shabz

Before i start with this i would just like to say that i have used the search function and tried looking this up in any way that i possibly could..

Ok so here goes...

I switched over from a Mazda RX-8 about a year ago becuz of the fact that it had no torque and wasent a car that did it for me when it came to power and pickup... I have always loved the Z and its attractive HP and Torque numbers along with a 3.5 V6. I have an 05 Anniversary edition and have recently taken off the stock exhaust and added a custom setup... Now heres my problem... im losing power and it feels NOTHING like a v6 with 300hp..

I posted a pic of my setup... its been altered from what the pic shows... ive taken out the resonator and got a 3 chamber muffler installed in its place.. so NO resonator... I also have a JWT popcharger.

On many occasions i have been at a traffic light and tried to push my car to the limit.. I make the most out of every gear and shift high... i know how to drive standard and have no problems wit that... but it seems like in 1st and 2nd gear i have NO low end power!!.... Almost every night i do this when the roads are dead and try and see how much i can push it and get dissapointed every time... i raced my boi the other day who drives a 6speed TSX and i was only 1 car length away the whole time!!... Why is this????

Am i losing power because of my exhaust set up and the fact that i dont have a muffler anywhere near my tips and the fact that i have just straight pipes instead?... I can only take 2nd gear so far before the car starts screaming with my LOUD exhaust and makes me shift... The potential of 2nd gear has gone down and something definately feels REALLY wrong..

The car has lost that KICK and dosent feel like it can keep up with a 3.2TL...

Id really appreciate all the input i can get, especially from those of you who know alot about the Z, i know theres some smart guys on this forum and i come to you right now in dire need of help!... its really killing my day when i think about it...

thanks for takin the time to read this... hope to hear ur feedback!

THE_SCHROED

iTrader: (21)

Your setup looks like you just eliminated the muffler. So basically you are runnin cats and the resonator, I would say thats your problem. I had an old truck with just cats and it lost a tremendous amount of torque. I may be wrong though, but thats what I would say.

shabz

I took out the resonator that you see in the pic and installed a 3 chamber muffler in its place though...

anything??

token5gtd

if you're trying to keep costs down, i would try a Magnaflow x-pipe mufler to eliminate all the Y's in your system. It just looks pretty restrictive IMO

zonic03

iTrader: (18)

Check the pipe bends!!! Any leaks? Check the bushings. How big is the piping? Clogged cat? Theres many cases.

shabz

There are no exhaust leaks and its all 2.5 inch piping... same as stock... do you think because of the way it splits into a Y?...

Could someone photoshop a solution for me?... id appreciate that more than anything rite now... take the pic and show me what i need to change in my setup..

i dont have the stock anymore and im willing to do whatever to ALTER this setup and make it work!

thanks guys!

Eazzy

iTrader: (8)

I don't keep up --are you turboed, if the answer is no ---you need need back pressure---You NEED restrictions

jray8

+1 take that answer and google backpressure see how it affects that "KICK" you lost!

davidv

iTrader: (2)

Without seeing the results of a dyno test I cannot tell a thing.

The Captain

iTrader: (3)

+1

That's what I was thinking.

Also, to the OP... That exhaust looks sooooo riced, man... lol.

macs350z

iTrader: (1)

I also think you need to put some restrictions in. Also how smooth is the Y it looks like the exhaust will not flow smoothly?

wgd9891

lol...don't alter ur car if you don't know to do it right..this is how it ends up...

MUZZY

iTrader: (28)

1. Check for leaks
2. loosing too much back pressure messes up your tune, might need to retune it.

JCat

iTrader: (4)

Your exhaust modifications are causing your engine to run lean (not enough fuel).

Either go to a shop and get it tuned, or change the exhaust back.

T_K

iTrader: (5)

This whole back pressure myth is pretty misconstrued. You don't need backpressure at all. You need exhaust velocity to maintain good scavenging. Back pressure is counter productive to power at any RPM, exhaust diameter determines exhaust velocity, and in that set up, most of the piping is unchanged. Theres really no extreme changes to the exhaust other than from the resonator back.

Did the car feel the way it does immediately after the exhaust install, or did it run fine for a bit then started to degrade?

TK

DaytonaRoadster

iTrader: (2)

exhaust doesnt equal random pipeing, there is testing and design in making one.

WhiteNoiz

Backpressure: The myth and why it's wrong.

I. Introduction

One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Hondas need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory

Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity

Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?

I often wonder how the myth "Hondas need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?

The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).

VI. Conclusion.

SO it turns out that Hondas don't need backpressure, they need as high a flow velocity as possible with as little backpressure as possible.

WhiteNoiz

Now from reading the article there, it seems to me your piping is not restrictive enough for the powerband, your loss in lower rpms tq is a good indicator.

DraGonAlchemist

damn. .its not a mustang bro. .i believe you'd done away with the back psi needed for the Z to equalize both sides of the engine. .so the computer can function properly. .

WhiteNoiz

He lowered the exhaust velocity, nothing to do with the computer bruv