Honda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone Hoses

Project Honda Civic EJ: Staying Cool with Koyo and HPS

By Annie Sam
Photos By Chuck Johnson

The last time project Civic was at the racetrack, it overheated and blew a head gasket, warping the head along the way. Since then, Chuck Johnson took apart the motor and filled it up with all sorts of goodies that you can read about here in the last installment of Project Honda Civic EJ.

 Honda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone Hoses

Now that the motor was back in the car ready to be buttoned up, we decided to give it a little bit of a cooling upgrade to avoid another Buttonwillow incident. Naturally, the next logical step was to replace the stock Civic radiator with the biggest, baddest one we could find. Ok, maybe not the biggest, but we were definitely looking for the baddest. Although the stock radiator was reliable for over a decade for daily driving, our beefed up Civic would also need a beefed up cooling system.

The radiator we opted for was the Koyo All Aluminum Racing radiator for the Honda Civic SI. The inlet/outlet diameters between the B16 and B18 motors were the same at 1 1/4", whereas the outlets for the D16 were 1 1/8". So, what we did was order the radiator meant for the Civic SI which ran the B16. Not only is this critical for consistency in the diameter of the openings, it eliminated the bottleneck which occurs when you use the stock Civic's radiator with the B18. It may sound like common sense but there are a lot of people that run this set up with the B18 swap. Hey it worked for over 100,000 miles for me and would have ran even longer if I didn't abuse it at the racetrack the way that I did.

 Honda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone Hoses
 Honda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone Hoses
Honda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone HosesHonda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone Hoses
Right off the bat you could see the huge difference in width between the two radiators. The Koyo full race radiator was more than three times the width of the factory Civic radiator.

Because we had ordered the Civic SI radiator for my Civic EX, my stock radiator fan wasn't an exact fit. The lower brackets to the fan had to be modified because the threaded holes to the radiator were in a slightly different location. It might not look pretty but I didn't have to buy a whole new radiator fan and it got the job done.

Honda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone Hoses
Not the prettiest modification but it gets the job done.
 Honda Civic EJ: Koyo All Aluminum Racing Radiator and HPS Silicone Hoses
Aside from the bottom brackets, the rest of the radiator fan bolted right in place.


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Wednesday, October 31, 2012 7:47 AM
Still amazes me how little surface area is needed to keep a B-series cool...
Wednesday, October 31, 2012 8:03 AM
Why not go with a full size radiator? It holds more cooling and really ensure no cooling issues at the track.
Wednesday, October 31, 2012 9:48 AM
@ JDMized: I say why add the weight of a full width radiator and its attendant fluid out at the front end of the car if it's not necessary?

Sure it's a high compression NA motor but it's not as if the car is turbocharged, the stock width Koyo already represents a big upgrade in cooling capacity over stock.
Wednesday, October 31, 2012 7:50 PM
I asked because few months ago I was in the process of swapping in a B18b1 in my 93' hatch, and I had the dilemma of going half size (koyo) or full size.

I talked to few friends who race in the H1 Honda Challenge and they all agrees to go full size if I were to track the car (which I do a bit).
(My B18b1 runs Type R pistons, knife-edge rod, P8R head and the whole engine is rebuilt)....
That's why I brought it up. But I can see your point about keeping it half size to have less weight on the nose, to have it less pitch sensitive.
Friday, November 02, 2012 10:07 PM
A track day fun-car is different than a race car. In racing, and it seems especially Honda Challenge (in SoCal at least), there's a lot of bump drafting going on. Of course, when your front bumper is on the rear bumper of the car in front, you're not going to get much airflow to the radiator. So a much bigger one is needed. NASCAR has to run massive radiators because they're always in the draft.
Saturday, November 03, 2012 12:46 AM
Good point. I stuck with my big Koyo rad....despite the weight penalty...I hope I will never encounter cooling problems :)
Thursday, November 08, 2012 6:55 PM
I've been told that doubling the frontal surface area of your radiator pretty much doubles your cooling capacity, whereas doubling the thickness only got you a 25% increase. Don't know how accurate that is, but it makes sense as the more core the air has to flow through, the hotter it gets as it passes through the rear most part of it.
Mike Kojima
Mike Kojimalink
Tuesday, November 13, 2012 6:57 AM
We wanted to run a full width radiator but Kokyo wanted us to demonstrate how well their drop in replacement radiator works so that's what we will do.

JDMised, pitch sensitivity has nothing to do directly with CG or suspension, it is an aerodynamics function which usually pertains only to cars with underbody aero.
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