User Guide

Dyno2000 Advanced Engine Simulation—27
model 4-valve cylinder heads. These are very interesting choices since they simulate
the effects of very low-restriction ports and valves used in many import stock and
performance applications. The individual ports in 4-valve heads begin as single,
large openings, then neck down to two Siamesed ports, each having a small (rela-
tively) valve at the combustion chamber interface. Since there are two intake and
two exhaust valves per cylinder, valve curtain area is considerably larger than with
the largest single-valve-per-port designs. In fact, 4-valve heads can offer more than
1.5 times the curtain area of the largest 2-valve heads. This large area, combined
with high-flow, low-restriction ports greatly improves air and fuel flow into the cylin-
ders at low valve lifts and at high engine speeds. Unfortunately, the ports offer an
equally low restriction to reverse flow (reversion) that occurs at low engine speeds
when the piston moves up the cylinder from BDC to Intake Valve Closing (IVC) on
the final portion of the intake stroke. For this reason, 4-valve heads, even when fitted
with more conservative ports and valves, can be a poor choice for small-displace-
ment, low-speed engines, unless camshaft timing is carefully designed to comple-
ment the low-lift flow capabilities of these cylinder heads. On the other hand, the
outstanding flow characteristics of the 4-valve head put it in another “league” when
it comes to horsepower potential on high-speed racing engines.
The first choice in the 4-valve group is “4-Valve Head/Stock Ports And Valves.”
This simulates a 4-valve cylinder head that would be “standard equipment” on fac-
tory high-performance or “sports-car” engines. These heads offer power comparable
to high-performance 2-valve castings equipped with large valves and pocket porting.
However, because they still have relatively small ports, reasonably high port veloci-
ties, and good low-lift flow characteristics, they often show a boost in low-speed
power over comparable 2-valve heads.
The next choice, “4-Valve Head/Ported With Large Valves” incorporates mild
performance modifications. Larger valves have been installed and both intake and
Custom Port Flow Dialog
The Custom Port Flow
dialog box allows the direct
entry of flow bench data.
From 4 to 10 data points for
each port can be entered.
Virtually any test valve
diameter and pressure drop
can be used.
Cylinder Head Menu