Part 1: Geek Theory Vs. Hands-On Reality
Ever since we drove Endless Racing's Z Car Challenge machine in Japan (naturally aspirated, 400bhp), building the same engine here has topped our list of geek obsessions. The only reason we haven't gone ahead with it is because Project Z has already been committed to turbocharged power. Plus, the cost of building such a fully prepped engine gets pretty outrageous-and it would only drink 100-octane. But automotive karma works in strange ways.
Castrol has invited us to face off against our sister magazines (Super Street, Modified, eurotuner, Import Tuner, Turbo, and Lowrider) by teaming up with a shop of our choice to build a no-compromise engine in its Castrol Syntec Top Shop challenge. Naturally, everyone else is going for the one-pull-wonder, ranging from a GM crate motor small-block with twin turbos to the usual big-power 2JZ or 4G63. The competition is based on peak horsepower and torque per displacement (displacement is multiplied by two for anything with forced induction), total horsepower under the curve, a 30-minute endurance death match (all tests administered on an engine dyno), and an engineering challenge to impress a panel of engine-guru judges. All of which sounds suspiciously like our USCC rules. We're looking to build something real-world that might one day end up in some lucky raffle-winning schmuck's engine bay (the victorious engine will be given away to a member of the public).
Picking a naturally aspirated (NA) engine to go into a horsepower battle with turbo engines might not sound like the smartest thing to do, until you look at the rules and consider real-world performance. For example, if we chose to build a 3.0-liter Supra motor targeted at 1000bhp, the numbers would break down to around 166bhp/liter, since a turbo motor has its displacement multiplied by two. A 5.7- liter small-block would really suffer, even at a wishful 1500bhp. That would land it somewhere around 131bhp/liter, just a little more than Honda's out-of-the-box S2000 engine.
Even if we can't make the most power per displacement with a naturally aspirated VQ, there's another side of the equation: power delivery, or area under the curve. If you've ever seen the power curve of a big-turbo, small-displacement 1000bhp car, it's essentially useless until the last 1000rpm and undriveable, regardless of engine speed. For most of the powerband, the engine will be struggling to make a fraction of its peak power until the monster turbo needed to flow this amount of air finally spools and sky-rockets the power at an uncontrollable rate. Do the math and the area under the power spike won't compare to the steady power coming from a naturally aspirated engine.
The Engine And The Shop
We decided on Nissan's VQ35DE as our platform. It has the ideal combination of displacement, rpm, fundamental design and flow capabilities, plus a respectable amount of low-end torque. Add in the 100-octane gas everyone will be using and we'll be able to raise the stock compression ratio to a respectable race engine standard. Our aim is to build an easily replicated, street-usable, 400bhp naturally aspirated VQ. Several respectable tuners like Tomei, Nismo, Cosworth and Jun Auto already have extensive research and racing programs based around this V6.
When it came to picking a shop among the notable VQ tuners, we decided on Cosworth Engineering for several reasons: they spoke English (though with a strange accent at times), its US headquarters are right in our backyard here in Southern California, most of the parts we would be using are off-the-shelf, and, mostly, because few organizations have the engineering capabilities, expertise and experience to rival Cosworth.