What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Pick my next mufflers *VOTE*

http://www.autospeed.com/cms/article.html?&A=0877

There's another one.

Check out any search engine and type in exhaust system backpressure and see what you get for results.

Pretty much 99% of them are going to say the same thing.

Backpressure is never good. To say that it is required is a myth.

Some pipe is necessary for cylinder scavenging. That is why I run small tube headers...they help keep the velocity high near the cylinder head for optimum torque at low RPM.

Everything after the headers is restriction and I know this. I run a full exhaust so I don't have to breathe fumes or deal with the noise, but I KNOW that this is costing me power across the RPM band, not just at high RPM (although there it makes more difference).

If you noticed a reduction in torque with open headers the answer to why is simple. Your fuel mixture was/is not tuned to the performance of open headers. If your engine had been tuned correctly you would see some pretty serious gains, even off-idle, with open headers.

Open headers are not practial or legal for street use though, so obviously we have to run exhaust systems....but cetainly not to add "backpressure" which can only take away our power and torque, and certainly add nothing.

Engines are big air pumps. Adding restriction to the outgoing air to try to help the incoming doesn't make any sense to me at all. In fact it's scientifically impossible.

This is not an opinion. This is scientific fact. Exhaust system backpressure takes away from power. Adding backpressure, no matter how small of an amount, can only done one thing, and that is reduce the power/torque output from the engine.
 
I got 2 forceaflows. Its not crazy loud, ive been told same sound as flowmaster and the same amount of flow. they were very enexpensive too. if u are really stuck on those 2 id go with #2
 
Wow tim, I learn something new from you every day, this statement really explains alot to me. Thanks /forums/images/graemlins/thumb.gif
[ QUOTE ]
If you noticed a reduction in torque with open headers the answer to why is simple. Your fuel mixture was/is not tuned to the performance of open headers. If your engine had been tuned correctly you would see some pretty serious gains, even off-idle, with open headers.


[/ QUOTE ]
 
tim explain to me how a 2 stroke exhaust works. it REQUIRES backpressure to even run.

a stock 350 needs SOME backpressure to create torque. with out backpressure it has no torque. the exhaust valve does not stay open long enough for it to work properly. the gases are going out fast the valve closes, and the gasses stop, nothing pushing them or pulling them. with backpressure the gasses never stop. yes the motor does have to work to get rid of them but once they get to a certain point they all blend together and helps pull the exhaust out of the cylinder. this is why long tube headers work better than shorties.

edit: with a bigger cam the gas burst are closer together require even less backpressure. the top fuel drag racers tune their exhaust by the lenght of the exhaust, longer tube, more backpressure, shorter, less backpressure

but i would still like for you to expain how a 2 stroke exhaust works /forums/images/graemlins/thinking.gif
 
[ QUOTE ]
[ QUOTE ]
Some back pressure is good down low. /forums/images/graemlins/peace.gif

[/ QUOTE ]

Once again, *.

Provide just one reputable source that states otherwise and I'll retract my statements.

Anything you can do to reduce backpressure will improve power and efficiency.

[/ QUOTE ]

Are you serious?!?!?!? On EVERYTHING but high RPM dragsters and full on racecars (cars that live between 5 & 8 grand) you LOOSE power. You want proof. Pick up any hot rod mag and read the dyno pulls. Unless that thing has got a mega lift cam and solid lifters capable of turning serious RPM, don't even think about straight pipes! Another thing, if you are still running hydraulic lifters you will not even be able turn up to the RPM where open pipes will produce power. Between idle and 5 grand you need mufflers. I could give you many stories about people getting worse ETs after loosing the mufflers.

If you want good advice on what exhaust to run, ask your engine builder. If you don’t have an engine builder then you either already know what to run because you are a professional engine builder yourself or are probably not up there in HP and RPM where you should consider running without one IMO.
 
[ QUOTE ]
tim explain to me how a 2 stroke exhaust works. it REQUIRES backpressure to even run.

a stock 350 needs SOME backpressure to create torque. with out backpressure it has no torque. the exhaust valve does not stay open long enough for it to work properly. the gases are going out fast the valve closes, and the gasses stop, nothing pushing them or pulling them. with backpressure the gasses never stop. yes the motor does have to work to get rid of them but once they get to a certain point they all blend together and helps pull the exhaust out of the cylinder. this is why long tube headers work better than shorties.

edit: with a bigger cam the gas burst are closer together require even less backpressure. the top fuel drag racers tune their exhaust by the lenght of the exhaust, longer tube, more backpressure, shorter, less backpressure

but i would still like for you to expain how a 2 stroke exhaust works /forums/images/graemlins/thinking.gif

[/ QUOTE ]

As to how a two stroke exhaust system works, that is not part of this discussion. Automobiles do not use two stroke engines the last time I checked.

Zero backpressure is impossible to produce. The exhaust port is always going to provide at least some measureable backpressure, and as I stated, the head ports are most efficient with a length of pipe on them. This is unquestionable--headflow numbers go up significantly with a pipe to help with scavenging. This is also why long tubes see deeper gains than shorties.

After the headers, it's all about reducing restriction and doing so without having an overly loud exhaust system. It is certainly not about adding backpressure to the system. Adding backpressure will make the vehicle quieter, but will certainly do nothing else except take away torque and horsepower across the RPM band.

No engine requires backpressure to operate. It requires velocity of both the incoming charge and outgoing exhuast. This is not produced with backpressure, but with the properly sized pipe to produce scavenging. I think you do have some understanding of how this works, but your terminology is certainly flawed if you believe backpressure breeds torque or power of any kind.

I am my engine builder. And you still have not proven anything.

I think this is absolute nonsense that you guys believe this longstanding myth of bullshit.

Do some research and I think you'll find that you're incorrect.

Backpressure does nothing but cut your power.

Once again, my statement is,

"Anything you can do to reduce backpressure will increase power across the RPM range".

Nobody here has proven otherwise. You have stated that some pipe helps with scavenging but I said that a long time ago. Nobody here has proven that adding restriction after the headers increases power on any level and for good reason. It's scientifically impossible.

I've stated fact, posted up other websites with others stating the same fact, and recieved nothing other than responses like, "I felt less power" or "Read this magazine".

Back in reality where we understand the scientific process, those are unrealistic experiments. If you felt less power, as I said before, your fuel mixture was probably too lean and the exhaust was so efficient that your fuel system couldn't keep up with it and that's probably why you lost power. As to the, "Read this magazine" comment, there are so many variables in a magazine test that it's hard to comment, but the reality is that they don't know any more than the rest of you do, and they've probably heard this widely published bullshit myth their whole life too.

Sorry guys but you're preaching something as fact that is just not scientifically possible, and so, once agian, I am dispelling this exhaust system backpressure bullshit myth, because the reality is that it could not be further from the truth, yet many people still actually belive this crap.

Do the slightest bit of studying, even a quick internet search on, "Exhaust System Backpressure" and you'll find that I'm 100% dead on with my findings in these posts.

Or, just do a search. I've covered this myth before.
 
This post is proof positive how deeply rooted this myth is......

So much, that you guys think I'm crazy for saying that it is nonsense.

It's almost like saying Pigs can fly.....
 
once you learn how a 2 stroke exhaust works you will understand (well maybe not you) why you need backpressure. and yes you need backpressure on a 2 stroke for it to run.
 
[ QUOTE ]
once you learn how a 2 stroke exhaust works you will understand (well maybe not you) why you need backpressure. and yes you need backpressure on a 2 stroke for it to run.

[/ QUOTE ]

Once again, car engines are not two strokes. They are four strokes.

Do some more homework and you'll find I'm dead on with my four stroke theories above.

As to two strokes I really couldn't care less. I don't own any, never intend on it, and I love my OHV V8s, they're simple.

And for the third time, every engine has backpressure. It is impossible to eliminate backpressure completely. Reducing it as much as possible after the headers will increase power, but it is impossible to eliminate it entirely.

All this in the quest to make an engine that is 100% efficient without the use of a supercharger or turbocharger. I'd say that is nearly impossible too with a dual plane intake, but you can get into the 90% range where your average stock V8 is probably in the high 70-80% efficient.
 
[ QUOTE ]
car engines are not two strokes. They are four strokes

[/ QUOTE ]

oh i didn't know that oh so smart one /forums/images/graemlins/bow.gif /forums/images/graemlins/bow.gif /forums/images/graemlins/bow.gif
 
[ QUOTE ]
1. There are no opinions being stated here. What I have stated is scientific fact not subject to opinion.

[/ QUOTE ]
That’s interesting.... How long have you studied Physics?!?!?! You most certainly must be familiar with Daniel Bernoulli.... well apparently not, because many of your assertions run contrary to his equations. He could be wrong though; his principles have only shaped EVERYTHING we’ve done with fluid and air since the 1700’s (including internal combustion engines, jet turbine engines, and heavier-than-air flight [that would be airplanes])!!!!!!
[ QUOTE ]
3. I do not enjoy arguing but I get extremely pissed off when people spread the wrong bullshit information.

[/ QUOTE ]

I'll let that one speak for itself.
 
[ QUOTE ]
...This is unquestionable--headflow numbers go up significantly with a pipe to help with scavenging. This is also why long tubes see deeper gains than shorties......
No engine requires backpressure to operate. It requires velocity of both the incoming charge and outgoing exhuast. This is not produced with backpressure, but with the properly sized pipe to produce scavenging....

[/ QUOTE ]
Apparently you haven’t heard of the venturi effect either…. How do you think velocity is created… what do you think is the by-product of this exhaust gas velocity…. Hmmmm…. Could it be a scavenging effect? An effect (in a roundabout way) created by the slight vacuum (or void) created as accelerated exhaust gas exits? Perhaps you should look up veturi along with Bernoulli.
 
[ QUOTE ]
...Back in reality where we understand the scientific process, those are unrealistic experiments... Sorry guys but you're preaching something as fact that is just not scientifically possible...

[/ QUOTE ]
I'll tell you in Lyman’s terms... in order to increase the velocity of a charge of air (such as exhaust gas AFTER it is expelled from the combustion chamber) it must pass through some sort of venturi (this is wide open here and could be a simple as a collector). This veturi will inevitably create a small amount of back pressure but will also create the velocity as the air is forced to speed up to pass through the venturi (like your carburetor). That, my friend, is scientific fact… just like Newton’s Law or the Law of Conservation of Mass (all topics you should look up next time you try to tout Science to back up your theories).
 
aw man! No reply yet????
Well, I'm gonna go hunt down some poor bastards on Splinter Cell-Pandora Tomorrow /forums/images/graemlins/peace.gif
All that science stuff made my head hurt /forums/images/graemlins/screwy.gif
Catch up on this tomorrow....... /forums/images/graemlins/thumb.gif
 
[ QUOTE ]
which of these two mufflers would be better for max HP, and have a more aggresive sound. louder the better.

motor is a 355 chevy built more for hp than torque. around 400 hp and 380 ft-lbs torque.

im leaning towards the dynomax, i've never heard them but they sound like they'd be badass. i've heard a single 3" magnaflow w/ cat that sounded good, but a little tame for this truck. maybe duals w/o cats would be better.

Or, if you have a better option for around $150 a pair chime in. I've got a Flowmaster 40 series on my blazer and i want to try something different.


Heres the links to the mufflers

Dynomax: #289-17218

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1363&prmenbr=361

Magnaflow: #642-11216


http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=85512&prmenbr=361
.

[/ QUOTE ]


Shoot me a PM, I can do a lot better then those prices on a set of MagnaFlow's.
 
[ QUOTE ]
Apparently you haven’t heard of the venturi effect either…. How do you think velocity is created… what do you think is the by-product of this exhaust gas velocity…. Hmmmm…. Could it be a scavenging effect? An effect (in a roundabout way) created by the slight vacuum (or void) created as accelerated exhaust gas exits? Perhaps you should look up veturi along with Bernoulli.

[/ QUOTE ]

As I said above, that is what the headers are for.

Yes, they inevitably create some backpressure, as do the exhaust ports. And yes, I agree with you, that is why tuned length headers and collectors exist.

However, that does not prove anything after the headers can help increase scavenging. The reality is quite the contrary.

[ QUOTE ]
I'll tell you in Lyman’s terms... in order to increase the velocity of a charge of air (such as exhaust gas AFTER it is expelled from the combustion chamber) it must pass through some sort of venturi (this is wide open here and could be a simple as a collector). This veturi will inevitably create a small amount of back pressure but will also create the velocity as the air is forced to speed up to pass through the venturi (like your carburetor). That, my friend, is scientific fact… just like Newton’s Law or the Law of Conservation of Mass (all topics you should look up next time you try to tout Science to back up your theories).

[/ QUOTE ]

Once again, true. As I stated above, some pipe is proven to increase headflow numbers significantly, and this inevitably creates SOME backpressure.

That venturi you speak of is the headers. After that tuned length of exhaust ends, anything you can do to reduce restriction will improve performance.

As I stated above, it is impossible to have ZERO backpressure.

What you're saying is pretty much dead on. It seems like you see the point here that velocity is the name of the game, not backpressure.

Force opposite the direction of flow in any amount more than the headers can create can only do one thing--force the engine to push the gasses from the engine instead of using the above stated venturi effect to "pull" spent gasses from the combustion chamber.

How all of this has anything to do with the exhuaust system 5-10 feet after that tuned length where someone installs a restriction like a muffler, then claims that it increases, "torque" is beyond me. That doesn't make any sense, and there is absolutely no scientific logic to that at all.

So, we've established:

Elimination of backpressure entirely - impossible
Flow of head ports without pipe - horrible
Using a tuned size header and collector to increase power/torque in the RPM range you're looking for - definitely a good idea.

We still have not addressed the issue as to how increasing backpressure after the tuned length of exhaust helps power though.

Performance enthusiasts that use muffers have for years, placed them as far back in the system as possible. This is done so that after they cool (and the engine is pushing the exhaust when it gets that far back in the system anyway) at least their volume is minimized before they entire something like the mufler, which even the best designs are still quite restrictive.

Scientific theories are great and all, but I've yet to find one to support the theory that you need, "Backpressure" to create flow at low RPM. Inevitably, small tube headers and slighly longer collectors will create some backspressure in the tuned portion of the exhaust, more so than large tube headers would. The backpressure is not what is creating the increased flow and RPM though, it is just impossible to fill and maintain velocity in a larger pipe. It is still not the backpressure creating this increased torque. It is the velocity and scavenging effect which I'm sure are proven in the experiments of the above scientists.

/forums/images/graemlins/waytogo.gif Actually a civil, but heated discussion here without personal attacks. I love it. /forums/images/graemlins/thumb.gif

I have to go to work now, and I look forward to the responses when I return. As I stated earlier, if anyone can prove me wrong I will gladly retract my statements. I enjoy a heated discussion but if I talk out my ass (which I have done in the past....duh) I'll be glad to be a man and retract my statements.
 
Combustion engines are only 25% efficient if I remember correctly.

-Chris
 
So which mufflers did we pick??? /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/ignore.gif /forums/images/graemlins/thinking.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/screwy.gif /forums/images/graemlins/dunno.gif
 
[ QUOTE ]
a stock 350 needs SOME backpressure to create torque. with out backpressure it has no torque. the exhaust valve does not stay open long enough for it to work properly. the gases are going out fast the valve closes, and the gasses stop, nothing pushing them or pulling them. with backpressure the gasses never stop. yes the motor does have to work to get rid of them but once they get to a certain point they all blend together and helps pull the exhaust out of the cylinder. this is why long tube headers work better than shorties.

[/ QUOTE ]
big83chevy4x4, what I don't understand then is how can the back pressure be strong enough to help keep the valve open and yet it does not restrict the exhaust flow? I think your confusing a venturi effect with back pressure. Or am I just misunderstanding what you are trying to say?

fad2blk99, If I'm reading yours and Tim's posts correctly you agree with each other. /forums/images/graemlins/dunno.gif /forums/images/graemlins/ears.gif
 
You must log in or register to reply here.

Latest Posts

Top Bottom