LS3 Head Flow Numbers: A Pocket Note Everyone Should Have

Smart drivers would never underestimate the power of a high-quality cylinder head, which helps seal automobile combustion chambers, facilitates larger intake, and cools down the engine.

Among numerous cylinder head models on the market, the LS3 receives rave customer approval due to its smart designs and tried-and-true performance.

My insightful guide will delve further into the LS3 head flow numbers, included components, and corresponding updates. Keep scrolling.

What Is The LS3 Head? 

ls3 head flow numbers

The LS3 (or LS3 Gen IV) are cylinder heads specifically designed by GM (General Motors) to use in high-performance cars.

LS3 is a recognized member of the entire LS engine line, which has thrived in popularity due to its versatility and performance capabilities.

A typical LS3 head is characterized by innovative and masterful designs – featuring exhaust and intake ports in rectangular shapes.

When pitched against other LS heads, LS3’s ports are undeniably much larger, allowing increased air to and fro the combustion chamber.

Such extra airflow enables better breathing, raising the engine’s performance and additional clearance ten fold. 

Better yet, cylinder filling processes amidst intake strokes are also improved, resulting in great average torque and extra power output.

Your car also enjoys quicker and more precise exhaust gas evacuation, which enhances engine speed and reduces back pressure.

With all these premium attributes, LS3s are widely used in multiple GM vehicles other than LS3 engines.

One can find LS3s in 6.0L trucks, CTS-V Cadillac, and even Corvette ZR1 LS9, further showcasing their versatility and beyond-average power production.

I will return to this issue in the latter half of my article.

What Are The LS3 Head Flow Numbers?

What are the LS3 heads flow numbers? Average LS3 head studs top at 296.9 CFM (intake lift of 600-in) and 208 CFM (exhaust lift for mid of 700-in).

As you can see, the airflow level of cylinder heads is measured by CFM (or cubic feet a minute). Long story short: the larger these CFM numbers are, the more air intake a headset allows.

Still, while healthy peak CFM numbers are wonderful, it is the mid- and low-lift towards the exhaust valves that truly define a head’s overall efficiency.

Hence, choosing a cylinder head is not just all about flow numbers: for instance, large intake volumes with high peak power might end up overworking the chamber volume.

To ensure exceptional flow, it would be best to closely compare/examine the whole flow bench and flow capacity from max to low lifts.

What Are LS3 Head Casting Numbers? 

stock ls3 heads

“LS3 heads casting number” is a distinct identifier GM cast onto its cylinder heads during manufacturing.

These numbers help identify the production details, features, and specific designs of particular cylinder heads.

LS3’s casting number is 821, meaning drivers will recognize a cylinder head is LS3 if it has the 821 heads specs embedded.

821 heads have lighter valve intakes and yellow spring packages, which separate them from other heads (say, 823 or 799).

Usually, the dedicated casting number is designed on the head top, whose valve housings have to be pulled out for drivers to access the numbers.

As that process can be quite time-consuming (not to mention, troublesome and risky if you have no expertise), I suggest clicking this guide or referring to the user’s manual.

The Impressive Power Of LS3 Heads: How to Enhance It

One can power the LS3 heads further through cylinder CNC porting – a critical engine optimization aspect for high-performing applications.

The process involves modifying your intake/exhaust ports to allow better air processing, which paves the way for Frankenstein engine dynamics, boosted RPMpeak torque, and additional power as a result. 

These adjustments and careful shaping also reduce turbulence and restrictions amidst the airflow paths, maximizing your car’s breathing capabilities.

And while you are at it, some surface smoothing can do wonders for the car, too;

I usually use abrasive tools or fine sandpaper to remove irregular/rough textures within the cathedral ports for my Chevrolet performance.

As the flow path is slicked out, your airflow will not likely encounter any disruption, fostering better combustion and cylinder filling.

What Features Are Included In The LS3 Ported Heads?

I have discussed more than enough about the LS3’s overview and basic manufacturer numbers. This section will detail further the included compartments and features within this superior head.

High-Quality Castings for The LS3

Explicitly produced for LS3 and other similar LS engines, these heads arrive with premium, sturdy castings made of quality materials (mostly titanium and aluminum blocks) to boost power, improve air circulation, and reduce the overall weight.

Those are a huge step up over regular stock heads and factory castings, allowing LS3 to go beyond the manufacturer’s production aim and work with numerous engines other than LS.

Exhaust and Intake Valves

Another critical feature to discuss is the valve package, which features 2.165-inch (intake flow/hollow stem intake valves) and 1590-inch ones (exhaust port volume, stainless steel).

These LS3 head valves, like aftermarket castings, are made much larger than their stock counterparts to foster substantial airflow increase and yield awesome power output.

Better yet, these valve size measurements have not yet reached their limit; larger options are still out there!

By illustration, a scour through aftermarket head options will bring you huge LS3 heads of 2200 inches (for intake port volume) and 1625 inches (for exhaust flow/ exhaust valve size).

Improved Locks, Valve Springs, and Retainers (For Ported Heads)

LS3 heads usually offer 550 inches for sufficient spring pressure; however, ported ones raise that number to 650.

Ported LS3 heads also include new valve seals, spring seats, and retainers to guarantee optimal durability.

Whether you wish for naturally aspirated engines, supercharger technology, or turbo to increase power output, or look for more effective ways to polish the LS engine, ported LS3 heads are wonderful options that take your car to a new level.

What Are The Applications of The LS3 Heads 

823 head specs

High-speed applications and LS3 heads often go hand in hand due to the latter’s exceptional power output and impressive flow rates.

They are eagerly sought by engine builders seeking maximized performance.

During racing or competitions – where every RPMaverage horsepower bit matters – LS3s can lend mast motorsports drivers excellent competitive advantages.

On another note, LS3s can also be installed for regular street engines with occasional track usage, as they offer excellent street drive-ability.

The large ports enhance power delivery, throttle response, and overall responsiveness, offering noticeable power improvements without compromising the longevity and durability needed for daily street manners.

Upgrading The LS3 Engines: Factors To Keep In Mind For Custom Builds

Ported LS3 heads introduce tons of impressive benefits; however, remember that a crate engine is more than a bunch of cylinder head porters.

Consider upgrading the following to turn your custom projects into powerful beasts in racing scenarios: 

Engine Blocks

LS3 engines are around 4000 inches in bore diameters, with cylinders bored as deep as 4080 inches.

While these numbers are pretty good already, I suggest leaving them extra thick while running boost to race the displacement to 427 C.I.D.

Rotating Assemblies

Stock pistons have always been the notorious weak point, cracking the cylinder walls whenever the engine revs up to higher average horsepower.

Hence, a premium, high-quality forged piston set should be on your list for head upgrades. Also, pick pistons with minimal skirting tapers to prevent scraping and rocking issues.

Throttle Body and Intake Manifold

LS3s already have great peak flow due to their rectangular-port head; still, aftermarket intake upgrades can step up the game by several notes.

And here is one important tip: single-plane intakes and shorter runner manifolds yield better top-end output, yet they might sacrifice low-end power in the process.

Hence, ensure the peak torque converter and gear ratio matches your desired power targets.

Tuning and Fuel System

Standard fuel pumps are often limited to around 570 HP or lower, failing to meet increased power potential.

Thus, I always remind myself to upgrade the fuel system as well for my Chevy performance.

To add a final touch, tune the automobile computer with specialized tools or with laptops; it will change the ignition and fuel curve to accommodate newly improved performances.

FAQs on LS3 Heads Specs

How Good Are LS3 Heads?

LS3 heads can easily support more than 650 HP, lending impressive speed and gas mileage to even the most standard and outdated car.

There are reasons why they are always among GM’s best-sellers! 

Are LS3 Heads Interchangeable?

Yes. And not just LS3; my recent experiments have proven that almost any LS cylinder head can be used interchangeably, except for L92s on LS6/LS1 engines.

Can A Stock LS3 Handle A Supercharger?

Yes, stock LS3 heads can handle superchargers just fine. Operating and maintaining the two does not differ much from any regular usage, so there is nothing to worry about.

What Heads Are On A LS3?

To my delight, LS3 engines are compatible with almost any LSA heads, not just LS3 heads. Examples of suitable factory heads include:

  • Stock LS1 heads
  • CNC-ported heads/CNC-ported LS9 heads
  • Cathedral heads/ cathedral-port AFR heads


Are LS3 Heads Better Than LS2?

Yes. Even when both go through the same adjustments and upgrades, LS3 can still deliver much more impressive outcomes. That explains why LS3 has become a crowd’s favorite.


I hope my detailed and insightful guide on the LS3 head flow numbers and features can lift your lingering confusion about these cylinder heads.

If any aspect of the LS3 head specs or cylinder head flow has not yet been covered in my analysis, feel free to leave suggestions or comments below;my devoted and awesome customer service team will reply to them all.

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