Tweet
Over the past 4 years I have taken the opportunity to tear down and rebuild just about every variation of DOHC b6 engine. I've gotten the chance to race them, daily drive them and blow them up a couple of times. With the help of friends and forum members I have learned a lot of tricks to these engines and I have gathered a list of why they make such great donor engines for the Festiva. I figured this would be a good topic for a thread and it will clear up some common misunderstanding.
The DOHC B6 engines came in the following vehicles for the North American market.
1986-1989 Mazda 323 GT- B6T
1986-1989 Mazda 323 GTX- B6t
1994-1998 Mazda MX3- B6D
1989-1993 Mazda Miata- B6ZE
1991-1994 Mercury Capri- B6D
1991-1994 Mercury Capri XR2- B6T
Here is a list of quick facts about the DOHC B6 engines that are relevant to swapping them into a Festiva.
#1. The b6 DOHC engine block is essentially identical to a b3 block on the outside. That means all the stock festiva parts will bolt right up to the block, just like they did the b3. The only reason a custom engine mount needs to be used is because the DOHC timing belt and respective covers get in the way of the stock festiva mount. This can be solved by spacing the mount back from the block 1 3/8" and modifying the stock mount to compensate for the spacers. If a transmission swap is being done at the same time as an engine swap then you can use the stock engine mount with the spaced bracket and then move the transmission mounts to compensate. That means that there is no point in putting a 16V head on a b3 to make things easier, because you will run into the same problems as with the DOHC b6. You do not need to clearance the frame rails of a Festiva to run a DOHC B6 engine. It fits like the b3 Did other than the bulkier timing covers. The DOHC engines use a different water pump than the B3, but the b3 water inlet bolts right up to the DOHC water pump.
#2 All of the B6 DOHC engines use the same exact block and head. They all use the same crank and all use the same rods except the 323 gtx b6t which has heavier rods. The capri and 323 gt rods are the same as the Miata.
#3 The DOHC B6 engines are an easy swap into a Festiva, and they are a huge upgrade over the b3. These engines have much stronger components than the b3, they have a stronger crankshaft, stronger block, oil squirters to cool the pistons, stronger rods and pistons and a head that will outflow even the wildest port job on a B3, without sacrificing low rpm port velocity. These engines make a minimum of 40 more HP than a B3 in stock form and the B6t makes 80 more HP stock.
Here is a list of some other differences between the DOHC B6 engines.
Oil Pans: The b6d uses a baffled steel oil pan. It is a nice upgrade for a B3 and will bolt right up, but is deeper than a b3 pan and has a nice 2 level baffle. The b6T uses an aluminum pan with a single row baffle, it has 2 return ports in it. The b6ZE uses an aluminum oil pan with a windage tray and a baffle, but it can't be easily used in a transverse mounted setup (not a good FWD choice). The b6ZE dip stick tube is in the oil pan and the other B6 engines have the dipstick in the oil pump housing. The oil pumps are the same, the Miata/ B6Ze just has a removable plug where the dipstick goes in the other engines. The rear main seal plate is different depending on if the engine has a steel oil pan or aluminum. The pickup tubes are different for each application. Use the pick up that goes with the pan you are using.
Cranks: All the DOHC B6 variants use the same crank, but there are two common versions (just like all the other Mazda B series engines). The small nosed crank came in engines produced before the middle of 1992, and the big nosed crank came in engines produced after mid year 1992. The oil pumps are different for each, as are the front pulleys. There is no difference in clutches or flywheels. There is also a very very rare long nosed version of the small nosed crank. It was a factory fix to the problems that mazda was having with the small nosed crank and the chances you'll ever find one are rare.
Pistons: The B6D and B6ze share pistons. The automatic versions of both engines have 9:1 compression, whereas the manual transmission versions have 9.4:1 compression. The B6t has deep dished 7.9:1 compression pistons.
Camshafts. All the engines share Intake Camshafts, but the exhaust camshafts vary from Automatic transmission, manual transmission and Turbocharged. From my personal testing, I do not recommend using an automatic exhaust camshaft in a B6t, especially in a Festiva. The slight improvement in low end isn't noticeable in such a light car and the auto cam chokes the engine at higher RPM and can promote detonation under higher than factory boost levels.
Manifolds: The B6T and B6D use the same intake manifold, but different exhaust manifolds. the B6ZE is placed longitudinally in the Miata, and it's manifolds require extensive modification to fit into a Festiva. The B6D can be used with a stock Festiva intake pipe and air box, but the idle conrol valve is on the other side of the manifold and will require some creative routing to work properly. The Mx3 B6D uses a different intake manifold than the rest of the DOHC B6 engines, but it is quite large and doesn't fit well into a Festiva without moving the engine forward or modifying the firewall.
B6D MX3 cars are very rare. The head design is different than the other DOHC b6 engines. The block is also slightly different. The mx3 b6d is sort of an evolution engine between the small block b series engines and the Z series engines that followed.
Engine management: All the different variants use different engine management. They are all Denso versions of the Bosch L- Jetronic system. The B6T management is the most advanced, with Barometer sensing, Knock control and a true throttle position sensor, it was extremely advanced for it's 1985 release date. The Miata B6ZE management uses a wasted spark twin coil ignition with a cam angle sensor, rather than a distributor. Though this system looks more advanced and modern, it is actually not really an advantage. The B6ZE system is the closest in similarity to the stock B3 management from 1990 to 1994. They both use many of the same connectors and plugs. The B3 management system will run a DOHC B6 engine with some very simple modifications.
Valve Cover: The B6T and Capri B6D use the same valve cover. The Mx3 B6d uses it's own unique valve cover and the B6ZE uses it's own valve cover. The Miata B6ZE valve cover can not be used with the Capri intake manifold because it sits to high. I assume the Mx3 valve cover has the same problem, but I haven't tried one to tell you for sure.
I will further update this thread with pictures of these engines and examples of ways to fit them into a Festiva.
The DOHC B6 engines came in the following vehicles for the North American market.
1986-1989 Mazda 323 GT- B6T
1986-1989 Mazda 323 GTX- B6t
1994-1998 Mazda MX3- B6D
1989-1993 Mazda Miata- B6ZE
1991-1994 Mercury Capri- B6D
1991-1994 Mercury Capri XR2- B6T
Here is a list of quick facts about the DOHC B6 engines that are relevant to swapping them into a Festiva.
#1. The b6 DOHC engine block is essentially identical to a b3 block on the outside. That means all the stock festiva parts will bolt right up to the block, just like they did the b3. The only reason a custom engine mount needs to be used is because the DOHC timing belt and respective covers get in the way of the stock festiva mount. This can be solved by spacing the mount back from the block 1 3/8" and modifying the stock mount to compensate for the spacers. If a transmission swap is being done at the same time as an engine swap then you can use the stock engine mount with the spaced bracket and then move the transmission mounts to compensate. That means that there is no point in putting a 16V head on a b3 to make things easier, because you will run into the same problems as with the DOHC b6. You do not need to clearance the frame rails of a Festiva to run a DOHC B6 engine. It fits like the b3 Did other than the bulkier timing covers. The DOHC engines use a different water pump than the B3, but the b3 water inlet bolts right up to the DOHC water pump.
#2 All of the B6 DOHC engines use the same exact block and head. They all use the same crank and all use the same rods except the 323 gtx b6t which has heavier rods. The capri and 323 gt rods are the same as the Miata.
#3 The DOHC B6 engines are an easy swap into a Festiva, and they are a huge upgrade over the b3. These engines have much stronger components than the b3, they have a stronger crankshaft, stronger block, oil squirters to cool the pistons, stronger rods and pistons and a head that will outflow even the wildest port job on a B3, without sacrificing low rpm port velocity. These engines make a minimum of 40 more HP than a B3 in stock form and the B6t makes 80 more HP stock.
Here is a list of some other differences between the DOHC B6 engines.
Oil Pans: The b6d uses a baffled steel oil pan. It is a nice upgrade for a B3 and will bolt right up, but is deeper than a b3 pan and has a nice 2 level baffle. The b6T uses an aluminum pan with a single row baffle, it has 2 return ports in it. The b6ZE uses an aluminum oil pan with a windage tray and a baffle, but it can't be easily used in a transverse mounted setup (not a good FWD choice). The b6ZE dip stick tube is in the oil pan and the other B6 engines have the dipstick in the oil pump housing. The oil pumps are the same, the Miata/ B6Ze just has a removable plug where the dipstick goes in the other engines. The rear main seal plate is different depending on if the engine has a steel oil pan or aluminum. The pickup tubes are different for each application. Use the pick up that goes with the pan you are using.
Cranks: All the DOHC B6 variants use the same crank, but there are two common versions (just like all the other Mazda B series engines). The small nosed crank came in engines produced before the middle of 1992, and the big nosed crank came in engines produced after mid year 1992. The oil pumps are different for each, as are the front pulleys. There is no difference in clutches or flywheels. There is also a very very rare long nosed version of the small nosed crank. It was a factory fix to the problems that mazda was having with the small nosed crank and the chances you'll ever find one are rare.
Pistons: The B6D and B6ze share pistons. The automatic versions of both engines have 9:1 compression, whereas the manual transmission versions have 9.4:1 compression. The B6t has deep dished 7.9:1 compression pistons.
Camshafts. All the engines share Intake Camshafts, but the exhaust camshafts vary from Automatic transmission, manual transmission and Turbocharged. From my personal testing, I do not recommend using an automatic exhaust camshaft in a B6t, especially in a Festiva. The slight improvement in low end isn't noticeable in such a light car and the auto cam chokes the engine at higher RPM and can promote detonation under higher than factory boost levels.
Manifolds: The B6T and B6D use the same intake manifold, but different exhaust manifolds. the B6ZE is placed longitudinally in the Miata, and it's manifolds require extensive modification to fit into a Festiva. The B6D can be used with a stock Festiva intake pipe and air box, but the idle conrol valve is on the other side of the manifold and will require some creative routing to work properly. The Mx3 B6D uses a different intake manifold than the rest of the DOHC B6 engines, but it is quite large and doesn't fit well into a Festiva without moving the engine forward or modifying the firewall.
B6D MX3 cars are very rare. The head design is different than the other DOHC b6 engines. The block is also slightly different. The mx3 b6d is sort of an evolution engine between the small block b series engines and the Z series engines that followed.
Engine management: All the different variants use different engine management. They are all Denso versions of the Bosch L- Jetronic system. The B6T management is the most advanced, with Barometer sensing, Knock control and a true throttle position sensor, it was extremely advanced for it's 1985 release date. The Miata B6ZE management uses a wasted spark twin coil ignition with a cam angle sensor, rather than a distributor. Though this system looks more advanced and modern, it is actually not really an advantage. The B6ZE system is the closest in similarity to the stock B3 management from 1990 to 1994. They both use many of the same connectors and plugs. The B3 management system will run a DOHC B6 engine with some very simple modifications.
Valve Cover: The B6T and Capri B6D use the same valve cover. The Mx3 B6d uses it's own unique valve cover and the B6ZE uses it's own valve cover. The Miata B6ZE valve cover can not be used with the Capri intake manifold because it sits to high. I assume the Mx3 valve cover has the same problem, but I haven't tried one to tell you for sure.
I will further update this thread with pictures of these engines and examples of ways to fit them into a Festiva.
Comment