Introduction: The LS-Swapped RX‑7

The Mazda RX‑7—particularly the FD3S and FC3S generations—has long been a darling of the enthusiast community. Its lightweight chassis, near‑perfect weight distribution, and iconic styling make it an ideal candidate for engine swaps. And no swap is more popular than dropping in a General Motors LS‑series V8. The LS engine family (4.8L, 5.3L, 5.7L, 6.0L, 6.2L, etc.) offers a potent combination of power, reliability, and aftermarket support that the original 13B rotary simply cannot match in terms of torque and ease of maintenance.

But an LS swap is not a “drop‑in and drive” proposition. The rotary engine was compact and lightweight; the LS is larger, heavier, and generates significantly more heat. Without proper supporting modifications, an LS‑swapped RX‑7 will overheat, handle poorly, and leave power on the table. This guide focuses on the three critical areas that every builder must address: cooling, exhaust, and suspension. Properly engineered upgrades in these areas will ensure your RX‑7 is not only fast but also reliable and enjoyable to drive.

Cooling Upgrades: Keeping the LS in Its Happy Zone

Heat is the number‑one enemy of any LS‑swapped RX‑7. The rotary engine originally lived in a relatively tight, low‑heat environment. The LS, by contrast, dumps a tremendous amount of thermal energy into the engine bay. If you take nothing else from this article, understand that cooling is the single most important supporting system for an LS‑swapped RX‑7.

The factory RX‑7 radiator was designed for a 1.3L two‑rotor engine. Even in good condition, it cannot dissipate the heat generated by a 350+ horsepower V8. You will need a comprehensive cooling package that addresses the radiator, fans, oil cooling, and water pump.

High‑Performance Aluminum Radiator

An aluminum radiator with a larger core volume is the foundation of any LS swap cooling system. Look for units with dual‑pass or triple‑pass cores, which increase the time coolant spends in the radiator, improving heat rejection. Many aftermarket radiators designed specifically for the LS‑swapped RX‑7 are available from vendors like Griffin, Mishimoto, and CXRacing. These are often direct‑fit for the FD or FC chassis and include integrated mounting brackets, hose outlets in the correct locations, and provisions for electric fans.

Key specification: Aim for a radiator with at least a 2‑inch core thickness and a fin density that balances airflow with cooling capacity. A 40mm to 52mm core is common for street and mild track use. For serious road racing or high‑boost applications, consider a 60mm+ core, though packaging becomes tight.

Electric Cooling Fans

The factory mechanical fan (if retained) is bulky, inefficient, and often cannot fit in an LS‑swapped RX‑7 engine bay. Electric fans are the standard solution. They provide consistent airflow at idle and low speeds, and they can be removed entirely for high‑speed running where ram air takes over.

Choose a pair of high‑CFM, slim‑profile fans (1.5 to 2.5 inches thick) that mount directly to your aftermarket radiator. Spal and Flex‑a‑lite make reliable units commonly used in these swaps. Wire the fans through a temperature‑controlled relay kit so they come on automatically at a preset coolant temperature (typically 185–195°F). A manual override switch in the cabin is a nice touch for track days or stuck‑in‑traffic situations.

Oil Cooler: A Non‑Negotiable Addition

Many LS swap builders overlook engine oil temperature. The LS engine relies heavily on oil for internal cooling, especially in the piston squirters that reduce piston crown temperatures. Without an oil cooler, sustained high‑RPM driving or track use can push oil temperatures past 280°F, leading to oil breakdown and potential engine failure.

Install a thermostat‑controlled oil cooler with a 19‑row or 25‑row core. Mount it in the front bumper area or behind the lower grille where it receives direct airflow. Use AN‑10 or AN‑12 lines for minimal restriction. A Setrab or Earl's performance oil cooler is a proven choice in the LS swap community. Do not skimp on the mounting brackets—vibration fatigue can cause line failures.

High‑Flow Water Pump

The stock LS water pump is adequate for a stock engine in a factory chassis, but in a swapped RX‑7 the cooling system often has longer hose runs, tighter bends, and a different thermostat location. A high‑flow, aftermarket water pump (such as those from Meziere or Stewart Components) moves more coolant at lower engine speeds, reducing hot spots and improving overall temperature stability.

If you are using a mechanical pump, ensure you have the correct pulley ratio so the pump spins fast enough at idle. An electric water pump is another option—it frees up engine power and allows you to run the pump after shutdown to prevent heat soak. However, electric pumps add complexity and require a reliable electrical supply.

Coolant Hoses and Expansion Tank

Old, cracked rubber hoses are a failure point waiting to happen. Replace all coolant hoses with silicone hoses from a reputable manufacturer (e.g., Samco or Gates). Use constant‑tension worm‑gear clamps rather than standard hose clamps—they maintain consistent tension as the engine heats and cools. Add a dedicated expansion tank (also called a coolant overflow tank) that is plumbed to the radiator cap. This allows the system to self‑purge air and recover coolant as it cools, preventing air pockets that cause overheating.

Pro tip: Before your first start, pressure‑test the entire cooling system at 15–18 psi. A leak that appears only when hot is much harder to find than one you catch on a cold pressure test.

Exhaust Upgrades: Letting the LS Breathe

The LS engine is a high‑flow, high‑revving V8 that needs a free‑flowing exhaust system to reach its potential. A restrictive exhaust not only chokes power but also increases exhaust gas temperatures, which can further stress the cooling system. A well‑designed exhaust system for an LS‑swapped RX‑7 should prioritize flow, ground clearance, and sound control.

Long‑Tube Headers

Headers are the most impactful exhaust upgrade for an LS swap. Long‑tube headers (typically 1.75‑inch to 2‑inch primary tubes, 3‑inch collectors) offer superior scavenging compared to shorty headers or stock manifolds. This improves cylinder evacuation, increases torque across the RPM band, and can add 20–30 horsepower on a mild LS build.

For the RX‑7 chassis, clearance is the primary challenge. The steering shaft (especially on left‑hand‑drive cars) and the frame rails create tight packaging. Many LS swap header manufacturers offer “RX‑7 specific” long‑tube headers that are designed to clear the steering shaft and fit within the FD or FC engine bay. Look for stainless steel headers with 3/8‑inch flanges to minimize warping. Brands like Stainless Works and LSX Headers have proven fitment in these chassis.

High‑Flow Catalytic Converters

If you need to pass emissions or simply want to reduce the smell of raw exhaust, high‑flow catalytic converters are a sensible addition. Choose a 200‑cell or 300‑cell metallic matrix unit (such as those from Magnaflow or GESI). These flow far better than the factory 400‑cell bricks and will not become a restriction in a 400–500 horsepower build. Position the cats in the mid‑pipe area, not directly at the header collector, to keep them out of the heat zone that can damage the substrate.

Cat‑Back Exhaust System

A cat‑back exhaust system is the final piece of the puzzle. The goal is to maintain a 3‑inch diameter throughout the entire system (from headers to tailpipe) to minimize back pressure. Avoid crush‑bent tubing; use mandrel‑bent sections for smooth interior surfaces that do not obstruct flow.

Consider a straight‑through muffler design, such as a Borla XR‑1 or a Vibrant bottle resonator. These provide excellent sound attenuation without the power loss associated with chambered mufflers. A single 3‑inch exhaust can support up to about 550 horsepower; beyond that, a dual 3‑inch or 3.5‑inch single system becomes necessary. Most street LS‑swapped RX‑7s are fine with a single 3‑inch system, which also simplifies routing under the car.

Exhaust Tips and Aesthetics

While exhaust tips are largely cosmetic, they can affect flow if they are too small or have restrictive designs. Choose a tip with an inside diameter at least as large as your exhaust pipe (3 inches is standard). Rolled or double‑walled tips look clean and hold up well to heat cycling. Avoid “turbo tips” with narrow outlets—they create a velocity mismatch that hurts top‑end power.

For a truly clean installation, exit the exhaust on the driver’s side (on left‑hand‑drive cars) to avoid interference with the fuel tank and rear suspension on the passenger side. This is a common routing for FD LS swap exhausts.

Suspension Upgrades: Taming the Extra Weight and Power

An LS engine adds roughly 80–120 pounds over the front axle of an RX‑7 compared to the rotary engine. While this weight is not extreme, it changes the car’s balance and requires suspension adjustments to maintain proper geometry and handling. Even more important: the LS produces significantly more torque, which the stock suspension was never designed to manage. Without upgrades, the car will understeer, squat excessively under acceleration, and feel vague in transitions.

Adjustable Coilovers

A high‑quality set of coilovers is the single best suspension upgrade for an LS‑swapped RX‑7. Coilovers allow you to independently set ride height, spring rate, and damping, giving you precise control over the car’s attitude and response.

For the FD chassis, spring rates in the range of 8–10 kg/mm front and 6–8 kg/mm rear are a good starting point for a street‑focused car. For track‑focused builds, go to 10–12 kg/mm front and 8–10 kg/mm rear. Brands like Öhlins, Fortune Auto, and Stance are popular in the RX‑7 community. Ensure the coilovers are designed for the RX‑7 chassis—some “universal” coilovers will not have the correct shock travel or mounting points.

Pay attention to ride height. The LS engine’s oil pan sits low in the RX‑7 chassis. Lowering the car too much can result in the oil pan contacting speed bumps or driveway aprons. Set the ride height to maintain at least 4.5 inches of ground clearance at the oil pan.

Anti‑Roll Bars (Sway Bars)

Upgraded anti‑roll bars are a low‑cost, high‑impact modification that reduces body roll without significantly changing the ride comfort. For an LS‑swapped RX‑7, a larger front sway bar (typically 30–32 mm hollow) and a slightly larger rear bar (22–24 mm) help counteract the understeer tendency introduced by the heavier engine.

Adjustable sway bars allow you to fine‑tune the balance. Start with the softest setting on both bars and increase stiffness as needed. A stiffer rear bar relative to the front will promote rotation (oversteer), which is generally desirable for a car that is front‑heavy from the LS swap.

Performance Bushings and Spherical Bearings

The factory rubber bushings in an RX‑7 are likely old, cracked, and compliant—meaning they flex under load. This flex introduces slop in the suspension geometry, making the car feel vague and unresponsive. Replacing all suspension bushings with polyurethane or spherical bearings is a transformative upgrade.

Polyurethane bushings (such as those from SuperPro or Energy Suspension) are a good compromise for street use. They are stiffer than rubber but still absorb some road noise. For dedicated track cars, spherical bearing (heim joint) replacements for the control arms, trailing arms, and differential mounting points provide zero compliance and the highest level of precision. Be aware that spherical bearings transmit more noise and vibration into the cabin.

Key bushings to upgrade: lower control arms front and rear, trailing arms, differential carrier, and steering rack. Do not neglect the steering rack bushings—slop here translates directly into imprecise steering feel.

Strut Braces and Chassis Reinforcement

The RX‑7 chassis is already stiff for a 1990s sports car, but an LS swap adds both weight and torque that can twist the chassis under hard acceleration. A front strut tower brace connects the two front strut towers, reducing flex and improving steering response. A rear strut tower brace (or a four‑point brace) provides similar benefits to the rear end.

For the FD, a carbone‑fiber or aluminum strut brace from a manufacturer like Mazdatrix or Racing Beat fits well and adds minimal weight. Beyond strut braces, consider a subframe brace or a roll bar if you plan to track the car. These add significant torsional rigidity and improve consistency in cornering.

Steering Rack and Alignment

The RX‑7’s steering rack is a quick‑ratio unit that works well even with the LS engine’s weight. However, the power steering pump on the LS engine may produce higher pressure than the factory Mazda pump, leading to overly light steering or potential seal damage. A power steering pressure reducer (available from LS swap specialty shops) dials the pressure down to a level that feels natural.

Alignment settings matter more with an LS swap due to the changed weight distribution. A good starting alignment for a street‑driven LS‑swapped RX‑7 is:

  • Front camber: −1.5 to −2.0 degrees
  • Front toe: 0.0 to 1/16 inch toe‑in
  • Rear camber: −1.0 to −1.5 degrees
  • Rear toe: 1/16 to 1/8 inch toe‑in

These settings provide good turn‑in response, stability under braking, and predictable rear grip. Adjust based on tire wear and driving style.

Beyond the Big Three: Final Considerations

Cooling, exhaust, and suspension form the foundation of a successful LS‑swapped RX‑7. However, a few additional systems deserve attention to ensure completeness.

Fuel System Upgrades

The LS engine requires higher fuel pressure and volume than the stock rotary system can provide. You will need a high‑flow in‑tank fuel pump (such as a Walbro 450 or AEM 340), a fuel pressure regulator adjustable to 58 psi (GM LS standard), and larger fuel injectors matched to your power level. Use a dedicated return line (AN‑6 or AN‑8) to prevent pressure spikes and maintain consistent delivery.

Engine Management and Tuning

A proper tune is what makes everything work together. Whether you use a factory GM ECU with a reflash (such as a P59 or E38) or an aftermarket standalone (like a Holley Terminator X or MoTeC), the engine calibration must be tailored to the RX‑7’s cooling system, exhaust, and fuel system. Pay special attention to the idle airflow table and fan control settings. A poorly tuned LS will run hot, run lean, or simply not make the power it should.

Brake Upgrades

With more power and weight, the factory brakes become a weak point. At a minimum, upgrade to high‑performance brake pads (e.g., Hawk HP+ or Ferodo DS2500) and braided stainless steel brake lines. For track use, consider a big‑brake kit from Wilwood or StopTech with larger rotors and multi‑piston calipers. Brake cooling ducts are a simple and effective addition that significantly reduces pad fade during aggressive driving.

Conclusion: Build It Right, Drive It With Confidence

An LS‑swapped RX‑7 is one of the most rewarding projects a car enthusiast can undertake. The combination of a lightweight, balanced chassis with a torquey, reliable V8 creates a driving experience that few other cars can match. But the gap between a “running” swap and a truly excellent one is filled with careful attention to supporting modifications.

Prioritize your cooling system to protect the engine, build a free‑flowing exhaust to unlock performance, and dial in the suspension to handle the extra weight and power. When these three systems are properly engineered, your RX‑7 will be not just fast, but reliable, predictable, and a joy to drive—whether you are carving canyons, lapping a road course, or simply cruising to a car meet.

Do the work once, do it right, and you will never look back.