Reinforced valve spring kit Mazda MX-5 1.8 BP

Mazda MX-5 1.8 BP engine covered

The BP is Mazda's 1.8 litre four-cylinder with 16 valves and twin overhead camshafts. It powers the MX-5 (Miata) NA 1.8 from 1993, then the whole 1.8 range of the NB until 2005, turbo versions included.

The kit replaces the original springs together with their upper retainers and lower spring seats; only the factory collets stay in place.

SUPERTECH reinforced valve spring kit

When the lobe has done its work, the spring brings the valve home on its seat. Up in the rev range a valve is slow to stop: too little load and it bounces, lands late, can strike the piston (valve float).

Seat pressure: 334 N at 33.6 mm (SPRK-1012-M18D), 374 N at 33.6 mm (SPRK-MM18-D), 249 N at 34.2 mm (SPRK-MM18-S, single springs).

Valve spring kit technical specification

Valve spring kit fitting details

Each of the three SUPERTECH kits holds 16 springs, 16 RET-TS60/MA2 upper retainers and 16 SEAT-TS/MA18I lower spring seats; the original collets are kept. Two kits carry double springs, the third a single spring.

The installed height is the fitted spring's length with the valve closed, measured between its two seats. Each seat pressure given is valid at that length only: raise it, say after machining the head, and the load eases off following the rate of the spring. Heights and pressures of all three kits are grouped in the table below.

Technical guide

Our brands

SUPERTECH is a California company, in business for over thirty years, that specialises in racing parts for the cylinder head. Its spring wire is a chromium, silicon and vanadium alloy, and every batch undergoes X-ray, ultrasonic and laser checks before it is shipped to customers.

How to choose

Firmer springs press the valve onto the cam at engine speeds the original fitment cannot sustain: the limiter can be raised, a livelier camshaft chosen or a turbo added without the valve floating. The three kits give 334 N, 374 N and 249 N at the seat, at the heights listed in the table above. One limit applies: cam lift must stay under the maximum lift of the double-spring kits, 13.6 mm for the SPRK-1012-M18D and 12.9 mm for the SPRK-MM18-D; SUPERTECH publishes no such value for the single-spring kit, so ask us before pairing it with an aggressive camshaft.

When reinforced springs become necessary

• Camshafts lifting higher than the original ones
• Revs ceiling to push higher
• Turbo or supercharger added to the BP
• Cylinder head overhauled for circuit, drift or rally
• Tired springs, floating before the limiter

Compatible vehicles

Related products

Head already off? Have valves and guides checked too, to save a second teardown. The pages below lead to the BP's inlet and exhaust valves: