Project FD RX7 Restomod: Part 30 – Finishing the V-Mount with a CSF Intercooler and Vibrant Performance

We finish our high efficient V-mount intercooler setup for the FD RX-7 using a CSF intercooler core, custom fabricated the end tanks, and charge pipes fastened with Vibrant Performance HD Clamps.

As we discussed in Part 29, a V-mounted radiator and intercooler is the best cooling system layout for track cars, street cars, and the majority of modified RX-7s.  However, almost all V-mount setups have pretty poor ducting that allow air to escape around the radiator and intercooler rather than trapping that air and creating a pressure differential across the coolers, which makes a massive difference in heat transfer and cooling ability.

We designed the Billy Johnson Racing FD RX-7 Cross-Flow Dual-Pass Radiator to be the largest and most efficient radiator that fits within the factory frame rails.  We came up with a cohesive V-mount setup that efficiently seals off all of the air entering the bumper to create the greatest pressure differential possible to force air through the intercooler, radiator, and feed fresh air to the turbo.  With the radiator mounted, we were ready to tackle the intercooler.

We decided on a 700-horsepower rated 20”x12”x3” bar-and-plate intercooler core from CSF Race (PN: 8067).  These heavy-duty cores are pressure tested to 120psi for maximum reliability in extreme boost applications.  They are hand-built in clean rooms using jigs and fixtures to ensure the cores are straight and easy to weld.  Their intercooler core features high-precision staggered fin designs in both the ambient and pressure sides of the core.  Batch brazed in one-of-12 of CSF’s state-of-the-art digital vacuum brazing ovens, strict quality control, testing and pressure testing ensures reliable and durable heat exchangers.

CSF is a fourth-generation family business that has been around over 75 years, creating the most advanced, efficient, and reliable cooling systems in the world.  In the 1970’s, they were the first company to create aftermarket cooling solutions for import vehicles such as Honda, Datsun, and Toyota.  By 2009, they grew to sell over 650,000 cooling units annually despite being in the middle of a recession.  Today, the racing and high-performance division of CSF (CSF-Race) is the pinnacle of the company’s engineering and manufacturing expertise.  They actively support and compete in Formula Drift, Pirelli World Challenge, Pikes Peak, NHRA, Global Time Attack, and the Optima Street Car Challenge.

Packaging is important and taking the function and needs of the turbo inlet, intercooler, and radiator into consideration will greatly affect the power and efficiency of our engine.  Many RX-7s use the widest intercooler they can fit in the engine bay, which creates a major problem and inefficiency where the turbo sucks in the hot, less-dense air that exits the intercooler and radiator.  On a dyno where the hood is up and the turbo can suck in ambient air from the dyno room, this problem does not really occur, but with the hood closed in actual driving conditions, feeding the turbo hot air will make far less power than it did on the dyno.

The turbo’s job is to compress ambient air and make air denser, so more fuel can be added, so more power can be made.  If you starve the turbo with hot, less-dense air, it will have fewer air molecules to compress to make power.  If you have ever driven a turbocharged car on a hot day or at the top of a high-altitude mountain, you can relate how the car makes far less power than it does on a cool day at sea-level.  Feeding the turbo the coolest air possible is crucial for making power.

We chose a narrower core width of 20” in order to leave an opening to feed the turbo with fresh, ambient air, and we chose a narrower 3” core for ease of fitment and installation, tucking the intercooler under the front hood latch crossmember and headlight bucket.  Since the turbo inlet is the start of the power production of an engine, from an efficiency standpoint, it is generally better and more important to feed the turbo cooler air than it is to have an extra 2-4 inches of intercooler length to cool less dense air.