When I started this project, I had always envisioned mounting two radiators ahead of the rear wheels just like the authentic F355. Having the huge door scoops be anything less than functional seemed like sacrilege. The three inch frame stretch certainly freed up some real estate, but there were still so many questions: How much room was there? Were there radiators small enough to fit yet big enough to cool the V8? How about fans? Intake ducting? Hot air exhausting? Plumbing? Maintenance access?
The first thing on the agenda was to find out how much space I had to play with. I reinstalled the suspension to get some measurements with the wheels in place. Then, to get the chassis at the right ride height without the weight of the engine and transmission, I fabricated two rigid, but adjustable links to replace the shocks and springs. They measured 14.5" eye to eye.
With the suspension in the right physical location I was ready to start brainstorming cooling system layouts. Ferrari's concept was pretty simple: Cold air entering the door scoops flows through the radiators and hot air gets exhausted into the wheel well through louvered wheel well liners. The louvers open downward so debris flying off the rotating tires won't get thrown into the radiator.
I planned to change the flow a little on my car though. First, I wanted to merge the airflow from the rocker panel scoops with those in the door to increase airflow. Next, because of the intrusion of the Fiero's B-pillar into the airstream leading to the radiators, I figured I'd notch the B-pillars for a straighter path. I also wanted to use puller-type fans behind each radiator as a means to protect the radiators from potential rock damage from the wheels. And finally, because I worried about not being able to exhaust enough hot air through louvered wheel well liners, I wanted to route some of the hot air up over the wheel well liner to exit through a "Challenge"-style grill between the tail lights. Since pictures are worth a thousand words, I'll let this drawing do some more talking:
Of course the sheet metal surrounding the Fiero engine bay wasn't optimized for side-saddle radiators so that meant a little surgery was needed. I started by cutting out the stock sheet metal shrouds between the upper and lower rear frame rails. The curvature needlessly constrained the space for the top inside corner of the radiator. This one is from the driver's side:
The sheet metal isn't structural, it's just a means of sealing off the engine bay from the wheel well area. Here's what it looked like with the piece removed:
I did the same on the passenger side as well, but this next photo shows how much space was obtained on the driver's side by removing that shroud:
I then made a series of cardboard templates to define a new radiator compartment:
As the design started to gel, I began replacing the cardboard templates with sheet metal:
With the basic radiator compartment roughed in, the next job was finding a pair of radiators that would fit. I figured if I couldn't find off-the-shelf radiators, I could probably get a set custom-made by a local shop. I scoured the internet and found two that would work, but decided to opt for those from the 1992-2000 Honda Civic:
These are all-aluminium, 2-core radiators with a "cooling capacity rated at 200 HP each" according to Yonaka. Since calculating heat exchange rates is beyond the scope of this blog (and my education) I decided to take their word for it. Two radiators capable of cooling 200 HP each on a 300 HP engine seemed like a good margin of safety.
I felt better though after double checking the core volume (frontal area of the core multiplied by the thickness) of the Caddy radiator (9800 cm3) to that of the two Honda radiators combined (11500 cm3). That's an 18% increase over the Caddy.
Next, I needed to find a pair of electric fans since the combined dimensions of the radiators and fans would dictate where the assembly could be mounted. Once again I hit the internet looking for tech data on fans. Most sites gave flow rates, sizes, current draw, availability, and cost of their products and there was quite a wide range of performance for low profile fans. In the end, I chose a relatively inexpensive fan from Perma Cool (Summit part number PRM-18124) which on some websites sold for as much as $160 but at Summit they were on sale for half of that:
They are 14" in diameter, have ten "S"-shaped blades, have an advertised flow rate of 1850 cfm, draw 8.5 amps, and are 2.75" thick. The fans fit the Honda Civic radiators perfectly although they weren't specifically intended for them:
And here is the rad & fan assembly mocked up in the prototype radiator compartment (notice the high-tech tape):