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[Greg Locock]

Sorry, no free link

"Paper Number
2005-01-2113
Author
Fredrik Westin
Paper Title
Optimization of Turbocharged Engines’ Transient Response with Application on a Formula SAE / Student engine
Description of Paper
In this study a 1D simulation model of a turbocharged engine is built up and verified. Using this model, the transient response of the engine, for which the speed-up time of the turbocharger is central, is minimized. A method is developed where stepwise fractional factorials is utilized to first determine the relative importance between a wide range of design parameters and then successively come closer to an optimal setup.

This method is then applied to the 2004 KTH Racing Formula Student engine. The engine was first designed entirely by using steady-state GT-Power simulations. These simulations are described and the designed explained. The philosophy behind turbocharger selection, manifold tuning etc. is described in detail.
After initial design the engine was optimised for transient response. Measurement data from steady state transient measurements on the dyno is showed for verification. "

Anyway, it's a great paper, with both modelled and real test results, on how to minimise turbo lag.

Here's the same guy's thesis, haven't read it, it's 285 pages long, probably covers the same ground.

http://www.diva-port...1__fulltext.pdf

Incidentally the appendix to the SAE paper adds:

"When the ratio of static pressure at the narrow section of
the restrictor, and the total inlet pressure is 0.528 and
below, sonic speed will be reached at the narrow
section. Depending on the recovery of the dynamic
pressure in the diffuser that means a pressure ratio over
the entire restrictor of approximately 0.7. Once sonic
speed is reached, decreasing the restrictor exit pressure
will not increase the mass flow rate further."

I think Gregg asked me to find that one time. the implication is that there is an absolute limit to the volume flow rate you can push through a given orifice, for a given upstream pressure.