Early B6 and B3 differences?

[Advancedynamix]

For those who have had both engines torn down, what are the differences between the early B6 (BF 323/tracer) and the Festiva B3?

Can I use a B6 crank, rods and Pistons in a bored out B3 to make a B6? Can I make a roller rocker B6 with an aspire head? are the blocks cast differently? Are the heads different?

Reason I ask, I have a brand new short nose B6 crank, bearings, seals gaskets and a B3 engine in need of rebuild. I can get early B6 engines fairly easy, but it'll cost about the same to just buy new pistons and have the B3 block bored if that's all I need to do, and I'd rather use an aspire head anyway, so it makes no sense to buy a B6 engine. The engine won't be for all out HP, just a better mill for the Auto Festiva (Low end TQ increase is the goal here). It may get a turbo at some point, but again just for drivability (pulling steel hills on the freeway in third at speed).

Thanks for any advice, I did a search but didn't find anything about this.

[eurotiva]

FestyBoy is the guy to talk to on this

[drddan]

Festyboy does know the most of anyone I can think of, but I can give some limited notes on said subject.

I believe cams and cranks will interchange. The B6 is a bored out B3, but my B6 block has a few extra strenghtening ribs on the outside of the block, that the B3 does not have.

As far as I know almost everything will interchange.

[Advancedynamix]

Good to know. So it may be worth getting a B6 block, if Mazda thought the block needed more strength. What is the difference between a B6 sohc block and the B6 dohc block? Will the 8v head bolt to the b6d block? I have some B6D blocks. I haven't had any of the SOHC engines torn down, definitely a Mazda sohc nube. Thanks for the help guys!

[zoe60]

I don't think it will work. I've had the heads off of a B3 and a B6 and you'd have to bore about 3/8" off the B3 cylinders to make a B6 out of it. I'm pretty sure it doesn't work that way. You'll probably need to find a B6 block.
I think you could just use the rockers and cam out of an Aspire easy enough. Wouldn't use the head though, it's not matched up to a B6. I've though about switching to the Aspire cam and rockers myself. just need to do something about my fuel pump (carb). Someone tell me if I'm wrong.

[Safety Guy]

I've read here in the past that the B3 block can't be safely bored to B6 piston dimensions.

They are the "same block" in "engine block family" only, I think.

Karl

[FB71]

not enough material in the B3 cylinder walls to machine out 7mm. I think it was MattDickMeyer that had posted a B3 cut-away.

[blkfordsedan]

The B6 and B3 crank are the same stroke and the main journals are the same diameter, however, the rod journals are different. Not sure which is larger, but you could look in a bearing book to find out. Also, the connecting rods are a different length between the B3 and B6. I believe the B3 rods are slightly longer, and consquently the B3 pistons have a slightly lower compression height. Since the 71mm B3 block can't be safely bored out to a 78mm B6 (7mm = approx .276"), there really is not much "mix-n-match" you can do between them. I've barked up that tree already, LOL.

That said, my next project will be to try something different. I think I can use a stock bore B6 block, a B3 crank and rods and a set of +1mm over pistons from an early Mazda GLC 1.5L. With a little work, I think I can assemble a B6 with the same longer rod-to-stroke ratio as a B3. May be a better option for pistons, but I haven't gotten too deep in the search yet.

[Movin]

The B6 and B3 crank are the same stroke and the main journals are the same diameter, however, the rod journals are different. Not sure which is larger, but you could look in a bearing book to find out. Also, the connecting rods are a different length between the B3 and B6. I believe the B3 rods are slightly longer, and consquently the B3 pistons have a slightly lower compression height. Since the 71mm B3 block can't be safely bored out to a 78mm B6 (7mm = approx .276"), there really is not much "mix-n-match" you can do between them. I've barked up that tree already, LOL.

That said, my next project will be to try something different. I think I can use a stock bore B6 block, a B3 crank and rods and a set of +1mm over pistons from an early Mazda GLC 1.5L. With a little work, I think I can assemble a B6 with the same longer rod-to-stroke ratio as a B3. May be a better option for pistons, but I haven't gotten too deep in the search yet.

A better rod ratio will really help these tight heads to breath!! You are
really on to something here!!

[blkfordsedan]

Yes, several advantages to a longer rod. Some disadvantages as well, but I think it would be fun to build and mess with.

[Advancedynamix]

Hmmm, a long rod b6. I like it.

Thanks for the info guys. That helps a lot. Does anyone know if an 8 valve B6 head will work on a Dohc1.6 block? That would save me the trouble of a day getting another block at the yard.

[gauge_half_inch]

I know the early Miata dohc head gaskets match up perfectly to the b6 sohc block and head. They use the same bearings throughout.

[Advancedynamix]

Nice! That's good to know. That means that I can most likely use a b6d block to build a b6. And since I'll eventually turbo the b6 that gives me oil squirters and provisions for turbo oil and water supply.
so, has anyone put the aspire rockers and cam in a b6 8 valve head? What are the differences between the early B6 head and the Aspire b3 head?

[blkfordsedan]

I suppose the only issue with a SOHC head on a DOHC short block would be the pistons. Obviously, you have potential valve relief issues....but I was thinking the pistons were also different in terms of compression height and dish volume. I can look in my Sealed Power catalog tonight and see what the differences are. IIRC, the B6D pistons had a much lower CD and more dish volume.....but I'm not positive. Worst case, you could use the B6D block and crank and B6 SOHC rods and pistons (if B6 pistons won't fit B6D rods that is).

The Aspire cam & roller followers should fit in the B6 SOHC head, from what I've heard. I'm sure someone has done it already. As far as the heads go, manifolds will interchange (early B6 only) but the B6 SOHC head has larger ports, valves and chambers when compared to a B3.

[gauge_half_inch]

The b6 sohc rods have press type pins IIRC the B6D have floating pins.