Exhaust

[FutureEcotecOwnerAgain]

i know i just got my cat back exhaust installed a couple months ago, but ive been thinking of a new setup to maybe give a little more power and sound. so here it is. does anyone know if would could put a muffler right after the cat, doesnt really matter what muffler and then have like a y - pipe from the muffler to the back of the car so then you couldnt see the muffler from the back like you can now and should it give more power?

[thehammer07]

if you want to do a muffler right after the cat. get a muffler where the exit pipe comes out of it bends down towards the pavement. that way you dont need all that extra piping. will prolly be load.

[BLK03GXS]

Straight pipe. enuff said.

[alerosport.com]

wont the Exhaust rise up towards the underside of the car? when hes sitting?

[FutureEcotecOwnerAgain]

isnt straight pipe illegal? if not than i might do it. i know it will be louder, but and extra performance? as long as i keep the cat i good get rid of the muffler.

[Youngblood77]

Keep in mind that straight pipes above and beyond being illegal, will actually hurt the performance of our cars....we need back pressure to retain the torque. The hp benefit we'd receive on the top end of the powerband would be minimal, if anything @ all, so it's definately NOT worth the trouble. Finding the correct balance of back pressure and flow has been an on-going battle for decades, and it just comes down to finding out what works for certain engines, then sticking to it.

[Spilner521]

actually its not backpressure thats needed for torque. its exhaust gas velocity. your goal is to get the least restrictive, most free flowing exhaust piping thats the right size for your application. a straight pipe will be incredibly loud and obnoxious but if you choose the right size piping, you'll maintain the low end torque and it'll also flow extremely well without all that extra piping and bending. if it were me, i would put in one or two glasspacks/resonators after the cat and do a side exit straight pipe right in front of the left rear tire. piping size depends on your mods. 2.25" for minimal mods (intake, header, exhaust) and no more than 2.5" for further engine mods (fuel mods, port and polish, cams)

[BLK03GXS]

awsome finally someone who knows what they are talking about, Spilner hit it on the head. When GM tested the eco it was done with Straight pipe.
I would if you want to dump the exhaust go with 2.5inch pipeing, and at LEAST one glasspack.
But dont dump it under the car, your car dosent have over 3 inch piping, and it isnt a V8 so doing a undercar dump would be trashy... IMPO.

[BLK03GXS]

OH and muffler location dosent matter in the HP made with your car... If you simply dont want to see the muffler anymore then get a glasspack after the cat, and then some new pipe run.

[Youngblood77]

If no backpressure was needed, then why was there a straight pipe on the Eco they tested? Why not test the engine with open ports? I don't doubt that GM has the facilities to test engines outside, so ridding the technicians of exhaust fumes shouldn't be an issue. I'm just wondering why people even bother with exhaust pipes @ all if there's no need for them? Take top-fuel cars for instance: They're not subject to noise restraints like most racecars, yet they still route the exhaust through pipes.

[Spilner521]

exhaust pipes do not cause backpressure unless they are way to small for the application. that's why you open it up a little with bigger piping, to let off on the back pressure without going too big so that you maintain decent velocity for low end torque.

think about it...any type of backpressure what-so-ever makes the pistons work that much harder to push out the exhaust. a good example is to take 2 straws...one real skinny and the other a little fatter. now blow into the skinny one. and then blow into the fatter one. it may not be incredibly noticeable but your using more force to blow the same amount of air through the skinny one than the fat one. now cover half the opening with your finger to create more backpressure. now you have to use even more force to blow the air through than before. in an engine backpressure would cause the pistons to push harder on the exhaust to get it out, causing a decrease in power output.

the deal with exhaust gas velocity is this: the intake valve starts to open when the exhaust valve is just starting to close, so there is a few miliseconds when both valves are open at the same time (valve overlap). as the exhaust exits the cylinder, it creates a vacuum effect that pulls the air/fuel mixture into the cylinder. this vacuum helps the piston work less to pull in the air/fuel mixture which will help the power output. backpressure hinders the exhaust flow, decreasing the velocity at which the exhaust exits the cylinder, which in turn decreases the vacuum effect. piping that is too small lets the exhaust maintain its velocity at low rpms, but doesnt flow well enough at higher rpms to decrease the backpressure. piping that is the right size is big enough to get all the exhaust out without any backpressure at higher rpms, but is small enough to maintain its velocity at low rpms, maximizing the vacuum effect, letting the piston work even less to pull in the air/fuel mixture. with piping that is too big, the exhaust has to fill up the space inside the piping before it can continue moving, which slows down the velocity of the exhaust, providing less of a vacuum to pull in the air/fuel mixture.

the less work the pistons have to do getting the air in and out of the cylinder, the quicker and faster they can rev, and the more power the engine will make over the entire rpm range. and more power is a good thing :thumb:

[Spilner521]

and i have no idea why they dont test the engines with open ports. i'm guessing its so they can route the toxic gasses out of the way instead of having one big cloud of exhaust around the engine. and i also dont know why top fuel cars use short headers instead of open ports...i dont own a top fuel car to test it and figure out the difference. i just know how car exhausts are setup and what works to make the most power on a naturally aspirated engine.

forced induction, however, is a whole different story.... :thumb:

[BLK03GXS]

Short headders like on top fuel are there to keep the heat and flame away from the engine, use your brain... Oh and dont forget the myth that running without exhaust BURNS the valves....

[Youngblood77]

Originally posted by BLK03GXS@Apr 25 2005, 04:56 PM
Oh and dont forget the myth that running without exhaust BURNS the valves....
Quoted post


:P Never heard that one before...

[BLK03GXS]

Really? or are you being sarcastic... ? cus ppl allways say that when people talk about not runing exhaust, like just off the headder people allways are like "your gunna burn the valves!!!" it just makes me angry... wow, your mom teaches you good about cars... haha

[Cliff8928]

Oh, I've heard that one a few times before... If that burned valves, I'd have many engines with no exhaust valves left...

And, having the pipes on racecars and test engines can also help with scavenging, The exhaust flow from the cylinders help each other to maintain the velocity.

[BLK03GXS]

scavaging only really applys if the pipes are into a colector... then the pulses from other cyls help to scavange... individual pipes would have little to no effect...

[Youngblood77]

No, for real..I've never heard that before. hehehe

[Youngblood77]

Originally posted by BLK03GXS@Apr 26 2005, 03:42 PM
scavaging only really applys if the pipes are into a colector... then the pulses from other cyls help to scavange... individual pipes would have little to no effect...
Quoted post


Exactly. A good example of this would be the tri-"Y" header style....

[Cliff8928]

Originally posted by BLK03GXS@Apr 26 2005, 02:42 PM
scavaging only really applys if the pipes are into a colector... then the pulses from other cyls help to scavange... individual pipes would have little to no effect...
Quoted post



I knew that, I just wasn't thinking about having the pipes without a collector...

[Redog]

Gotta have a muffler and cat to be street legal

Try a Flowmaster

[BLK03GXS]

Originally posted by Cliff8928+Apr 27 2005, 03:41 AM--><div class='quotetop'>QUOTE(Cliff8928 @ Apr 27 2005, 03:41 AM)</div><div class='quotemain'><!--QuoteBegin-BLK03GXS@Apr 26 2005, 02:42 PM
scavaging only really applys if the pipes are into a colector... then the pulses from other cyls help to scavange... individual pipes would have little to no effect...
Quoted post



I knew that, I just wasn't thinking about having the pipes without a collector...
Quoted post
[/b][/quote]Oh i know we were just off on a side tangent, listen to redog haha i got a flowmaster its saweet

[FutureEcotecOwnerAgain]

well i already have a flowmaster 80 series muffler with 2.5 inch piping into it. is this all i need and is it gonna give me the biggest hp gain? what is the hp gain with this exhaust and my intake and header if anyone knows?

[BLK03GXS]

IF you have full 2.5 piping with that. then maybe 15 hp, or so... with a headder, intake and stock piping maybe 6-8 hp

[AleroSS]

Expect a Thrown Code and a CEL/SES lite if you run without a cat btw

[Spilner521]

get an O2 simulator and plug it in the harness that the after-cat O2 sensor plugs into...no code thrown, no check engine light, and a free flowing exhaust.

[BLK03GXS]

I was under the impression that there wasnt a o2 sim for the eco yet... if there is where can i get one?

[Cliff8928]

Originally posted by Redog@Apr 27 2005, 06:01 PM
Gotta have a muffler and cat to be street legal

Try a Flowmaster
Quoted post



Have had a few cars without mufflers and nobody ever complained...

[Spilner521]

Originally posted by BLK03GXS@May 1 2005, 01:32 PM
I was under the impression that there wasnt a o2 sim for the eco yet... if there is where can i get one?
Quoted post


did some searching and your right. no O2 sim for the ecotec as of yet...

[BLK03GXS]

ahhhhhhrg i neeeed like 3 of em.. haha