 hp||Steady lope||Converter recommended. Still can drive daily.|
|230° - 240°||+100 hp||Lopey||Fly-cutting the pistons may be required. Heads and intake good for another 50+ hp.|
Drop-in .500-in. lift cams are popular, but LS6 springs 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. Beyond that, .600 in. isn’t a problem with a good beehive or dual valve springs.
The stock rockers are good up to 175 lbs. of seat pressure and 450 lbs. open. You will want to install a trunnion kit for added reliability.
LC8 Power Adders
In general, an LC8 upgrade will involve adding boost or nitrous before starting any serious work on the cylinder heads.
Before we get into the power adders, there are a couple of 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 will put you well past the limitations of the early injectors. We’ll address those in the next section.
Okay, here’s the fun stuff:
- 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 are available with larger turbines and make plumbing easier. Although twins are a little more expensive out of the box, you’ll have more room to grow.
- A roots-style supercharger is dependable and makes great torque in the low- and mid-rpm range. It’s great 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.
Upgrading the LC8 Fuel System and Tuning
The good news is the factory injectors are already rated at 49.2 lbs. Second only to the shorter LSA/LS9 injector. If you use the LS9 injector, a spacer will be required to fit the fuel rail.
|Year||Part Number||Flow @ 58 PSI||Connector||Length (Inches between O-rings)||Approx. WHP Limit|
|2011-19 stock||12613412||49.2 lbs.||USCAR EV6||1.730 in.||650|
|LSA/LS9||12598646||59 lbs.||USCAR EV6||1.496 in.||800|
The factory pump is good to about 430 whp.
Many fuel system upgrade options are available including using the flex-fuel pumps which are good for another 100+ whp, but the modules (baskets) are different and it may be easier just to swap the entire tank.
When running boost, you can use a water-methanol system to supply extra fuel and lower charge air temps.
One last note on tuning: The LC8 has a 58x reluctor ring and isn’t compatible with the early ECMs. It’s best to keep the E38 ECM as it’s faster and tunes better with bigger cams.
Upgrading the LC8 Intake Manifold and Throttle Body
If you have a power adder, the intake and 87mm throttle body can take a backseat for a while longer.
The factory truck-style manifold has long runners for better low-end torque and makes good power from idle through 6,000 rpm. It’s also very good for a little over 25lbs. of boost
Porting the intake is an option and a good value.
If you have the LC8 in a vehicle with deeper gears, bigger converter, cam, and the rev limit bumped, you may want to trade a little of that low-end torque for some top-end horsepower. If so, go with a tunnel ram. Gains of 35 whp are possible with the crossover point starting at around 5,500 rpm.
Ask your tuner about going with a speed density tune. Doing so will remove the MAF restriction and will give you a bit more power.
Upgrading LC8 Cylinder Heads
The LC8 cylinder heads are similar to the LS3 heads, and make good power. Here’s the unique upgrades to the LC8 come in. The intake valves were made of SIL-1 Nitride stainless steel. The exhaust valves used Inconel. The valve seats were upgraded to Brico 3010 for maximum durability.
- 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 373 cfm at .700 lift. Lightweight hollow stem LS3 valves will drop right in. Between the light valves and better springs, the engines will pull cleanly to 7,000 rpm. Keep in mind, if you’re looking to boost to 800+ hp; a heavy duty aftermarket stainless intake valve is a bit tougher and won’t tulip as quickly from the heat.
- A better option is aftermarket 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. They flow better and the cross-sections are great for naturally aspirated or boosted engines. When comparing heads, look at the .400 in. lift numbers as a general indicator of how the heads will perform. With a medium-sized cam, 475+ whp naturally aspirated is common even with the heavier truck drivetrain.
Upgrading the LC8 Rotating Assembly
On the LC8, the pistons are the weak link 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. If you’re going over 1000 hp, a set of .200 wall tool-steel pins is a good idea.
The LC8’s Gen. 4 rods are stronger than the Gen. 3 rods and have full floating pins. They can handle about 800 hp and 7,000 rpm in boosted applications (at least for a while). They are likely to bend before they break when subjected to real track conditions.
If you’re getting forged pistons, upgrade to forged connecting rods at the same time. Big 7/16-inch rod bolts will go a long way to keep things together over 7,000 rpm.
The LC8 crank was cast but strong. They’ve been known to handle over 1,000 whp.
The main reason for going with a forged stroker crank is for the added cubic inches. The extra cubes bring boost on quicker which means you can use bigger and more-efficient turbos.
Performance rotating assemblies are available in many combinations.
A few notes of caution:
- The 6.0L iron blocks had shorter cylinder sleeves than the aluminum blocks (5.430 in. vs. 5.500 in. on average). Much of the piston skirt drops out of the bottom of the cylinder at BDC. The best piston manufacturers have compensated for this by eliminating skirt taper until a point well above where it meets the bottom of the cylinder sleeve at BDC. Any skirt taper at this intersection acts as a razor blade and will wear out the piston quickly.
- The blueprint deck height of the block is 9.240 in., but it’s common to find them in the 9.230-in. range. It’s best to measure deck height before ordering your rotating assembly. Thicker head gaskets or using an aftermarket 6.098-6.100 in. rod will ensure enough piston-to-head clearance.
|Engine Size||Bore Dia.||Piston Comp. Height||Stroke||Rod Length||Wristpin Dia.|
(364 c.i.d. Stock)
|4.000 in.||1.338 in.||3.622 in.||6.098 in.||0.9431 in.|
|6.0L to 6.7L (408 c.i.d.)||4.030 in.||1.110 in.||4.000 in.||6.125 in.||0.927 in.|
Upgrading the LC8 Engine Block
Four head bolts per cylinder aren’t optimal, but you can O-ring the block if you’re aiming for 1,000+ whp.
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.
Main studs should be added any time you’re this deep in the engine.
The blocks have been known to withstand 1,300+ whp with proper machining, racing fuel and an excellent tune.
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.