Turbo piston for BP

Maruha’s priority is a natural intake and for Miata/Mx-5 tuning we propose the ultimate 2.1L-4 throttle injection. However, many times we get inquiries from outside Japan about line-up for superchargers.

Turbo chargers and superchargers are available on many markets, that’s why first as a representative of engine parts we would like to propose a piston.

Mahle’s special features

The machine used for machining has been developed by Mahle and the same machining is not being used by other companies.
Mahle’s forged piston is special with a very refined shape.
If you take a look at the piston pin’s surrounding, the thickness of the skirt’s back side, the back side of the piston top (roof) etc. you can easily see the refined design.
The feature of Mahle’s piston is its extremely light and compact design.
The characteristic outside appearance is the slipper skirt design.
The slipper skirt has been used for the first time by Mahle. It contributes a lot to weight reduction.
Even these days’ Japanese genuine pistons use a short skirt in the case of a high performance engine, but the fusion of Mahle’s technique of appropriate profile, very good machining accuracy, original coating is summarized in these days’ pistons.

85.0mm bore

The earlier piston used to be high compression type, in other words 85.5mm. However, considering the block’s hardness it has been re-set to 85.0mm.
The cylinder capacity is 1928cc.
It is only 0.5mm less, but the thickness between the block and bore grows with 1.0mm and it becomes harder.

Piston volume

The piston top is dish type-4cc and the compression ratio is 9.0. The compression ratio of the old type turbo engine was 8.0, but in the recent years the priority is a low speed torque supercharger.

Even Maruha’s super charger system’s development is progressing and that’s why we too set the compression ratio to 9.0.

Piston, pin diameter

By the piston top it is possible to receive the energy from the combustion explosion and through the piston pin conduct that power to the conrod.
It is set up at the supercharger, that’s why in the case of natural intake, an extremely big energy is concentrated on the only 22mm pin.

The standard pin diameter is 20.0 mm.
We have changed it to 22.0mm. It is only a difference of 2.0mm, but the size grows with 10%.
The bending strength reaches a progress of 30%.

The turbo piston for BP used up till now, even in the case of maker genuine ones (for Mazda 323 and for BP turbo) was 20.0mm. However, with the premise of 83mm bore, the power announced by the maker doesn’t go above 180PS.

The later supercharged engine, even in the case of BP, can reach an output of over 400PS.
At Maruha we set our goal to 250-300PS.
Of course, some reinforcement is necessary. One of it is the pin’s diameter.

Because of the pin’s diameter’s change, neither a genuine conrod nor an equal sized conrod can be used at the same time.
Please use our company’s conrod.

DLC coating

In the case of the BP turbo piston pin DLC coating is being applied.
DLC means DIAMOND LIKE CARBON, in other words a diamond-like hard carbon film.
Which means that the film is very hard and thick, and the goal is a decreased sliding friction.

The thickness of the film is on a nano-level, and so it doesn’t affect the accurate clearance.

In the industry DLC coating has been used in the case of many parts. However, we at Maruha use it for the BP turbo piston’s pin.

Slipper skirt & Grafal coating

The world’s leader piston manufacturer, Mahle has got an established reputation with its peculiar shape.
The slipper skirt is Mahle’s product and on the skirt part black grafal coating is used.

The grafal coating's thickness is like a cushion, it reduces the slap sound that arises during the continuous contact of the piston and the cylinder and reduces the piston's resistance.
It is not a simplified spray coating but a secure coating carried out by manufacturing process, that’s why it cannot wear out easily.

The material

We use Aluminum 4032.
It contains lots of silicone and its thermal expansion is low.
This is the reason why compared to the aluminum forged pistons the piston clearance is more accurate.
If the clearance is done properly, the tap tone doesn’t arise and it becomes possible to construct a silent engine with controlled oil and fuel consumption.

The conrod

The diameter of the pin is 22mm, that’s why a genuine conrod cannot be used.
Please use Maruha’s conrod.

For further information see the site about the POWER ROD for Turbo.


Maruha Motors Co., Ltd.
Ushizuma 2095-6, Aoi-Ward
421- 2106 Shizuoka city, Shizuoka prefecture
TEL: 0081-54-294-0076
FAX: 0081-54-294-1312
E-mail: info@maruhamotors.co.jp