Intake/Exhaust Systems
Assuming the Cosworth cylinder heads are no longer the gas exchange restriction, we have to address other restrictions further up the intake and down the exhaust path. Echoing much of the general trends in engine operation, intake and exhaust system requirements change as the engine operating characteristics change. For peak power optimization, the intake air box, or plenum, must be of considerable size in order to feed all of the cylinders without becoming the bottleneck. Also, smooth transitions and equal length runners help balance the mass of air and fuel that enter and exit each cylinder. In a perfect world, we would have a variable geometry intake and exhaust system to parallel the variable valve system.
For a performance engine, infinitely variable intake and exhaust systems might be overkill; optimizations within the power band will have to suffice. The Cosworth Twin Plenum intake system targets peak power production with a larger plenum volume. To increase intake port flow velocities at low rpm, velocity stacks, or venturies, are used. Velocity stacks help increase low end torque by increasing the charge velocity to maximize cylinder filling.
On the exhaust side, Cosworth stepped out of their norm to design and build this one-off exhaust manifold specifically for this challenge. While Cosworth Engineering has the know-how and technology to design, test and build the ideal exhaust manifold, the cost to do that is something only a race budget can warrant. So, instead, their gas flow geeks took a best guess and built a 3-to-1 design that focused on creating equal length primaries that optimized top end power. The first manifold used 35-inch primaries which didn't work quite as well. Ultimately, the manifolds were modified with shorter 31-inch primaries which are near the space limitations of the chassis.
The Verdict
Although Cosworth can model and simulate much of this intake, exhaust and cam tuning, these tools exists only to predict behavior and act as a guideline. Ultimately, everything still requires bench testing in order to validate the design since no simulation can completely predict all the dynamic complexities involved in an engine. If you've been holding your breath all this time to find the final outcome and our VQ power numbers, flip ahead to the special insert in this month's issue. Inside, you'll find the final power numbers of every engine entered and who finished where in competition (all entrants were tested on an engine dyno).
But keep in mind that while other competitors can build one-shot dyno queen motors that make stupid power, our Cosworth VQ would be the only one we'd race on for its useability, as well as durability. In the real world, that really does count for something extra.
Previous Installments
Part 1: Geek theory vs. hands-on reality
July '08
Part 2: Sizing up the competition
August '08
Part 3: The Cosworth difference
October '08
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Cosworth Engineering
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Castrol Syntec
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