i have a few things that i wanted to know, and no i'm not planning on getting it done for my 7 (not now at least), just wanted to get a knowing on it... and i'm talking about a 20b switched to higher compression n/a rotors...

1. it is suggested to use lower octane gasoline for 13b n/a, would it be the same suggested for a 20b n/a?

2. if i were to rebuild a 20b, i would pretty much use the same gaskets and stuff for 13b right?

3. if i switched the rotors to 13b higher compression ones off 13b n/a, would i be able to find couterweights for this? or is it possible to use the original turboed version?

 

Gas ratings would be the same as you are only adding rotors not compression over the 13B n/a
The gaskets for a 20B are very much different to the 13B.
If you use rotors from a 1989/91 n/a 13B, the rotors should be the same weight as the 20B as far as I know. Anyone actually weighed a 20B rotor to be sure? I always assumed they are the same weight as the 13B ones of the same era.

Gary

 

not gaskets (like exhausts and intake), i meant to say the seals and o-rings and stuff (forgot the names, internal stuff)

how does counterweight work? what's the purpose of it? never really understood that part

 

The rotors from my most recent rebuild were 4339g +/- 3 grams.

 

Yes, the water seals and oil O rings will work. I guess T2 parts or simply any '86-'92 seals and O rings can be used. I'll need to double check with j9fd3s though.

The counterweights of a 20B are a little different I think. Normally, when the front weight is up, the front rotor is down, and the rear rotor is up, and the rear weight is down. They're all 180º from each other. It forms a nice balanced assembly. The 20B, however, has three rotors spaced 120º apart and only two counter weights. Yet the 20B runs smoother than a two rotor engine. How can this be? I think the front and rear weights have 240º of influence, or not. I'm not sure. Basically, each rotor is like the tip of a larger triangular rotating assembly. They offset each other in a way that must work well enough. I guess I won't really know untill I get mine and rebuild it (if necessary).

 

1. you would use the same octane as for the 13b

2. mazda stocks 20b gasket sets or you can use 2 13b sets and buy the intake, and dowel pin gaskets seperately

3. all 89+ rotors have the same (compatible) wieghts

mike