CatBack/ Exhaust size.

[KBeezy]

...uhm, what did you say that nobody else didn't? ^^^

[Adrenaline_Z]

Quite a bit.

Read again, especially the part about the catalytics.

[Turbo V6 Camaro]

just put a turbo on you'll have all the back PSI you need and run like 8' exuast out the back or in my case lack there of

[Turbo V6 Camaro]

Originally posted by Adrenaline_Z:
Hello All,

Harlan asked me to view this post and share my
thoughts.

Initially I was given bits and pieces of this
thread via e-mail, but now reading the entire
story I'm able to give better judgement on the
topic.

First off, this thread is so far gone, it's probably
not my place to interfere and there are so many
opinions over fact, I'm not so sure I want to
get too deep into this.

For what it's worth, everyone has a valid point
to a certain extent.

One thing everyone fails to realize is the 3"
pipe IS too big for the 3.8L displacement.

What is happening is, the frontal surface area of
the catalytic converter creates a backpressure
(resistance of flow) which causes a reduction
in power.

This is due to a high pressure value residing the
the exhaust system.

By increasing the surface area of the catalytic
internals, the exhaust gas has more area to flow
through which allows the pressure in the exhaust
system to drop.

This is why you are seeing a modest increase in
horsepower.

If the pressure in the exhaust is lower than the
pressure in the manifold and cylinder, the air and
fuel charge will move downstream at higher velocities
according to the pressure differential.

If you were to install a tuned performance exhaust
system which consisted of a high flow catalytic
(let's say 800 CFM) with a 2 inch diameter pipe,
the pressure before and after the catalytic would
be less because the smaller diameter pipe will
increase the gas flow velocity.

With a catback system that is properly sized and
tuned, you would allow the power band to stay
relatively stable while augmenting the power across
the entire range.

In addition, you'd see more than 8 HP with tuning.

If you don't understand pressure differential with
fluid/gas in a pipe, have a read on Bernoulli's Principle.

http://www.mste.uiuc.edu/davea/aviat...Principle.html

You would find without a doubt that installing
a higher flow catalytic (800 CFM+), or removing it totally
while installing the correct length and diameter
intermediate pipes will see a gain over a 3" inch
pipe and 3" cat.

This all has to do with, pipe volume (velocity)
resonance and pulse tuning using valve timing.

EDIT: The muffler flow also has the very same impact
on the exhaust system internal pressure.

More flow = more power.

Short pipe, large diameter = top end resonance, High RPM
Long pipe, small diameter = low end resonance, Low RPM

so basicaly what your saying is even tho the pipe is smaller it still flows more lb/min because of the higher velocity?

way i see it, just because its flowing faster does not mean its flowing more. kind like a water hose and a fire hose, you might be able to get the water hose to spray farther then the fire hose but theres know way in hell its sprayin the same amount of water. gal/min terms

please explain howsstuffworks don't go into it.
also on a car with a turbo would this even matter ?

[Adrenaline_Z]

The first thing you need to understand is how
fluids and gas react in a tube. Read that link
about Bernoulli's Principle in an earlier post.

Once you have a grasp on that link, you can relate
that information to this example:

Let's assume that atmospheric pressure never changes.
Let's also assume that the engine puts out the
same amount of exhaust gas at any RPM and the
pressure is constant.

If we were to measure the pressure at a few points
along the exhaust system, we would see different
values.

Atmospheric pressure is ~14.7 PSI at sea level

When the engine is off, the pressure in the intake
manifold, cylinders and exhaust equals atmospheric
pressure.

Once the pistons are moving, the pressure throughout
the engine is different.

The exhaust for this example has a 3" catalytic
conveter that flows 400 CFM @ 28" depression, and
a 3" intermediate pipe, and a 3" muffler that flows 600 CFM.

For one instance in time, assume the pressure at the

Y-pipe is - 5 PSI.

Though the catalytic is - 2 PSI

In the intermediate pipe is - 5 PSI

In the muffler - 2 PSI

Manifold Absolute Pressure is + 16 PSI

The rate of flow is relative to a higher pressure
in the manifold moving itself down to a lower
pressure area (which is the exhaust).

For the next scenario:

The exhaust for this example has a 2.5" catalytic
conveter that flows 800 CFM @ 28" depression, and
a 2" intermediate pipe, and a 2" muffler that flows 800 CFM.


Y-pipe is - 7 PSI.

Though the catalytic is - 5 PSI

In the intermediate pipe is - 7 PSI

In the muffler - 6 PSI

Manifold Absolute Pressure is + 18 PSI

You see that the reduction in pressure (lower than
atmospheric) allows more charge to enter the
manifold and cylinders.

How did we achieve this?

We used a smaller pipe with less restrictive catalytics and mufflers.

Since the fluid/gas can create higher velocities
in a smaller diameter tube (of proper size), the
pressure will drop in the exhaust.

What everyone else is doing, is somewhat incorrect
technically.
Everyone thinks that getting a larger pipe and
cataltyic is better.

The truth is, you could have a smaller diameter
catalytic that flows more and proper tubing which
increases gas flow speeds (velocity) to make better
power.

With the hose example, it's the same thing.
It IS flowing just the same amount, as long as the
pressure is allowed to increase at the water pump.

IE: ~100 PSI into a 2" hose will flow the same as
~80 PSI into a 2.2" hose.

One thing we can't do is equate a fluid and a gas.
If we pressurize gas it compresses. Fluids can't compress, therefore we can't use the water hose
and exhaust system as an example.

With a turbo, it's another comparison we can't relate.
Boosted motors always have their manifold pressurized
higher than a naturally aspirated motor.
Therefore, using a larger pipe will be fine because
the Manifold pressure is not AS dependent on the
exhaust pressure.

All of the above is one piece of the pie when it
comes to exhaust tuning.

There is pressure reflections which can be timed
with valve events to create even more power.

There is lenght of pipes tuned to RPM which dials
in a certain window of power.

There is also shape of the pipe, thermal characteristics
of the pipe, etc. which attribute to laminar flow
and making even more power.

[ October 02, 2004, 06:03 PM: Message edited by: Adrenaline_Z ]

[Turbo V6 Camaro]

read like 8 times......
ok i think what you was trying to say was
the freeer flowing exaust put more PSI in the intake and there for a "more full" intake charge make more power....

but how are you getting more the 14.7 whit out boost?

[Adrenaline_Z]

Good question.

It's called a 'standing wave' effect.

If you know how tunnel rams work, you can apply
the same idea to intake tuning.

Think of the atmoshpere (Air) as water.

Remember I said not to equate water and air
before? Well, forget it for now ;)

Let's pretend we are dumping water down the intake
runner of cylinder #1 with the intake valve open.

The water is rushing down the intake runner and
flowing past the valve.

When we close the intake valve, the water that
still has motion (kinetic energy) hits the back
of the valve and literally reflects backward.

We have now created a wave going the opposite
direction in the intake runner.

On the next intake stroke the valve opens and
we begin to pour more water down into the intake
runner.

Remember that wave that reflected backward? It has
already hit another reflective surface and is
travelling back toward the intake valve.

Now we have a wave and a fresh charge of water
rushing toward the intake valve.

This creates an additive effect.

There is the inital wave reflected back which has
energy along with the new charge of water we
are pouring in.

So if we've added 2 PSI of the reflected wave, and
14.7 PSI of new water, the result is adding 14.7+2=16.7 PSI

Or

2 PSI over atmospheric pressure.

You have to imagine the intake and exhaust as one
string. When both valves are overlapping, this
scavenging effect can create standing waves
to fill the cylinder with more charge.

This is why it's very important to tune the engine
as a system...not just change one piece and hope
it works.

There is so much going on beyond our imagination.

Did you know acoustic energy also helps make power?
The sound waves in the intake and exhaust are also
another part of tuning that not many people are aware of.

[mdchaser]

Wow, it's nice to see that someone with real knowledge chime in. I've got a 3.8l with a CAI and a 3" catback system. The torque curve did move up a bit, it doesn't have quit the low end it used to. If you aren't going to mod the car too much then it's probably not a great tradeoff (in my opinion). Adrenaline_Z, I've got a turbo kit on the way (from FFF) and plan on running a full 3" exhaust (headers, high flow cat, 3" pipes). Is this a good idea? I'd like to hear some real logic as to why it's a good idea (and do you have any good sources we can read, I like that type of information).

[Turbo V6 Camaro]

Originally posted by Adrenaline_Z:
Good question.

It's called a 'standing wave' effect.

If you know how tunnel rams work, you can apply
the same idea to intake tuning.

Think of the atmoshpere (Air) as water.

Remember I said not to equate water and air
before? Well, forget it for now ;)

Let's pretend we are dumping water down the intake
runner of cylinder #1 with the intake valve open.

The water is rushing down the intake runner and
flowing past the valve.

When we close the intake valve, the water that
still has motion (kinetic energy) hits the back
of the valve and literally reflects backward.

We have now created a wave going the opposite
direction in the intake runner.

On the next intake stroke the valve opens and
we begin to pour more water down into the intake
runner.

Remember that wave that reflected backward? It has
already hit another reflective surface and is
travelling back toward the intake valve.

Now we have a wave and a fresh charge of water
rushing toward the intake valve.

This creates an additive effect.

There is the inital wave reflected back which has
energy along with the new charge of water we
are pouring in.

So if we've added 2 PSI of the reflected wave, and
14.7 PSI of new water, the result is adding 14.7+2=16.7 PSI

Or

2 PSI over atmospheric pressure.

You have to imagine the intake and exhaust as one
string. When both valves are overlapping, this
scavenging effect can create standing waves
to fill the cylinder with more charge.

This is why it's very important to tune the engine
as a system...not just change one piece and hope
it works.

There is so much going on beyond our imagination.

Did you know acoustic energy also helps make power?
The sound waves in the intake and exhaust are also
another part of tuning that not many people are aware of.

ummmm my brain is full going to have to look some of this up///

[Vyse]

This topic has been discussed before. Do a search next time that's what it's there for! *****es.

[HBHRacing]

but it's obvious by the lack of understanding that a search will not reveal any good information.


Tino. Thank you for your interest. I am glad to see you here. I find is 100% funny that KBeezy would even ATEMPT to argue with you. and again, he trys to shift the direction of a point to confuse and detor the statemnts made instade of dissagree and show proof of his ideas.


I hope everyone can see now that there is a lot to learn. and there is no better person that I know of to explain then tino.

[pontiac nino]

Man this is some way cool interesting and knowlegable information. Thanks guys! [img]smile.gif[/img]

[KBeezy]

Originally posted by HBHRacing:
but it's obvious by the lack of understanding that a search will not reveal any good information.


Tino. Thank you for your interest. I am glad to see you here. I find is 100% funny that KBeezy would even ATEMPT to argue with you. and again, he trys to shift the direction of a point to confuse and detor the statemnts made instade of dissagree and show proof of his ideas.


I hope everyone can see now that there is a lot to learn. and there is no better person that I know of to explain then tino.

No, I've just been working for 9 days straight now and this is my 10th day. Just wait until I have a day off [img]smile.gif[/img]

[KBeezy]

All I want to see is PROOF that you guys can back up. You can bring up scientific laws, principles, theories.. But you guys have NOT given me what I am looking for with proof. I want to see actual TESTING that SAYS a 3.8 LOSES exhaust flow and exhaust velocity with a 3" system over a 2 1/2" system. PROVE it. You guys can say all you want but you still have only stated theories laws and principles. Not actual data, which in this case still doesn't prove ****. All we still have to go by is data which actually PROVES something -- which is a 3" exhaust is currently the BEST KNOWN setup a V6 F-Body driver has in a PERFORMANCE oriented exhaust. N/A, Doped, or Blown....


Because without ACTUAL testing all you guys have is a theory -- atleast we have dyno tests and timeslips to backup our results.

[ October 03, 2004, 01:25 PM: Message edited by: KBeezy ]

[HBHRacing]

sigh.. Now that you are here tino I am going to let you handle him. I already of 3 pages worth and he is still being ignorant.