What factory cylinder heads should I run on my 6.0L LS?

The question is somewhat loaded, as the answer depends on your desired outcome. Are you looking to maximize low-speed towing torque, or do you want said 6.0L to charge hard on the big end? Is it a daily driver with a stock converter or is it a street/strip weekend warrior?

Obviously, the other components (like cam and intake) also come into play here, but most folks just want to know how the different (cathedral and rectangle port) factory heads perform, and then how they compare to a good set of aftermarket cylinder heads.

Sure, we expect aftermarket heads to outperform stock heads, or why would they have gone to all the cost of making them? But how much better are they? How much power do we get for our hard-earned money?

The only real way to find out how they all perform is to run them back to back on the same motor, but as with any test, there are always “other” changes that become necessary when comparing even factory heads. Get those comments ready!

man installing an intake on a 6.0L LS Engine
What are the best stock cylinder heads for your 6.0L LS? (Image/Richard Holdener)

GM LS Engine Cylinder Head Comparison Test Parameters

For this test, we lined up four different sets of cylinder heads. This list included stock 706/862 heads (used on the small-bore 4.8L and 5.3L motors) and a set of 243/799 heads (used on both the small-bore motors and larger 5.7L and 6.0L versions). Rounding out the stock heads was a set of rectangle port 821/823 heads, since they came factory on our 6.0L LY6 test motor.

Naturally, the rectangular port heads required a few other changes in the test, namely offset rockers (not really a big deal since they shared the same rocker ratio as the cathedral port rockers), but the rectangular port heads did require a different intake manifold. For this test we used an LS3 intake, though it bears mentioning that the LY6 (truck) intake was also tested and produced an identical power curve to the lower-profile LS3.

The 706, 799, and TFS 225 heads were all run with a Dorman LS2 intake, which my previous test showed produced an identical power curve to the factory TrailBlazer SS (TBSS) intake.

To conclude the test, the most-powerful (not surprising spoiler alert) TFS heads were also run with a FAST LSXR intake. For the rectangular port folks out there already crying foul: a FAST LS3 intake adds no power over the factory LS3 intake (but ported rectangular ports would have been interesting).

The Baseline

To kick things off, we first equipped the 6.0L LY6 with a suitable cam to replace the factory VVT set up. The Comp 54-469-11 cam offered a 617/624 lift split, a 231/247 degree duration split and 113 degeee LSA.

This cam allowed the 6.0L to take better advantage of what the heads had to offer in terms of flow and power potential. The cam lift and rpm potential require a dual valve spring upgrade for all the heads. Brian Tooley Racing supplied the necessary dual spring kit to allow us to safely run the Comp cam and rev the motor easily to 7,000 rpm.

The air/fuel and timing were controlled by a Holley HP management system (controlling 80 pound injectors), while exhaust chores were handled by a set of Hooker 1-7/8 inch (long-tube) headers.

The 6.0L was first equipped with the 706 heads, Dorman intake and 92mm throttle body, which resulted
in 513 hp at 6,300 rpm and 483 lb.-ft. of torque at 4,800 rpm.

Having our baseline established with the smallest of the cylinder heads, it was time to starting swapping.

The LS Cylinder Head Comparison Begins

After installation of the 799 heads (bigger ports & bigger valves produced more flow), the power output of the 6.0L increased to 525 hp at 6,400 rpm and 485 lb.-ft. of torque at 4,700 rpm. The additional flow offered by the 799 head added peak power, but the torque production suffered below 5,000 rpm compared to the (smaller valve, port & chamber) 706 heads.

Next came the rectangle port LY6 heads, which also required the aforementioned offset rockers and LS3 intake. The added flow offered by the LS3 heads (near 315 cfm compared to 250 cfm) pushed peak power up to 544 hp and 492 lb.-ft. of torque. The high-flow rectangular port heads added power above 4,200 rpm, but lost torque below that point to the cathedral port offerings.

The Trick Flow GenX 225 Cylinder Heads came next, and (not surprisingly) offered the most power with peaks of 561 hp and 501 lb.-ft.

Knowing the intake was now holding back the combination, we replaced the Dorman LS2 intake combo with a FAST LSXR intake manifold and 102mm throttle body. This resulted in the highest power output of the test, with peaks of 576 hp at 6,700 rpm and 509 lb.-ft. at 5,300 rpm. Given their flow potential, the TFS 225 heads will support well over 600 hp, so what mods do you think would be necessary to push this 6.0L past the 600 hp mark? Time for those comments!

ls engine cylinder head dyno comparison chart
The graph illustrates what happens when we compared the 706 heads to 799 heads to 832 (rectangle port) heads to Trick Flow GenX 225 heads, then added a FAST intake to the TFS heads. Starting with the 706 heads, the cammed 6.0L produced 513 hp and 483 lb.-ft. of torque, which jumped to 525 hp and 485 lb.-ft. with the installation of the 799 heads. The 799 heads lost torque to the 706 heads below 5,000 rpm, but added power above that. After adding the factory LY6 heads, the power output increased to 544 hp and 492 lb.-ft. The rectangle ports added 19 hp and 7 lb.-ft. of torque, but suffered torque losses below 4,200 rpm. Installation of the TFS 225 heads with the Dorman intake resulted another power gain over the rec port heads to 561 hp (+17 hp) and 501 lb.-ft .(+9 lb.-ft.). This increased to 576 hp and 509 lb.-ft. with the installation of a FAST LSXR intake and 102mm throttle body. (Dyno Chart/Richard Holdener)

***

6.0L LS Engine on a dyno
The test motor started out life as an iron-block, 6.0L LY6. The 6.0L featured factory rectangle port heads and (rectangle port based) truck intake. (Image/Richard Holdener)
close up of timing chain assembly on n ls engine
The LY6 also featured factory VVT, which was obviously removed to make way for a much more serious camshaft. (Image/Richard Holdener)
camshaft partially removed from an ls engine
The Comp 54-469-11 cam offered a 617/624 lift split, a 231/247 degree duration split, and 113 LSA. (Image/Richard Holdener)
valve spring tool in place on an ls engine
To ensure adequate valve control, we replaced the factory springs on all the test heads (except the Trick Flow GenX 225s) with dual springs from Brian Tooley Racing. (Image/Richard Holdener)
valvetrain in an ls engine cylinder head
Every test was run with factory rockers. The same rockers were run on the 706, 799, and TFS 225 heads, while the LY6 heads utilized the LS3-style offset (factory) rockers. (Image/Richard Holdener)
Headers on an LS Engine dyno run
All heads were run with the same 1-7/8 inch Hooker long tube headers feeding collector extensions. (Image/Richard Holdener)
intake and throttle body on an ls engine
The 706, 799, and Trick Flow GenX 225 heads were all run with the Dorman LS2 intake (equivalent power to TBSS). (Image/Richard Holdener)
throttle body mouth on an ls engine
The Dorman intake was equipped with a 92mm FAST (manual) throttle body. (Image/Richard Holdener)
holley HP EFI engine control module
We relied on a Holley HP management system to optimize the A/F mix and timing for each combination. (Image/Richard Holdener)
706 casting number on an LS engine cylinder head
Run on the dyno first with the factory 706 heads, the cammed 6.0L produced 513 hp at 6,300 rpm and 483 lb.-ft. of torque at 4,800 rpm. (Image/Richard Holdener)
dressed ls engine on a dyno test run
Next up, we ran the 799 heads on the 6.0L LY6. Equipped with the 799 heads, the peak numbers jumped to 525 hp at 6,400 rpm and 485 lb.-ft. at 4,700 rpm. The greater flow offered by the 799 heads increased power production above 5,000 rpm, but torque suffered compared to the smaller heads below that. (Image/Richard Holdener)
ls engine on a dyno pull
After running the 799 heads, they were replaced by the factory LY6 (rectangle port) heads and LS3 intake (run with the same 92mm throttle body). Equipped with the rectangular port heads, 6.0L produced 544 hp at 6,600rpm and 492 lb.-ft. of torque at 5,200 rpm. The larger heads added power above 4,200 rpm (compared to the 799s), but lost torque below that point. (Image/Richard Holdener)
trick flow ls engine cylinder head
Next up were aftermarket GenX 225 heads from Trick Flow Specialties. The heads featured full CNC porting (including chambers) and enough flow to challenge the factory rectangle port heads (Image/Richard Holdener)
ls engine with trick flow heads on dyno
The TFS 225 heads were first run on the 6.0L with the Dorman intake and 92mm throttle body. The combo produced 561 hp at 6,700 rpm and 501 lb.-ft. of torque at 5,200 rpm. This was a gain of 17 hp and 9 lb.-ft. over the LY6 heads. (Image/Richard Holdener)
fast lsxr intake manifold on an ls engine
Knowing the Dorman intake was likely hurting power on the TFS-headed 6.0L, we replaced it with a FAST LSXR. (Image/Richard Holdener)
fast 102mm throttle body on an LS engine
The FAST LSXR was designed to accept the 102mm FAST Big Mouth throttle body. (Image/Richard Holdener)
dressed ls engine with trick flow heads during dyno run
Run with the FAST LSXR and Trick Flow GenX 225 heads, the 6.0L produced 576 hp at 6,700 rpm and 509 lb.-ft. of torque at 5,300 rpm. The FAST intake added 15 hp and 8 lb.-ft. over the Dorman. (Image/Richard Holdener)
Keywords
6.0L LS, cylinder heads, LS Engine, Trick Flow Specialties
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Author: Richard Holdener

Richard Holdener is a technical editor with over 25 years of hands-on experience in the automotive industry. He's authored several books on performance engine building and written numerous articles for publications like Hot Rod, Car Craft, Super Chevy, Power & Performance, GM High Tech, and many others.