User Guide

Dyno2000 Advanced Engine Simulation—61
in 2001). While flow restriction (back pressure) is accurately modeled using “pres-
sure-drop” techniques, the Dyno2000 does not resolve specific header dimensions.
However, the Dyno2000 can accurately predict engine power changes from various
exhaust manifolds and headers of large and small tubing diameters (sizes relative
to the displacement of the engine under test).
The exhaust menu choices are described in the following sections. Use this
information to make the most appropriate choice for your test engine.
Stock Manifolds And Mufflers—The first choice in the Exhaust menu simulates
the most restrictive exhaust system. It assumes that the exhaust manifolds are a
typical, production, cast-iron, “log-type” design, where all ports connect at nearly
right angles to a common log passage. These manifolds are designed more to
minimize clearance problems with various chassis and engine components than to
optimize exhaust flow. Exhaust manifolds of this type have widespread application
on low-performance production engines.
The Stock Manifolds And Mufflers selection assumes that the exhaust manifolds
are connected to twin mufflers with short sections of pipe. Because the engine
environment is a simulated dyno cell, the exhaust system terminates at the muffler
outlets.
The exhaust manifolds and mufflers cancel all scavenging effects, and the system
is a completely “non-tuned” design. Any suction waves that might be generated are
fully damped or never reach the cylinders during valve overlap. The restriction cre-
ated by this system mimics most factory muffler and/or catalytic-converter-with-muf-
fler combinations. Back pressure levels in the exhaust system nearly cancel the
blowdown effects of early EVO timing and increase the pumping work losses during
the exhaust cycle.
H.P. Manifolds And Mufflers—This choice offers a measurable improvement
over the stock exhaust system modeled in the previous selection. The high-perfor-
mance exhaust manifolds simulated here are designed to improve exhaust gas flow
and reduce system restriction. They are usually a “ram-horn” or other “sweeping”
design with fewer sharp turns and larger internal passages. The connecting pipes to
the mufflers are large diameter and the mufflers generate less back pressure and
produce more noise.
While this system is a “high-performance” design, it offers no tuning effects and
all suction waves are fully damped or never reach the cylinders during valve overlap.
All performance benefits from this selection are due to a decrease in passage
restrictions and lower system back pressure. System pressure levels mimic factory
high-performance mufflers and/or catalytic-converter with muffler combinations. This
exhaust system may allow some benefits from early-EVO timing blowdown effects
(depending on the engine component combination) and overall pumping work losses
are slightly reduced by lower back pressures.
IMPORTANT NOTE ABOUT ALL HEADER CHOICES: Some engines, in particular,
Exhaust System Modeling