The Koyo was also a direct fit. There was no extra labor involved. No trimming to the fan housings or any other adjustments were required.

 

I just turned on the A/C. That will switch the fans to medium speed. More info about cooling fans here: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/2-trigger-cooling-fans-462760/


-s-

 

Thats true, Allen installed a Koyo in my previous FD and had to do a little work to mount in the Koyo (I had a Fluidyne in it before the Koyo, the Blitz front mount intercooler installed by SP Engineering didn't have the proper brackets installed and punctured my Fluidyne, the Koyo was cheaper and I needed a new radiator fast so I got a Koyo from RXecret7 for $325).

 

Define "direct fit". Fluidyne tends to have fewer fitment issues, but not zero.
Agreed. But in addition to capacity and air flow, wouldn't the radiator's ablility to lose the heat to that air flow be a factor? And variables involved with that would include the number of fins, material use for construction and the time the coolant spends in the radiator.

 

Disagree. The OEM radiator is/was pretty efficient for a relatively stock, streeted car. Yes, it's smaller capacity, but as we've already discussed, capacity isn't the silver bullet for running hot. With a Miata thermoswitch, a good coolant/water ratio, a pair of clean oil coolers and foam plugging the gaps around my OEM radiator, I had no problems running it. The reason I changed was to avoid plastic end-tank failures on a then 12+ year old car and in prep for autocross. My old OEM radiator is still going strong in a friend's FD.

 

Absolutely correct, but I don't feel I know enough about those things to make comments about them. A friend of mine has spent some time talking to people who work for (a radiator manufacturer that has been named on this thread), and that company has all kinds of complex mathematical models for heat exchangers that they won't share. He said there are a lot of factors in their equations, probably more than 10. Here are most of the things I can think of:


Frontal Area
Radiator Thickness
Fluid Capacity
Fin Spacing
Fin Thickness
Fin attachment method
Tube & Fin material(s)
Tube Diameter
Tube Spacing
Inlet & Outlet size
Inlet & Outlet location


Since it would be pretty tough to research all those things and try to predict what makes a radiator work well, I think the best method would be to simply try a few different radiators, and make the test method as standard as possible. My plan is to measure time to warm up from 100-210F, then turn fans on and measure time to cool down to 180F. If you do a few tests on a few different radiators using the same car at the same ambient temperature, you should be able to find some sort of a trend. If you could measure inlet and outlet temps, that would tell you a lot about the radiator as well.


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+1 This is good advice. Get a good (and good condition) oil cooler on the car and put a fan on it. The oil can get very toasty during idle & low speed conditions. I would personally do this mod before a rad.

In order to really see the benefit of a thicker radiator (i.e., Koyo) you need increased airflow. This is the irony of a thicker radiator. Because the efficiency of heat transfer is a function of differential temperature and the gradient of that temperature, you run into a point of diminishing returns as you make the core thicker. This can only be mitigated if you increase the temperature differential or increase the airflow, period. The relationship between thickness and heat rejection is not linear.

What a larger core and more coolant capacity does do (that smaller cannot) is increase the specific heat capacity--the amount of heat the system can store or buffer as a heatsink--during periods of marginal airflow; however, keep in mind this effect is limited and that heat will eventually need to be rejected.

 

i got a fluidyne and love it, its my dd