I have been searching and read once that 92-94 pistons from a SOHC protege motor would make 8.2:1 compression with a Miata head. Can anyone confirm this is true? And I am assuming it would be because of the pistons and that the rods and crank are the same in a protege and Miata motor?

 

Valve clearance.

 

What about it?

 

My guess would be the lack of DOHC valve pockets, on SOHC pistons.

 

Ahh... I read they are dished, let me see if I can pull the link up. Maybe who said it will have good credibility around here.

 

Well, I can't find it now. Bump? Any drop in lower comp pistons

 

949 Racing - Engine
Flyin' Miata : Engine/Drivetrain : Internals
Wiseco Piston Sets for 1.8L Mazda Miata

 

if you're gonna attempt really weird crap, you gotta not be dumb and cheap too.
if you're dumb just buy proper pistons, because sounds like you put in a whopping 2 seconds of effort actually thinking about this and researching it, its quite obvious why it wouldn't work.

 

18psi, I've actually spent the better part of two hours scouring this website and a protege website. I found I once on this website at some point and they mentioned the pistons were dished, and you gave me this idea with your rods only method. I'm merely trying to minimize down time, and didn't want to have to bolt my head in and put clay on the piston...

 

Nevermind, signed up on a protege forum. They work well, hold up like Miata pistons do and drop the compression somewhere in the 8.3:1 neighborhood. DOHC swap is fairly common. So all I have to do is buy some good rods. Good info to know around here though.

 

Really?
News for me. We actually tried this before, installed some of those weird shaped pistons into a 99 and it ran like junk, clicking and clacking and making what sounded like piston to valve contact. You might want to double check clearances just in case.

 

Damn.... I guess I will. I read a few deals of people swapping on Miata heads.... When did y'all do this and what block and head?

 

I wonder if they have different widths between pistons?

 

Nope.

 

It was a 99 engine that was siezed. We took it apart, cleaned it up, the pistons were unusable, he replaced em with funky looking ones out of a protege, I remember the domes were completely different shape. They "fit", and didn't make contact when we spun the engine over by hand. Everything else was the same 99 bp4w engine.

Then when he started driving the car, it ran like absolute junk, clicking and clacking down low, and I'm guessing it pulled timing from all that noise because it was completely gutless down low, then opened up drastically up top after about 4500.

I wouldn't take my chances if doing this much work to be honest.

 

I'm just attempting to find a low compression option without buying forged pistons, but if it has to be, then so be it. Won't be my first nor last time lol.

 

Stock NA pistons are 9:1. I don't think you NEED anything lower than that at stock piston power levels, though obviously 8.6:1 is better.

 

That was my thought. Why do you want ultra low compression pistons? To run ALL OF THE BOOST! And what happens if you run ALL OF THE BOOST on cast pistons?


Go get forged low compression pistons, or stick with stock cast compression pistons.

 

I've got a BP4W swapped 91. So my compression is at 9.5:1. That's the reason I am looking around.

 

So what's the reason?