Ever since we had the opportunity to drive Endless Racing's Z Car Challenge 400hp naturally aspirated (NA) Z in Japan, building the same engine here has topped our list of geek obsessions. The only reason we never went ahead with it was because Project Z had already been committed for turbocharged power and the cost of building such a fully prepped engine gets pretty outrageous, not to mention an engine like this only drinks 100 octane. But automotive karma works in strange ways.
Castrol invited us to face off against our sister magazines (Super Street, Modified, Eurotuner, Import Tuner, Turbo, Lowrider) by teaming up with a shop of our choice to build a no compromise engine in its Castrol Syntec Top Shop challenge. The competition would be based on peak horsepower and torque per displacement (displacement is multiplied by 2 for anything with forced induction), total horsepower under the curve, a 30 minute endurance death match (all tests will be administered on an engine dyno), and a engineering challenge to impress a panel of engine guru judges. All of which sounds suspiciously like our USCC rules.
While everyone else might be building a dyno queen engine, we're looking to build something real world that might one day end up in some lucky raffle winning schmuck's engine bay (the winning engine will be given away to one lucky member of the public).
Picking a naturally aspirated engine to go into a horsepower battle with turbo engines might not sound like the smartest thing to do, until you look at our rules and consider real world performance. For example, if we chose to build a 3.0-liter Supra motor targeted at 1000 bhp, the numbers would break down to around 166bhp/liter since a turbo motor has it's 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 NA 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 1000 hp car, it's essentially useless until the last 1000 rpm and undriveable, regardless of the engine speed. For most of the power band, 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 skyrockets 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 NA engine.
The Engine and the shop
So we decided on Nissan's VQ35DE as our base engine platform. It's the ideal combination of displacement, rpm, fundamental design and flow capabilities, not to mention a respectable amount of low end torque. Add on the 100 octane gas that everyone will be using for the competition 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 VQ35DE. Several respectable tuners like Tomei, Nismo, Cosworth and Jun Auto already have extensive research and racing programs based around the VQ.
When it came down to picking a shop among the notable VQ tuners, we decided on Cosworth Engineering for several reasons. Namely, they spoke English (even though with a strange accent at times), the US headquarters was right in our back yard here in Southern California, most of the parts we would be using in the build are sold off-the-shelf and, mostly, because few organizations have the engineering capabilities, expertise, and experience to rival Cosworth.
Picking a manufacturer like Cosworth means that we suddenly have a wealth of engineering resources available such as engine simulation software, flow bench data and computational fluid dynamics (CFD) head flow analysis. These guys are real engineers and possess the same tools OEMs use to design an engine from the ground up. This way, in theory, we could run engine simulations of how different bore, stroke, rod length, piston, compression ratio, and displacement combinations would be offer optimal power, torque, flow and engine speeds.
Our hope was to be able to reverse engineer the VQ and analyze the engine from the bottom up to realize why Nissan made certain choices in its design and what could be optimized without sacrificing wear, durability or the innate character of the VQ. At least that's what we hoped. And while Cosworth does have the technology to completely design and manufacture motors from a clean sheet, the labor involved would be beyond the scope of this project. After all this isn't an IRL or F1 engine we're talking about here.
As powerful as all these analysis and modeling tools are, they are still only a guide to be used in conjunction with practical and real world knowledge. So we went with a much more conventional method of design and tuning, and worked around the basic architecture of what Nissan gave us in the VQ.
Real World Tuning
Our high output VQ will be based roughly on Cosworth's concept for a drop in crate motor, which will feature an assortment of parts that have already been released or are already in testing for the VQ. The Top Shop motor will just take it up another notch.
Obviously, since we're using a stock block, our engine design would be constrained by some basic physical limitations. Since the Castrol Syntec Top Shop Challenge makes no restrictions on displacement or flow, we would want to start from the bottom end and maximize our total displacement to take advantage of the lack of a displacement modifier for NA engines.
To read the full article, go out and pick up the July issue of Sport Compact Car.
CASTROL SYNTEC TOP SHOP CHALLENGE