My Exhaust

[redrider07]

Ok....I just got a cat back exahaust installed with Flowmaster 80 series and 2.5 inch piping with dual stainless steel tips! However, I was an idiot and forgot to tell the guy to remove the resonator....should I ask him if he did...or just check it myself...it is just behind the cat right...like another "smaller muffler"

Also...I actually seemed to loose some bottom end! the muffler sounds really good, looks good, but power down low seems worse! I wonder if I am just over exaggerating it...damn I should have asked about the resonator!

[Jferg2223]

thats probably because the muffler you got should go on a v8. way too big which means not enough back pressure which also turns into loss of bottom end power and torque.your piping is also slightly large. i would have stuck to 2.25

[alerocar01]

yeah your going to lose power because of the bigger pipe. as for the resonator i would just leave it on. not going to make a big difference.

[strtrydr]

for the 3400 a 2.5 inch pipe seems to be the "norm." I have the same exhaust but the only thing I regret is getting a 80 instead of a super 40. My 80 souned good for like the first 6 months but now it has picked up a little bit a raspyness.

[Jferg2223]

the norm piping should be 2.25 because the car requires atleast 2 pounds of backpressure to maintain torque specs. stay with stock size pipe you can run slightly larger muffler.

[Jferg2223]

and yes the super 40 is a very nice pick

[Spilner521]

Originally Posted by Jferg2223

the norm piping should be 2.25 because the car requires atleast 2 pounds of backpressure to maintain torque specs. stay with stock size pipe you can run slightly larger muffler.

No backpressure is the best. You don't want any backpressure at all, you want to maintain exhaust velocity to keep your low end torque. And 2.5" should be the norm for a 3.4L V6....in this case the N-body's 3400. 2.25" exhaust piping works well for the 2.2L Ecotec and 2.4L LD9 4 cylinder engines. It's even been dyno proven that 2.5" piping can also maintain low end torque for these 4 cylinder's, but everyone still likes 2.25". For a big V6 like the 3400, at least 2.5" is the way to go.

As for the mufflers, you'd be better of going with a straight through muffler like Magnaflow instead of a baffled design like the Flowmasters. No backpressure means the least amount of restriction possible, and with a baffled muffler, you have baffles blocking exhaust flow to quiet the tone. Yes, they will flow better than stock, but straight through mufflers flow better than baffled mufflers.

And if anyone else has ever seen the inside of the stock resonator, you'll know what I mean when I say it's very restrictive. Dump it when you can and if you think it's too loud, add a different one, also straight through like the muffler.

[Spilner521]

If I was me with a 3400 V6 and I just had the stock manifolds (no headers) and I wanted the best exhaust I could get for N/A, I'd start right from the manifolds with 2.5" piping the whole way and make a new downpipe. Then from there add a high flow cat, 1 long straight through resonator, and a straight through muffler. This would give you the most unrestricted flow as well as maintain exhaust velocity to retain low end torque.

[Cliff8928]

The outlet on the stock 3400 rear manifold is just about 2.5", so that would be a good thing too.

My 3400 runs a 2.5" downpipe which then flares out to a 3" catalytic converter, muffler, then right out behind the drivers door. Might be excessive, and noisy.. but i like it.

[MixtapeMessiah]

in an exhaust system u need a certain amount of backpressure. No back pressure is a bad thing. As for having 2.5 inch pipes ur gonna lose bottom end power, shoulda stuck with the 2.25'' inless ur running a boosted application

[Spilner521]

Originally Posted by MixtapeMessiah

in an exhaust system u need a certain amount of backpressure. No back pressure is a bad thing. As for having 2.5 inch pipes ur gonna lose bottom end power, shoulda stuck with the 2.25'' inless ur running a boosted application

No that's wrong and it's an old hot rodders myth. You don't want any backpressure at all....none. No backpressure is the best thing. Like I stated before, 2.25" pipes will maintain exhaust velocity and low end torque on a 2.2 or 2.4L 4 cylinder engine. Why would you use the same size for a larger displacement engine with 2 more cylinders and much more exhaust flow? The best exhaust for the 3400 V6 would be made with at least 2.5" piping and straight through mufflers. The baffled mufflers may sound nice, but they don't flow as well as the staight through mufflers. Instead of relying on the butt dyno to tell you if you gain or lose low end torque, get the car dyno'd and you'll see for sure.

If you just want a nice sounding exhaust and don't care about performance, get a baffled muffler on whatever size piping you want, but then don't come back complaining that you lost power/torque.

[Cliff8928]

backpressure is a myth, kinda like justifying an electric supercharger..

http://www.uucmotorwerks.com/html_pr...torquemyth.htm

I guess backpressure is good as long as it's driving a turbo.

[Spilner521]

Originally Posted by Cliff8928

backpressure is a myth, kinda like justifying an electric supercharger..

http://www.uucmotorwerks.com/html_pr...torquemyth.htm

I guess backpressure is good as long as it's driving a turbo.

Excellent write up. I just saved that one for myself to refer people to when they try to argue this myth again.

[MixtapeMessiah]

God I wish I still had my notes for Street legal performance and hotrod, here do this trick, get a piece of paper and put it against ur muffler tip, its gonna suck it against it showing you that there is backpressure even if its a little bit weither it be a 4, 6...16 cylinder whatever. Theres 3 cycles to an exhaust system giving you that pulse... now ur gonna make me look up my effin notes lol.

[Spilner521]

Originally Posted by MixtapeMessiah

God I wish I still had my notes for Street legal performance and hotrod, here do this trick, get a piece of paper and put it against ur muffler tip, its gonna suck it against it showing you that there is backpressure even if its a little bit weither it be a 4, 6...16 cylinder whatever. Theres 3 cycles to an exhaust system giving you that pulse... now ur gonna make me look up my effin notes lol.

Yes it's true that there is some backpressure in your exhaust. Even having a straight pipe out the side of the car will still give you a little backpressure. But you want to minimize it as much as possible. Having the straightest piping with the lowest restrictions and straight through mufflers will do this. Then you want to pick the right size piping to maintain exhaust velocity so that when valve overlap occurs, the velocity of the exhaust leaving the cylinder draws the intake mixture into the cylinder. This process is known as scavenging and is what allows an aftermarket exhaust system to help an engine produce more power and torque.

Here do this trick: Blow into a straw. Then pinch the end of the straw so that the opening is much smaller, creating backpressure. Then blow in it again. Which time was it easier to blow through?

[Jferg2223]

Mixtape thanks for the back up. Obviously spilner hasn't seen dyno's from a 3.4l with an oversized exhaust versus a properly sized exhaust. Another thing turbos not only are forced induction it creates forced exhaust which it would hurt a turbo cars power to have any backpressure. Besides if you still have an egr on your car the egr needs backpressure readings to work properly.

[Spilner521]

Please show me a dyno sheet from a 3.4 with a 2.5" exhaust vs. a 2.25" exhaust to back up your theory.

Here's a good article on exhaust: http://magnaflow.com/05news/magazine/05sportc.asp

In this article, this is what they have as pipe diameter guidelines for N/A engines:
1,500cc-2,000cc engines : 2-inch
2,100cc-2,500cc engines : 2.25-inch
2,600cc-3,000cc engines : 2.5-inch

Being that the 3400 V6 is roughly 3400cc, the previous statement that I made saying "For a big V6 like the 3400, at least 2.5" is the way to go" would be correct.

Now I'll show you a dyno sheet. This is a 2.4L Cavalier (same 2.4 engine Aleros have with same size stock exhaust and very similar routing) with stock 2" vs. 2.25" vs. 2.5" exhaust. 1000cc's smaller and 2 cylinders less than the 3400 V6 and yet the 2.5" still makes more power and maintains low end torque over the 2.25" setup:
And this is just with a cat-back setup. You'd see greater gains if the whole exhaust was replaced including the downpipe and a high flow cat, as well as greater gains still from adding a header (or headers for the V6).

Here's the website this information came from just in case you're wondering: http://www.iperformance.biz/dyno/exhaust01.html

And since you mentioned turbos, the reason for having the biggest exhaust possible on a turbo engine is not because of forced exhaust, it's because you want all the backpressure possible off the turbine so it can spool sooner and stay spooled longer.

[Jferg2223]

you have the evidence for your theory but why do our pcm give read outs for backpressure if nothing uses it.
egr still needs the back pressure
I also know that you dont want too big of exhaust bc it gives exhaust gases time to cool which cause them to flow slower because the gas becomes more dense. The deal is you need a compromise between sizes

[Cliff8928]

Originally Posted by Jferg2223

Mixtape thanks for the back up. Obviously spilner hasn't seen dyno's from a 3.4l with an oversized exhaust versus a properly sized exhaust. Another thing turbos not only are forced induction it creates forced exhaust which it would hurt a turbo cars power to have any backpressure. Besides if you still have an egr on your car the egr needs backpressure readings to work properly.

With a turbo i was referring to between the engine and turbocharger LOL..

Oh, and the EGR will do just fine with no back-pressure, that's what manifold vacuum is for.

[MixtapeMessiah]

cliff has a point but so does jferg, egr can run on manifold vacuum, but I wasnt talkin about different size pipes spilner, I can see if you have a 2.4 and put a 3 inch pipe on it with no turbo thats gonna rob ur hp and have no backpressure or pressure at all for that matter, and same goes for like a v-12 with a 2 inch pipe on it, its gonna have way too much backpressure and rob you. Different occurances depend on what your running and as for the charts for different CC engines with what size piping I know that, but what you are saying is that exhuasts have no backpressure and thats not true one bit weither it be F/I or N/A, like you said a "HOT ROD MYTH" a myth that hasnt been proven because its not true, someone should sticky this one