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1.8L 16v - BP
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1.8L 16v - BP
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Set of 8 reinforced inlet valves for MAZDA MX-5 and 323 BP 1.8.
The BP is a 1.8-litre four-cylinder with twin camshafts and 16 valves. It powered the 323 BG from 1989 to 1994, including the four-wheel-drive turbo versions and the GT-R, then the 323 BA and BW, as well as the MX-5 NA from 1993 and the NB until 2005, naturally aspirated or turbocharged.
The engine has 8 inlet valves, two per cylinder. More boost, a sharper camshaft or a higher rev limit load them more every time they open.
An inlet valve brings in the fresh charge, drops back onto its seat every cycle and slides constantly in its guide, at 400 to 550 °C. A standard chrome-silicon steel falls there from 500 MPa at 500 °C to 250 MPa at 600 °C: it loses 50 % of its strength.
The SUPERTECH valves are black nitride stainless steel, a treatment that hardens the stem surface and limits its wear in the guide. At standard size they come in a high flow and a standard flow version; at +1 mm, with a stellite seat or an extra hardened seat.
At +1 mm the head grows from 33 to 34 mm for the same length: air flows past the seat more freely, the cylinder fills better and the engine gains power, once the 8 inlet seats are machined to that diameter.
| Part number | Brand | Size | Head Ø | Stem Ø | Length | Grooves | Material |
|---|---|---|---|---|---|---|---|
| MAIVN-1204-8 | SUPERTECH | Standard | 33 mm | 5.97 mm | 102 mm | Black nitride stainless steel | |
| MAIVN-1208-8 | SUPERTECH | Standard | 33 mm | 5.97 mm | 102 mm | Black nitride stainless steel | |
| MAIVN-1206-8 | SUPERTECH | +1 mm | 34 mm | 5.97 mm | 102 mm | Black nitride stainless steel | |
| MAIVN-1206-HN-8 | SUPERTECH | +1 mm | 34 mm | 5.96 mm | 102 mm | Black nitride stainless steel |
MAIVN-1204: high flow, thinned under the head and profiled on the back. MAIVN-1208: standard flow.
MAIVN-1206: +1 mm, stellite seat. MAIVN-1206-HN: +1 mm, extra hardened seat, 5.96 mm stem.
| Part | MAZDA original | Reinforced |
|---|---|---|
| Collets | ||
| Valve stem seals | VS-TS6I-8 | |
| Valve guide |
The VS-TS6I-8 inlet valve stem seals match the 6 mm stem of the BP valves.
With a 33 mm head the inlet seats stay at their factory size; with 34 mm the workshop machines all 8 seats.
 | Founded in California, SUPERTECH Performance has worked for more than thirty years on valves, springs and guides for racing engines. Its parts are checked by ultrasound, X-ray and laser before they are delivered to engine builders. |
The groove is the recess at the end of the stem that takes the collets holding the upper retainer. On the BP the choice comes down to size, then version:
| Criterion | Option 1 | Option 2 |
|---|---|---|
| Size | Standard, 33 mm Seats kept. MAIVN-1204-8 (high flow), MAIVN-1208-8 (standard flow). | +1 mm, 34 mm 10 to 12 cfm more per mm of head, seats machined; also restores seats already reground. MAIVN-1206-8, MAIVN-1206-HN-8. |
| Seat (+1 mm) | Stellite seat MAIVN-1206-8. | Extra hardened seat MAIVN-1206-HN-8. |
| Model | Engine code | Power | Years |
|---|---|---|---|
| 323 C IV (BG) 1.8 16V 4WD, Turbo 4WD, GT-R 4WD | BP / BP Turbo | 103-209 hp | 1989-1994 |
| 323 S IV (BG) 1.8 16V Turbo 4WD | BP Turbo | 163 hp | 1991-1994 |
| 323 C V, 323 F V (BA) 1.8 16V | BP-ZE | 114-135 hp | 1994-1998 |
| 323 S V (BA) 1.8 16V | BP-ZE | 114 hp | 1994-1998 |
| 323 III Station Wagon (BW) 1.8 | BPF1 | 125 hp | 1992-1998 |
| MX-5 I (NA) 1.8 | BP-ZE / BPF1 | 130-135 hp | 1993-1998 |
| MX-5 II (NB) 1.8, 1.8 16V, 1.8 i | BPD / BP5A / BP6J / BP-ZE / BP4W | 139-154 hp | 1998-2005 |
| MX-5 II (NB) 1.8 SE i Turbo, 1.8 i Turbo | BP Turbo / BP8K | 165-214 hp | 2002-2005 |
With the BP cylinder head off, replace its 8 exhaust valves as well:
| MAZDA MX-5 1.8 BP exhaust valves → |
