AFR vs Trick Flow vs Brodix LS3 Heads — Flow, Price, and the Honest Verdict

The LS3 rectangle-port head is the most upgraded casting in the LS world, and the three names that come up every time are AFR, Trick Flow, and Brodix. They all bolt to the same 6-bolt LS3/L92 deck, they all clear the same 4.065"+ bore, and they all out-flow a stock casting by a wide margin. That's where the simple part ends.

The wrong way to pick is by peak CFM on a flow sheet. The right way is to match runner volume, valve size, and chamber to your displacement, your cam, and your RPM target — then check the price against what the head actually returns. Here's how the three stack up when you stop reading marketing copy and start reading the build.

First, what "LS3 head" actually means

An LS3 head is a rectangle-port, 6-bolt cathedral-replacement casting. Stock LS3/L92 specs:

• Intake valve: 2.165"
• Exhaust valve: 1.59"
• Chamber: ~68-70cc
• Intake runner: ~257cc as-cast (large, which is why stock LS3 heads already flow well)
• Bolt pattern: 6-bolt per cylinder (NOT the 4-bolt LS1/LS6 cathedral pattern)

That 6-bolt pattern and the big 2.165" intake valve are the whole reason people start with an LS3 casting instead of an LS1 cathedral head: more clamping load, more valve, and a port shape that doesn't choke at high lift. The aftermarket heads below keep that architecture and add CNC porting, better chambers, and serious valvetrain.

Bore clearance warning: the large intake valves on every head here want a big bore for clean breathing — each manufacturer publishes a minimum-bore callout per model, and the biggest-valve versions can shroud even on a stock 6.2L bore. On a 4.00" bore (5.3/6.0 truck blocks) these heads will be valve-shrouded and you're paying for flow you can't use. Match the head to the bore first.

AFR Mongoose LS3 — the flow-bench benchmark

Air Flow Research's LS3 line (marketed under the Mongoose name) is the head most often cross-shopped on raw flow. AFR offers it in multiple runner volumes — a street runner, a larger street/strip runner, and a competition runner — all fully CNC-ported as standard, not a hand-port upcharge; check AFR's current lineup for the exact volumes and part numbers.

• Valves: LS3-size on the street versions, larger on the big-runner race head (see AFR's spec sheet)
• Chamber: more than one chamber volume offered for compression tuning (see AFR's spec sheet)
• Flow: the street head is the strongest out-of-the-box intake flow in this comparison, and the larger runner steps up from there — pull the current AFR flow sheet for the numbers at your lift.
• As-delivered: assembled with AFR's own valvesprings, titanium retainers on the higher models, and CNC chambers — generally the most "complete out of the box" of the three.

Where AFR wins: mid-lift flow and chamber quality. The Mongoose tends to make its power through a broad mid-lift curve rather than a single peak number, which is exactly what a street stroker wants. The chambers are clean enough that you rarely need to chase a tune to control knock.

Where it costs you: AFR is usually the most expensive of the three, often by a meaningful margin once you spec the assembled head with upgraded springs for a big cam.

Trick Flow GenX — the value-per-CFM pick

Trick Flow's GenX LS3-pattern heads (commonly the GenX 255 and GenX 260, by runner volume) are the heads that win most "I want big power without AFR money" builds.

• Valves: LS3-size standard (see Trick Flow's spec sheet)
• Chamber: CNC-profiled, with a smaller-chamber option on some models for compression (see Trick Flow's spec sheet)
• Flow: the GenX 255 is a solid step over a stock LS3 casting, the GenX 260 a step above that — pull the current Trick Flow flow data for the numbers.
• As-delivered: sold as bare, or assembled with a spring package rated to a stated lift — read the spring rating before you order, because the base assembled spring may not handle an aggressive solid-roller (Trick Flow publishes base and upgraded spring lift ratings).

Where Trick Flow wins: dollars per CFM. On a 6.2L/376 or a 416-427 stroker street build, the GenX 255 gives up very little to the AFR 245 on the dyno and costs noticeably less. For the largest slice of LS3 customers — a 500-600 hp naturally aspirated street/strip car — this is the head that returns the most power per dollar.

Where it costs you: the very top of the curve and the highest-RPM race builds, where AFR's bigger runners and Brodix's competition castings pull ahead. Also double-check the supplied spring against your cam; the entry spring package is conservative.

Brodix BR3 — the boost and big-cube head

Brodix BR3 (and the higher BP-series) LS3-pattern heads are the forced-induction and big-displacement answer. Brodix has a long pushrod-V8 race pedigree and the BR3 reflects it — thicker deck, robust casting, and runner/valve combinations aimed at engines that are either boosted or well past 416 cubes.

• Valves: LS3-size on the street BR3, larger valve and runner packages up the line (see BTR's spec sheet)
• Chamber: CNC chambers sized for boost-friendly compression (see BTR's spec sheet for chamber volumes)
• Flow: the street BR3 is competitive with the AFR/Trick Flow street heads; the larger BP race castings flow well beyond any street head here — pull BTR's model-by-model flow data.
• As-delivered: bare or assembled; Brodix's higher castings are aimed at builders speccing their own valvetrain.

Where Brodix wins: boost and durability. If there's a turbo or a blower in the plan, the thicker deck and chamber design tolerate cylinder pressure better, and the bigger castings have the runner to feed a 427+ at high RPM. This is the head for the 1,000+ hp boosted LS that started life as an LS3.

Where it costs you: on a mild naturally-aspirated street 6.2, you're paying for casting strength and runner you won't use — the engine can't pull enough air to need it. Overkill is a real cost.

Flow and spec at a glance

Flow comparisons above are relative — pull each manufacturer's current published flow sheet for the numbers at your lift and bore.

How to actually choose

Forget the peak number on the sheet. Choose in this order:

1. Bore size first. Stock 4.065" 6.2L bore? Stick with the street-runner version of any of the three. 4.00" truck bore? None of these are right — the valves shroud. Big-bore stroker (4.125"+)? Now the big-runner heads earn their keep.

2. Power adder? If there's boost in the plan now or later, Brodix BR3 — the casting strength is the point. Naturally aspirated, go AFR or Trick Flow.

3. Budget vs last 20 hp. For a 500-600 hp naturally aspirated street build, Trick Flow GenX 255 returns the most power per dollar and gives up almost nothing. If you want the broadest mid-lift curve and the cleanest chambers and the budget is there, AFR Mongoose.

4. RPM target. Planning to spin past 7,000 on a 427? The bigger AFR and Brodix runners hold flow up top where the GenX 255 starts to fall off. A 6,500-RPM street stroker never sees that part of the curve.

The parts that ride along with the head swap

A head swap on an LS3 is never just the heads. Every one of these needs to go on the invoice next to the casting:

• Head bolts or studs — torque-to-yield factory bolts are single-use. On any of these heads, ARP head studs are the right call, mandatory on anything boosted (confirm the ARP kit number for your block).
• Head gaskets — multi-layer steel, sized to your bore. Match the gasket bore to the block bore, not the head.
• Valvesprings matched to the cam — the single most common LS head-swap mistake is bolting a big solid-roller cam under a head whose supplied springs are rated for a mild hydraulic. Confirm the assembled head's spring lift rating against the cam's lift. If they don't match, spec the upgrade spring before the head ships.
• Pushrods — a head/cam change almost always changes pushrod length. Measure with a checking pushrod; don't reuse stock and hope.
• Rockers / trunnion — if you're keeping stock rockers, a trunnion upgrade is cheap insurance under the higher spring pressures these heads run.

What to do next

• Confirm your bore size and match it to the street vs race runner — this decides more than the brand does
• Decide boost or not up front; if yes, start with Brodix
• Match the assembled head's spring rating to your cam before ordering — call it out at the SKU filter
• Add head studs, MLS gaskets, correct-length pushrods, and a trunnion upgrade to every LS3 head order

Related reading

• LS Gen IV Engine Parts Hub
• Cylinder Heads — LS
• Camshafts — LS
• Head Bolts and Studs
• Valve Springs