[Editor’s Note: No offense to the LS4 intended, but the most notable thing about it is that it’s usually the worst-possible choice for an LS engine swap project because it’s designed specifically for front-wheel drive (lovingly called “wrong-wheel drive” by some) cars, so if that’s why you’re here, save yourself the time and hassle and choose a different LS or LS-based Vortec engine for your build. We are growing our collection of LS engine upgrade guides, courtesy of our LS-expert friends at Summit Racing. If you already possess an LS4 engine or LS4-powered car and are looking for tips to add more performance capabilities, you’re in the right place. 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 LS4 FWD Engines
The LS4 is unique in the LS engine family because it was a transverse-mounted engine used only in front-wheel drive (FWD) cars from 2005-09, namely the Pontiac Grand Prix GXP, the Chevy Monte Carlo SS and Impala SS, and the Buick LaCrosse Super.
While the LS4 is likely a poor choice for an engine-swap project, it’s not out of the question that you own one of these likable V8-powered vehicles, and want to add a little giddy-up to that sideways 5.3-liter.
We can help with that.
To make this engine work for those FWD cars, GM made several major modifications to the engine:
- The engine was mounted in a transverse position, using unique motor mounts.
- The intake manifold was smaller than other LS manifolds and reversed, placing the throttle body over the flexplate. It also had a unique (small) 4-bolt throttle body pattern.
- The engine used a metric, 60-degree, Chevrolet V6 bellhousing. The engine shaved about 3mm off the flexplate side and 10mm off the crank snout, and featured a unique timing cover.
- The starter was mounted on the transmission—not the engine block.
- The timing cover, crankshaft, and accessory drive were all modified to fit in a FWD engine bay.
[Every engine spec you’ll need can be found here: LS4 Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More.]
How to Get More Power From Your LS4
The LS4 is a bad choice for an engine swap, but it can be improved when used in a FWD car or mid-engine kit car swap.
- A cold air intake kit
- An aftermarket exhaust
- A computer programmer
- Install a 160-degree thermostat before heading to the chassis dyno tuner as it will give them a wider tuning window.
For the rest of this article, good fabrication skills and probably more research will be required.
Upgrading the LS4 Intake Manifold and Throttle Body
The LS4 has a smaller throttle body and intake manifold than other LS engines.
The intakes were necked down behind the throttle body to clear the oil pressure sender. As a result, a larger throttle body doesn’t offer big gains.
It’s possible to upgrade to an aftermarket intake manifold. However, be prepared modify the following components to make it fit:
- PCV is on the wrong side
- Valley cover—use a non-PCV cover and delete AFM
- MAP sensor
- Oil pressure sender
- Injector pigtail adapters
- Alternator bracket
- The underside of the intake manifold (if you’re trying to keep AFM active)
- A throttle body and/or adapter
WARNING: Throttle bodies came with either silver or brass blades during this time period. They differed in rotation and pinouts between different models. The LS4 had a unique brass blade and smaller 4-bolt pattern (as used in V6 models). Further, the airflow tables and ETC scaler may require work by your tuner to get proper throttle response after an install.
Upgrading the LS4 Camshaft and Valvetrain
You will need to drop the entire engine cradle to do a cam swap, but that’s more cost-effective per horsepower than an intake swap.
Keep in mind that going bigger than about 220 degrees of intake duration (at 0.050 in.) is pushing it with the stock intake and torque converter.
The 2005-2006 models came with the 3-bolt cams with a 1X-single pole to match the 24X reluctor and E40 ECU. Halfway through 2007 however, it changed to a single-bolt 4X-4 pole gear to match the 58X reluctor and E67 ECM. The cam is also a few degrees bigger than the early cam.
GM switched to a spring-loaded timing chain tensioner in 2007+. If you’re performing a cam swap, going back to the 2005-06 wedge-shaped plastic guide adds reliability.
The trunnion bearings in the stock rocker arms are a known weak point. A trunnion upgrade kit should be installed whenever you upgrade the valvetrain.
The LS4 was equipped with Active Fuel Management (AFM). It’s good for gas mileage, but not for performance. If the valvetrain is in good condition, an AFM disabler plugs into the OBD-II port and will turn it off.
When upgrading the camshaft, an AFM delete kit is strongly recommended. These kits replace the AFM components with standard parts. It also becomes easier to fit an LS6 intake or aftermarket LS2 manifold. A smooth, non-PCV / non-AFM valley cover won’t interfere with underside of the manifold. You may need to modify the oil pressure sender bung to avoid the throttle flange area.
Upgrading LS4 Cylinder Heads
The cathedral port cylinder heads are based on the LS6 heads and make good power. You can mill them about 0.030 in. for more compression. They can also be CNC-ported for better airflow.
There are a few aftermarket LS4 heads available. The heads will flow better than stock and have thicker decks to maintain a proper head gasket seal.
Upgrade the LS4’s 4T65E Transmission Before Adding Power
The 4T65E wasn’t made to handle a lot of horsepower beyond stock output.
There are transmission builders that specialize in the 4T65E who can build it to withstand 400-450whp.
Once you have the transmission equipped to handle more power, a single-nozzle nitrous kit is adjustable and allows you to sneak up on the limits of the drivetrain.
We found examples of advanced fabricators building turbocharged LS4 engines, so it’s not impossible if you have the knowledge and resources to add significant power to an LS4-powered FWD vehicle, but adding that much power will require a number of potentially expensive and labor-intensive upgrades and reinforcements elsewhere.