If you thought we were at the peak of development with the Mazda Rotary engine, especially in naturally aspirated form, you’d be dead wrong. The rise in popularity of billet alloy means that we are entering an exciting phase of development, one that Mazda itself never had the opportunity to take advantage of, uncracking a whole new level of performance and reliability in high-power applications.
Long-time rotary rally driver and engine builder by trade Wade Henshaw, of Henshaw Race Engines in Christchurch, has devoted the past three years to developing his own after his experiences using billet in piston engines drove him to purchase some off-the-shelf plates to try in his 13B peripheral-port (PP). However, the quality was not what he’d expected, and, after a lengthy process of wrecking parts, modifying the parts, and then wrecking more parts, he decided to cut his losses and design and produce his own billet parts from scratch.
With rally his focus, Wade has engineered his plates to be OEM replacement with integrated engine mount bosses for all RX-7 models, along with significant improvements in the block stability, strength, wear, friction, cooling, and also the ability to improve oil scavenging from the rotors. The development started with his existing 13B PP on the engine dyno. “I did a lot of dyno testing and I lost count after about 25 strip-downs with the purchased plates. I put 15 EGT (Exhaust Gas Temperature) sensors and some pressure sensors on the motor and then sat it at 9,000rpm to see where the temps would climb,” he explains.
From there, new billet plates were designed in CAD to be considerably lighter than the OEM iron type, featuring 20–30 per cent more cooling capacity with priority cooling passages to feed the spark plugs in the housings. They also feature new replaceable, hardened ductile iron-wear surface liners, which have 20 per cent more surface area on the backside of the wear surfaces to further aid heat transfer. Although Wade also has Nikasil seal-coated alloy inserts ready for testing.
The 13B runs CLR Motorsport peripheral ported housings; although, with a stack of original Mazda Factory Racing (MFR) housings sitting there, his next plan is to design a process to refurbish using Nikasil seals, just as Mazda used from its factory.
A replica MFR dry-sump cover has also developed in billet, and he has gone one step better by installing a floating bearing in the front cover to support the crankshaft pulley at big RPMs. The internals include a Super Finished RX8 crank, MFR rotor bearings. MFR stationary gears, Lanetti ceramic apex seals, and Series 5 RX-7 9.7:1 compression rotors that have been considerably lightened. On the scales, the 13B weights only 68kg, and so far Wade has extracted 378hp on his engine dyno, but expects to push this upwards of 390hp with injection fitted. “The biggest gain is not the HP number, it’s the torque improvement from a block that stays square under extreme loads”. Currently, fueling is old school due to classic rally rules, in the form of a heavily modified 51mm IDA carb sitting on an MFR manifold; however, a full Group B car is planned, so Borla tapered ITBs and MoTec ECU are on the shelf waiting. The ignition is taken care of by an Electromotive XDi CDI unit that runs off a trigger wheel sitting between counterweight and flywheel, as was run on the original MFR engines.
The idea is to eventually sell the components, but not before extensive dyno and rally stage time has proven their worth. Then, further testing will also be carried out in the US by Carlos Lopez, someone who Wade credits as being a massive help. The new engine will be back on the dyno by the time you read this for the next round of longduration big RPM tests!