DOHC B6 Information

[Advancedynamix]

If you ever do dig into it, I'd love to see what it's made of. Most likely a grab bag of other Mazda bits. The Capri b6d oil pan is baffled as well, but it's deeper (I think, but feel free to correct me) than the b3 pan.
Would (or have?) You please take some close up and detailed pictures of this rare gem of an engine and it's associated parts? Are you driving the gtx to madness?

[F3BZ]

well if your home is near my home it's out in the front yard and the hood is unlatched so feel free. as long as it runs good i have no plans to dig into it. it may be difficult to even source a valve cover gasket. a lot of parts are unique to the 1.3 BJ that do not cross to a B6D or B3. even the oil pan is different but that may just be baffled. the bore is the same as the B6D (78.0mm) and uses the same rings but the pistons are unique. some specs from wikipedia and other sources:
BJ - 87hp @ 7000 rpm. 72 ft/lb @ 4500 rpm. 78.0mm bore x 67.5mm stroke. 4.058 final drive ratio
B3 - 63hp @ 5500rpm. 75ft/lb @ 3500rpm. 71.0mm bore x 83.6mm stroke. 3.777 final drive ratio

[jhntu]

I've never seen one in person, but by the pictures and specs it looks like a b6d (Capri/Laser) with either a shorter stroke or smaller bore. I can't remember which is different. A destroked b6d would be fun in these cars, but probably not worth the effort because the 1.6 seems to work great with the stock transmission and clutch. I've been driving mine around all week on the 4 speed and it makes enough TQ everywhere to make the car very easy to drive, but not so much that it's hard to manage.
The benefit to a shorter stroke b6 dohc engine would be an improved rod ratio ( especially if longer rods were used with custom pistons). This would provide a more stable engine which could ( in theory) produce higher usable HP levels than the b6. I would like to build a destroked z series engine to test this, rather than a b series though. That's a topic for another thread.

Paging f3bz

[Advancedynamix]

Ever been fortunate to investigated a B3 DOHC or no need?

I've never seen one in person, but by the pictures and specs it looks like a b6d (Capri/Laser) with either a shorter stroke or smaller bore. I can't remember which is different. A destroked b6d would be fun in these cars, but probably not worth the effort because the 1.6 seems to work great with the stock transmission and clutch. I've been driving mine around all week on the 4 speed and it makes enough TQ everywhere to make the car very easy to drive, but not so much that it's hard to manage.
The benefit to a shorter stroke b6 dohc engine would be an improved rod ratio ( especially if longer rods were used with custom pistons). This would provide a more stable engine which could ( in theory) produce higher usable HP levels than the b6. I would like to build a destroked z series engine to test this, rather than a b series though. That's a topic for another thread.

[jhntu]

Ever been fortunate to investigated a B3 DOHC or no need?

[Advancedynamix]

Okay, so I have been informed (thanks goes to Rocketman) that the MX3 b6D is a totally different animal. I have only ever seen 1 close up and it was years ago and I barely remember it. The MX3 b6D uses a different head all together. It seems to use the same head as seen on the DOHC B5 engines. That also clears up the B5 confusion. I have not actually had my hands on any of these parts, and would like for someone who has to chime in or at least PM me with some specifics. Meanwhile, I'm looking of one of these engines to play with.

EDIT: After doing some research, it looks like the block is also different. The MX3 B6D uses a block that looks like the z series block. It has more ribs and no crank vent. This seems to have been a transition engine from the B to the Z series.

[Advancedynamix]

Harmonics crack hardened steel parts, like gears and oil pump internals. Increasing the torque levels will often amplify these harmonics, but most of these shattered oil pumps have been on engines with lightweight under drive accessory pulleys and lightened flywheels. Lightened flywheels and lack of any harmonic balancer or dampener will lead to problems down he road. Also, a lot of these cars have stiffer engine and tranny mounts, which further amplifies these issues. That is all besides the point, but since we are talking B series engines, it is important to discuss the facts about where fatigue originates. TQ loads alone are rarely the cause of many of the drivetrain failures that plague these cars. Harmonic shock is what causes stress fractures to develop in hardened steel parts. Once the stress fractures spread deep enough into the part, it will fail. Hardened steel parts are more brittle than non hardened parts, so they are more susceptible to the harmonic shock loads. Also, Hardened steel parts often amplify certain frequencies, rather than dampen them. This is a reason why materials like 4140 are not ideal for flywheels, because hardened 4140 does a poor job at absorbing harmonics.

[bhearts]

The oversize valves are being tested shortly. I do believe they are worth the effort. These engines have very small valves. Larger bore will also help with flow because the valve area of the chamber can be relieved more.
They will support 220 stock though. It's been done hundreds of times for over a decade. Visit turbomiata.com for lots of builds. Disregard all the "just go BP" banter. The same guys who push that also think Mazda makes bad oil pumps that explode from engine TQ. As if that makes any sense at all.

"This or big F/I power pulses are what explodes oil pumps" torque kills oil pumps?

[bhazard]

I think euro runs a super 60, or maybe just a "regular" 60.

[Advancedynamix]

iirc the 16g setups usually net around 200hp on the miatas with an FMU and injectors, but I haven't looked at that stuff in awhile. A gt2560r will get you past that 220 mark. I don't know about the 20g on a b6d, but I'm sure it's been done before.

[Advancedynamix]

The oversize valves are being tested shortly. I do believe they are worth the effort. These engines have very small valves. Larger bore will also help with flow because the valve area of the chamber can be relieved more.
They will support 220 stock though. It's been done hundreds of times for over a decade. Visit turbomiata.com for lots of builds. Disregard all the "just go BP" banter. The same guys who push that also think Mazda makes bad oil pumps that explode from engine TQ. As if that makes any sense at all.

[bhearts]

I was looking at those 16g turbos today. And the 20g

[Advancedynamix]

What's the order of operation for keeping these engines reliable at 20+ psi? Are OS valves worth it? More than just a mild head port? Are pistons and rods even with it at 220hp levels?

That's like asking if a beagle is a good dog for a single mom. There are so many ways to make and use 20psi. Same goes for 220hp. I can tell you that the b6t is easy to destroy with more than 15psi on a rhb5 vj turbine. 190hp is the most I would run on that setup. But, a stock b6d bottom end will take 220+ ft.lbs of tq with no issues if the system is designed right. The miata community has had good luck with the 16g and the gt28r. Even a good old super 60 with an external gate will get you 220.

[bhearts]

"Doing it right"the first time can get really expensive quick. Because I couldn't stop any mods from getting done. Race port job, sure. Super balancing of assembly, definitely

[bhearts]

What's the order of operation for keeping these engines reliable at 20+ psi? Are OS valves worth it? More than just a mild head port? Are pistons and rods even with it at 220hp levels?