LS Engines

L33 5.3L Engine Upgrade Guide: Expert Advice for L33 Mods to Maximize Performance

L33 engine turbocharged tunnel ram

(Image/Yellow Bullet)

[Editor’s Note: This L33 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.]

The Gen. 3 aluminum block L33 engine came in Chevy and GMC trucks from 2005-07.

It was known as the Vortec 5300 HO and made more power than the older LM4. This was due to higher flowing Cathedral port heads, more compression, and a slightly bigger cam.

In many ways it’s the “327” of this era. When it comes to modifying the L33, it’s easiest to think of it as a small bore LS6. In fact, they can make more power than a LS6 or LS2 with boost due to the thick cylinder walls.

They can be found for around $1,300 which is inexpensive for an aluminum block engine. The cherry on top is it’s not saddled with Variable Valve Timing (VVT) or Active Fuel Management (AFM) found on some Gen. 4 engines. This reduces expense when you build it up.

Intro to L33 Engine Upgrades

Modifications usually start with a cold air intake and aftermarket exhaust. This will definitely free up a few horsepower and gives the little engine a big personality.

Trucks often came 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-in 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 tuning window.

Below are some more upgrades you can make to improve the performance of an L33.

Upgrading the L33 Engine Camshaft and Valvetrain

L33 cam

(Image/LS1Tech)

The factory cam is tiny and really holds the engine back. An LS3 or LS9 cam makes good power, but not where you want it if you’re using the L33 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.

If the engine is going in a lighter car with deep rear-end gears and a high stall converter, you can be more aggressive with duration.

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.

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.

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.

Intake Duration (@ 0.050 in.)Horsepower at the wheels after bolt-onsIdle QualityNotes
193° (Stock)235-245 whpSmoothHeavy drivetrain.
210°+50 hpSlightly noticeableGood with auto and stock converter.
215° - 225°+75 hpSteady lopeConverter recommended. Still can drive daily.
225° - 230°+100 hpLopeyHeads 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, .575 to .600 in. isn’t a problem with 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.

There are a few other parts needed for a L33 cam swap such as an LS2 timing chain, LS7 spec lifters, LS2 timing chain damper and thick-wall chromoly pushrods.

Upgrading the L33 Engine Fuel System and Tuning

Tuning the computer changes the fuel and ignition curves to increase performance. Plug-in programmers are easy to use but have limits.

If you plan on running a power adder or have a long list of upgrades planned, it’s recommended that you take your truck to a chassis dyno tuner who can give you a custom tune. Knowing you’re running high octane and having the before-mentioned 160-degree thermostat opens up the tuning window.

Depending on how much power you intend to make, upgrading to larger fuel injectors may be needed. Ask your tuner what injectors they prefer and have them ready to save yourself an extra trip to the dyno. The Mini-Delphi/Multec II connector 25-pound injectors are a limitation at around 380 whp. If you upgrade and depending on the injectors you run, you may need a fuel injector adapter harness.

The factory fuel pump will become a limitation around 430 whp, so you should plan on upgrading the fuel pump as well.

The L33 is a returnless system. In-tank fuel pumps and external pumps are popular, but mild fabrication will be required. Other options to maintain or increase pump pressure include electronic voltage controllers and hotwire kits.

When running boost, you can use a water-methanol system to supply extra fuel and lower charge air temps.

Upgrading the L33 Engine Intake Manifold and Throttle Body

The L33 intake wasn’t particularly good and had a 3-bolt 78mm DBW throttle body.

A better option is the Chevy Trailblazer SS or the 2007.5+ “NNBS” truck intake. They are the best of the factory manifolds with a 4-bolt 87mm throttle body, bigger standard EV6 style injectors, and will pick up about 15 horsepower.

Keep in mind, the original throttle body had an 8-pin connector. To run the newer style 6-pin throttle body requires a Torque Rush X-Link harness adapter. You will need re-route the EVAP line and may have to extend the MAP sensor harness. If you’re looking for the last bit of power, the long runner FAST LSXR-T is recommended and accommodates larger 102mm throttle bodies.

[Trying to find an LS engine for a swap or build? Check out Part 1 and Part 2 of our LS Spotter’s Guide.]

Upgrading L33 Engine Cylinder Heads

L33 cylinder heads

(Image/LS1Tech)

Looking for 400+ hp at the wheels naturally aspirated? You can achieve it with good drivability and power across the entire rpm range by upgrading the cylinder heads. Aftermarket heads reduce downtime and are cost-effective when you sell your old heads in good condition. The decks are thicker to withstand more boost.

A 205cc runner head is a good match with the TBSS intake. The combination of the two will pull strongly up to 7,000 rpm.

Don’t mind a little downtime? The 799 and 243 casting Cathedral-port cylinder heads can be CNC ported to flow close to the aftermarket heads. With a bigger cam you can mill the heads for up to 10.8 compression which runs on pump gas.

Keep in mind, if you’re running a cam in the 230 range, piston to valve clearance needs to be checked and fly-cutting may be required. If you are going through the heads, it’s recommended to switch to the light hollow-stem intake valves from an LS3. They can be cut to 2.000-inch to fit the standard valve seats and extend the rpm range up to 7,000 rpm.

Adding an L33 Engine Supercharger or Nitrous Oxide System

Although an iron block 5.3 will handle more power, the L33 can still support over 850 whp.

You’ve likely upgraded the fuel system and injectors if you’re looking at power adders. Remember, a 4-corner steam kit reduces hot spots that cause the rings to butt and snap the piston’s ring lands.

  • 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.
  • roots-style supercharger is dependable and makes great torque in the low- and mid-rpm range. It’s great for melting tires.
  • 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.

Still looking for more? Let’s talk about bottom-end upgrades.

Upgrading the L33 Engine Rotating Assembly

L33 rod and piston

(Image/LS1Tech)

The flat-top L33 pistons added some much needed compression. They are okay naturally aspirated, but are the weak link with boost 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 800 hp, a set of .200 in. wall tool-steel pins is a good idea.

Another bonus of the L33 is it had beefier connecting rods than earlier Gen. 3 engines and had full floating pins. They can handle about 750+ hp and 7,000 rpm in boosted applications (at least for a while). They are likely to bend before they break when subject 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 L33 crank was cast but strong. It’s 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 boost on quicker which means you can use bigger and more-efficient turbos.

Here’s a table with common performance rotating assembly combinations.

Engine SizeStroke Rod Length / WristpinBore Size / Compression Distance
L33 (5.3L)3.622 in.6.098 in. / 0.9431 in.3.780 in. / 1.338 in.
Common Stroker CombinationsStroke Rod Length / WristpinBore Size / Compression Distance
5.3L to 5.7L3.622 in.6.098 in. / 0.945 in.3.903 in. / 1.338 in.
5.3L to 5.7L3.622 in.6.125 in. / 0.927 in.3.903 in. / 1.304 in.
5.3L to 6.3L4.000 in.6.098 in. / 0.927 in.3.903 in. / 1.115 in.
5.3L to 6.3L4.000 in.6.125 in. / 0.927 in.3.903 in. / 1.110 in.

Upgrading the L33 Engine Block

L33 engine block

(Image/LS1Tech)

The L33 engine block has a 3.780-inch bore diameter. The cylinders can be bored to the LS1/LS6’s 3.905 inches, but it’s recommended that you leave them as thick as possible with common .020 /.030 / .040 in. oversize forged pistons.

You can make 700+ hp with a couple of simple upgrades like head studs and LS9 head gaskets.

The head gasket bore diameter isn’t optimal, but with careful tuning and race fuel it can withstand 850+ whp. 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.

The factory main caps aren’t doweled. Main studs should be added any time you’re this deep in the engine.

Something to keep in mind is the 2004 and later engines (even Gen. 3) had two head bolt lengths vs. three on the earlier engines.

(Information for this article originally appeared in this Upgrading the Gen. 3 5.3L, Aluminum Block, LS Truck Engine article at Summit Racing’s searchable database of FAQ tech infoGo there and search “LS engines” for a comprehensive collection of LS engine tech information.)

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15 Comments

  1. Pingback: LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family - OnAllCylinders

  2. Rick siegfried says:

    Awesome article!!
    My son and I are looking for the L33 now for a swap into his 1992 F150 extra cab short bed.
    Would love to see somewhere between 350 and 400 hp at the rear wheels, sounds like it’s very doable. Any other suggestions or maybe even a specific direction to go would be helpful thank you.

    • Hi Rick. If you’re looking for something close to 350-400 hp at the wheels, you’re in the right place. Putting a truck cam in puts you in the zone by itself. If you are looking for a daily driver cam, the Summit Racing Pro LS SUM-8712 stage 1 is a great one–lots of power and a slightly noticeable lope and uses stock springs.
      The other cams I’ll point out next use LS6 springs and you’ll want to do a tune. There is a .550 lift version of the SUM-8712 coming soon called the SUM-8719. There is a medium sized stage 2 cam called the SUM-8701 that has a nice lope. If you are looking for something a pretty stout and you put a 2,500 rpm converter in it (or stick), you might want to bump up to the SUM-8713.
      You’ll be knocking on 400 whp which is where the stock injectors max out anyway…so it’s a fairly inexpensive proposition for the power you’ll be making!

  3. I want to switch my 04 ls1 long block out for a l33 because I want to boost over 7psi. Only issue is I want to keep my cable throttle body and I’m not idée how I can run a gen ov block with a Gen 3 ecu

    • The L33 swap is a pretty common one as LS1s are getting hard to find. The L33 was built later, but was still a Gen. 3 engine. It still has the same 24X reluctor ring, cam sensor location, knock sensor location etc. The accessory drive will swap over, but there’s a chance you’ll need to drill and tap one of the holes for the alternator bracket. The injectors are only 25 lbs. and won’t support more than about 380 whp, but that’s an easy fix.

  4. I’m doing a l33 swap in to a old s10 with manual.
    I like the sum-8712 cam idea, but my issue might be keeping it under the hood. What intake should I use?

    • The Dorman 615-901 has proven itself to be very close in power to the TBSS intake manifold. It also accommodates a 90mm throttle body, but doesn’t clear the truck accessory drive without modification.

      ICT billet offers an idler location kit (part number ICB-551353 https://www.summitracing.com/parts/icb-551353) which allows a car intake to be used with the truck accessory drive. Some trimming of the intake and alternator bracket may be required.

  5. REYNALDO BADILLO JR says:

    I am looking at 5.3 with 862 heads to put in a 1950 fleetline. looking for reliability with a little get up. any recommendations would be appreciated.

  6. Dallas Shepherd says:

    Hi, I’m looking at putting an L33 into a Barbarian V8 motorcycle custom built to take an LS engine, it will be married up to a single speed direct drive gearbox, will not be able to use its usual intake due to space under the fuel tank so what would be the best lowest profile intake/throttle body unit I could use without sacrificing performance, what would the best cam to use given the direct single drive, like the lumpy sound yet be a daily driver, Frame in transit at the moment so just looking at a direction to go with its powertrain. kind regards.

  7. Hunter Gordon says:

    Swapping a L33 into a 96 Silverado with a fresh NV3500. Looking at the BTR Stage 3 truck cam. Any tips and pointers for this?

    Won’t really be a daily driver but a toy I can get out and turn heads with.

    Thanks

  8. Brian Nutter says:

    Reynoldo, you’ll love it after doing a LS swap. When you are getting a donor engine, be sure and get the entire harness and throttle pedal if it’s a fly by wire throttle body. Trans computers were external early on and switched internal later.

  9. Brian Nutter says:

    Hunter, the BTR Stage 3 truck cam is nice. It’s a fairly straight forward swap and Summit has the cam swap kits that include the gaskets, LS2 timing chain, and damper bolt. You may need a bit longer of a pushrod as well. Usually about 7.425, but we recommend the use of a length checker before ordering just in case. That can change if the heads are milled too.

  10. Great article! I’m in the planning stages of swapping an L33 into an 87 porsche 944 turbo. I’ve got the engine tore down and ready to go to the machine shop. I plan on having the mill the block and heads, but would like to do the rest of the build myself. With some modification, I am mating it up with a 4l60e. I would like to keep it as budget friendly as possible, and make around 500-600 whp. I would also like to keep my 799 heads as well. If I keep my original crank and have the block bored .020 over with new pistons, do you think I could do enough modifications to the crank, intake, and heads to get this kind of power? If so, what would you recommend?

  11. Stumbled across a 2005 ext cab Silverado. Not knowing it is a vin(b) 5.3 l33ho. Started jumping up and down. Bought a perfect running truck for 2800$. After reading these recommendations, I cant stop grinning

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