EXHAUST SCAVENGING IT THE METHOD OF USING EXHUAST PULSES FROM ONE CYLINDER TO HELP PULL MORE OF THE NEXT CYLINDER.
AS YOUR ENGINE IS RUNNING, THE EXHAUST FROM EACH CYLINDER IS COMING OUT IN PULSES- 1 EVERY 2 REVOLUTIONS FOR A 4STROKE ENGINE.
AS THIS PULSE IS LEAVING THE CYLINDER PAST THE EXHAUST VALVE, IT HAS ALOT OF ENERGY AND MOMENTUM, AND PUSHES ITS WAY DOWN THE EXHAUST TUBE TO LOWER PRESSURE AREAS.
Life-size example:
THINK OF THIS PULSE AS A CAR DRIVING PAST YOU ON THE ROAD. AS THE CAR GOES PAST YOU AT SPEED, YOU FEEL YOURSELF GETTING PULLED ALONG AFTER IT.
THIS EFFECT IS SAME AS WHEN THE PULSE GOES THROUGH THE COLLECTOR AND MAKES MINI VACUMMS IN THE OTHER TUBES.
THIS VACUMM HELPS TO ACCELERATE THE NEXT PULSE FROM AN ADJACENT CYLINDER, AND THE CYLCE REPEATS AS THE SECOND PULSE PASSES THE COLLECTOR AND PULLS THE THIRD PULSE.
FINDING THE CORRECT TIMING OF THESE PULSES LEADS TO DIFFERENT LENGTH HEADERS GIVING DIFFERENT POWER BOOSTS TO THE ENGINE.
LONG TUBE HEADERS
LONG TUBE HEADERS ARE BETTER FOR HIGH RPM APPLICATIONS WHERE THE EXHAUST GASSES WILL ALREADY HAVE ALOT MORE SPEED AND WILL BENEFIT FROM BEING INDEPENTENT LONGER.
SHORTY HEADERS
SHORTY LENGTH HEADERS WILL GIVE A MORE SUBSTANTIAL BOOST TO MID RANGE POWER AS THE SCAVENGING EFFECT WILL TAKE PLACE SOONER IN THE SHORTER PIPES.
LOG HEADERS
LOG STYLE HEADERS ARE USUALLY SIMPLE PATHS THAT RAM DIFFERENT PULSES INTO EACHOTHER, AND DO NOT HAVE ANY NOTICIBLE SCAVENGING EFFECTS.
WHICH IS THE BEST HEADER DESIGN?
TO BENEFIT FROM EXHAUST SCAVENGING, A TUBULAR DESIGN IS THE MOST COMMON, BUT THERE ARE SOME CAST MANIFOLDS THAT SCAVENGE EFFECTIVELY.
IF CHOOSING BETWEEN SHORT AND LONG TUBE HEADERS, NEITHER IS A BAD OPTION FOR PERFORMANCE, BUT THE DESIGN OF THE COLLECTOR, DIAMETER OF THE PIPES, AND TRAVEL DIRECTION WILL HAVE THE LARGEST IMPACT.
FOR BOOSTED APPLICATIONS WITH ADDITIONAL PRESSURES BEFORE THE TURBO, EXHAUST SCAVENGING IS LIMITED AND USUALLY NOT CONSIDERED.
BACK PRESSURE ↗
Get an overview of how exhaust scavenging works and increases power.
CATALYTIC CONVERTERS ↗
How do Cat’s work and how do they effect power output? Should I keep my catalytic converters?
HEADER TYPE AND DESIGN ↗
Get to know the different types of exhaust manifolds and how they effect power ranges and sound.
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