To be a little more specific though, the ‘ports’ inside a rotary engine are the paths through which the air/fuel mixture travels into the engine (via ‘Intake Ports’) and the spent exhaust gasses travel back out (via the ‘Exhaust Ports’).
The shape and size of the ports have an immediate and direct impact on the airflow and efficiency of the engine; opening a port for slightly longer than standard, can reduce airflow velocity and actually result in decreased power at certain stages of the rev range. While leaving port timing standard might have a detrimental effect on power if you were trying to spool up a huge turbo.
Rotary Revs cater for all requirements, from simple Street Porting right through to Full Peripheral Ports.
There are a number of porting ‘types’ or options, each with their own merits and drawbacks. In reality, no port design is perfect, but rather each port is designed to be suited toward specific performance objectives. We’ll begin with the Standard Port which comes as stock from Mazda and then list each of the additional modified port types and their price points for you below. Click any of the porting options to learn more about that type.
The stock porting from Mazda actually varies quite a bit, from turbocharged to naturally-aspirated. Even on a standard RX-8, the 192-bhp model has different ports from the 231-bhp model. With any of the standard ports, the engine will realise some of the best driveability and fuel economy possible, but will also suffer limited power in the upper rev ranges when compared to modified ports.
Entry level porting and one of the most widely used. This type of porting is ideal for the road-going daily-driver, be it for your RX-7 or RX-8, the Street Port will offer an increase in horsepower at the high end and a little more torque in the mid range on naturally-aspirated and forced-induction engines. Generally a Street Port will involve opening the intake a couple of degree’s longer and the exhaust a couple of degrees sooner, while trying not to impact port timing overlap.
Sometimes referred to as a ‘Monster Street Port’ or an ‘Extend Port’, this is essentially a regular Street Port but with even more aggressive port timing.
In an Extended Port, the ports are open for a longer duration which will cause the power band to climb up the rev range. In an RX-7 engine an Extended Street Port will begin to introduce the rotary’s, almost signature, rough idle, though it will not give a full ‘Brap’ effect at idle. In an RX-8, this option will…
Bridge-porting was developed in the 1970’s for racers who were banned in their various race-series from running a full peripheral engine port. Rules such as ‘Must retain original intake manifold’ were easy to add to a rulebook, with the intention of sniping the then new-rotary engines initial successes. The design of the rotary engine prevents the engine builder from being able to extend the existing ports in either direction towards the e-shaft (or the housings) because of the oil seals and the necessity for a track used by the corner and apex seals of the rotor to run over. Early racers needed more port area without impacting on timing too much, and so they introduced an eyebrow port over the existing ports leaving a ‘bridge’ for the seals to run over, preventing them from falling into the port. This strip of metal was later coined the term ‘Bridge Port’.
Introducing ‘the eyebrow’, means that at bottom dead-centre, both the exhaust port and eyebrow port are fully open resulting in an intake exhaust overlap, this overlap creates the rotary’s characteristic lumpy idle or ‘brap’, but as a side effect sacrifices low-end drivability and power in place of bigger gains higher up the rev range.
A ‘half-bridge’ refers to when only the secondary ports are bridged. By only cutting an eyebrow over the secondary ports, which remain closed at idle and low RPM’s, we avoid inducing overlap at low throttle positions and so can retain much of the drivability and power at lower RPM’s whilst still gaining some benefit from the extra port overlap at higher RPM.
Note, that some rotary engines do not isolate the primary and secondary runners. And in these cases, the owner would see no benefit from the Half vs. Full Bridge Ports. We can help diagnose if your car would be effected by this issue and discuss the options with you further should that be the case.
When cutting a Full Bridge Port an ‘eyebrow port’ is cut over all of the intake ports (primary, secondary and in 6 port configurations, the auxiliary ports as well).
This type of porting brings with it all of the benefits and short-falls of bridge porting; high RPM increases in power but poor drivability in the lower RPM ranges. The effects are much more dramatic in RX-7 and earlir engines, but still present in the RX-8 MSP engines. Also with RX-7’s, idle speed must often be increased to as a much as 2000 RPM in order to develop a stable idle.
We don’t often recommend this as an option and in all cases where it might be, prefer to use Peripheral Porting instead. J-porting really is only for racing applications where rules prevent the use of a P-Port.
J-Porting is almost exclusively used in racing applications where Peripheral (P-Porting) is outlawed.
Over the years as racing teams continued to develop bridge ports, the inner water seal on the housings or irons prevented making the eyebrow port any larger. Cutting past the water seal turns a ‘bridge port’ into a J-port or monster bridge. The catch with this, is engine life is severely impacted by this type of porting and if it is not perfectly implemented, the water jackets will seep coolant directly into the combustion chambers.
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A Peripheral or P-Port is the ultimate level of rotary induction.
Exactly as the name suggests, the intake and exhaust ports are literally, straight-shot along the outside, or periphery of the rotor housing. All pre-RENESIS production rotary engine’s already use a peripheral exhaust port as standard from factory.
Generally speaking though, when referring to a P-Port engine, you would be focusing on adding a custom Intake P-Port, although major alterations are usually made to the Exhaust Port as well.
The Peripheral Port design results in engine behaviour similar to what you might find on any serious piston race engine; giving significant increase to the intake port area is likened to oversized valves and a long-duration camshaft. Having both intake and exhaust ports on the periphery of the housing, gives the greatest amount of overlap which is most favourable for power production at the upper end of the powerband.
Likewise, this massive overlap allows a significant amount of exhaust noise out through the intake, resulting in what can be considered a phenomenal amount of noise, on par with a Formula 1 car. This type of rotary engine design is truly the best of all specifications for a race engine, with the greatest power output, peak power and torque figures which usually occur around the 7k and 10k RPM marks respectively, and sometimes even higher than that.
That said, with an idle-speed between two and three thousand RPM and the torque production being flat below 5k, it requires a die-hard enthusiast to drive a loud, thirsty, peripheral-ported engine on the street …but it can be done! 🙂
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All advertised porting prices are for the service of physical porting only and do not include any additional tuning. In some applications, a Base Map will be required and then a further Custom Re-map on our Dyno. Noted pricing is subject to change without prior notification should your application be a little more ‘exotic’ we reserve the right to increase the cost of the work also (especially for 3 and 4 rotor applications).
If you have any questions, queries or would like to discuss the benefits of a particular port and look into which type of port may be best for your RX-7 or RX-8, don’t hesitate to get in touch with us! We’re friendly, ready and waiting to help.