Maruha 2.1 L Stroker Kit for MIATA 1.8 BP Engine

Supported MIATA Models: MAZDA MIATA NA8C and NB8C

This product upgrades the standard 1.8 L engine to a 2.1 L torqueful engine.
The enlarged 85.5 mm bore and 89.0 mm stroke produce enough torque power to get more powerful acceleration through all ranges of driving speed.

Maruha 2.1 L Engine Stroker Kit includes a finely machined 89.0 mm crankshaft, a durable lightweight connecting rod set and a special MAHLE 85.5 mm piston set.
The Maruha 2.1 L Engine Stroker Kit is the best quality engine stroker on the Miata market.

[The kit Components (Included)]
Maruha 89.0 mm Crankshaft
Maruha Connecting Rod
MAHLE Power Piston

[The Engine Accessories (Sold Separately)]
Maruha Power Metal Main& Rod Bearings
Maruha Oil Jet
Maruha Fuel Injector Set

Maruha Crankshaft

Maruha's crankshaft made from finely machined alloy steel (chrome molybdenum 4340 steel ) has a 89.0 mm long stroke that provides the vehicle with more torque.
Furthermore, the crankpin diameter of 48.0 mm is designed 3.0 mm larger than the standard ones.

It can provide the crankshaft with more durability by enlarging the overlapped area between the crankpin and the journal.

The full counterweight design for perfect balance allows bolt-on installation for the engine block.

A crankshaft requires continuous oil supply. Maruha designs the crankshaft main journal with the two chamfered oil holes. When Maruha Power Metal Main& Rod Bearings are used together with it, their oil holes designed in the center will allow smooth oil flow into the crankpin at each crankshaft revolution.
Figure 1 shows the continuous oil circumstances. The red arrow in the figure indicates oil flowing.

Miata with B6 and BP engines have generally less strength of the connection between the crankshaft snout and the pulley boss because they do not have length to be sufficiently overlapped.
We kept on R&D to develop Maruha Crankshaft, that's snout is enlarged to retain enough connection to the pulley boss.
Our design can enhance the durability of the pulley boss and can also avoid product damages in severe driving conditions.

Maruha Connecting Rod

Connecting rods have more loads according to higher engine outputs.
Maruha's H-beam style rod designed for lightweight and strength will fulfill your needs with the remarkable performance even at higher engine revolution speeds.
The rod weighs about 460 g and our product is approximately 80 g lighter than MIATA stock Rods.

Our newly designed big end has a 3.0 mm larger diameter than the conventional conrod to reduce loads on the crankpin journal.
The ARP rod bolts with enough diameters to withstand loads can provide more durability to our conrod.

NOTE: Maruha Connecting Rod is only for Maruha 2.1 L Engine Stroker Kit. Our conrod cannot be used for any other product.

MAHLE Power Piston

MAHLE's 85.5 mm piston is designed for Maruha's 2.1 L Engine Stroker Kit.
The lightweight piston features its high end specification including its unique piston skirt shape, and strong and anti-fractioning GRAFAL coating.
MAHLE Power Piston can also be used for MIATA stock crankshaft.
The recessed piston skirt avoids interference with Cooling oil jet.

Maruha Power Metal Main& Rod Bearings (Sold Separately)

Maruha's main and rod bearings are most suitable for Maruha's 2.1 L Engine Stroker Kit.
They can supply more oil to the crankpin journal.
The bearings forged from F112 alloy have superior performance by their durability as racing spec.
You can choose from 3 sizes to make proper oil clearance adjustment.

Maruha Oil Jet (Sold Separately)

An oil jet device injects oil to the back side of the piston for piston cooling.
However, the uniquely designed MAHLE Power Piston may cause interference with the oil jet.
A conventional oil jet device has a boss for installing it to the engine block.
When it is fixed with Maruha 2.1 L Engine Stroker Kit, the oil jet's boss can rub on MAHLE's piston.

Maruha Oil Jet is designed to prevent any interference with the piston.
Such improvement avoids the interference with the piston, without the jet nozzle bending.
A hole on our oil jet replaced the conventional boss and is used for inserting the positioning knock pin into it.

2.1 L Fuel Injector Set (Sold Separately)

Without any question, Maruha 2.1 L Fuel Injector Set, 4 pieces has superb performance for our power stroker kit.
The injector size is 300 cc/ min, while the flow of MAZDA MIATA NA8C Injector is about 250 cc/ min.
MAZDA MIATA NA8C and NB8C models with Naturally Aspirated (NA) engines feature their direct response, though you are required to choose the suitable injector sizes because the NA engines deliver limited power.
The 2.1 L Fuel Injector sends more fuel to provide more torque and power to your MIATA.
It is the best choice to be used with the 2.1 L Engine Stroker Kit.

For more direct response and easier ECU operation, Maruha 4 Throttle Injection Units and our high lift camshafts are available.

NOTE: When Maruha's 4 throttle Injection Unit is installed additionally, the fuel delivery spacer (included in the kit) must be used together.

Maruha 2.1 L Engine Stroker Kit for MIATA 1.8 BP Engine Dyno Graph

Figure 2) Horizontal Axis: engine RPM (rpm)
Vertical Axis (Left): horse power (PS) /Vertical Axis (Right): torque (kgf-m)
Red Line: horse power (PS)/ Yellow Line: torque (kgf-m)

Maruha 2.1 L Engine Stroker Kit provides sufficient speed and torqueful driving even at lower engine speed.
Even our early prototype power stroker was installed with the 4 throttle kit (45.0 mm body size) a Maruha Racing Camshaft, the engine power surpassed by far 230 PS.
Figure 2 shows that the maximum torque was approximately 25.0 kgf-m at 6,000 rpm and the maximum horse power was more than 230 PS at 7,600 rpm.

EThe product should be installed by a professional.


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