AFR 245 vs Trick Flow 255 vs Brodix BR 7 — The LS3 Rectangle-Port Flow Showdown

TL;DR: These three heads are separated by 12 CFM at .600" lift — AFR Mongoose 245 at 340, Trick Flow GenX 255 at 345, Brodix BR 7 at 352 — which is under 4% spread and less than the run-to-run variation between two flow benches. Peak flow is not the deciding spec. What actually separates them is runner volume against your displacement (245cc vs 255cc vs 257cc), chamber volume against your compression target (68cc vs 70cc), and whether the assembled spring package will live behind your cam. Pick on those three and every one of these heads is a good head; pick on the flow sheet and you will buy a port that is too big for your engine.

Existing coverage: AFR vs Trick Flow vs Brodix — the brand-level guide covers the three companies and their full model lines. This post is narrower on purpose — it puts the three specific street models head to head with their real numbers, because that is the comparison people are actually stuck on at the checkout page.

The three heads, side by side

Every number below is the manufacturer-stated spec carried on our own listings for these parts.

Flow figures are single-point manufacturer values at .600" lift and are not from a common bench. Different manufacturers publish on different benches, at different test pressures, and with different bore fixtures — a 12 CFM spread across three sources is inside the noise floor of that comparison. Our own brand-level post quotes a higher AFR 245 figure sourced from a different sheet; treat any cross-brand CFM comparison, including this table, as directional rather than decisive, and confirm current numbers against each manufacturer's own flow data before you commit.

That caveat is the entire point of the next section.

Why peak CFM at .600" is the wrong number

A flow number is one measurement, at one lift, in a fixture, with no piston moving underneath it. Three things make it a poor proxy for power on a running engine.

It ignores the rest of the curve. An engine spends far more crank degrees between .200" and .450" lift than it does parked at .600". A port that gives up 8 CFM at peak but carries an extra 10 CFM through the mid-lift range will make more area under the torque curve on the same cam. None of the three published numbers above tells you anything about that region.

It ignores velocity. Flow and velocity trade against each other. A bigger runner passing the same air is a slower runner, and port velocity is what fills a cylinder at part-throttle and at low RPM. Look at what these heads do per cc of runner:

Brodix has the most absolute flow. AFR has the most flow per cc — it is doing nearly as much work through a runner 12cc smaller, which means higher velocity at the same airflow demand. On a 376ci engine that is the more useful trait. On a 427 turning 7,000 RPM it stops mattering and raw capacity takes over. Same three heads, opposite answers, depending entirely on the engine underneath them.

It ignores the exhaust side. The exhaust runners here run 85cc / 90cc / 92cc in the same order as the intakes, so all three keep roughly the same intake-to-exhaust proportion. That matters more than it sounds: a head with a weak exhaust side needs more exhaust duration in the cam to compensate, which costs overlap quality and idle. Exhaust flow figures were not published alongside the intake numbers on these listings; ask for the full flow sheet — both columns, .100" through .700" — before you buy any head in this class.

Browse the full LS rectangle-port head selection with runner and chamber volume listed on every row so you can compare these specs directly instead of chasing peak numbers.

Runner volume is a displacement decision, not a power decision

The single most common mistake with rec-port heads is buying runner volume in proportion to horsepower goals instead of in proportion to cubic inches and RPM. A big runner does not make power. A big runner makes room for an engine that already moves enough air to need it.

Rough working brackets for a naturally aspirated rec-port LS:

On a 376ci LS3 with a 6,600 RPM shift point, the AFR 245 is the right port for the engine and the two larger heads are giving up mid-range velocity to buy top-end flow the combination cannot reach. On a 416 that lives at 7,000, that reverses: the 245 becomes the restriction and the extra 12cc of runner starts paying.

Nobody's marketing copy will tell you the head is too big for your engine. The cubic inches will.

Whichever way that lands for you, the camshaft is the other half of this decision — runner volume and cam duration have to agree on an RPM range, or you have bought two parts optimized for two different engines.

Chamber volume: the spec that quietly changes your compression

Two of these heads are 70cc and one is 68cc. That 2cc looks trivial. It is not.

On a 6.2L LS3 — 4.065" bore, 3.622" stroke — the total clearance volume above the piston at TDC is chamber + head gasket + deck clearance, minus any dome. That total is somewhere near 75cc on a typical flat-top build, so removing 2cc from it is a ~2.5% reduction in clearance volume, worth roughly 0.25 to 0.30 of a compression point. The exact figure depends on your gasket bore and thickness, deck height and piston dish or dome — run your own numbers.

Which direction you want that to go depends entirely on the build:

• Naturally aspirated pump gas: the Trick Flow 68cc chamber is a free quarter-point of compression, which is a free small gain in torque and efficiency across the whole range. Useful.
• Boost or nitrous: that same quarter-point is working against you. On a forced-induction build the 70cc chambers on the AFR and the Brodix are the safer starting point, and you are more likely to want a dished piston besides.
• Already at the knock limit: if you are running 11.5:1 on 91 octane, do not add compression by accident. Choose the 70cc chamber.

The failure mode here is not dramatic — nobody's engine explodes over 2cc. What happens is you finish an expensive build, it rattles on the fuel you have, and you pull timing out of the tune until the head upgrade you paid for is giving back most of what it made.

The bore gate: 4.065", or these are the wrong heads

This is the hard fitment rule, and it eliminates more prospective buyers than any other spec on the page.

All three heads carry a 2.160"–2.165" intake valve and all three require a 4.065" minimum bore. Put any of them on a 4.00" bore — that is a 5.3L, or a 6.0L truck block — and the bore wall stands directly beside the valve. The valve shrouds, the low- and mid-lift flow collapses, and you have paid rec-port head money for less airflow than a well-chosen cathedral-port head would have given you on the same engine.

The complete gate for all three heads:

1. Bore 4.065" minimum. 6.2L LS3/L92/L99, or a cathedral block bored out to suit. A 4.00" truck bore does not qualify.
2. Rectangle-port intake manifold required. These heads will not accept an LS1/LS6 cathedral-port intake — the flange is a different shape. You need an LS3-pattern manifold, a FAST LSXR 102, a Holley Hi-Ram rec-port, or equivalent. Budget for it up front; see intake manifolds.
3. LS3-bore head gasket. A 4.065"+ gasket bore. An LS1-bore gasket will hang into the cylinder. Gaskets and seals.
4. 6-bolt-per-cylinder deck. The LS3/L92 head pattern is 6-bolt; LS1/LS6 cathedral decks are 4-bolt. The block has to match.
5. Pushrod length has to be re-checked. Any head change moves the rocker geometry. Measure with an adjustable checking pushrod — do not assume stock length carries over.

If you are on a 4.00"-bore truck engine and you got here anyway, the honest answer is that a good cathedral-port head is the better part for your engine. Our ported factory casting comparison covers that market in detail.

Bare vs assembled — the spring package is the real decision

Every one of these three is sold both bare and assembled, and the price gap between the two is not just the hardware.

Bare means a casting with a valve job and nothing else. You supply valves, springs, retainers, locks and seals, and you pay a shop to assemble it. That is the right path when you already have a spring package chosen for a specific cam, when you are running a solid roller that needs a spring nobody ships as standard, or when your builder has a valve job they insist on.

Assembled means the head arrives complete and ready to bolt on. The AFR 245 ships with PAC dual springs rated to .660" lift; the Trick Flow 255 ships with a dual spring also rated to .660". Those are genuinely capable packages — they will run most hydraulic roller cams in this class without a second thought.

The rule that matters: check your cam's gross valve lift against the assembled spring's rating before you order, and leave margin. A spring rated to .660" and a cam at .650" gross lift is not a comfortable pairing — you want coil-bind clearance beyond the maximum lift, not up against it. If your cam is over .650", plan on a spring upgrade regardless of which head you buy, and price it into the comparison. See valve springs.

The Brodix BR 7 assembled listing does not state a spring lift rating. Confirm the supplied package against your cam's gross lift before ordering the assembled version.

This is where more head projects go wrong than anywhere else. The head is fine. The cam is fine. The spring that came in the box was never rated for that cam, it floats, and the customer blames the head.

Which head for which build

Every one of these is a legitimately good head. There is no loser in this comparison — there is only a mismatch between a port and an engine, and that is a decision you make, not one the manufacturer makes for you.

What else the swap needs

Budget these with the heads, not after them:

• Rectangle-port intake manifold — mandatory if you are coming from a cathedral-port engine.
• LS3-bore head gaskets and fresh head bolts or, better, head studs — head bolts on an LS are torque-to-yield and are not designed for repeated re-use.
• Correct-length pushrods, measured on the assembled engine, not guessed.
• Rocker arms inspected or upgraded — a stiffer spring package raises the load on the stock trunnion. See rocker arms.
• A tune. New heads change airflow enough that the factory calibration will be wrong. Nothing about this swap is complete without a re-tune.
• Fitment confirmation for your specific engine and bore — check fitment before ordering, especially if you are on a bored cathedral block rather than a factory 6.2.

Shop the complete LS Gen IV parts range and the full cylinder head catalog to spec the whole job in one pass.

Frequently asked questions

Is the Brodix BR 7 worth it over the AFR 245 for a street 6.2? On a stock-stroke 376 running to 6,500 RPM, no — the BR 7's extra 12cc of runner and 12 CFM of peak flow are capacity the engine cannot use, and you give up port velocity to get them. On a 416 that spins to 7,000, yes. The head does not change; the engine underneath it decides whether the extra port is an asset or a liability.

Does 12 CFM between these heads mean anything on the dyno? Almost nothing on its own, and possibly nothing at all — the three numbers come from three different manufacturers' benches, which is not a controlled comparison. Even if the spread were real, a 3.5% difference at one lift point does not translate to a 3.5% power difference. Runner volume, chamber cc and the spring package will each move your result more than the flow spread will.

Can I put these on a 5.3 or a 6.0 truck engine? Not usefully. Both are 4.00"-bore engines and all three heads want 4.065" minimum. The 2.165" intake valve shrouds against the bore wall, low- and mid-lift flow suffers badly, and you would also need a rectangle-port intake to bolt to them. A quality cathedral-port head is the better and cheaper answer on a 4.00" bore.

Which head gives me the most compression? The Trick Flow GenX 255, by virtue of its 68cc chamber against the 70cc chambers on the AFR and the Brodix — roughly a quarter of a compression point on a typical 6.2 build. Whether that is a benefit depends on your fuel and whether you are running a power adder. On boost you generally want it the other way.

Should I buy bare or assembled? Assembled, unless you have a specific reason not to. The assembled AFR and Trick Flow packages are rated to .660" lift, which covers most hydraulic roller cams in this class. Buy bare when your cam exceeds the supplied spring's rating, when you are running a solid roller, or when your builder wants their own valve job — in those cases you would be paying for a spring package you were going to remove.

Do I need a rectangle-port intake manifold? Yes, without exception. All three heads use the LS3/L92 rectangle-port flange, which will not mate to an LS1/LS6 cathedral-port manifold. If you are converting a cathedral-port engine, the manifold is a required line item, not an optional one.

Will I need new pushrods? Plan on it. Any head change alters the deck-to-rocker geometry. Measure with an adjustable checking pushrod after the heads are torqued down and the correct valvetrain is in place — reusing stock-length pushrods on a head swap without measuring is how rocker geometry gets quietly wrong.

Do these heads need a tune? Yes. Airflow changes enough that the factory tables will be off, and if you have also changed the cam or the intake it is not close. Budget for a calibration in the same breath as the heads.

Structured data stubs

FAQPage schema — emit each Q&A pair above as a Question / acceptedAnswer node under a single FAQPage block. Eight pairs.

Article schema — headline from the H1, author Core Powertrain Parts Tech Team, about a Product reference to the LS rectangle-port head collection.

No HowTo schema — this is a comparison, not a procedure.

Specifications are manufacturer-stated values as carried on our listings, not measured on a common bench. Confirm flow data and spring ratings against each manufacturer's published sheets before purchase.