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Mazda 13B-REW Build - Target: 700 WHP

pbskids cover car gets ramped up for Time Attack

Richard Fong
Jun 28, 2019
Photographer: Jonathan Grunwald

How does one improve upon something seemingly perfect? By stepping up the game and proving there is more to be had.

You've probably seen this rare '94 Mazda RX-7, as it has appeared at the 2016 and 2017 SEMA Shows as well as on the cover of pbskids's October '17 print edition. What makes this machine so special? First of all, FDs are not that common. Second, this one has a unique and aggressive TCP Magic Type TT widebody kit, the second ever made and the first in the world with all the optional components available. That's just what's on the exterior, as it also previously featured a 550hp 13B-REW rotary engine with a Precision 6766H turbo supplying 26 psi boost pressure. That's right, it still has a rotary under the hood, but for its owner, Jonny Grunwald, this dream project had yet to see its full potential.

CENTER OF ONE'S ATTION

Many would have considered this masterpiece a done deed, but Jonny wanted more for his machine. Keep in mind, he is not your typical builder. He's managed several builds for Bulletproof Automotive and has built several of his own, including a 422hp Pandem RX-8 we featured in the past. Now, this RX-7 is his primary focus, and his goal is to create the finest machine he can. The aesthetics of his FD3S have found equilibrium, but the hunger for horsepower has left him wanting. While 550 hp is a healthy output level for most engines, he wanted more in the order of 700-plus horsepower to the wheels in order to be competitive in time attack. Since Jonny is a purist, he stuck with the 13B-REW rotary engine; however, he wanted to showcase how this could be accomplished with the latest technologies, in addition to increasing output with more boost pressure.

SORTING OUT THE ROTARY SANDWICH

To begin, a rotary engine is entirely different from a reciprocating piston engine, except for the fact that, by way of combustion, the energy released is transformed into mechanical power. However, the way a rotary engine accomplishes this is quite different from that of a piston engine. To understand the fundamental differences, just knowing what's inside a rotary engine explains quite a bit.

  |   Mazda 13B-REW Build - Target: 700 WHP

To begin with, a rotary engine has no pistons, connecting rods, cylinders, valves, or camshafts. Instead, it is a sandwich of components that accomplish similar functions but in a different way. In the case of the 13B-REW—a 1.3L, two-rotor engine—let's start at the middle, with the midplate, which is sometimes referred to as an "iron." On either side of it are triangular pieces, which are the steel rotors. These are the equivalent of pistons. The rotors rotate within the next components (rotor housings), which serve the same function as the combustion chamber and cylinder. These rotor housings each have an exhaust port. At each end of the engine are the side housing plates (also referred to as irons), which enclose the rotors contained within the rotor housings. Going through the middle of this engine sandwich is the eccentric shaft, the equivalent of a crankshaft. The eccentric shaft links the rotors and coordinates their movements within the rotor housings.

SPINNING TRIANGLES VS. RECIPROCATING PISTONS

Rotary engines often come under tremendous criticism and scrutiny due to perceived reliability issues. This bone of contention is hard to argue, and rotary fans don't necessarily deny it. Even Jonny admits he's been through three engines so far and the fourth was in the car when it went to SEMA in 2016. However, when one considers the output per displacement, the rotary engine seems incredibly efficient and potentially superior. After all, displacing only 1.3 liters yet producing output on the order of 255 hp (the factory rating for a stock 13B-REW engine) and up to the 550 whp of Jonny's half bridgeported engine, the argument is compelling. Imagine if that engine had a full bridgeport...

PARALLELS BETWEEN PORTING A ROTARY VS. CAMSHAFTS AND VALVETRAIN

Drawing another comparison between the reciprocating piston engine versus the rotary engine is volumetric efficiency. A piston engine relies on the valvetrain and the camshafts to ensure air flows in and out of the combustion chambers efficiently. By changing the camshaft profile (lift and duration), an engine can become more efficient anywhere on the power curve, affecting the output of the engine and dictating the shape of the power curve. Similarly, a rotary can be tuned to produce more at the bottom end, the midrange, or at the top end, depending on the style of porting and by how much.

PORTING FOR PURPOSE

How aggressively one ports a rotary engine will depend on the purpose or expectations of the engine. Mild port work, or a "streetport," will typically improve over the stock porting by removing material from the intake ports to permit air to be drawn in by the rotor for a longer period, increasing the volume of air in the combustion chamber. This will increase the engine output but will shift the power curve higher in the rpm range. This is the equivalent of swapping in larger, Stage 1 camshafts.

The next level is a bridgeport, which is a more aggressive streetport with a slit of additional material removed above the streetport to permit even more airflow to be drawn in sooner. This can be equated to a Stage 2 camshaft profile. Its namesake is for the "bridge" of material between the ports the apex seal travels across as the rotor turns. This shifts the power curve further up in the rpm range and sometimes results in a rough idle.

The most aggressive form of porting is called a peripheral port. In this instance, the stock intake ports are welded shut and an intake port is created on the periphery of the rotor housing, hence its name. This would be the symmetrical equivalent of the exhaust port on the rotor housing. This results in the greatest potential output at the top end of the rpm range, while sacrificing bottom-end driveability. It's rough and lopey, doesn't idle well, and consumes a lot more fuel, but it screams at wide-open throttle and raises the output potential of the engine.

GOING FROM HALF TO FULL

Jonny's initial build involved a half bridgeport, which means only one of the primary iron plates is bridgeported for each rotor. This offers a significant output improvement over a streetport while maintaining driveability. Upon initial inspection, the staff at Lucky 7 Racing determined the front, center, and rear iron plates were still within spec and proceeded to clean up the existing ports while completing the bridgeport work on the last streetports, thus making the engine a full bridgeport. Since the aluminum rotor housings endure some significant punishment, Jonny ordered a fresh pair of rotor housings from . Lucky 7 Racing then reworked the exhaust ports to complement the now higher-flowing intake ports. In anticipation of raising the boost pressure from 26 psi to somewhere between 30 and 35psi, the engine stud ports were enlarged to accommodate a stout set of Garage Life 12.7mm studs. The new engine studs lend to torsional rigidity in addition to containing the immense pressure that will be generated within the rotor housings.

TRIMMING THE TRIANGLES

With the irons and housings ported, attention shifted to the rotors. Jonny's tuner, Daniel Kuo at Garage Life, side cut and clearanced the rotors. This precision-machining process performed to both faces of each rotor ensures adequate clearance from the irons. This is particularly important when running at engine speeds in excess of 8,000 rpm. Without proper clearancing, the rotors could walk or wobble, making with the irons or housings, and potentially cause irreparable damage.

BALANCING ACT

It was then time to balance the engine. The rotors and eccentric shaft, along with the ancillary components driven by the crankshaft from the front pulley back to the flywheel, were then brought to Mazdatrix in Long Beach, California, to be balanced. Once finished, the rotating assembly was balanced to within factory spec by 0.5 grams. This process ensured the rotary engine would continue to spin smoothly all the way to its target peak engine speeds.

PUTTING THE SANDWICH TOGETHER

Once all the pieces to this puzzle were back in the shop, it was finally time to assemble the engine. The rotors were equipped with new E&J 2mm apex seals, which Jonny had utilized with great success in his half-bridgeported engine. To ensure smooth operation between the rotors and the eccentric shaft, Jonny turned to Mazda Motorsports. Standing behind its grassroots enthusiasts and racers, Mazda Motorsports assisted with an assortment of seals, rings, and a coveted set of competition rotor bearings. These bearings offer a 0.25mm deeper oil groove in addition to 0.0005-inch additional clearance compared to a set of stock rotor bearings, which would further ensure adequate oil flow keeps the rotating assembly well lubricated at higher engine speeds.

PRESSURIZING THE TRIANGLES

Attention now shifted to producing more boost. A Turblown cast 347 stainless-steel tapered manifold bolted to the exhaust ports directs the high-enthalpy gases into the turbine housing of a BorgWarner EFR 9180 turbocharger. Although it's capable of producing 900 to 1,000 hp in a piston application, Jonny selected this big, midsize-framed turbo because it would complement the bridgeported engine with nominal lag. The tapered runners of the Turblown manifold help increase the velocity of the spent gases entering the twin-scroll EFR turbocharger. Dual Turbosmart Comp 40mm Gen V wastegates divert excess exhaust gases away from the turbine housing to regulate boost pressure. After spinning the turbine wheel, the spent gases then flow from the turbine discharge through a custom 4-inch downpipe and a rare and discontinued HKS titanium racing exhaust to the rear of the chassis.

On the cool side of the turbocharger, the boost pressure flows through the custom V-mounted intercooler en route to the intake manifold. From the manifold, Injector Dynamics 2,200cc primary and secondary fuel injectors saturate the air charge with fuel as it flows through the bridgeported irons and into the rotor housings. With Kuo behind the keyboard, the Adaptronic Modular FD3S S6 M2000 engine management system monitors key engine vitals while orchestrating the fuel delivery and spark timing. With boost set to a maximum of 35 psi, Jonny's fully bridgeported and studded 13B engine is expected to smash his target of 700 whp on Lucky 7 Racing's Dynojet dynamometer (we weren't able to get dyno results before the article went to print, but stay tuned for an update soon!).

We asked Jonny if there were there any particular challenges with the engine build. He replied, "The biggest challenge was finding time to re-dedicate to the project. This car was running when I decided to take it apart and shelve it for six months. When you have time to take a step back and reevaluate how you could have done something differently or find new goals, it helps keep the build focus fresh. Whenever you think your build is done, it's time to sell the project. We should always be searching for ways to refine our craft and vision to push the next generation of builders to come. Build versus stagnation and lay the groundwork for what's next."

NEW ENGINE PARTS ADDED:

  |   Mazda 13B-REW Build - Target: 700 WHP

  • Elite Solid Dowel Pins
  • E&J Apex Seals 2mm Apex Seals
  • Mazda Treated OEM Corner Seals
  • Mazda Treated OEM Side Seals
  • Atkins Water Seals
  • Mazda Motorsports Treated Oil Seals
  • Mazda Motorsports Oil Control Rings
  • Mazda Motorsports Oil Seal Springs
  • Mazda Motorsports Rotor Bearings
  • Mazda Motorsports Main Bearing
  • Mazda OEM Rotor Housings
  • 5mm Laser-Cut Oil Pan Brace
  • Garage Life Machined & Race Clearanced Rotors
  • Garage Life 12.7mm Oversized Engine Studs
  • Lucky 7 Racing Porting Service
  • BorgWarner EFR 9180 turbo 1.05 A/R
  • Turblown Cast Tapered 347SS Twin External Wastegate Manifold
  • Turbosmart Comp 40mm Gen V Wastegates (x2)
  • Injector Dynamics ID2200 Fuel Injectors (x4)
  • Walbro 450-lph Fuel Pumps (x2)
  • CJ Motorsports Twin Fuel Pump Hanger
  • Spec Clutch Mini Twin-plate Carbon Clutch with Pull-to-Push Conversion
  • Turblown 4-inch Downpipe
  • HKS 4-inch Titanium Racing Exhaust
  • AEM Electronics EGT Sensors
  • AEM Flex Fuel Sensor

  |   Mazda 13B-REW Build - Target: 700 WHP

Mazda Motorsports rotor bearings are pressed into freshly clearanced rotors.

  |   Mazda 13B-REW Build - Target: 700 WHP

New rotor housings are being prepared for exhaust porting.

  |   Mazda 13B-REW Build - Target: 700 WHP

Rough outline laid out prior to extending the previously bridgeported iron.

  |   Mazda 13B-REW Build - Target: 700 WHP

Comparing the ported version to the factory intake iron.

  |   Mazda 13B-REW Build - Target: 700 WHP

Beefier 12.7mm Garage Life studs versus OEM.

  |   Mazda 13B-REW Build - Target: 700 WHP

Making some post bridgeporting measurements.

  |   Mazda 13B-REW Build - Target: 700 WHP

Carefully porting the intake runners on the intermediary iron.

  |   Mazda 13B-REW Build - Target: 700 WHP

Clearancing the 2mm E&J apex seals after rotor assembly.

  |   Mazda 13B-REW Build - Target: 700 WHP

A look at the engine rotor being placed on the eccentric shaft.

  |   Mazda 13B-REW Build - Target: 700 WHP
  |   Mazda 13B-REW Build - Target: 700 WHP

Overhead shot with the apex seals installed.

  |   Mazda 13B-REW Build - Target: 700 WHP

Inserting the apex seals with apex corner seal springs.

  |   Mazda 13B-REW Build - Target: 700 WHP

The closing of the keg.

  |   Mazda 13B-REW Build - Target: 700 WHP

Studs fitted with engine now closed.

  |   Mazda 13B-REW Build - Target: 700 WHP

Twin Turbosmart wastegates with Turblown's cast-tapered manifold.

  |   Mazda 13B-REW Build - Target: 700 WHP
  |   Mazda 13B-REW Build - Target: 700 WHP

Spec twin-plate carbon clutch installed.

  |   Mazda 13B-REW Build - Target: 700 WHP

Final engine assembly is ready for drop-in and tune. 700 whp, here we come!

By Richard Fong
16 Articles

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