So I'm about to do an engine rebuild. And I'm wanting to get a few spare rotors just in case I need them. So I have a friend who has 2 spare 1985 13b rotors. Other then the older rotors being heavier, what does that mean for me?

I understand that heavier is harder to turn which in turn makes less HP, but does it help at all when boosted? Does it give any better numbers? I assume it's a bad choice because everyone says use S5 blah blah. But has anyone tried it?

 

Actually, I've seen a lot of people rebuilding, for turbo purposes, S5 housings with S4 rotors, because of the lower compression in the S4 rotors which will allow for higher boost.

 

How would heavier help when its boosted? if its lighter it'll spin faster....

What are you building the motor for? If street, why not go for what's safer, more power, and more reliable?

will that s3 rotor fit in the s4 housing within spec?

 

Sorry I just have to laugh at your signature Mike... thats hilarious.

^^"

 

Yea, I understand it being lighter and spinning easier. I was just wondering if anyone has tried this. I understand it's most likely stupid, but a search brought up so much bs it's not even funny.

 

You will also need a S3 front and rear counterweight to use the 3 rotors.

If you are building an N/A don't even bother, S4 n/a rotors are super cheap and most people can't even get rid of them.

If you are going turbo then be sure to check into the compression ratio of the S3 rotors.

 

s3 are heaving with a 3mm seal, if you are building a torque monster maybe the heavier rotors will help down low a lil.

 

pointless unless you really want a 3mm seal

 

Don't.

The S3 rotors run 9-pin bearings, and they have been known to spin the rotor bearings.
Mazda upped this to 12 pins in 1986+, and this eliminated this problem.

I would never use S3 rotors for big power / rev applications due to this inferior rotor bearing pinning.

For 3mm, you're better off machining any 86+ rotor for the thicker apex seals.


-Ted

 

s3 rotors are doorstops.... or bbq tools (seriously, they will keep stuff warm)

3mm seals are a waste of time, like ted says, 9 pin rotor gear, so it falls out faster, same 9.4 compression as the s4's

theres just no gain, especially if you have to pick them up!