I used the Koyo HH for a while, seemed to work fine for my needs during that time.

Also something to consider is that there's more weight that typically comes with a dual-pass radiator that doesn't often get mentioned. I always thought the dual offered superior heat transfer by allowing the coolant to cycle twice during a single pass. Love to hear a more thorough explanation if I've misinterpreted the concept.

And R-Magic offers a 3 row radiator for extreme tuner / track vehicles but very expensive.

 

what most people miss is what I stated about turbulence. Increasing velocity to the point it creates turbulence can improve HTX efficiency under certain circumstances. Having a water pump that increases flow 2x is not as simple or as efficient as making the radiator dual-pass. What most people often don’t understand about dual-pass radiators is this alone usually isn’t sufficient. Typically a dual-pass radiator is supposed to also be used with a higher flowing water pump or pulleys. Except most rotary engine people are slowing their water pump down trying to decrease cavitation at higher engine rpms.

So as was previously stated, whether or not a dual-pass radiator will be any better than an equivalently sized single-pass depends on various factors. That above is just one factor. As with anything, it really needs to be understood in entirety rather than the usual shooting from the hip approach that somebody who read a little something on the internet now considers their self to be a qualified gunslinger armed with. There’s often more to it than that and if you’re not careful you can shoot your self in the foot. Having one of said radiators in my possession, it’s capacity is larger than any other RX8 radiator I’ve ever seen. So there’s a bit more to it than just dual-pass.

So dual-pass increased the velocity, but if you were astute to reading these posts then you should recognize how the capacity increase impacts the velocity as well …



Single-pass


Dual-pass
.

 

Decide to build the replica of it
Once for all to curve the Quality problem of RX8 performance radiator

 

I agree. If the contact time of the coolant in a dual pass radiator is half due to a higher velocity, but then runs through the radiator twice, than it may not be as efficient as a well built single pass. Heat transfer requires both contact time and temperature differential. My coolant temps saw the most decrease when I swapped over to a quality koyo single pass and properly sealed the entirety of the radiator with foam. The koyo may not be that inherently more efficient than stock (no plastic ends!), but the stock foam application is downright pitiful and sad, if it's even still attached, compared to the $20 I spent adding 2" 1/2" x 2" 1/2" foam strips.

 

Your coolant expansion tank likely doesn't have much more time in this world, unless your photos have a color filter on them.

 

Is filter
I just change them last year

 

It’s a common issue on this particular radiator and that was discussed in other previous threads on it.
.