Questions about BP4W (Mazdaspeed Miata) pistons?

[turbo4ag]

This is my first post on this site, so welcome me to your community. I have used the forum search and could not find anything that could answer my question.

I am trying to find out if the BP4W in the 98-2000 Miata and 04-05 Mazdaspeed Miata pistons are compatible with the standard BP-ZE found in most 323s, Protege's, Escorts and Miatas.

Do they have the same 20mm wrist pins? and also, if used in an older BP will it keep the same low compression ratio or is the deck height different on the newer blocks.

 

[kcbhiw]

The higher compression BP-4W pistons use the same wrist pin, rod length, and cylinder bore dimensions as their earlier 1.8L counterparts. FWIW, the rods found in, say, the 1.6L Miatas are nearly identical to those found in the 99-00 Miatas. The compression difference in the 4W pistons (9.5:1, IIRC) is made up by the piston dome design and will be maintained regardless of which BP block into which they are installed.

The older BP blocks are essentially identical to the later units. The only differences in the newer blocks can be found is some of the outer castings (I.E. external oil supply ports are not drilled, etc).

Welcome to the board!!

 

[turbo4ag]

Thanks alot.

So in essence I could use the OEM Mazdaspeed Miata pistons in my 92 323 With BP-ZE swap, and it would be a direct cheap replacement for aftermarket turbo pistons?

Im assuming the price from the dealer is something like $55-70/each which would be way less than any forged aftermarket make (Wiseco, Arias, JP, etc...).

Also, does anyone know if those pistons are forged or cast? Also what the stock compression ratio is? The NA (not MS) was 10.3 or so I was led to believe... but Im looking for the turbo pistons. These pistons would obviously be cheaper than trying to track them down from older Japan BPT models.

 

[kcbhiw]

Thanks alot.

So in essence I could use the OEM Mazdaspeed Miata pistons in my 92 323 With BP-ZE swap, and it would be a direct cheap replacement for aftermarket turbo pistons?

Im assuming the price from the dealer is something like $55-70/each which would be way less than any forged aftermarket make (Wiseco, Arias, JP, etc...).

Also, does anyone know if those pistons are forged or cast? Also what the stock compression ratio is? The NA (not MS) was 10.3 or so I was led to believe... but Im looking for the turbo pistons. These pistons would obviously be cheaper than trying to track them down from older Japan BPT models.

Yes, those pistons will work on any BP. I doubt you'll be able to source a piston for that price from the dealer, they usually have a huge markup. www.carparts.com has 'em for about $61/ea.

I'm pretty sure the pistons are cast. The original (NA) BP used a CR of about 8.8:1. Starting in 95/96, the Miata compression increased to 9.0:1. '99 Engines received 9.5:1 ratio pistons (BP-4W). If you want decreased compression from what you currently have, the 4W pistons aren't them. However, with good tuning, they'll work fine. There are a ton of boosted '99 Miatas running around with stock engines and no problems. I beleive all other BP's (used in Protege LX's, Escort GT's, etc) employed the 8.8:1 pistons.

How much boost do you want to push?

Lots of good info can be found on Randy Stocker's site. Engine info in particular can be found here: http://members.aol.com/solomiata/MX5Engine.html

 

[turbo4ag]

I am looking for forged units. I can't see why they would have forged pistons in the older BPT engine but in this newer turbocharged engine put a cast piston.

I am really looking for a BPT piston, but those are near impossible to get unless you have a contact in Japan who can order them. These would eliminate having to go to Japan for a forged piston.

I'm looking to run 20psi. My current setup is a T3 .63/.63 stock engine otherwise, and BPT ECU.

 

[Pitlab77]

They pistons should not be a problem. They are never really the problem on turboed miatas.

I also stay take a look at like mentioned above
www.solomiata.com

 

[TheMAN]

the GT-R and GT-X pistons were NEVER forged

 

[18sOnAiR]

I remember reading that GT-R's were squeezed cast.