Porting

[Marius]

ROTARY PORTING

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Standard Port.

The standard port is common to single dizzy rotaries fitted to USA and Australian RX-2s, 3s and 4s. In 12A form, it is good for about 130hp - with intake (carby / EFI) and exhaust mods they can produce up to 180hp with excellent driveability and fuel efficiency - outright air-flow being its ultimate limiting factor. These standard housings form the basis for mild, extend and bridge porting.

 

Pros: Standard driveability and fuel efficiency

Cons: Limited scope for power

 

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Mild Port

A mild port is the 1st step relating to rotary porting. This version has been "shaped" slightly with a metal porting tool towards the upper area of the port, enhancing air-flow and top-end power without introducing any significant drawbacks. The port design is suitable for the standard induction with around 200hp being achievable. A mild port is a popular choice for those wanting slightly improved performance without changing the standard engine’s characteristics.

 

Pros: Smooth driving, good for daily street use

Cons: Slight fuel consumption increase

 

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Extent Port

The extend port is a larger version of the mild port and works best with improved intake and exhaust systems. Typically with these modifications, the engine will start to exhibit the rotary’s signature rough idle, although the extend port’s is very slight. There is also a slight but noticeable loss of low-down torque below 4,000rpm. Importantly the increase in air-flow ability translates to the potential for around 220hp providing the best compromise for regularly-used street cars. This is the popular choice for those who don’t want the numerous drawbacks of a bridge-port.

 

Pros: Good power increase while retaining driveability.

Cons: Increase of fuel consumption and noise and the need for modified intake and exhaust systems to maximise power.

 

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BRIDGEPORT

The well bridge port uses an additional "eyebrow" opening alongside the original "modified" port and introduces the characteristic lumpy idling. The bridge that now exists between the 2 ports’ primary purpose is to ensure the rotors’ corner seals - which pass indirectly over the bridge - don’t fall out. The improved air-flow increases top-end power dramatically with a noticeable powerband peaking around 8,000rpm with a driveability, smoothness and fuel efficiency is reduced. Maximum power of around 260hp is largely dependent on the choice of intake and exhaust systems. Unfortunately for street cars, faster normally means louder.

 

Pros: Very good potential for power, increased rev-range

Cons: Poor driveability, fuel consumption and excessive noise

 

 

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J-PORT

The J ported engine (also known as monster port) is as big as conventional side-plate porting can go. It is the same as the bridge port in design, but the bridged port is now fatter and extends past the face of the rotor and into the housing’s water seal / O-ring requiring the need for the seal to be cut back and filled with a metal type sealant such as "Devcon", plus, depending on the side plate used, the water gallery requires blocking off and filling on the side plate and the rotor matching.

 

Cutting into the rotor housing is also needed for port matching. The main problem with this design of port is a short life-span as water does and will seep through the seals. The main field where a J-port is likely to be seen is on the track where restrictions don'’ allow peripheral porting, or a slightly wider power band is desired. Typically around 300hp can be expected.

 

Pros: Slightly better power than a bridge port (5 - 10%) without the expense of a PP

Cons: Short life-span, 6-12 months / 5,000 - 10,000km, narrow power band, need for free-flowing (loud!) exhaust system, poor driveability

 

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PERIPHERAL PORT

The peripheral port is the ultimate form of porting for a rotary engine without turning to forced induction. Instead of conventional metal shaping with a grinder, the side ports are actually filled and completely new circular - peripheral - intake ports are fitted directly through the rotor housing and is easily identified on an engine by its tubular intake manifold. This modification has potential for over 320hp but as it is developed for racing, exhibits very poor driveability, fuel consumption and requires an exhaust system deigned to produce excessive noise. Like the bridge port, the PP produces its maximum power past 8,000rpm creating increased stress and wear on components.

 

And instead of idling at around 1,000 - 1,500rpm for the previous porting methods, the PP engine will not idle much below 4,000rpm and is impractical and virtually unusable on the street.

 

Pros: The ultimate form of rotary porting for maximum power

Cons: Excessive noise, extensive intake mods, very poor driveability and fuel consumption, relatively short engine life, very expensive, narrow power band

 

NB: Some tuner have combined very small peripheral ports and conventional side ports but their success has not been great. These are referred to as mild peripheral port.

[Håkon A]

tror jeg går for Extent Port i år..