B6 Headers, etc. - Not a rehash

[MazdaNut]

I'm working on building a B6 SOHC for an autocross project car. Before you say "Get a BP", let me just nip that in the bud: 1) I have a B6-ME in my shed so it costs me nothing, and 2) It's the best engine legal for my car/class (Mazda GLC running EP). Well maybe not the best - the 8v SOHC actually has parts available - but I don't have one of those.

The part that may interest the most people is that I've discovered a header that should be relatively easy to adapt to this engine. It also looks like it may fit the DOHC B6 even better, but I'll let someone else do the legwork on that one. This particular header is readily available in a variety of cost/quality levels in both n/a and turbo form. The one I plan to get will be under $60.

Other plans include fitting a rack of Mikunis (because I have some I got for free), swapping in a set of 9.4:1 Miata pistons (you guessed it...), and possibly even doing something with the valvetrain. I have discovered that the B3 SOHC 16V engine (available everywhere - else) had solid lifters. In researching the engine's specs, it looks like the cam has a bit more lift, but slightly less duration. I'm still deciding whether or not that will help.

So there it is. Comment away, good or bad. Just don't tell me to get a BP. I promise you progress will be slow, but I'll try to keep this post updated as I go. When I reach my 30 posts, I can advertise the brand new B6 block and the used DOHC B6 head I have for sale. Since I'm working with a net zero budget, that would sure help move things along.

Thanks

[MazdaNut]

Here's a quick look at the gasket match on the headers I'm looking at.

The SOHC match. Will require minor porting of the manifold flange, drilling the bottom holes, and a flat bar to clamp across the top.


The DOHC match is even better. Most of the bolt holes could just be hogged out, with 3 bottom holes drilled. Looks like no porting would be required, due to the DOHC ports not being as wide as the SOHC. Both have lots of anti-reversion.

[myfirstmazda]

I'm curious abut the specs on that b3 cam... can you post up the specs for both b6 and b3?

[MazdaNut]

The numbers are as follows:

B6-ME
Intake Lobe 1.4106
Exhaust Lobe 1.4039
Intake open/close 5/52 BTDC/ABDC
Exhaust open/close 52/5 BBDC/ATDC
Duration 237d

B3-ME
Intake Lobe 1.438" (+.0274 lift)
Exhaust Lobe 1.4304" (+.0265 lift)
Intake open/close 5/40 (-12d duration)
Exhaust open/close 40/5 (-12d duration)
Duration 225d

There's an entry in a forum where a guy in Israel did the swap and was happy with the results. The cam and rocker arms are required. I haven't had much luck so far finding a source of these parts, but I'm looking. Eventually, a custom regrind would be nice, along with larger valves, heavier springs, etc. But we're talking money there. Keeping the hydraulic tappets may be better in that case.

[myfirstmazda]

thanks for the post, sounds like maybe a custom grind would be better though.

[Gunny1162]

So have you been able to get header that works with little modification to the header yet?
Can you offer me some advise on how to build up my b6me for more performance? I have acess to a machine shop to do alot of what might need to be done. Thanks

[MazdaNut]

All I've got at this point is plans. My plans are for a high-compression normally-aspirated carbureted engine
which will be used for racing only. I don't know what your goals and constraints are.

The header that I plan to use is from either the '02-'06 Mitsubishi Lancer 2.0L (4G94?) or the '97-'02 Mirage 1.8L.
From what I can tell, both have the same head flange. There are several vendors on eBay offering headers.
The one I'm looking at is eBay #180504266892. I'm not saying this is the most optimum header possible, but
anything will be an improvement over stock. And they are really cheap. You can also get a good turbo manifold
from Road/Race, incidentally. Like I said, some porting, drilling, and a little creativity should get the job done.

The intake side actually looks pretty good if you're sticking with fuel injection, but I plan to run a brace of Mikuni
bike carbs on a custom cobbled-up manifold. Yes, I expect tuning to be difficult.

A set of 1.6L Miata (manual trans) pistons should bump the compression ratio up. The pin is different, so
you'll need the rods as well. Shaving the head and/or block will raise the compression further. Shaving too
much, however, will retard the valve timing and require some type of adjustable cam pulley.

Larger valves would go a long way. I haven't pulled the head off yet to see if this is feasible. The ports
are way too big for the size of the valves, it seems to me.

One of the most effective mods would be a more aggressive cam. Since it would be 100% custom, this
may prove tricky to get right the first time.

And like many here will tell you, when It's all said and done, you would get more power from a stock BP.

[Pure-Powder]

Here are the makings of a Header Flange I cut on my cnc plasma table.. I will probably get a 2.0l Probe header and cut the flange off and tig weld on my flange.

[MazdaNut]

That makes me sick. "Look what I did on my CNC plasma cutting table!" If I had one of those, I would have built a car from scratch by now.
Is there a smiley for "I'm really envious and just pretending to be disgusted"?

Anyway. I got the engine torn down, and discovered severe rust in cylinders 2&3. So I'll end up needing that new spare block after all. It is from a DOHC MX-3, but it will work. It even has the piston squirters, which I'm not sure I'll need. The crank looks good. One question I have is can you swap main bearing caps around, or is that something that has to stay where they came from the factory? For some reason, the MBSP (main bearing support plate) is not bolted to the center main cap. I was thinking of using one of the caps with the bolt holes from the old engine so I could bolt the center cap down as well. Maybe the factory left it unsupported for a reason? I dunno.

I have the Miata pistons, but I'm looking at some high-CR motorbike pistons and Honda rods. I've got to sell some stuff before I can go much further.