JBrady

I don't think the 02 sensors are a function of this phenomenom.

Larger pipes slow the velocity and increase total volume of the system. The slower velocity and larger volume allows the flow to reverse as the engine exhaust pulsates. People forget that engines create intermitent pulsing flow in the exhaust. When the valve first opens pressure is very high and flow not a problem. It is when the piston is nearing the end of the exhaust cycle that reversion is a problem. The bigger pipes create a slower flow which looses its enertia sooner. If this happens before the exhaust valve closes then the pressure in the cylinder will push into the intake manifold during valve overlap. This contaminates the incoming charge and restricts the charges flow. Less flow combined with contamination = less power... simple as that. Big pipes flow backwards too easily. It is not until higher RPM when the volume in the pipes is sufficient to continue moving away from the engine AND the time even window for reversion is reduced that the engine overcomes this and begins making more power than with the more "restrictive" manifolding and pipes.

Fisher503

Hey Brady if a tree falls in the forest but know one is...........
I figured you know the answer to everything else .

BA_GS400

iTrader: (1)

Good reply JBrady!
Funny, without time for a good reply, I was just going to answer "this is wrong" to the quote below from the earlier post.

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it has been proven that backpressure is a myth regarding power curve both by aftermarket companies & SAE engineers, the only way a power curve can be modify is by the change of the header design
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JBrady

By definition a forest is an area full of living things... if nothing else other trees... there is no place on earth with a forest devoid of animals than can hear... if it is heard it is sound.

Oh and no, I certainly do NOT know the answer to "everything" else.

JBrady

My response? Or that which I responded to?

BA_GS400

iTrader: (1)

whoops, my post looks funny doesn't it? I'll fix it.

Jbrady, your post was perfectly understandable and I agreed with it. It was the other post that I did not agree with, at least IMO.

Chigga

Brad, as your explanation seems logical, I have to disagree in this term, although I must admit now days a technical discussion w/out *****ing each other is getting more rare than finding a BMW driver who will admit there are better cars out there.

the pipe size theory is only true if you apply it on the header, the shape of the header and the thickness of the material can change the characteristics in the combustion chambers, like all things in the nature that was taught in HS physics, everything has a frequency, and an engine is even more true, as the exhaust gas exit thru the valve, it hits the header and creates a special frequency, this is what we call hall-effect, it may have other terms depends on the profs & textbook that was taught, but during our test in Formula SAE we tested many headers/pipes. What hall effect does is it creates super wave which in terms creates a vaccum effect and force the burnt gas to sucked out faster to make room for the incoming air. Like you said in your explanation, YES a bigger header can often result in loss of power, but a bigger PIPE does not hurt the power curve, it will not affect it in any negative way. There's no way the exhaust gas could've gone in reverse direction in the exhaust piping UNLESS the total combine pressure is less then the pressure currently in the pipe, the only way it can reverse is when the engine is shut down or drop of RPM, which is why you should never let go of gas when go thru deep water.

LMSguy

Okay guys I'm a little late in the discussion here but It was me and my partner that first started using the twin X pipes.The reason we tried it was to get rid of the dreaded drone on Lincoln MarkVIIIs after aftermarket mufflers were added.
Our results were that the drone is virtually eliminated and the torque curve is brought on a few hundred RPM sooner.Oh, and the sound was awesome!

Hameed, just two days ago I did my before dyno runs.I'll post the graphs in a new thread.But I plan on doing a before and after for every mod I do to the car so people will KNOW what works and what doesnt.

Hameed

All I want is a growling deep bass rumble with minimal to zero power loss at the bottom end. That's it! Why is this so complicated???/

You know what Chris, I will wait till you get yours done and then I may or may not go ahead with this mod. It all depends on the outcome!

LMSguy

No problem bud. I thought you were in a hurry so I figured you already got it done with the crush bent pipe.
I have been SO busy but at least I found the time to get the first dyno done. LOL

Hameed

I went to a local muffler shop that does custom work and they quoted CDN $900.00 (approximately US$700.00) .

The guy said there is not enough space where the current Y-pipe is for an X-pipe (he saw mine as I took them there) and he would have to do something else to achieve what I was after. He said he would need to replace the cat with a high flow cat and and some other stuff. Once I heard the cost, my brain promptly forgot what components and pieces make up that cost as there was no way in hell I would pay $900.00 do this mod just for the sound effect.

That is why I am anxious to see what you do before I take the plunge. Please keep me posted Chris. What is even more intriguing is the comment you made about the increased torque that this mod creates.................. Now that would be just the icing on the cake for me!

LMSguy

well, it may or may not increase the torque in this application.Time will tell.
But what it DID do was bring the torque on sooner

Hollywood

Ah yes the battle of exhaust sizes.

Well on an NA car the bigger the pipe the louder/drony it will be. Will X pipe(s) change the sound? For sure. Will the xpipe make thing more quiet and reduce droneyness? Probly. Why? It's similair to what Chigga is talking about, harmonics and sound delfection play a key role.

On an exhaust that is strait thorugh design and lets say almost a strait pipe from header to the tail pipe, with a free flow non-louvered muffler it's going to be wayyy louder then the same exhaust making several 45/90 degree bends from header to tail pipe. This will casue the sounds to reflect a great deal more inside the exhaust system and also slows them down even.

With larger piping this gives evem more room for the sound to reflect off the inside of the exhaust making wider wave lengths, thus the more dronyness a 3" exhaust gives over 2.25 on an na car. The Xpipe will take the 2 separate exhaust flows and sounds and smash them together this will casue collisions creating more speratic sound waves, absorbtion and a less predictable sound pattern through the course of the flow to the tail pipes. Basicly it's a restriction of power which can reduce sound levels and dronyness.

I do respect Jbrady he is a smart guy, but I have to side with Chigga. I also found exhaust pipe size does not matter really. I have seen real life tests to prove it. A stock 240sx w/ cone filter, 2.4L 4 cyl made more power and torque from a turbo apexi exhast 3.5" over a 2.5 aftermarket system (greddy, apexi, hks, cant remember). But it was loud as hell! Also ther are supra's running 4" and 5" downpipes and exhausts and making power from it.

To add to Jbrady's statement 1 other negative effect from reversion is when the exhaust gasses are suck back into the head and mixes with the new air from the intake side the temperature of the combined air is higher, which also adds to the loss of power.

JBrady

Chigga my friend you started well but then jumped to a conclusion based on assumption. Are your really wanting to state that the secondary pipe diameter has no effect on flow characteristics? Sorry, secondary size and design DEFINITELY effects the pressure waves that can both help and hurt the flow through the exhaust valve.

Start with just the pipe, consider the volume of say a 2" pipe 15 feet long. Its volume holds mass. Now, release one exhaust pulse through this pipe. Consider what happens. The pulse must accelerate the mass ahead of it in the pipe as it flows into the pipe. Being compressable the gas acts like a spring absorbing energy and accelerating the mass through the pipe. After the exhaust valve closes the spring effect is reversed. Also consider that the pipe vents to atmosphere at apx 15psi ambient. This ambient pressure re-exerts itself back into the pipe end by the cross sectional area of the pipe. Now, change the size to a 3" and EVERYTHING changes. Mass inside pipe, spring effect, pressure pulses, flow direction, turbulance, cross section exposed to ambient, total volume, resonance, harmonics, etc. Now combine Y pipes, X pipes, resonators, mufflers, merges, alternating pulses from other exhaust events...

Generally stating, on a NON turbo application, increasing the secondary pipe size will hurt low speed flow, torque, power. Now, increase pipe size but improve intersections and you may have a wash or slight gain if the original was very poor. Remember, to get reverse flow as the exhaust cycle ends only requires a higher pressure in the exhaust port than the cylinder and this can be created in MANY ways.

This is very complicated stuff and therefore the ease in stating that bigger hurts low speed power. It is just the assumption that this must mean that the engine needs backpressure that I dislike.

That said there is actually a case for backpressure creating a slight improvement on early exhaust valve opening but I am not getting in to that here.

LMSguy

JBrady, let me ask you something, you say that there is a case for backpressure.
Are you talking in street only applications,or street strip, or stip only?
I have never seen one race car that made more power with a more restrictive exhaust.

I can KIND OF see an argument if you are talknig street only cars that live at lower RPMS but in shear power production I just cant see it.