Ran across this old article about the LMP team 4.0 Northstar used by Cadillac in 2002. I thought the last sentence was paticularly interesting.


ACO RULES SPECIFY MAXIMUM BOOST AND INLET RESTRICTORS FOR LMP ENGINE
The Automobile Club de L'Ouest (ACO) rules that govern the 24 Hours of Le Mans and the American Le Mans Series (ALMS) achieve performance parity among different types and sizes of engines by specifying inlet air restrictors and maximum turbocharger boost. Under the ACO formula, the 4.0-liter Northstar V8 is limited to 1500 millibars absolute manifold pressure (equivalent to 7.5 psi boost pressure) and its air intake is regulated by two 32.4mm (1.28-inch) diameter orifices.

"The ACO regulations do a very good job of producing equivalency between naturally aspirated and turbocharged engines with a variety of displacements," Keating said. "However, turbocharged V8 engines have enjoyed great success at Le Mans in recent years, and the architecture of both the PRODUCTION Northstar V8 and its racing derivatives is well suited to this particular configuration.



http://media.gm.com/news/releases/020115_engine.html

Ran across this old article about the LMP team 4.0 Northstar used by Cadillac in 2002. I thought the last sentence was paticularly interesting.


ACO RULES SPECIFY MAXIMUM BOOST AND INLET RESTRICTORS FOR LMP ENGINE
The Automobile Club de L'Ouest (ACO) rules that govern the 24 Hours of Le Mans and the American Le Mans Series (ALMS) achieve performance parity among different types and sizes of engines by specifying inlet air restrictors and maximum turbocharger boost. Under the ACO formula, the 4.0-liter Northstar V8 is limited to 1500 millibars absolute manifold pressure (equivalent to 7.5 psi boost pressure) and its air intake is regulated by two 32.4mm (1.28-inch) diameter orifices.

"The ACO regulations do a very good job of producing equivalency between naturally aspirated and turbocharged engines with a variety of displacements," Keating said. "However, turbocharged V8 engines have enjoyed great success at Le Mans in recent years, and the architecture of both the PRODUCTION Northstar V8 and its racing derivatives is well suited to this particular configuration.



http://media.gm.com/news/releases/020115_engine.html


This is good PR "speak".... The meaning of the work "architecture" defines the whole message here.... The engine architecture can mean a lot of different things so how it is defined makes or breaks the idea.

Any DOHC, 4 valve V8 reacts positively to turbocharging.....

Understand that the LeMans engines have little or nothing to do with the production Northstar. Both are DOHC 4 valve V-8's (hence the similar "architecture") but the designs, dimensions, etc. of the engines have little or nothing in common and share absolutely no parts. The LeMans engines are based on the second generation IRL Aurora engines that were application specific racing engines designed per the IRL rules for that series. Cadillac used those as the starting point for the LeMans developement and the final versions are very very similar to the IRL engines. The compression ratio and operation speeds are different as well as the exhaust and turbo intake plumbing but fundamentally the engines are virtually identical otherwise.

The LeMans rules required the engines to breath thru a small restrictor (exact same idea and principal as the NASCAR restrictor plates under the carb) to equalize and limit performance of the cars. Turbo cars had/have a very very slight advantage at LeMans due to the allowed restrictor size and fuel limitations....but the advantage is slight and debatable and is there only due to the arcane rules structure of LeMans...not due to any specific engineering principle.