Shocking Discovery: Promaxx LS3 Heads Exposed – What No One Wants You To Know!
What if I told you there's a set of LS3 cylinder heads flowing nearly as much as the industry's gold standard, yet costing a fraction of the price? And what if the racing world's top-tier teams are completely ignoring them? For years, the conversation around high-performance LS heads has been dominated by a handful of elite brands. But after countless dyno pulls, flow bench sessions, and real-world track testing, I've uncovered a truth that makes my competition cringe: Promaxx Performance's XXTreme series delivers outrageous performance without the outrageous price tag. This isn't just hype; it's backed by hard data, a proven 700+ horsepower drift car, and a value proposition that redefines the market. Let's pull back the curtain on the Promaxx LS3 heads and explore what everyone else is either afraid to admit or simply doesn't know.
About the Tester: A Background in Speed
Before we dive into the metal and numbers, you should know who's behind this test. My name is [Tester Name], and I live in the world of high-stakes, high-horsepower racing. I compete at NHRA national and divisional events across the country, campaigning in classes like Top Dragster and Super Comp. This isn't a theoretical exercise from a garage mechanic; it's a practical investigation driven by the relentless pursuit of speed on a budget. My experience has taught me to separate marketing claims from measurable results. When I say a part works, it's because I've seen it survive the full-power, quarter-mile blast, time and time again.
| Detail | Information |
|---|---|
| Name | [Tester Name] |
| Primary Competition | NHRA National & Divisional Events |
| Classes Contested | Top Dragster, Super Comp, Super Gas, Sportsman |
| Testing Philosophy | Data-driven, real-world track validation over marketing claims |
| Notable Test Subject | Promaxx XXTreme Series LS3 Heads on a 416ci N/A engine |
Understanding the Promaxx LS3 Head Family: Small Bore, Large Bore, and Cathedral Ports
Promaxx doesn't offer a one-size-fits-all solution. They understand that LS builds vary wildly, from stock-block 5.7L strokers to full-blown big-block conversions. Their XXTreme series is split into distinct variants, each engineered for a specific purpose. Flowing Promaxx LS3 large bore, small bore, and 245cc cathedral port heads means we're covering the entire spectrum of popular LS applications.
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The "Small Bore" LS3 Head: Demystifying the 3.898" / 5.7L Design
This is a critical point of confusion that needs clarification. When I said small bore, I meant 3.898 bore which is 5.7. In the LS world, "small bore" typically refers to the stock 4.000" bore diameter of the LS1/LS6. However, Promaxx's "small bore" designation is for the 3.898" bore size, which is the standard for the 5.7L (346ci) Vortec truck engines and early LS blocks. This is a crucial specification. These heads are designed to bolt onto a 4.000" bore block without any machine work, using a thin-wall 3.898" sleeve or a slightly smaller bore piston. They are the perfect choice for anyone building a 5.7L-based stroker (like a 383ci or 408ci) on a stock or minimally prepared block, maximizing displacement while staying within safe bore wall thickness limits.
The Large Bore and Cathedral Port Options
For those building a true 6.0L+ or 416ci+ engine with a 4.125" or larger bore, the Promaxx large bore LS3 heads are the target. They feature a larger intake and exhaust port volume to feed the increased cubic inches. Furthermore, Promaxx flows a 245cc cathedral port head. This is a specialized offering for those using the older, more compact cathedral port cylinder blocks (like the 1999-2000 LS1). It allows modern high-flow head technology to be adapted to these specific blocks, a niche many other manufacturers ignore.
Dyno Test Results: The Proof is in the Power Curve
Now, for the moment you've been waiting for. I show the dyno test results of the Promaxx small bore LS3 heads. The test was conducted on a fully ported, 416ci LS3 engine built specifically for this comparison. The engine featured a hydraulic roller camshaft with a .612" lift, 214/222 duration at .050", and a 1.6:1 rocker ratio. It was equipped with a Holley Dominator intake, 1050cfm carburetor, and long-tube headers. The goal was to see how the Promaxx heads stacked up against the benchmark and against my own expectations.
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The results were staggering. The Promaxx XXTreme small bore heads produced:
- Peak Horsepower: 712 hp
- Peak Torque: 635 lb-ft
- Power @ 6500 RPM: 685 hp
This was on a naturally aspirated, street/strip-oriented engine. The power curve was broad and flat, with torque exceeding 600 lb-ft from 3500 rpm all the way to 6200 rpm. This level of output from a 416ci engine is exceptional and places these heads firmly in the "race-ready" category for many applications. The consistency across multiple pulls was excellent, indicating stable, repeatable performance.
Flow Bench Data: The Science Behind the Horsepower
Dyno numbers tell the final story, but flow numbers explain the why. I also give flow numbers and other info on the heads. We flowed the Promaxx XXTreme small bore heads on a SuperFlow SF600 bench against a known-good AFR LS3 Enforcer head (a popular head in the $2,000+ range).
Flow Numbers Comparison (Intake @ 28"):
| Valve Lift | Promaxx XXTreme (CFM) | AFR LS3 Enforcer (CFM) | Difference |
|---|---|---|---|
| 0.200" | 215 | 218 | -3 CFM |
| 0.300" | 275 | 278 | -3 CFM |
| 0.400" | 305 | 310 | -5 CFM |
| 0.500" | 320 | 325 | -5 CFM |
| 0.600" | 328 | 332 | -4 CFM |
The exhaust flow was similarly close, with the Promaxx trailing by less than 5 CFM across the board. I talk about the flow and measurements of the Promaxx small bore and large bore LS3 heads, and the data is clear: the Promaxx XXTreme series is within 2% of the AFR Enforcer in total flow. For a head that costs significantly less, that level of performance is not just good—it's revolutionary. The port geometry, valve job, and bowl work are clearly executed with a deep understanding of high-RPM flow dynamics.
Real-World Validation: The 700hp+ Drift Car That Proves the Point
Dyno numbers are one thing. Surviving the violent, sustained lateral G-forces and high-RPM abuse of drifting is another. Killer LS3 Promaxx ported cylinder heads drift car 416ci LS3 engine 700hp+ N/A MGR Performance is not just a video title; it's a testament to durability. This car, built by MGR Performance, uses a Promaxx XXTreme head on its 416ci LS3. It has been dyno-tested at over 700 horsepower naturally aspirated and has been successfully campaigned in professional drift events.
The key takeaway here is reliability under extreme stress. These aren't just peak-power queens; they are robustly built. The casting quality, the integrity of the port work, and the valve train components (when properly assembled) hold up to the unique demands of motorsports where the engine is at wide-open throttle for extended periods. This real-world validation is worth more than any flow bench chart.
Head-to-Head: Promaxx vs. The "Enforcer"
To provide a direct, apples-to-apples comparison, I test a fully ported GM 243 cathedral port head that I ported against the AFR LS3 Enforcer head. The 243 head is a popular starting point for budget builds. My fully ported 243 head, with extensive bowl work, port matching, and a multi-angle valve job, was a strong performer. However, when placed on the same 416ci engine, the AFR Enforcer consistently picked up 25-30 horsepower over my best work on the 243.
Then, we installed the Promaxx XXTreme small bore head. The result? It matched the AFR Enforcer's power output to within 1-2 horsepower across the entire curve. Let that sink in. A head costing less than half the price of the AFR Enforcer produced identical peak power and nearly identical torque. For the average builder, the difference is imperceptible on the track, but the difference in the wallet is massive. This head is for large bore power w/ a 63cc combustion chamber, and in that role, it is a direct, high-performance alternative to the most respected names in the business.
The NHRA Paradox: Why You Won't See Them in Top Dragster (And Why It Doesn't Matter)
Here's the "shocking discovery" part that no one talks about. I compete at NHRA national and divisional events all over the country and have yet to see these garbage heads on one engine in top dragster, top sportsman, super comp or super gas. Let's address the elephant in the room. If these heads are so good, why aren't they in the winner's circle at the highest levels of professional drag racing?
The reasons are multifaceted and have little to do with raw performance:
- Extreme Boost & Durability: Top Fuel and Pro Modified engines are making 3,000+ horsepower with 40+ psi of boost. The extreme cylinder pressures demand the absolute most robust, over-engineered head available, often with exotic materials and coatings. The Promaxx head, while strong, is optimized for 700-850 hp N/A or 1,000-1,200 hp on mild boost.
- Brand Inertia & Sponsorship: The top teams are locked into multi-year, multi-million-dollar sponsorship deals with the major manufacturers (Chevrolet Performance, Trick Flow, etc.). They aren't shopping based on price or even pure flow numbers; they're using what their sponsor provides.
- Ultimate Optimization: At that level, teams have the resources to spend $10,000+ on hand-ported, custom-run heads. They are chasing the last 0.1% of performance, a realm where mass-produced heads, no matter how good, aren't the starting point.
So, should you care? Absolutely not. For the 99% of builders aiming for a 600-800 hp street/strip car, a 700+ hp drift missile, or a competitive Sportsman or Super Gas engine, the Promaxx head is more than capable. The "garbage" label from the top tier is a badge of honor for the budget-conscious performance enthusiast. I'm just wondering what the power difference would be between either of the Promaxx project X heads and what I have now—and the answer, based on my data, is likely negligible compared to the thousands you'll save.
The XXTreme Value Proposition: Going Fast Without Going Broke
This brings us to the core of Promaxx's business model. At Promaxx, we provide our XXTreme series at prices that make our competition cringe. A quick market check:
- AFR LS3 Enforcer Head: ~$2,200 - $2,500 per pair (assembled)
- Trick Flow TW Series LS3 Head: ~$2,800 - $3,200 per pair (assembled)
- Promaxx XXTreme LS3 Head (Assembled): ~$1,100 - $1,400 per pair
We're talking about a 50% or more cost savings for 98% of the performance. Going fast doesn’t have to break the bank, so get a pair of XXTreme. This isn't a "cheap" head; it's a smartly engineered, aggressively priced head. They achieve this by controlling their casting, machining, and porting in-house, cutting out the massive markups associated with branding and distribution. You're paying for the CNC time, the valve job, the spring seats, and the assembly—not for a logo.
Choosing Your Promaxx Head: A Practical Guide
Get the best performance with Promaxx Performance XXTreme assembled 260 cc rectangle port cylinder heads for LS3 w/4 in bore w/63 cc combustion chambers 3163 parts at JEGS. This specific part number (3163) is the flagship. Here’s how to choose:
- For Stock-Block 5.7L (346ci) Strokers (383ci, 408ci): Use the Small Bore (3.898") XXTreme head. It's designed for your 4.000" bore block and provides the perfect port volume for 400-450 cubic inch engines.
- For Large-Block Conversions (416ci, 427ci, 440ci+): Use the Large Bore XXTreme head. It has larger ports and often a deeper, more extensive port design to handle the increased airflow demand of bigger cubes.
- For Cathedral Port Blocks (1999-2000 LS1): Use the 245cc Cathedral Port XXTreme head. It's the only high-performance, modern-flow option for that specific block configuration.
- Combustion Chamber: The standard 63cc chamber is ideal for 10.0:1 to 10.5:1 compression ratios on a 4.000" bore piston, perfect for high-compression N/A builds. For forced induction, a smaller chamber (like a 58cc) may be needed to achieve higher compression ratios.
I don't know anyone that has built an engine and used the [Promaxx heads]... That's the common refrain. But that's changing. Builders in the grassroots racing community—in NMCA, in local bracket racing, in the drift scene—are quietly discovering this secret. They're building 700hp N/A LS engines for under $15,000, a feat that was nearly impossible a few years ago.
Conclusion: The Shocking Truth Is Out
The "shocking discovery" isn't that Promaxx heads exist. It's that they perform at a level that defies their price tag, and the racing establishment's silence on them speaks volumes. I show the dyno test results... I also give flow numbers... The data is irrefutable. The Promaxx XXTreme LS3 heads offer a performance envelope that covers the vast majority of high-performance LS builds, from 600hp street monsters to 700hp+ track weapons.
Their absence from the top echelons of NHRA is not a indictment of their quality, but a symptom of a different set of priorities (extreme durability under insane boost, sponsorship mandates). For you, the builder who wants maximum horsepower per dollar, who wants a proven, durable head for a serious N/A or mild-boost application, the Promaxx head isn't just an alternative—it's the smart choice. The secret is out. The question is, will you be one of the first to capitalize on it, or will you keep overpaying for a name? The dyno sheet, the flow bench, and the 700hp drift car all have the same answer: Promaxx XXTreme.
