The Mazda B6 and BP Engine Guide

When multi-valve technology and turbochargers combined forces in the late ‘80s, Mazda was leading the way. Their B6 and larger BP series engines combine sophistication with excellent torque and power for the cubic capacity and, not surprisingly, they performed well in contemporary Group A rallying.

In this article we’ll look at this largely forgotten range of hi-po fours.

B6 Engines

The first truly high performance Mazda B-series four appeared in 1987 with the release of the BF-series Familia GT-X.

The ’87 Familia GT-X is powered by the base B6 1.6-litre engine design (a 78mm bore and 83.6mm stroke) having a relatively low 7.8:1 static compression ratio, DOHC four-valve-per-cylinder head, IHI turbocharger, air-to-air intercooler and multi-point injection. This engine comes alive above about 3000 rpm and delivers a 186Nm punch at 5000 rpm. Peak power is 103kW when running premium unleaded fuel. The B6 DOHC turbo is arranged for transverse mounting and comes attached to a five-speed manual gearbox delivering drive to either the front wheels or all four.

The Familia GT-X was released locally as the 323 Turbo and a Ford TX3 twin was also available. Interestingly, the top-line Ford Capri soft-top was also available with the B6 turbo donk. Note that the local cars are rated at 100kW when using normal unleaded fuel.

A naturally aspirated version of the DOHC B6 was available in the 1989 released Eunos Roadster (aka MX-5 and Miata). With a 9.4:1 compression ratio, the Roadster’s B6-ZE engine is arranged for longitudinal mounting and delivers drive to the rear wheels. Manual or auto transmissions are available. Output is 88kW and 137Nm at 6500 and 5500 rpm respectively. Note that the atmo B6 DOHC was available in the base-spec Eunos Roadster until 2005. Australian-spec versions make 85kW and 130Nm.

Atmo DOHC and SOHC versions of the B6 were also fitted to the FWD Ford Capri, Laser and 323. But, really, you’re better off with a later model and larger cube BP engine...

BP Engines

In late 1989 Mazda introduced the BP 1.8-litre engine.

The then newly released BG series Famila hatch was available in turbo GT-X guise boasting the new BP turbo engine. The BP uses similar design to the B6 but larger bore and stroke dimensions (83 x 85mm respectively) increase the swept capacity to 1839cc. A DOHC, four-valve-per-cylinder head, multi-point injection, knock sensor, 8.2:1 static compression ratio, air-to-air intercooler and electronically controlled boost pressure give the little 1.8 good torque and power. In Japanese guise, the BP turbo engine punches out 132kW at 6000 rpm along with 237Nm at an accessible 3000 rpm. Premium unleaded fuel is required to generate this sort of grunt – expect slightly less on normal unleaded fuel. This engine comes attached to a standard five-speed manual gearbox with AWD.

The same spec BP turbo engine was also fitted to the locally delivered KF – KH Ford TX3 AWD turbo. In Australian spec, the engine is rated at 117kW/206Nm – probably due to lower octane fuel.

In early ‘93, Mazda released a 154kW/250Nm BP turbo powered Familia GTR homologation special. And it’s a whole lot more than a higher boosted version... The GTR-spec BP turbo engine was reworked by Mazda's Motorsport Engineering Group and features reshaped combustion chambers, raised piston crowns (maintaining the GT-X's 8.2:1 compression ratio), stronger rods, a water-to-oil cooler, larger sodium filled valves, more aggressive camshafts, minor cylinder head mods and a match-ported intake manifold. A larger capacity ball-bearing turbocharger, a 70 percent larger intercooler and more boost are also added. Of course, ECU mapping is optimised to suit and we believe the airflow meter and fuel pump were changed. These mods delivered those 154kW and 250Nm maxima at 6000 rpm and 4500 rpm respectively (much later than the GT-X spec BP turbo engine). Again, a five-speed AWD gearbox comes fitted but the GTR ‘box features shot-peened gears, a strengthened housing and upgraded clutch. Unfortunately, the Familia GTR was produced in very limited numbers.

A high-performance naturally aspirated version of the BP engine was also released in the Japanese Eunos 100, Mazda Astina and Familia GT. The BP-ZE doesn’t score forced induction but it does use a 9:1 compression ratio and can put out 99kW at 7000 rpm and 157Nm at 4500 rpm. Front-wheel-drive four-speed autos and five-speed manuals were manufactured. The same engine was also fitted to the 1994 released Lantis and BH-series Familia (aka 323).

The 1993 updated Eunos Roadster was also released with the atmo BP-ZE making 98kW/157Nm. The biggest difference is this engine is built for longitudinal mounting and delivers drive to the rear wheels.

As far as we’re aware, the Eunos Roadster was the last vehicle to continue using BP engine power. In 1998, the Roadster’s atmo 1.8 was treated to a slightly higher compression ratio (9.5:1), larger ports and valves, a twin-tract inlet manifold (with the switch-over occurring at 5500 rpm), revised exhaust, ECU remap and knock sensor. We believe the cam profiles were also altered. These changes elevated peak power to 106kW at 6500 rpm and torque swelled to 165Nm at 4500 rpm. Normal unleaded is all that’s needed for this engine.

In 2000, the Eunos Roadster received S-VT variable inlet cam timing. These S-VT equipped engines are labeled BP-VE and the variable cam timing mechanism can be identified by a bump in the valve cover at the end of the inlet cam. With an accompanying compression ratio increase to 10:1 (now making premium unleaded recommended), the BP-VE puts out a tidy 113kW at 7000 rpm and 181Nm at 5000 rpm. Japanese versions use a 10.5:1 compression ratio and make about 5kW more on higher octane fuel. A close-ratio six-speed gearbox also stepped in to replace the existing five-speeder.

A return to turbocharged performance was seen in 2002 with the release of the Australian-market MX-5 SP Turbo and, later, the MX-5 SE Turbo.

The Australian MX-5 SP Turbo is a local development which is essentially a turbo kit mounted to the existing 10:1 compression BP-VE engine. The SP Turbo package employs a nickel-alloy cast iron exhaust manifold, a ball-bearing Garrett turbocharger, front-mount air-to-air intercooler, a carbon-fibre airbox, Bosch blow-off valve and large diameter exhaust. Supporting mods include bigger injectors, different spark plugs and an upgraded coolant radiator. The factory ECU has also been re-mapped to suit. With around 0.5 Bar boost, the turbocharged MX-5 SP cranks out 150kW at 6800 rpm and a massive 280Nm at 4600 rpm – that’s 39 percent more power and 60 percent more torque than a contemporary atmo version! This engine is second only to the rally-bred Familia GTR spec BP turbo.

A ‘world market’ turbo version of the MX-5 was released in late ‘03/early ’04. The SE turbo engine has almost identical internals to the atmo version except the static compression ratio is brought down to 9.5:1, the S-VT system is removed and a single scroll turbocharger with a air-to-air intercooler give it a boost. Around 0.5 Bar boost is delivered and breathing is improved with a revised rear muffler. Max output is a relatively mild 121kW at 6000 rpm with 206Nm of torque at 4500 rpm. This engine was discontinued for the all-new 2005 Mazda Roadster which uses a different family engine.

In the Japanese importer yards you’ll find a plentiful supply of ex-Familia GT-X BP Turbo engines available at attractive prices. These are quite strong engines so long as you don’t expect too much from them. If you’re after 200+ kilowatts, the Familia GTR spec BP turbo engine is the one to go for – though these are rare and you’ll pay at least AUD$2000 for the motor alone. The rear-wheel-drive ex-MX-5 turbo engines are the next most attractive engines however, given the modest output of the later model turbo engine, you’d be wise to consider purchasing one of the many off-the-shelf turbo kits to suit an original atmo engine. There are plenty to suit!