Alright so the one thing I know for sure collector length can enhance torque below, at or above
peak torque. Hi my name is Norm welcome to another quick flicks episode brought to you
by Summit Racing. Today we are going to pick up where we left off the last time discussing
headers, a little technology, a little FYI stuff but today primarily focusing on collectors.
Okay so we did our math the last time with our primary tube diameters and I am just going
to take you right to the sweet spot the collector diameter. You are basically going to do a
math problem again, simple multiplication. Take your primary tube o.d. diameter that
we established in the first episode, multiply that by 1.6, 1.7, 1.8 or so for a street or
dual purpose vehicle. If you are a more aggressive street vehicle, a limited street vehicle,
more of a weekend warrior you might want to use a 1.75, 1.8, 1.85 multiplication factor
times your primary tube diameter. And if you are a race car you may want to start with
a 1.8 looking all the way up to a possibly 1.85, 1.90 perhaps even a 1.95. Now there
are some instances where you could use a 2 to 1 multiplication factor but those guys
usually have no need of my technology. Okay so now collector length, hopefully that is
where I got you at the beginning. Collector length okay if you think about what do I want
to say here, if you think about the peak torque thing okay, if you remember kind of like my
homemade drawing the last time okay, so peak torque it happens at a certain RPM it is a
certain number. If I want to enhance below my peak torque I am going to run some type
of collector length. Alright so, let�s look at this in a little more detail particularly
for let�s say a street application. A milder street, a moderate street, even trucks again
okay. Think about this, I know I have got to extend my collector to enhance my torque
below peak torque. How do I do that when I get this kind of short collector out of the
box? I stay with at least some section length in my exhaust system that is this same diameter.
That is the best I can make out of this package oaky. I mean you�re going to be limited
by what is available from the manufacturer unless you have deep pockets and the software
to determine what you need for a header build, okay. So I am limited to what the manufactures
are making available to me, first of all and of course what will fit. But if you need to
extend that collector I would encourage you to think about considering another six inches,
eight inches maybe even twelve�fourteen inches of same diameter tubing before you
take that reduction into two, two and a half inch dual system. Reason for all of this has
to do with reflective waves. Okay. Reflective waves, here I am going to take you to the
other side so the combustion thing is going on up here in the block, the flow is coming
in and out of the cylinder head and think about this, as the piston goes down its pulling
gases in right? It is evacuating perhaps also. There is some evacuation going on, on the
other side but that is usually where the compression thing starts to happen as the piston starts
to go back up. These reflective waves occur as the exhaust valve opens, you get the big
rush of exhaust gases leaving the cylinder. What�s going to happen is their traveling
very fast, you know particles travel oh you know in the 340 oh I am sorry 240 � 250
� 260 feet per second range. The actual wave is a at or near or beyond sometimes the
speed of sound so we are talking 14 � 15 � 16 � 1700 feet per second. Really really
fast. So anyways, these gases, this wave if you will, is moving and traveling down my
primary tube as it reaches as in this case reaches a collector it opens up into a greater
expanse as that expansion occurs you get a drop in the velocity and as that wave hits
against ( I am thinking about invisible things okay) as that wave hits that expanse, the
velocity drops, also as it hits that expanse there is a reflective wave that is generated
and actually travels back up the primary tube to the cylinder. Now if all things are going
as planned and it is possible for that negative wave, that reflective wave, if its negative
compression it is actually a vacuum and if its negative pressure, it�s a vacuum. So
as this vacuum reflective wave comes into the cylinder, if both valves are hanging open
at the same time if your in overlap. You have the potential to really evacuate that chamber.
If you think about this, all of this is going on Nano-seconds.. Micro-seconds, it�s very
very quick. And it is only happening at certain RPM�s that is why their tuned headers. But
when it does happen it�s like the crescendo of exhaust technology. ahhhh. So here we are,
this wave is coming back in its coming in past both valves are up. You can thing about
this, you know, the vacuum occurs its saying �hey fill me, I�m a void�. You always
want to travel from high pressure to low pressure, that is just the way things are I mean look
at the clouds, look at the atmosphere, look at the water. That is the way flow happens.
So it wants to fill this void, well all of that fresh air, the potential exists to have
all of that fresh air on the other side of the intake valve to come sweeping in, fill
the void of the chamber, and maybe even come in the exhaust track for air depending on
the amount of overlap and how quick this is happening, engine RPM, displacement, all of
that comes into this. But that is basically what scavenging is about okay that is what
makes headers a beautiful thing. So I think without getting any crazier, I hope you enjoyed
the video and I�ll see you next time on quick flicks. If you like what you saw, please
let us know, and post your comments down below. Thank you very much. Bye.