Geek Theory
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.
A simple approach to increasing displacement is to punch out a motor as far as its bore spacing will allow and add as much stroke as possible. This works for old rev-limited V8s with cast iron blocks (where piston speeds aren't such a concern, since reciprocation mass ultimately limits revs). But in a VQ with the potential to spin up to 9000rpm, that's not the case. From a basic displacement perspective, the available room allows Cosworth to increase stock stroke by 6mm from 81.4 to 87.4mm and bore (limited by the factory bore spacing) from 95.5 to 96.0mm, increasing total displacement from 3498cc to 3796cc, or 3.8 liters.
Increasing the stroke by 6mm has a noticeable effect on piston speeds-a significant concern for an NA engine designed for high-rev power. The original dimensions are over-square (larger bore than stroke) with a bore/stroke ratio of 1.17, while the 3.8-liter dimensions would bring the engine closer to square (equal bore and stroke) with a ratio of 1.10. Although the engine is still over-square, which is typically good for higher revs, the mean piston speed at 8500rpm has increased from 23.1m/s to 24.8m/s; 25 m/s is roughly F1 engine territory.