Do you read what you say in earlier posts? I asked is it the additional air that makes more power and you said "I don't think additional CFM of air is going into the engine with a larger exhaust".... Now you are saying "a larger exhaust allows more air into the cylinder"...Which is it?

 

when you're doing high revs, there's more air going into the engine, but there's less time for the air to fill up the cylinder chamber.

all you're doing with a larger exhaust is allowing the air that's already being sucked in to pass out easier so the engine doesn't have to work as hard to get the air out. It just makes the flow of what's already happening more efficient

the larger exhaust doesn't start sucking in additional air, it just makes high rpms more efficient and gains more power from that efficiency. At the same time it can possibly lose low rpm efficiency and thus lose power there.

the exceptions is when the stock exhaust is just a horrible design and a better design will improve efficiency through all the rpms

 

No it's more air going into the engine!!! Because of less restriction getting out the tail pipe

 

whoa calm down there

what happens when you turn a hose on full blast?

Does more water come out when you don't restrict the nozzle vs putting your thumb over the nozzle to create high pressure and shoot the water out faster and further? Does more water come out when you take the hose itself off and the water just comes out of the spigot? What if you had a 5 inch diameter hose? Would there be a lot of pressure/velocity?

having different sized exhausts at all isn't going to make an engine suck in more air, you're just going to effect the velocity of how fast the exhaust exits. The only way to physically suck in more air is with larger displacement or forced induction. Otherwise all any of us are doing with cams, breathing mods, and tuning is messing around with the efficiency of what's already there and often making some trade offs for low rpm power for high rpm power. The stock car is already pretty efficient over a broad range of rpms

 

I just switched from Nismo to 3" true dual on my vortech setup and gained a decent amount of power but lost PSI. Personally PSI is just a number to me and I am out for the power

 

Comparing a "hose" to the operation of an engine is sublime...Unbelievable...If you truly want to understand the physics go back and re -read the article I posted particularly this section:

Methods on How to Improve Efficiency and Power

After the above discussion of the components in an automotive exhaust system, it is obvious that the principle of the engine as a pump is not being utilized to the fullest. Air is not allowed to flow too freely because of restrictions in the form of the catalytic converter, the resonator, and the muffler. However, these components are necessary by regulations to maintain safe exhaust gas emissions and minimal sound levels (noise suppression). Also, in part, it takes time and money to design an excellent performing and free flowing exhaust system; something that car manufacturers just can’t afford to waste resources on. This is where aftermarket companies come in to create cost effective options for performance minded car owners. Of course, a free flowing exhaust would be expected to make more noise than a normal one. But a good manufactured system has a deep throaty tone, while yielding increases in horse power and also passing emission tests. I will now go through some of the modifications of the exhaust system that would "unleash" some horsepower and efficiency, while still being street-legal.

bottom line: opening exhaust allows in more air =more power

 

I think part of the reason aftermarket intakes are useless for the DE is because the engine is already sucking in more than it can expell; Plenum / Spacers help with intake CFM, but how much?? Adam from Z1 is making 305whp NA with a 1/4" spacer... Therefore, I think Sentry is correct that the stock headers/ cats are a bottleneck. Opening those up increases the effeciency of the engine, and more whp.

Of coarse nothing works in a vacuum. All the parts work together and affect each other.

 

true about being required for emissions and sound, but their restriction is exactly what makes them more efficient at low rpms. Most cars have bad/cheap exhaust designs with cheap bends, cheap mergers, cheap but inefficient mufflers, etc. There's usually a lot to improve on and gain overall power at all rpms by using a well designed exhaust. But if you start removing the cats for test pipes, you're trading low rpm power for high rpm power

oh wait they just said what I just wrote, go figures

this is an oversimplification because in real life the air compresses if it can't get out easily enough.

 

Anything that restricts flow limits air through the engine, be it headers, cats etc... Opening the path allows more air into and out the engine which acts like a pump...Sentry is arguing that no additional air flows through the engine..when you open the exhaust..

 

it's all about velocity and pressure

if you have air and gas and no pressure, they're not going to explode violently, it'll just light on fire. But if you have the air and gas pressureized and ignite it, then there's a force

the intake/exhaust works the same way. There is not "best" exhaust for all rpms since the air going in varies. This is exactly the reason porsche has come up with variable intake manifolds and even their variable turbos

 

Sentry, you are a master of obfuscation..You take a simple question and turn it into a convoluted esoteric discussion when a straight yes or no answer would suffice.... Does additional air flow through thru an engine when you open the exhaust...It requires a yes or no response.

 

Haha~ You sound like my dad... Dad, is that you?!

 

I don't like simplifying things into yes/no answers. I think that line of lawyer thinking skims over other truths/factors and tells a misleading story

to simplify the answer, NO it doesn't really suck in additional air that it wasn't previously sucking in, it just optimizes air pressure/velocity for higher rpms to work more efficiently

it may suck in a slight amount extra just because air doesn't naturally like to compress, but that's probably moot

think about what sucks air into an engine - it's the act of the piston going down which creates a vacuum. It's the rpms and displacement that really dictate the CFM of air being sucked into the engine

the key point is at high rpms with a restrictive exhaust the air can't get into the cylinders as fast and the air won't leave easily which creates addional friction.

things like v-tek and DOHC, the whole point is optimization of airflow

 

Never met your Dad but it sounds like he is a wise man...

 

Typical response "NO" ... "it may suck in a slight amount" .. You are grossly underestimating the net effect on power that simply what opening up the exhaust contributes...Again you state the obvious...rpm's and displacement dictate the CFM..No one argues the obvious..Cylinder scavenging improves...More power because more air is entering the engine due to the simple fact that the exhaust allows for more flow..A/F ratios go lean when changing from a restrictive exhaust to an open exhaust.. Why lean? More air. Thats the only configuration change made to the engine...

 

On normally aspirated engines . . . if you open the exhaust before the cats or muffler, you will notice less power at low RPMs. Try it and you'll see.

 

look at an average NA torque curve and notice how it drops as rpms rise. The engine is becoming more inefficient because it's having trouble actually getting the air the engine sucks into the cylinder chamber fast enough. Then when it does it can't exit fast enough.

larger exhaust scavenges the the cylinder chamber and increases the sucking ability of each cylinder chamber to get the air the engine already sucked into the plenum from the previous stroke cycles

the intake isn't seeing any real additional air pass through it - except for maybe some a negligible amount

if bigger is truely better, why do the civic people end up losing power when they put on a 4 inch exhaust?
the answer is they wouldn't if only they could rev to something like 15k rpms

 

The OP asked about a TD and Test pipes and effect on power..

 

here's where I think the confusion is. We're both right really, we're just not thinking of it the same way.
With a larger exhaust, more air actually makes it's way into the cylinder chamber, but the engine doesn't actually suck in more air at the intake

Let's look at it step by step

at low-mid rpms with small exhaust:

- a cylinder drops down creating suction

- air goes in and completely fills up cylinder

- exhaust exits out easily since rpms and the CFM going into the engine isn't high.

- the small exhaust is able to maintain high velocity which also helps suck the air fully into the cylinder



now for high rpms near redline with small exhaust:

- a cylinder drops down sucking in air

- however because rpms are so high the air can only travel so fast. It has trouble filling up the cylinder because of the high speed

- because it can't fill up the cylinder, the air gets backed up into the heads and intake manifold and compresses. The air is still moving in though the intake and going into the cylinders, but not ALL of it makes it's way into the cylinders.

- that excess volume of air ends up compressing just slightly because gasses do that when under pressure.

- Osmosis decides it's easier to compress the air just slightly inside the intake manifold than to compress it all much more to exit out the exhaust

- that excess air stays there unable to make it's way into the cylinder chamber because there's not enough time to take it all in, but at the same time can't exit out the intake because more air is coming in that way too.

- having a restrictive exhaust means air can't enter the cylinder chamber as easily because there isn't as much scavenging or suction where the exhaust's ability to pull the air out helps suck that excess air into the cylinder

- then you shift at redline and that excess volume of air is finally able to exit out the exhaust since the throttle plate briefly almost closes





at high rpms with large exhaust:

- more air can make it's way into the cylinder chamber because there's a greater amount of scavenging or suction pulling the air into the cylinder chamber

- the air doesn't get backed up into the intake manifold

 

LOL..in simple words...he just likes to argue and will never admit when some one else is right and he is wrong . He Split hairs , takes a simple question and tries to make into something more , When proven wrong , he will only partially agree and quickly move onto another hair to split . With all my dealings with him and reading other incounters he has had with others . NOT ONCE have Ive ever read him saying....sorry..I was mistaken your right ....lol
Must have been a bad childhood.....