There are several "articles" incorporated into this one page.. They
address different areas and aspects of the exhaust system.. Please
check out AND ENJOY, ALL the information in this page.
There is a bit of confusion as to why most aftermarket
silencers are not working well with mod engines..
FIRST and foremost... It has nothing to do with a silencer and a
piston or head, or porting, working well together..
What it is related to is TOTAL ENGINE POWER!
Nearly all aftermarket silencers are more restrictive in air flow
than the OEM muffler! Since the main jet on ALL stock sleds is too
large, then you can effectively lean down an engine via restricted
exhaust flow and no jet change.. OR you could reduce the main jet to
proper size and accomplish the same thing for a lot less $$
Let me explain.. If you have a exhaust system or exhaust component
(like a pipe or silencer) that is designed to work and perform well
on an engine that is making 140HP.. Then that is a matched component
for that 140HP engine.. Now if you take that same component (pipe or
silencer) and install it on an engine that is making 20-35 MORE HP (i.e.
flow more air) than the engine it was designed to run on (140HP)
then you have a mis-match in the component to the engine...
So, it does not matter if you are running RKT pistons, RKT head, or
some other piston or head ... IF the engine is making ANY
SUBSTANTIAL amount of increased power.. then the exhaust system is mis-matched.
So whether it be the RKT drop in kit, RKT 172HP 827 kit , RKT 860R,
RKT 925 or anybody else's big bore or
piston kit.. if the aftermarket silencer is working well on it..
there is a very good chance that the performance package (what ever
it may be) is not making big power (like you may have been lead to
believe when you bought it).
This is why the stock exhaust components work so well with the
modified engines (at least the ones that are making power)
The OEMs build their engines to survive on low octane fuel for
pro-longed running and high EPA standards/regulations.. So, they
design an engine and exhaust system that is a bit handicapped so
they can meet these warranty and EPA demands... One easy way to meet
these demands is to make an exhaust system that is a bit "loose" so
that there is not too much heat put back in the engine under heavy
running. Another way is to add a single ring piston design that will
lose power the longer it is run.. and then they always have it
jetted up 1-3 sizes larger than it really needs to be. So, basically,
you have an exhaust system that is too loose and an engine that will
making less power the longer it is run and the harder it is tasked..
and Oh, the excessive main jet installed by the factory... Pretty
smart heh?? you start off with 800 power and after a bit of hard
running you have 700 power...
So, NOW you add an engine package like the drop in (+18-20HP) or the
827 (+30-32Hp) and your engine is able to make more power and ,
better yet, SUSTAIN, this power during repeated running..
OK, now that loose OEM exhaust system is suddenly not so "loose"!
Make sense?? So, now you have a stronger running engine that is
flowing more air and you Stuff a restrictive exhaust can on the end
on your pipe... WOW.. what happens??
YUP.. the O'LE Banana in the tail-pipe syndrome
try stuffing a potato in your truck's tail pipe someday and see how
So, the jist of all this.. IF your engine is making SUBSTANTIALLY
(like more than 10HP) more power you can not run a restrictive
exhaust or you RISK placing too much heat back in the engine..
is to determine which exhaust components are more
restrictive than stock or less restrictive than stock..
To add even more confusion to the whole "can" issues.
Most cans are what is called a straight passive bleed system..
Meaning it is no more than a bleed valve for the main exhaust.. This
is why you could have the center dump pipes.. It did not really
matter where the bleed was located, you just had to have one and one
that was not restrictive (there's that word again
Some (like the Arctic Cat) silencers are actually a resonator
silencer.. without going into too much detail... it is a "tuned"
silencer and will resonate at certain frequencies and provide pulse
assisting to the main pipe.. So, it is not a passive bleed system
but rather a tuned system...
I have my suspicions that the DOO cans may also be this type
(resonator). But have no verification of this. I DOO know that the
CAT cans are this type and are VERY sensitive to aftermarket cans
So, if you consider putting a passive bleed can (like all
aftermarket) on an exhaust system that is designed around a
resonating can system.. You can see how this would hinder
Just a thought: But do you EVER see a silencer on any of the
Drag Sleds?? If the silencer was just a player in performance, then
all drag sleds would surely have them attached. Most drag sleds will
have no silencer attached and this just strengthens the theory that
silencers are not and should not be an active "player" in the
tune of the exhaust system!
HERE IS A BIT ON PIPE
FUNCTION/PRESSURE AND HEAT
The main relationship between the head and the exhaust is how much
heat it (the head) puts into it and how much pressure (not to be confused with
back-pressure AT ALL) or more appropriately VOLUME of F/A and air is
returned to the cylinder (and eventually the head) via stuffing pulse
from the TUNED PIPE.. NOT THE Y PIPE OR THE CAN!...
These "tuned" stuffing and suction pulses are a direct result of the
cones in the TUNE PIPE. They (the cones) are the major players in the control these pulses. The pipe's
back-pressure is determined by the STINGER outlet that is directly
after the convergent cone. The silencer is nothing more than a bleed valve and
does should not be used as a method to control back pressure. What it does effect
is how fast it can dump HEAT out of your engine. Do not confuse heat
with back pressure.. They are not the same... Think of the silencer
as the drain in your bath-tub and think of the tub water as the
exhaust HEAT.... Now, the bigger the drain (silencer) , the faster
the water (HEAT) drains...and the vice-versa is obviously true...
Keep in mind.. the back pressure has already been determined via the
STINGER..BUT.. can be altered via a restrictive silencer.
So, what really happens is that if you have a tighter silencer is:
The returning pipe stuffing pulse is hotter and since heat effects
the speed of sound. The timing (via speed) of the pipe pulse
can be wrong and this can cause you performance issues and possibly
Is the pressure increased from this?? possibly..
Again, the combustion process (head) is a player in how much HEAT is
put into the pipe and less heat in the pipe means a MORE efficient
combustion process (giving all things equal). MORE HEAT in the pipe
means a LESS efficient combustion process ( ie. LESS push on the
piston and less work being performed on the crank train)
Of course this is a simplified explanation of the system.. but it
should get the concepts across..
NOW.. So, where does this leave the idea that a silencer and a head
have to work together?? Or a head and a Y Pipe working together??
Hmmm....they do not.. The silencer is nothing more than a bleed valve.
When you have an engine that makes MORE power than a silencer is
designed for.. you can not "dump" the HEAT fast enough and CAN get
too much HEAT back into the cylinder OR change the "tune" of the
exhaust system via excessive HEAT.. Does this added heat increase
Gas laws will tell you YES... Is this added pressure going to cause
your engine problems?? IMHO.. no (read above) I believe it to be
more related to the heat and out of time exhaust pulses vs. the
actual pressure rise..
Now onto the Y Pipe...Is the Y Pipe and the head related?? IMHO..
NOT IN ANY WAY! The Y pipe is not a critically tuned component.. Its
length and diameter , IMHO, are the only critical portions. Changing
either one of these dimensions can effect the heat transfer and
pulse timings.. Are these related to the head?? IMHO.. NO..
So, Y pipes adding big power?? Mainly if there is a mis-match with exhaust
outlet diameter and Y pipe diameter.. then yes, this will help a
bit.. Can you fix the mis-match and achieve the same results?? Most
You can alter the length of the pipe via Y pipe shortening or
lengthening and THIS can change performance for the better and
also for the worse.
Are these aftermarket Y pipes for these engines smaller or larger in
diameter? Longer or shorter in length? If so, then they could very
well alter the timing of the pipe and this can add or lose power!
MORE ON PRESSURES AND PIPE
Sound waves are pressure waves, but pressure is
To accurately measure the pressure of any
oscillating wave one needs sophisticated high speed transducers.
These are very expensive and are generally computer controlled.
It should be noted that waves in a medium (pipe
for example) are oscillating. With an oscillating waveform, the
amplitude of the wave will be constantly varying. There is usually a
negative and a positive component (value). The shape of the wave can
be uniform or very non-uniform (like I suspect an exhaust pressure
wave would mimic)
When measuring any wave with a mechanical
device (such as an analog pressure gauge) this gauge is very over-tasked for
this sort of a measurement. The result would be a RMS (root mean
squared) value, AT BEST, and would not accurately represent the
Let’s assume you have a steady frequency
sinusoidal wave in the pipe (which we do not but we will assume for
the moment) Taking a measurement with a gauge will give you the RMS
value of this wave. The RMS value will be an “average” at best.
Now assume a pressure wave that is constantly
varying it frequency, and amplitude (like a true pipe pulse) and
now, you get a pressure that can not be measured
correctly with a
simple analog gauge-type device.
As we rise in elevation, atmospheric pressure
decreases. This is a given. So, if you do NOTHING but rise in
elevation, you drop pressure. So, ANY pressure measurement in a non
sealed medium will be LOWER just from the rise in elevation.
Now the pipe pulses are treated as sound waves
and the speed of sound is used in these calculations. The speed of
sound (in a non-sealed medium) is temperature dependant. As we rise
in elevation, temperature usually decreases and therefore; the speed
in which the pipe waves travel are slower and this why we need to
have increased pipe heat as elevation increases. You can increase
the pipe heat via several methods. 1) Minimize radiation losses via
wrapping the pipe with a TRUE heat barrier. 2) Increasing the
internal gas heat via added power (engine enhancements etc.) these
are a few. OR, you can alter the tuned length of the pipe to
compensate for the slower travel.
So, one would surely benefit from a pipe that
is designed around the lower atmospheric pressures that are present
at the higher elevations.
BUT, let’s say you increase your engine’s
internal heat and pressure via some true power increasing
modifications. Now the internal pipe pressure may still be lower
than if you were at sea–level BUT, it would be higher than if your
engine did not have the power enhancements and you would have more
rapid travel in the pipe.
So, the higher in elevation we go, the less
power the engine makes unless something changes to process more air
through the engine (Engine enhancements etc.). The naturally
aspirated engine loses power because it can't process any more air.
The engine can't magically grow displacement or increase rpm
So, what is the point to all this?? ONE point
would be that the increase in elevation will produce less internal
engine pressure and, as a result, less pipe pressure. Increasing the
pipe’s internal pressure via stinger choking or restrictive
silencers CAN allow for more pressure to be placed back in the
engine via the “plugging pulse” of the pipe.
BUT, this can come at a
The pulse’s strength and length are determinant mainly by the
cone sections of the exhaust, NOT the stinger. The diameter of the
stinger is a critical component. WHY? Because it has some control
over the pipe’s operating temperature (internal heat). Too large of
stinger and you can lower the pipe heat to a point of power-loss.
Too small and you get an exhaust that can not bleed off pressure
effectively and the engine will be the recipient of this
“non-exhausted” heat and can cause engine failure, especially on
long WOT pulls).
Get the stinger diameter just right and the
engine acts like a tad shorter pipe and you can gain some power.
NOTE: I said “STINGER” not “SILENCER”!
The silencer is located AFTER
the stinger. Yes, the silencer does effect the rate of exhaust
bleeding but having too large of a silencer does not effect the
stinger’s operation... having too small of silencer diameter can
effect overall pipe operation due to internal heat and can cause
OK, so what do we know?
1) Increasing elevation will decrease pressure
2) Pipe pressures are determinant on the power
of the engine.
3) Internal pipe heat effect the speed of the
waves in the pipe.
4) The proper way to increase pipe heat and
pressure is to design a pipe that accounts for the higher elevation.
5) The Stinger section of the pipe has a strong
effect on the RETURNED internal pipe heat to the engine.
6) Increasing the returned pipe pressure via
stinger or silencer choking can cause severe engine failure but can
also aid in some cases.
7) Internal pipe pressure can not be accurately
measured via ANY mechanical gauge.
8) More power creates more internal
pressure/heat and can allow a pipe designed for low elevation to
work at high elevation.