So I figured now would be as good a time as any to come out of lurking as any.
My 99 Miata has developed a pretty nasty rod knock and I've been looking for a replacement engine. I've been having trouble finding a reasonably priced 99 long block, so I've been looking at the FWD BP engines. I've found a few lower mile BPs out of a 1st generation Kia Sephia for cheap locally. From what I understand Kia manufactured the BP under license from Mazda. I was wondering if the Kia engine has the forged crank and threaded plug access in the block for turbos like the Mazda engines.
Also, will this swap work for the NB? I haven't found any evidence that anyone has done this.
Any help would be much appreciated!
Look at escort GT's too.
Don't know about the crank/oil plug boss.
The fwd motors have it... your 99 doesn't, actually.
All BPs have forged cranks. Many of the fwd motors have mbsps as well.
That all said...you'll want to stick with the bp4w. Going back to a bp05 is a downgrade, in the head/ignition department.
Is your current head salvageable?
Have you thought about a re-manufactured engine? If you want to keep your Miata for a long time, it may be worth it for a practically brand new engine.
I rebuilt a BP last year that came out of an Escort GT and even with 100 K miles it still had the OEM cross hatch on the cylinder walls with a very, I mean very slight ridge at the top. The crank was just cleaned and reused as is with new bearings. What I'm trying to say is that if the rod bearings are worn it may be as easy as installing new ones to return your engine back to a useable engine. I've done this on other engines as well. A Ford 5.0 and a BBC.
In reply to Swank Force One:
I'm not sure. I pulled a few cam caps today and the surface didn't look great. But this is my first time opening a motor so I don't know what acceptable wear looks like.
This is one of the caps on the exhaust side.
I would prefer to keep the BP4W if possible. I asked about the fwd versions because of the price and that I've heard some of them are already tapped for turbo if I'm inclined to go that route later on.
And thanks for the replies guys.
In reply to rodknock:
You don't need to pick a motor based on that oil galley tap, it's a convenience that steals oil flow from your main bearings. I did a Mazda Motorsports crate motor with no galley tap on a turbo car. I teed the turbo feed line off the post filtered oil cooler feed line. It's been fine for years.
Dashpot wrote:
In reply to rodknock:
You don't need to pick a motor based on that oil galley tap, it's a convenience that steals oil flow from your main bearings. I did a Mazda Motorsports crate motor with no galley tap on a turbo car. I teed the turbo feed line off the post filtered oil cooler feed line. It's been fine for years.
It's the place that mazda used on those motors in factory turbocharged form. It's fine.
But yeah... i wouldn't choose a motor based just on that.
OP, i think i misunderstood your original question. Yes, the Kia engine will have the forged crank like all BPs, and i believe all of the Kia BPs had the main bearing support plate. I don't believe the MBSP does anything worth talking about, but it's fun to tell people you have.
But again, the old FWD head doesn't flow as well.
My Miata runs a 95 block, pulling oil from the factory location as Mazda intended for turbo, but has a ported BP4W head sitting on top of it. No way i'd go back to a BP05. 
