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What’s So Special About 243 Heads

What’s So Special About 243 Heads?

The 5.7L V8 LS6 engine is a family member in the third generation of small block designs produced by General Motors. It was briefly used for the C5 Corvette and first-generation Cadillac CTS-V.

What makes it confusing for some is that Chevy used the LS6 designation in the past for a 7.4L engine that was made from 1970 to 1976.

The engine’s first iteration was found in the Monte Carlo, El Camino, Chevelle, Caprice, and Corvette. GM also put it into the Sprint.

The big-block V8 doesn’t have a mechanical relationship with the 2001 LS6 engine with the 243 heads.

It originally produced 385 horsepower. The LS6 bumped up to 405 HP and 400 foot-pounds of torque in 2002. Both options are significant improvements over the LS1 from the previous generation.

What’s So Special About 243 Heads?

The 243 heads came on the LS6 engine produced from 2001 to 2006. It was typically found in the C5 Corvette, but it was eventually ported to the LQ4 and LQ9 to meet truck specs. The latter offered 6cc larger combustion chambers to accommodate the working style vs. speed and acceleration.

When you look at the Chevy small block engine, several virtues are on display almost immediately. What makes it such a popular choice is that the design is practically universal for the different makes and models.

GM has the habit of engineering engines to accept several variant parts, whereas Ford tends to create items that are model specific. You won’t get the option to put a Ford Focus engine into an F-150.

With Chevy’s 241 and 243 heads, also referred to as the LS1 and LS6, you get to take advantage of the brand’s modular approach. What you choose depends on your power design, future mods, and overall budget.

Highlights of the 243 Heads with the LS6 Engine

The LS6 worked with the titanium exhaust system in the Corvette to deliver a marginal power increase. It also featured an aggressive camshaft, stiffer valve train, and other improvements that made the engine an excellent choice at the time.

You can still use the 243 heads when modifying current vehicles because of the many benefits the technology offers.

Here’s an overview of the LS6 engine highlights so that you can see why it is still considered one of the best specialty designs of its type in the past 30 years.

Cylinder Block:• The LS6 cylinder block shares several design elements with the original small-block V8, including a 90-degree cylinder angle and 4.4-inch bore centers.
Rotating Assembly:• It includes a cast-iron crankshaft with powder-metal connecting rods and M142 hypereutectic-cast aluminum-alloy pistons.
• The rods maintain the I-beam design from the LS1.
Cylinder Head Design:• The cylinder heads on the LS6 maintained the all-aluminum construction, using steel intake and exhaust valves held at 15-degree angles to maximize flow.
• The components include beehive valve springs and roller-pivot rocker arms using a 1.7 ratio.
Camshaft Design:• The LS6 uses a hydraulic roller-lifter design, receiving two slightly varied specs based on the model year and application.
Exhaust Manifolds:• The LS6 engine uses the same four-into-one short-header design that was common to the LS1 and the 241 heads.
Intake Manifold:• This component features 30 pound-per-hour fuel injectors and a. Higher-flowing intake manifold.
• The results were so impressive that they would later become the standard configuration on the later versions of the LS1.
24X Ignition System:• Every LS6 engine uses a 24x crankshaft reluctor wheel to maintain its timing.
PCV System:• General Motors redesigned the positive crankcase ventilation system for the LS6.
• Instead of pulling the gases and oil blow-by from the valve cover, it has pick up in the valley cover between the cylinder banks. That places it beneath the intake manifold.

What You Need to Know About the LS Castings

If you’re interested in finding out why the 243 heads are so special for some vehicles, here is the information you’ll need to consider when looking at this critical component.

◼️ GM produced seven versions of the LS engine.

Almost all the different LS engines come with unique heads. You can identify the one you’re looking at by reviewing the three-digit stamp next to the valve cover. You can find the 243 heads on the impressive LS6 engine manufactured from 2001 to 2006, used in the C5 Corvette.

In comparison, the LS1 used 339 and 806 heads until 1998. GM then transitioned to 853 and 241 heads until 2004 with that option, although the engine design in the later models incorporated the advantages discovered with the LS6.

◼️ Three fundamental differences exist between the LS1 and LS.

The first difference involves the port shape between the two heads. With the LS6, you’re getting a reshaped intake port with a D-shaped exhaust for better flow. That’s different than the oval-shaped option with a 200 cfm intake than with the 241s.

Secondly, the LS6 heads use a hollow, sodium-filled valve stem to reduce the valve train inertia during operations. This design element offers a better heat transfer experience between the exhaust valves and the head.

The final difference is that the combustion chamber for the 243 heads. It is 65cc, compared to the 67cc for the LS1 241s.

◼️ The 243 heads produce about 5% more power on flow alone.

If you were to judge the 243 heads vs. the 241s on head flow alone, you’d get a slight power edge. This benefit occurs because of the hollow valve stem, delivering a better RPM potential that stands up to more supercharger or turbo applications.

Although the 243s aren’t as reliable as the LQ5 or LQ9 heads (317s or 873s), it’s because the chamber is 71cc for the slight compression drop you want for forced induction.

What If I’m Already Using 241s? Should I Upgrade to 243s?

If you already use reliable LS1 241 heads, you don’t need to toss them away for the 243s. As long as you have some experience with basic porting, the outcome is remarkably similar. You’ll need to do some bowl blending and gasket matching to maximize your results, but the work is enough to reach that extra 10 cfm that comes with the LS6 design.

You can order the sodium-filled valves from the 243s as a part through General Motors. It’s a direct retrofit to the LS1s, as are the valve springs from the LS6 engine design.

The only reason to get rid of the 241s in favor of the 243s is that you want absolute power. Switching to the LS6 gives you a stronger foundation, especially in its naturally aspirated form, to deliver the results you want for almost any circumstance.

How to Proactively Protect Your Engine

When you start running with the 243 heads, you’ll want to take some proactive steps to ensure the engine works as intended.

Here are some maintenance tips that I’ve discovered over the years that can help you keep this investment running at its peak condition for as long as possible.

1. Check the engine oil regularly.

The oil keeps the moving parts lubricated to minimize the wear and tear potential during operations. It also traps the sediments, dirt, and dust to remove it from the places it shouldn’t be while using the engine. Try to check levels monthly and refer to the manufacturer’s recommendations for getting it changed.

I like to use Castrol Edge 0W-30 for most applications. It takes 6.5 to 7 quarts to top it off at the dipstick. 

2. Check on the cooling system.

If your engine gets too hot, the 243 heads won’t perform as expected. Lots of energy gets lost during combustion with heat generation, which means the alloys and metals can try to cause damage.

I prefer to use Zerex DEX-COOL organic acid technology antifreeze to take care of my engine. It’s approved by General Motors to the company’s 6277M specs.

3. Let the engine breathe.

Constricted air flows on the LS6 cause the 243s to lose their advantage. I highly recommend checking the filters routinely to ensure you’re giving the engine what it needs. While you’re taking this step, review the compartment to see if any leaks have sprung during recent operations.

If you’re in a pinch, the K&N Air Filter Cleaning Kit can keep you going until a replacement is possible.

4. Give the fuel system a cleaning.

Once you start running the LS6 engine for a while, the fuel tank will eventually develop sediments that can clog your fuel filter. You can avoid this problem by not running on fumes, but it also helps to clean your system regularly.

I prefer to use the Fuel System Treatment products from AC Delco for this step. It coats the metallic surfaces to give the entire system an extra protective layer.

The 243 heads deliver that extra boost of power and performance that can give your GM vehicle new life. This modular design offers a maximum level of flexibility while promoting an appropriate acceleration profile. If you want an upgrade, the LS6 design is worth the investment.


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