I was looking into replacing my stock radiator with a Fluidyne "Direct-Fit" high performance radiator, and i was wondering if that would boost engine preformance and cooling much or should i just stick with the stock.

 

A fluidyne or Koyo is one of the best safety mods you can do to these cars.
-a

 

My question is: What's better Fluidyne or Koyo?

 

It's not going to boost performance. The modification is really done to replace the stock radiator since it has plastic end tanks. Those can crack and leak over the years due to the high underhood temps.

Neither.

Pick the size radiator for the application. If you are just driving the car on the street and want to replace the plastic stock radiator, get a direct replacement like the Fluidyne.

If you are road racing and need more coolant capacity, then look at something like the Koyo.

 

Mazda_Power,
IIRC for the FD,
KOYO = 100 % larger than OEM but more reports of fitment issues.
Fluidyne = 50% larger than OEM but with less (but not zero) fitment issues

 

AWR crossflow

 

I bought a Fluidyne for my 91 TII, I don't think it is necessarily worth the money. Take some measurements and buy a nice universal the right size for half the price. Fab up some 20 dollar or less brackets and run some radiator hose.

-Marques