V-Mounted Radiator & Intercooler
The V-Mounted radiator and intercooler is arguably the best and most popular option of the three because it is the most well-rounded option in terms of its benefits with the only major negative being a higher cost. Generally speaking, V-mounts tend to be the best option for sustaining high power levels for extended periods of time, eclipsing the performance of SMICs without having the heat soaking issues of SMICs. While FMICs will usually support more peak power than V-mounts, they can only do so in short bursts before water temps start to climb, and they also suffer from worse A/C and coolant performance.
Like SMICs, V-mounts have relatively short charge pipes (which is good for transient throttle response) and share the inlet air from the front bumper between the radiator and intercooler, ensuring both heat exchangers get the coolest air possible. V-mounts don’t tend to heat soak like SMICs because the hot radiator exhaust is evacuated under the car rather than directly onto the intercooler. V-mount intercoolers can be larger than SMICs but are usually not as large as FMICs. When properly designed, V-mounts can feed the turbo with a lot of cool ambient air like an SMIC.
However, many V-mount kits are not properly designed and use oversized cores that block the airflow to the air filter and cause the turbo to suck in hot air that exits the intercooler. While this might not be a problem on the dyno when the hood is open and the turbo is sucking in ambient air, when the hood is closed and the car is actually moving, the turbo will suck in hot air that is less dense, and the engine will make less power than it did on the dyno.
The biggest negative of V-mounts is the cost. The radiator mounting and configuration has to be completely changed, from leaning towards the front of the car to leaning towards the back of the car. A new radiator needs to be purchased or an existing radiator needs to have a lot of fabrication work done to change the coolant flow to work in a V-mount configuration. There are a few bolt-in kits on the market that require little to no fabrication to install a V-mount. At twice the price of the Pettit Charge III SMIC, the Greddy V-Mount Kit is the most popular V-mount setup for the FD RX-7.
V-mounts might be the most popular option for moderate FD builds, but almost all of them have poor ducting that allow cool air to flow around the radiator and intercooler rather than through it. Air takes the path of least resistance, and a lack of sealed ducting can greatly affect the effectiveness of the radiator and intercooler when not properly ducted.
Overall, V-mounts are the best configuration for sustained heavy use such as road courses, autocross, hill climbs, and standing mile competitions, as well as street cars making a lot of power.
OUR PLAN
To maximize the cooling efficiency and performance of the FD RX-7 on the street and sustained use on the track, the V-mount radiator and intercooler setup was clearly the best configuration for our uses. We closely measured and analyzed the physical area in the FD engine bay and conceptualized a cohesive V-mount cooling configuration with proper ducting to maximize the physical size of the radiator and intercooler while feeding the turbo, intercooler, and radiator the coldest and highest-pressure air possible from the front of the car. There is a limited amount of air that enters the front bumper of the FD RX-7. Utilizing that air as efficiently and effectively as possible will make a huge difference in the cooling and power of the car.
The 56mm Billy Johnson Racing FD RX-7 Radiator pushed the limits on the overall width of the radiator that can fit between the factory frame rails. This radiator has a dual-pass configuration where the hot coolant enters the top right (passenger) side end tank, flows across the radiator to the driver’s side, then back to the passenger side and into the engine. The location of the radiator inlet and outlet are positioned to have the radiator hoses be as short as possible and to be packaged well in the RX-7s chassis.
4 comments
Fantastic update and all the custom work on the cooling system is so cool to read about. I am patiently waiting to see this thing finally unleash some HP!
Technically, you should have a ‘blade’ that bifurcates upper, and lower flows at the start of the duct. If you modeled this in CFD, there would be obvious turbulence that could easily be avoided.
Cheers.
Was about to comment the same thing.
Also, the air out of the IC needs to go somewhere… I don’t remember what the hood looks like for this project, but a proper vent with gurney flap and ducting would do wonders at speed.
Can’t wait to read the next articles.
It’s not that crucial to bifurcate the ducting. Many morern OEM cars don’t separate the inlet ducting of a common duct/plenum that feeds multiple heat exchangers because airflow is not laminar in the ducting and the important aspect here is creating a pressure differential across the heat exchangers. Proper ducting that seals the air from the front bumper to the heat exchanger creates a high pressure area on the front side of heat exchangers in the V-mount setup (or “L”-mount in many OEM applications) when using a common plenum (or air box, or radiator ducting).