HKS talks about intakes for the RX-8

This is the first of my translated Japanese magazine articles. More to come I promise.

“RX-8 air intake is a difficult subject and it is very sensitive to change. One must choose carefully,” said the intake designer at HKS.

Normally an open type intake works well for every car, since the best suction rate you can get is from this type of design. Totally open type in an Mazda RX-8, however, has an opposite effect.

If you want to increase the engine performance, the volume of air intake has to be increased. However, one must ensures cold air being taken in. Since high temperature air arising from an RX-8 has an increase total volume than colder air. Hence, a lower density of air particles, resulting from less air being taken in the end. The ECU also very sensitive to intake heat, and it may be the reason for reduction in engine power.

“On the other hand, if the box is totally sealed, the amount of air is certainly less than open type, hence performance of the intake will not be fully used. Therefore, the amount of open air expose to the intake, and the shape of the box, and where it opens are important.”

“We have produced the best intake whereby the intake amount and the air temp is balanced.”

Therefore, HKS opted for a suction intake has a shape not totally open or totally closed.

 

This is their analyses using different set ups.

 

 

Discussion

In my opinion, it is a very confusing article since the parameters on the graft are confusing.

The first graph indicates the temperature of the intake over engine revolution. It is very confusing since it is a difficult concept of the fact that the intake temp will reduce in hard revving. Does it mean more continuous air being sucked in and the actual temperate reading is being record by the sensor?

The dyno graph on the right shows marginal benefits. The max power difference at the top of the rev range is a mere 1-2kW. I hope they have factored in variations of power between runs on the same set up. This marginal result may not be argumentative enough.

To confuse me even more, the middle graph indicates a big variation between intake resistant versus the intake flow. The actual amount of flow in respect of the engine revolution/speed was not shown. I wonder how much of this graph translate to actual benefit of amount of air being taken in across the rev range.

The actual resistance benefit of the HKS filter element itself can be shown by comparing the result from both closed type boxes (the black graph and the blue graph). According to this, there is approximately 20-30% increase (~0.21 m3/sec to ~0.27 m3/sec at 4kPa of suction resistance). So I interpret that in the same type of box you use (close type), you will have increase of flow by 20-30% when you change to the HKS filter type alone. That is not great amount considering just changing the filter itself from MazdaSpeed, Pipercross (RMagic) and ITC will get at least 10-15% of improvement in filtration effort.

 

Conclusion

HKS has its point of balancing the amount of air and its temperature of an intake. I reckon there may be a better way then just merely opens the box and get more air flow, knowing they have done some sacrifice by getting small amount of bonnet air. 

I think some sort of ram air via the bonnet may be a good solution, although it will not be rain proof.