CatBack/ Exhaust size.

[HBHRacing]

""There has to be a balanced design to enhance the maximum engine output, exhaust gas velocity, and sound. For example, imagine blowing air through a straw (comparing it to a smaller diameter pipe). This would take time to release all the air from your mouth, and you would feel pressure in your mouth while doing so. Now imagine blowing air through a paper towel roll (comparing it to a larger diameter pipe). You will relieve all your air much faster and feel little or no air pressure in your mouth because of the larger capacity of the tube. This is why it is important to get the correct size piping in order to relieve backpressure while maintaining thermal efficiency""


do you understand that?

[KBeezy]

Originally posted by HBHRacing:
""There has to be a balanced design to enhance the maximum engine output, exhaust gas velocity, and sound. For example, imagine blowing air through a straw (comparing it to a smaller diameter pipe). This would take time to release all the air from your mouth, and you would feel pressure in your mouth while doing so. Now imagine blowing air through a paper towel roll (comparing it to a larger diameter pipe). You will relieve all your air much faster and feel little or no air pressure in your mouth because of the larger capacity of the tube. This is why it is important to get the correct size piping in order to relieve backpressure while maintaining thermal efficiency""


do you understand that?

You're comparing human lungs with a limited capacity going thru a straw and something nearly 100 times as large. How about you do 2 straws and then double it. ****. What a crappy way to put it or relate it. I totally disagree with that comment. [img]graemlins/twak.gif[/img]

[HBHRacing]

OMFG.. you will argue anything. that also came from magnaflow. you want to dissagree with one of the worlds leaders in exhaust technology? I pitty you, I really do. you seem lazy to me, instead of actualy doing your homework and understanding what would work best you just throw 3 inch exhaust at and think it's best cause you saw a 8HP gain.


ponder this. what if you went 2.75 and only gained 4HP but gained .2 in the 1/4 over the 3 inch. would you still say the 3 inch works better?

[Blue98camaro]

[img]graemlins/popcorn.gif[/img] [img]graemlins/rock.gif[/img] HBHRacing!

[KBeezy]

Originally posted by HBHRacing:
OMFG.. you will argue anything. that also came from magnaflow. you want to dissagree with one of the worlds leaders in exhaust technology? I pitty you, I really do. you seem lazy to me, instead of actualy doing your homework and understanding what would work best you just throw 3 inch exhaust at and think it's best cause you saw a 8HP gain.


ponder this. what if you went 2.75 and only gained 4HP but gained .2 in the 1/4 over the 3 inch. would you still say the 3 inch works better?

Ponder this, what if he didn't ask about 2 3/4 pipes?

[KBeezy]

Look HBH, we (V6 F-Body drivers) have done the 2.5" vs 3" debate OVER and OVER and OVER. EVERY time its the SAME conclusion. 3" exhaust is if you plan on/are racing it. Get 3" if you want the most gains and dont mind it being loud as hell. Get 2.5" if its a street car, you wont race it, and just want a nice little growl to your exhaust note....


You're arguing with people who've been doing this for YEARS.

[shortdog273]

When I had a 3" exhaust on the V6 bird I had, it didn't hurt my 1/4 times at all. But, I also upgraded to a 3" exhaust because I started spraying it also. ;)

[HBHRacing]

but if you have been doing it wrong for years does that make it right?

you are a master at avoiding my questions. I say AGAIN..


what if you went 2.75 and only gained 4HP but gained .2 in the 1/4 over the 3 inch. would you still say the 3 inch works better????


come on that is a simple simple question. you can not fualt that logic. you are stuborn and it is draging EVERYONE else down the same path that you take.


with your next post ANSWER that quetion or be labled as someone how would rather avoid that admit.


now. I have been talking to a friend of mine that is without a doubt the smarted person that I talk to on a regular basis. He is the one that I learned most of the theory from. he has great examples inclusing the straw example that you again AVOIDED.

this is what he says for an example.

As for the 8 HP increase with the 3" exhaust,
that has probably happened way up around 5000 RPM.

What that guy doesn't realize is peak power is
not as important as AVERAGE Horsepower.

Big F'n deal if you gained 8 horsepower at 5000 RPM. He probably dropped a bunch of torque and
Horsepower from 2000-5000 RPM.

Compare the before and after curves

Before (stock exhaust system):

175 HP @ 2000 RPM
180 HP @ 2500 RPM
185 HP @ 3000 RPM
190 HP @ 3500 RPM
195 HP @ 4000 RPM
200 HP @ 4500 RPM
205 HP @ 5000 RPM
207 HP @ 5500 RPM

After (large exhaust pipe):

145 HP @ 2000 RPM
150 HP @ 2500 RPM
155 HP @ 3000 RPM
160 HP @ 3500 RPM
165 HP @ 4000 RPM
190 HP @ 4500 RPM
200 HP @ 5000 RPM
215 HP @ 5500 RPM

Check out where the power sits in both charts.

Where does this guy happen to spend most of his
time shifting?

What sort of transmission ratios is he using?

He would have to have a transmission and final
ratio setup that kept the motor between 4500-5500
at all times to take advantage of that small 8 HP
increase.

In the above examples, if he dropped below 4500 on
any shift he will run slower than the stock setup.

This is why horsepower peak means absolutely nothing.

It's all about the most average power over a band
of RPM. Normally, most transmissions are geared
to use at least a 2000 RPM window.


now. if you can actualy understand all this. and really honestly think about it logicly and NOT avoid the points then maybe we will have someone.


My msg to everyone other then KBeezy is this:

Don't listen to someone esle. Don't even listen to me. Look at the facts and deside for your self. Just because he refuses to use logic and basic education doesn't mean that everyone has to. yes, you can make 3 inch work, but the point is that it might not work well or you have to do other things in other areas to make it work.

Be your own person and make your own choices. Don't just follow him because he labled me a V8 guy who knows nothing about the V6's even tho it's the same theory that aplys.

Thank you for your time everyone.

[Linxs]

Originally posted by HBHRacing:

Compare the before and after curves

Before (stock exhaust system):

175 HP @ 2000 RPM
180 HP @ 2500 RPM
185 HP @ 3000 RPM
190 HP @ 3500 RPM
195 HP @ 4000 RPM
200 HP @ 4500 RPM
205 HP @ 5000 RPM
207 HP @ 5500 RPM

After (large exhaust pipe):

145 HP @ 2000 RPM
150 HP @ 2500 RPM
155 HP @ 3000 RPM
160 HP @ 3500 RPM
165 HP @ 4000 RPM
190 HP @ 4500 RPM
200 HP @ 5000 RPM
215 HP @ 5500 RPM

Check out where the power sits in both charts.

Where does this guy happen to spend most of his
time shifting?

What sort of transmission ratios is he using?

He would have to have a transmission and final
ratio setup that kept the motor between 4500-5500
at all times to take advantage of that small 8 HP
increase.

In the above examples, if he dropped below 4500 on
any shift he will run slower than the stock setup.

This is why horsepower peak means absolutely nothing.

It's all about the most average power over a band
of RPM. Normally, most transmissions are geared
to use at least a 2000 RPM window.

I'm catching the tail part of this..

The above numbers you posted:
I assume they were on the same car?
Were they on the same dynojet/mustang?
same temp and humidity on the testing days?
With or without (after market) headers?
Please define "Large exhaust pipe" new cat? Hiflow cat? 3".. 4"? what muffler? ect....?

ECT.....

The only reason why I am even posing these questions is because those numbers look funny to me (I am no expert just trying to understand that's all)....

Exactly 5 HP for every 500 RPM's? Did you round your numbers?

I'm not trying to be a jerk just trying to understand where and how you got your numbers?


My car is not stock (you can see in my sig) but I am going to run her on a dyno this weekend. I'll post my results (I have a 3" exhaust).

[ October 01, 2004, 01:18 PM: Message edited by: Linxs ]

[HBHRacing]

the numbers are just to be used as an exmple to try and elaborate on exactly what I am trying to say. Sometimes actualy showing some exampled works a lot better then talking till your blue in the face.

The dyno I am sure WILL show you that you gained HP, but the question is where did you gain it and where did you lose it. If you could dyno with the stock diamiter and then the 3 inch and place it side by side it would look a lot like the numbers above. It shows you what RPM's your motor needs to be running to actualy make power.

I thik that Kbeezy is just stuck on the idea of "it showed more HP so it must me faster" which I hope that I have shown everyone is not always the case at all.

[memphis_raines]

Originally posted by shortdog273:
When I had a 3" exhaust on the V6 bird I had, it didn't hurt my 1/4 times at all. But, I also upgraded to a 3" exhaust because I started spraying it also. ;)

This statement here should have put an end to all the bickering and help him make a decision as well. It all depends on how far he's gonna go with his mods. If one day he plans on spray, an engine buildup, turbo, etc. he should go with 3". If all he's gonna do is intake, exhaust, and a couple of other bolt-ons then stick with the 2.5". 'Nuff said....

Personally, I love my 3" setup. I just switched to a Hooker muffler with dual/dual tips, and the look and sound of it is pure sweetness.

[Ender2664]

The only end to this depate is what someone mentioned earlyier, and i don't have the money to do it. Go out and buy something like a dyno max exhaust system that comes with 2.5 or 2.75 or 3 inch pipes, and one by one dyno them and stock. This way you are using the same companys muffler every time and the same type of bends and piping, and then there will be evidence to show who is right.

[tdaddyz]

remember when the rumbler just came out and they dynoed with a cutout and with it, and the rumbler showed a gain in horses over the cutout
ever wonder why?

[HBHRacing]

The main thing that I wanted everyone to learn here is that conventional thinking is not always 100% correct. It's unfortunete that along the way i met with such resistence and from that 1 high resistence many people followed. I hope that some of you, even one of you looks through this post and desides to challenge tradition a little bit. Maybe then some of you can actualy use your own minds to make your choices and plans for exhaust and can fell really good about it when your done knowing that it was all about you. [img]smile.gif[/img]

[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 in
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

[ October 02, 2004, 05:34 PM: Message edited by: Adrenaline_Z ]