Does anyone know what the stock size is of the turbo flange is on a stock 13bt s5 manifold T3/T4? any suggestions...

 

Neither. It's a proprietary flange design.

 

So there's no point of buying a manifold unless i buy a new turbo is that correct?
Is there any turbo manifolds that are better than the stock one for the stock s5 turbo?

 

There are one or two manifolds produced, I think available in Japan only and at a high cost, for the stock turbo. Generally not worth it for the minor gains. The stock S5 manifold is fully divided anyway.

 

http://www.rotary-works.com/products...F-RX7-FC-4.JPG


Turbo Manifold for 86-92 Mazda RX-7 - 2nd Gen FC
This a new Re-designed Manifold to Fit the FC
It fits FC chassis without hitting any other parts
- It has T4 Standard Turbo Flange
- 40mm or 50mm Wastegate Flange
- Most other RX-7 manifold is for FD which does not work on FC, this Manifold is Specifically re-designed for FC.


What about this one?

 

That manifold has a standard T4 flange. It will not fit the stock turbo. The stock turbo flanges are proprietary.

 

What does or should i say what is proprietary and how is it different from the others?

 

it doesn't fit. square peg and round hole. if you looked at them side by side, it'd be obvious.

The stock turbo is tapped out at 250whp anyway and if you fart it'll spool. There is really nothing gained by putting a better manifold on it. If you want more than 250whp, you need a new turbo anyhow, and if you're below 250whp you don't have spool problems, making the manifold a moot point.

Keep it simple: new turbo, new manifold. Old turbo, old manifold.

 

Proprietary meaning it's Mazda's design. It's not a standard shape.

S5 flange design: http://atkinsrotary.com/store/catalo...t-p-17164.html

T4 undivided flange: http://www.spdexhaust.com/images/Sec...o/T4_Specs.gif

T4 divided flange: http://www.himni-racing.com/images/T...ange%20101.jpg

 

Proprietary meaning it's Mazda's design. It's not a standard shape.

S5 flange design: http://atkinsrotary.com/store/catalo...t-p-17164.html

T4 undivided flange: http://www.spdexhaust.com/images/Sec...o/T4_Specs.gif

T4 divided flange: http://www.himni-racing.com/images/T...ange%20101.jpg