It’s not enough to just make the radiator exit bigger – air management under the front clam is of critical importance if you want to manage engine and passenger compartment heat.
If radiator discharge air is allowed to flow freely out it will then crash into the components in the radiator box, heat up the foot box, then squirm its way through a too-small opening. This results in poor flow through the radiator and adds a TON of heat to the passenger compartment – not to mention killing your battery if you’ve opted to locate it in the radiator box.
The factory offers a heat shield to protect the foot box and battery from excessive heating. With the addition of some insulation/thermal shielding I’m sure the factory option does a great job of keeping things behind it cool.
Unfortunately that’s about all it’s good for.
It’s a fairly basic design and has a vertical surface located (too) close to the fan exits. The tight spacing to the fans combined with its near vertical surface causes the flow to choke down, effectively reducing the ability for air to flow through the radiator.
My guess at what the airflow looks like …
Secondary issues with this design is it’s blowing hot air over the brake and clutch reservoirs and makes fitting a fan shroud more difficult.
My solution to these issues was to fabricate a duct that could be fitted against my fan shroud. The idea is to give as much room as possible for the radiator air to flow out and gently bend toward the hood vent. Increasing the hood vent size dramatically decreases radiator backpressure and increases the minimum flow cross-section. This was the primary motivator for me locating the battery at the back of the car – even though it meant more mass to an already rear-biased weight distribution.
What I think is going on …
Making the cross-section at the duct entry increasingly larger than the radiator discharge creates a decrease in local air pressure, thereby promoting flow through the radiator by reducing backpressure. My hope is that the recirculation zone is relatively small. The lower edge won’t be sealed against the fan shroud; some air “bleed” into the radiator box may further reduce this recirculation zone.
Chaotic airflow management – check. What about heat management? I plan to cover the entire duct with heat shielding. This will (hopefully) keep all that heat energy coming from the radiator away from the bodywork and from the passenger foot box – getting it out before it’s able to transfer much energy into the car.
I then made up some attachment flanges; this duct will remain fastened to the chassis when the front clam is removed.
That’s a lot of hot air about hot air!