It's not really a question of need when we talk about big HP, is it? For many of us, these cars evoke a time in our lives when we were much younger, and, in my case at least, without the financial means of doing much about stock HP. Now, in later life, we are less constrained by financial shortfalls or technical inabilities that kept us from becoming true modifiers in the past. Our hands are still important. For some of us, that means wrenching. For others, writing a check.
The platform difference with a Subi engine also allows for doubling HP without some of the constraints of an air-cooled engine. This is not to say there aren't unintended consequences of raising the HP of any engine. For Subis, heat elimination is the single most important factor of going big HP, in my experience. One third of engine power goes to turning the wheels, one third goes out the exhaust as waste heat, and fully one third goes through engine cooling system.
That means when you get to 300 HP, you now have 100 HP that needs to be cooled. In a stock Subaru engine and chassis, it's not tough to get to the 450-500 HP range on a street car. Some lower end work to beef up the rotating mass, a big turbo, larger intercooler, and a pile of associated add-ons. Companies like Crawford and Cosworth routinely offer big street motors in the $15K range. One surprising fact about increasing Subaru power is that most successful Subi tuners agree that you can safely double the stock HP in a Subi engine with bolt-ons, no lower end work at all. Pretty amazing, eh?
We have lots of variables in our cooling systems: radiator size, placement, number of circuits, number of fins/inch, and material type. Then we have shrouds, ducting, fans, water pumps, and on and on. This doesn't even consider the intercooler and options for that-air/air or air/water. There are very few experts we can turn to with our cars, as much of this is new ground. I'm not suggesting that we are the first hard-to-cool cars, since there are lots of historic examples of those types of vehicles. However, our replicas provide challenges that most shops/companies haven't been exposed to, with big HP Subis and a VW or tube frame platform.
There is a predictable shortage of space to hang all the additional pieces of cooling equipment. Of course, every manufacturer of a cooling device, whether it be radiators, oil coolers, other heat exchangers, or an a/c condenser, all tell give you the same instructions: mount MY equipment in the best possible space, where you are guaranteed a sufficient amount of uninterrupted cooling air. You quickly see the problem.
I have now made the following changes: new larger aluminum rad with proper ducting and shrouding, high-performance puller fans, placed in the compartment where the engine sits in a conventional rear-engine car. I finally had to cut out the entire deck lid, leaving only the outer perimeter, using grill mesh to cover what was previously a solid surface. The reason is that you need a good, uninterrupted flow of air coming into AND leaving the radiator. That means that a fairly closed space downstream of the puller fans inhibits the flow needed for proper heat transfer of the coolant.
That's just the start, but I'll continue explaining my build in the future when I have more time.
