doublea

iTrader: (7)

LI_Max_WOT: I hear you. For a daily driver it's a different situation, cost wise there is no benefit for you doing a Dual. If i were you I would buy a 3" Cattman cat-back you get the maximum power out of the engine and it's all SS, no fitting issue and it look and sound good.

BobPezz

iTrader: (5)

I'll disagree about the need for the X-pipe and try to save you some more money. It will work fine on a V8 engine but not so well on a V6 considering what you're trying to accomplish. Because an X-pipe or H-Pipe is tuned to 90/180deg and will increase turbulence in the V6 exhaust due to the difference in firing impulses. Here's an explanation; 4/8cyl. engines power impulses occur at 90/45deg. intervals. Optimum exhaust header tuning can be at 90/180deg. (Y-Header) since a V8 is basically 4cyl.x2 banks. Turbulence/imbalance can happen for many reasons i.e: cam timing/exhaust reversion and/or header pipe length discrepancies. 6cyl. power impulses occur at 60deg. intervals. So optimum tuning occurs at 60/120deg. (Y-Header). This is why an equal length Header/Y-Pipe minimizes imbalance/turbulence vs. unequal length setups that can cause problems unless the pipe lengths are carefully tuned to those frequencies. I.E: OEM VQ manifolds look to be tuned at 120deg. by the way 2cyls. are mated to 1 runner, the Y-Pipe is equal length though restrictive, and doesn't tend to cause turbulence even with gutted pre-cats.

The most unique adaptation/exception I ever encountered was on the 1973 Mercury Capri's German built 2.6L V6. It had only 4 exhaust ports on the heads/manifolds and ran a full dual exhaust through 2 triangular Helmholtz resonators just off the manifolds (similar to where the pre-cats are located) 2 offset inlet/outlet mufflers (I replaced with straight through units) before the axle, and dual exhaust pipes over the axle, right up to a dual inlet/outlet resonator where the 2 banks interconnected as far back as possible. A concept VERY similar to what you initially described.

BobPezz

iTrader: (5)

Check out this supplier, Good quality stuff. Recommended by my exhaust guy.
http://www.mandrelbendingsolutions.c...let/StoreFront

Scottwax

iTrader: (8)

The original factory y-pipe is pretty restrictive, probably part of the reason 7th gen Accords and 2nd gen TLs are so quiet.

95VQ30

HMAX08

Tell me I am wrong

There was mention of dyno numbers and runfiles

TunerMaxima3000

iTrader: (4)

I'ma going to chime in on this "backpressure" thing, because it seems anyone to use that phrase is getting bashed on here.

Let's look at the basics:

-Flow and Pressure are different
-Pressure is caused by restriction to Flow
-Flow itself doesn't cause any pressure

Now, with exhaust it's common practise to use the term "backpressure" to describe a restriction 'built in' to the exhaust. The error is not in the term itself, but in the connotation that "backpressure" is beneficial in some areas, and overall, a poor understanding of the term which results in such poorly educated statements.

Backpressure is just another word for Pressure, it's just a term that's used in exhaust. Because of the work "back" people assume somehow that exhaust is flowing backwards (I know we aren't stupid, we don't think this EXACTLY, but most people assume something of the like, or that the restriction forces exhaust back toward the engine, etc.)

I don't like the term, but that doesn't make it incorrect, nor does it mean it "doesn't exist" as some people have been claiming. That's nonsense. Exhaust pressure surely does exist, the bulk of it is pressure differential from the exhaust and intake valves, as well as the combustion process of course. The largest POST-HEAD percentage is attributed to the Exhaust Manifold, after that, the impact of restriction on PRESSURE itself is quite minimal, but the impact of changes in restriction after the headers on flow and velocity can be quite large.

This is why guys who know anything about intake and exhaust, like Sparks, and our other members who've been posting, prefer to use the word VELOCITY when talking about exhaust especially, because this is the most important thing we want to acheive, increased velocity, not increased pressure or decreased pressure

LI_Max_WOT

iTrader: (9)

Thanks for chiming in! Now you have brought up some interesting points here. Just to clarify a few things, I have some questions about what you have stated.

So, if I understand correctly these are some things you stated, in other words.
If flow is restricted or is decreased by (back)pressure and flow is caused by the combustion process kicking out spent air/fuel mixture by the valves (Question: Is the rate of flow out of the combustion chamber effected by different engine speeds? I'm going to assume that that answer is a yes and keep going on my idea here). Wouldn't (back)pressure exist throughout the exhaust system with all the bends, with the flow or velocity rate slowing down through each curve or restriction in the exhaust? So, therefore, a restriction to flow caused by (back)pressure would almost act as a "flow regulator" throughout the engine rpm, and be one of the primary factors in power distribution within the motor, as far as exhaust goes?

For example: If I have a stock vq35de Maxima, with everything else held constant, and a 2.5" catback exhaust would produce a peak torque at 3800rpm and peak horsepower at 5600rpm. However, with a 3" catback, the engine produces peak torque at 4200rpm and peak horsepower at 5900rpm. The difference in the power curves could then be attributed to the amount of (back)pressure which is a determining factor in the flow of the exhaust? The only difference between the two power tests would be the amount of restriction in the catback system. I'm just stating this as a hypothetical example.

IMO (back)pressure is a tangible, as well as essential part of tuning the power curve of an engine. Engine speeds, and thus the velocity of the incurring exhaust ("tuned" through (back)pressure) throughout this power range, is a determinant of the power distribution of the engine.

So, the ultimate question is, can (back)pressure and the resulting flow or velocity be used to tune the power curve of an engine? This is my belief of the beneficial part of (back)pressure, by acting as a "flow regulator" (like a tampon).

I said (back)pressure 10 times!! oh sheeeeeeet!

hahahah now that's comedy

LI_Max_WOT

iTrader: (9)

BobPezz: You make some good points about the usefulness of an x-pipe in different engine configurations. Even though it might not be the most beneficial addition to this setup, I'm still convinced that the x will have a large part in keeping all of this expanded volume inside the exhaust piping as quiet as possible. The volume of 2 2.25" pipes combined is comparable to the volume of a single 3" pipe, and the sound level will need to be tamed in my opinion. I'm going to basically double the size of the exhaust piping in about a seven foot section of the exhaust, and I'd prefer to err on the side of caution with regards to how loud this thing will be. Also, you have saved me money, the website you directed me to has the exact same x-pipe at $50 less than the Magnaflow I was looking at. Cool beans!

BobPezz

iTrader: (5)

You're still thinking in terms of even number exhaust pulses in a V8 vs. odd number pulses in a V6. The X-Pipe will most likely NOT be quiet or beneficial in a V6 exhaust! Due to throwing off the 60/120deg. tuning, creating turbulence/velocity/flow issues. The X-Pipe induced turbulence would probably decrease flow/velocity and make the exhaust rasp/fart like a Honda! Two suggestions if you're worried about quieting the exhaust. Use the largest 2 to 1 resonator you can find that'll fit. That way the (high velocity) expanded volume you're worried about will interconnect/balance inside a (large volume/low velocity) resonator with maximum sound damping capabilities. Minimizing exhaust turbulence/noise inside the resonator, before exiting into the (lower volume/higher velocity) single pipe. And/or put 2 resonators on the dual pipes upstream from the 2 to 1 resonator, just like in the Capri exhaust.

CMax03

iTrader: (3)

You could always use a merger from the header secondaries to the round 7" muffler>the your twin 2.25" dual piping......The real question is.....Will (2) 2.25" pipes fit thru the rear axle Matrix????? The 3" barely fits!!!!!

colombian4u_61

iTrader: (3)

there's this one dude who has a 2 tone black and white maxima that actually has a dual exhaust on his maxima. check out cardomain, his at the very first page. GOOD LUCK

TunerMaxima3000

iTrader: (4)

Yes of course it is.

Yes, Pressure exists in the exhaust system, this is obvious. The cause of this pressure is restriction to flow.

The easiest way for you to grasp this is the old straw analogy:

If you blow through a normal sized straw the pressure out the end is high.
If you blow hard (high RPM) through that normal sized straw the pressure stays high but you feel high restriction in your mouth (the engine).

Now, if you have a LARGE straw and you blow into it, the pressure out the end is VERY low. All your air in your mouth (engine) just kind of puffs out all in one shot.
If you blow HARD (high RPM) through this LARGE straw, you still don't feel restriction in your mouth but you acheive some pressure out the end.

This is true, but mainly in the Exhaust Manifold and Y-pipe. After that point restriction in the exhaust normally is a Negitive thing. You want to acheive the balance between a LARGE straw and a SMALL straw after the cat-back. The closest option we have for the 3.5 in the Maxima is the 3" Catback with Mandrel bends, Cattman is the best way to spend your money if you are going to put this much coin into it.

It can be argued, and I personally believe, that 2.5" is sufficient for the 3.0 DE-K with little to no modifications for a DD that usually operates under 4000RPM.


Is Backpressure real? Yes. Is it essential? Yes. Is it the medium used to create power? Not really. Is it the main variable measured to tune and create proper velocity? No.

You need to come out of the backpressure pit you're in, just as all of us do once we truly understand the basics of exhaust and intake dynamics.

CFM (flow rate of air) is the main thing we need to look at. Pressure isn't all that important actually because it's pressure drops that the engineers want to acheive in order to create turbulence and velocity, which when tuned properly will allow ideal velocity and scavenging in the Intake and Exhaust Manifolds.

The thing you want to acheive is optimal VELOCITY. You are not messing with the Intake Manifold or the Exhaust manifold, and thusly, you don't need to worry about Venturi's, Pressure drops, restrictions, etc. These are things that are important CLOSE to the engine. The Catback system is not a "tuned" item in a car that is Daily driven and not in excess of 300 WHP. Even then, you likely wouldn't bother.

If you really feel like tinkering the Y-Pipe is where you'll do it. Extending the Ypipe is a good idea if you can afford it. I would recommend you just move the Y (dual pipes) back to where the Stock CAT ends, mount the cat there, and put a Resonator directly on the CAT, then run 3" back from there. You can use a 3" Cattman or equivalent AXEL-BACK system to ensure you'll get a decent tone out of it.

The biggest problem with this is you're going to endure DRONE. If you can live with it, go nuts. I'd try to jam in the longest resonator possible though.

BobPezz

iTrader: (5)

'Tuner' is correct on all counts. The one point I might differ on is this.

"CFM (flow rate of air) is the main thing we need to look at. Pressure isn't all that important actually because it's pressure drops that the engineers want to acheive in order to create turbulence and velocity, which when tuned properly will allow ideal velocity and scavenging in the Intake and Exhaust Manifolds."

What I think he meant to say is 'minimize turbulence and create velocity'. Since turbulence is cumulative and will restrict the smooth (laminar) flow of a gas or liquid. And why engineers do lots of R&D to prevent boundary layer turbulence. Which is important in everything from intake/exhaust port/manifold/system design and especially in aerodynamics for both automotive and aerospace applications.

TunerMaxima3000

iTrader: (4)

I used to think this too, but turbulence is a WANTED effect in some locations, it's one of the cheapest and easiest ways to ensure a constant or near-constant quantity of air flowing, which means an increase in velocity because there aren't "hicups" in the air flow, which in itself would cause unwanted uncontrolled turbulence.

It's a tricky thing, and I don't profess to fully understand it, but I have found that they do use turbulence to increase velocity, it's a trick of how much, and where. Not something I'd recommend trying to duplicate in your driveway, just stick to the basics and you'll do fine.

BobPezz

iTrader: (5)

You may have turbulence confused with Vortices which are a form of controlled turbulence and VERY efficient flow inducers. From working with aeronautical engineers, I know there's a difference based on the terminology. Turbulence is considered bad and increases drag impeding flow, vs. Vortices that can be desirable and used increase/maintain high flow characteristics over variations in actual flow velocity. I.E. the small vertical wingtips you see on many newer aircraft are not stabilizers. But are vortex inducers that allow the wings to develop lift at much lower airspeed than before. Because the vortices help to maintain laminar flow over the top of the wing at a higher angle of attack, than would've been possible without creating turbulence from air spilling off the sides and trailing edges of the wings. Boy did I go off topic on that one!

TunerMaxima3000

iTrader: (4)

LOL ok I will just assume I stand corrected

LI_Max_WOT

iTrader: (9)

@BobPezz: The x-pipe has been dropped out of the equation. After finally getting some spare time to see under the car in person, its actually going to be pretty difficult to get two separate mandrel bent stainless steel pipes under there in the place of the one pipe and somehow route them to the position of the main cat without losing ground clearance, so this will be my focus for the time being.

@tuner: Thanks for the help with understanding exhaust theory better. I was wondering if you had any knowledge on exhaust scavenging? I also would like to get your opinions on how just changing the y-pipe to my newest design and keeping the stock cat-back would effect the powerband.

Here is the most updated design for the y-pipe, here is my design compared to the stock setup:


The current main problem is to somehow get the pipes to be side by side, which at the point I will be extending them from (which is the stock point where they collect in the y), they are one on top of the other. And they need to make a 15 degree right turn. I was thinking to turn the pipe on the bottom first, then around 2-3 inches past that, have the pipe on top make a 15 degree turn diagonally down and right with around a 3" offset, which should place it about next to the other pipe, and could be slightly corrected with the flex pipes. Any ideas?

BobPezz

iTrader: (5)

Au contrair, mon ami. You're 100% correct, it's only a matter of words. I.E. your explanation re: backpressure as a misleading term. The long dual pipe idea isn't as crazy as it seems. That said, it has to be carefully designed to reap any real world benefits over something like Cattman headers/exhaust. Since Brian has already done the R&D to optimize his design.

TunerMaxima3000

iTrader: (4)

Gotcha


As to the YPipe, I do believe that a properly made Y-Pipe would perform just as well. As long as the internals are smooth, well transitioned, and proper size. The other big thing is remembering where to mount the 02's depending on application.

You have to remember, Brian made those Y-Pipes the best he could while still acheiving the ability to Re:Re stock for his. This means that the OP could be correct, from a performance standpoint, that a Longer Y pipe is better. Because it would require more modification to make a longer Y-Pipe from a retail standpoint it probably wouldn't sell.

To keep things fair, if you don't upgrade the intake (I'd recommend FIRST), then this whole thing is a bit of a moot point, you won't see any real signifigant gains regardless of your method.

BobPezz

iTrader: (5)

All good points. The guy's basic premise is sound, the final design depends on if he plans to use OEM manifolds or something else. If OEM's he'll have to ditch the front manifold (for a 4th gen?) due to the pre-cat flange. From the drawings it looks like he's going catless so a dual 02 Sim is mandatory. If not the Random downpipe cats are probably the only ones that'll fit upstream from the resonator due to space limitations. I agree it's likely "that a properly madeY-Pipe would perform just as well". Cattman's design looks to be really good for maintaining velocity and IMHO the rear bank 'corkscrew' pipe is genius. I doubt he'd compromise performance for cost savings! Anyway, the dual pipe is a neat mental exercise at any rate since there's nothing wrong with thinking out of the box. I even drew up a cheesy sketch of what I think might be a doable design. An upgraded intake is a given and Sparks is doing custom production. I could see one of his long tube IM systems working well with the long tube exhaust.

LI_Max_WOT

iTrader: (9)

Drawing contest!!!!! hahaha

The precats and all o2 sensors will be untouched in this project. Instead of trying to mount a completely new pipe onto the precats, and worrying about the secondary o2 sensors, the y-pipe will be cut at the point where the collector is and extended to before the main cat with 2" pipes. Which, after talking to my exhaust shop guy, it seems like a much easier task to accomplish than trying to fit 2 2.25" pipes in the same spot. After that, two 2.25" pipes will run straight back and will be collected in a magnaflow dual inlet resonator with a 2.5" outlet and attached to the stock exhaust. If my bonus comes through in time, after the resonator will be placed 2.5" pipe and muffler. This setup would eventually lead to the installation of a dual inlet/outlet catalytic converter, gutted precats, and extended secondary o2 sensors to behind the installed cat.

As far as having intake mods, this has been taken care of. Short ram intake with k&n inverted cone filter installed (which will eventually be boxed). NWP spacers with a port-matched UIM/Elbow, here is a pic of about how much I ported each part, I ported down to no lip at each joint. The 30 hours of polishing the outside just shows how much time I put into that whole job.

LI_Max_WOT

iTrader: (9)

This is with a completely stock exhaust. Not filmed on level ground.

http://www.youtube.com/user/the2k3ma.../2/FjoB9kJqTvw

luvlexus101

iTrader: (6)

I want a cattman exhaust

CMax03

iTrader: (3)

I think coming down from the headers thru 2 x 2.25" pipes into the dual resonator outlet (reversed for the inlet) and leaving out into a single 3" pipe is a good idea....simese the down piping would save the most room...

BobPezz

iTrader: (5)

Not to sound like a naysayer. FYI; the pre-cats and sharp bends of the stock y-pipe before the collector, are the MOST restrictive section of the exhaust system. In the worst place possible, just after the manifolds! Deleting the section you want to retain, is why aftermarket Y-Pipes/Headers net gains in both torque and horsepower. What your exhaust guy suggests would be easier. But would probably be a big disappointment due to time and money spent for minimal or no performance gains. As said in a previous post, the secondary O2 sensor issue could be solved by an O2 Sim or dual "downpipe" cats. You've done a good job on the intake, don't half step on the exhaust!

BobPezz

iTrader: (5)

Oval tubing might work well too.

BobPezz

iTrader: (5)

2 of these will fit almost anywhere and could even be staggered.

http://www.mandrelbendingsolutions.c...-MBS%2C/Detail

LI_Max_WOT

iTrader: (9)

It's ok, I understand

Yep that's basically what I'm doing. The length of the pipes will be the same, but not siamese, it took some careful calculations to determine how to get vertically aligned pipes to be horizontally aligned. (Who says you don't need math?) The resonator will be a dual 2.25" inlet, with a 2.5" outlet. After the resonator.. it's 2.5" piping to the muffler. I was thinking about using the stock muffler, but it's too small. Now I'm looking at the g35 sedan muffler. But I'll probably go with Magnaflow 12158.

@ BobPezz: This round of fabrication is just to get the main pieces of piping in place which I anticipate will be complicated. Welding in a spun converter will be easy when all the pipes are set up or fixing up o2 sensor locations etc. I'm currently talking to "Insane Jeff" from mandrel bending solutions about some mandrel bent pipes to keep the y-pipe stainless steel.

Probably around 3 more weeks until install

BobPezz

iTrader: (5)

The 3.0L engine is low end torque limited and being smaller displacement can get by with a smaller 2.5" exhaust. The 3.5L engine inherently has more low end torque but falls off more at high RPM's due to restriction in the smaller OEM dia. exhaust. Don't confuse two different engines/power characteristics. I still think using 2.5" primaries with 2 x 2.5" spun cats will give better velocity/flow than a single cat setup, allow the longest primary length possible, and minimize secondary O2 sensor location issues. Mated to a Magnaflow12763 resonator, and 3" pipe back to a Magnaflow 12198 muffler will give better overall performance on your 3.5L. You could use some cheap 2.25-2.5" steel adaptors/clamps on the OEM (ahead of collector) front sections temporarily. Until you can get the dual 2.5" stainless front sections fabricated/installed.