Fyi Back Pressure

[Konservative]

Originally Posted by tricolor

I intend to have my Weapon R Street header AND my Megan Cat Delete (downpipe) installed this week end. How do I re-install both O2 sessor to avoid CEL?

I do not have any bung spacer of any kind but I read in another tread (that I can't locate anymore) that a fellow member simply screwed the sensor a little bit away from it's original position and that cured it.
Oh well, I am still debating about installing that pipe... it seems a bit trouble some.

Please help

You can get an o2 sensor simulator / CEL delete part on kingmotorsports.com i believe. Look around, maybe someone else can enlighten us but i believe it fools your ECU into thinking you have an o2 sensor when you dont have one or a cat.




Regarding down pipes. Is there a high flow cat available for the GE? I like the idea of more free flow but im not sure i want to sacrifice emissions control. Besides isnt it actually CA illegal to delete your cat? ( yeah yeah im a fuddy duddy about some things - ill drive 110 on the freeway but i dont wanna break emission laws)

[Fitting]

Yes, it's illegal to delete the cat in our state.
I haven't seen any high flow cat specific to the GE
but you can use a universal cat from Magnaflow.

[Konservative]

Is that magnaflow high flow cat mated to a down pipe or would i need to have that fabricated?


When would they pop me for that violation of emissions? Upon smog check? or could that be noticed when / if i get pulled over?



EDIT:

Regarding the Megan down pipe, does that have a cat or is that a resonator?

[chrisakasparky]

+1 raton for finding the article. if air has to be moving at a certain velocity to scavenge the cylinders, larger pipes would just change the rpm at which that happens, right? basically, every exhaust system is "tuned" to an rpm range? a range at which the force required to move air along the exhuast is most efficiently countered by its tendency to keep moving and pull more air along with it. so while a 60mm exhaust can be effective on a fit that is turboed and tuned for high rpm, its most efficient flow rate is out of range of a stock motor and rendered inefficient.. eye candy? just thinking out loud to see if i understand this.

PS Megan downpipe has a small resonator. the other b pipes are straight through, or at least the ones ive seen.

[SS RICH]

Read my post "the great debate" It is reflective of my experience with just installing an axle back system which greatly affected power delivery on many levels. needless to say I am back to stock.
I would never try to deter anyone from performing mods to there car but I feel with the fit you will spend lots of money just to relocate where the power comes in during the rev range with a little more pull at best in a limited rpm span.
remember also my car is an automatic which really magnifies this problem.
stick shift fits will handle mods better because you can more easily keep the car in the rpm range where the power is made.

SS RICH

[DOHCtor]

Just like i posted in another thread...

This is from neons.org and not from me!!


These are general guidelines I calculated from David Vizard's formulas.

1. For avoiding significant restriction from back pressure, the pipe should flow at least 2.2CFM per horsepower produced.
2. A straight pipe will flow ~115CFM per square inch of area (using inside diameter of the pipe)
3) I used the formula: (115*pi(diameter/2)^2)/2.2
4) The pipe size will become more restrictive the further you go above the zero loss horsepower.
5) Similarly, try not to go too big on piping for your set up. I think Vitor dynoed 2.5 vs 2.25 on a 160whp set up and had very minimal gain. Putting 3" on your stock Neon will be very loud for no good reason!
6) Add length as a factor.
7) Each 90° bend will reduce airflow by 8%!

Exhaust Diameter (inches): 2
Zero loss Horsepower 164.22

Exhaust Diameter (inches): 2.25
Zero loss Horsepower 207.84

Exhaust Diameter (inches): 2.5
Zero loss Horsepower 256.59

Exhaust Diameter (inches): 3
Zero loss Horsepower 369.49

Exhaust Diameter (inches): 3.5
Zero loss Horsepower 502.92

Exhaust Diameter (inches): 4
Zero loss Horsepower 656.88

Thats a dyno graph of Vitor with his (then!) 160Whp Neon... Notice how adding a 2½ catback Versus the 2¼ stocker didn't change a thing and even reduced high RPM power!!



I would stick to a Header and a Axleback except if i were to throw Nitrous or Boost into the Equation!

Marko!

[DOHCtor]

More excellent info i just found on a GM site!


Replacing the stock production exhaust system with a low-restriction, free-flow one is usually one of the first modifications made to any vehicle in the name of performance. We all know they're louder, but how much performance do they really add? We've all seen supposed dyno tests, usually run by the exhaust manufacturer's themselves on their own dyno, indicating vast power gains, and psychologically, we always equate a healthy exhaust rumble with increased power in the seat of the pants, but how much power are we really gaining? To find out, we're running a simple backpressure study, and our results will be posted here as they come. Admittedly this study is not totally scientific as there are many uncontrolled variables, but it should be sufficient to provide a rough estimate. It is generally accepted by automotive engineers that for every inch of Hg of backpressure (that's Mercury - inches of Hg is a unit for measuring pressure) approximately 1-2 HP is lost depending on the displacement and efficiency of the engine, the combustion chamber design, etc. Our sources indicated that in the case of the L67 3800SC, 1HP per inch of Hg is reasonable.
1 inch Hg backpressure = 1 HP lost
For reference, we have the following conversions factors:
1 ATM = 14.7 PSI = 76 cm of Hg = 29.921 inches of Hg = 1.013 bar



Also read this!!

How to Make your Own Effective Exhaust System > MotoIQ > Magazine Articles

Marko!!