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Old 05-02-2005, 04:22 AM   #21
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Quote:
Originally posted by mike2002@May 1 2005, 04:12 PM
for a 170hp car, 2.5 is ridiculously big. borla had a better setup with 2.25" mandrel, stock is 2" pressure bent. its my opinion that 2" mandrel bent is the best setup for a near stock car (like ours). but the companies know to sell the kits, people want bigger, the average person putting exhaust on there car will order the kit with the biggest pipe. 2.5" mandrel isn't needed unless you are running forced induction.


i agree......if it was a 170hp 4 cylinder. but you have to take into consideration this is a 3.4 liter v6, a decent size engine. you need room for all that exhaust to fit into. thats why the 2" stock piping is too restrictive. upgrade to 2.25" and you maintain velocity and it opens it up a little for the top end. upgrade to 2.5" and you push the peak power higher into the rpm band but also could gain a few hp with the bigger, more free flowing piping. swap to a high flow cat and gain a few more hp. ditch the cat for a completely unrestrictive exhaust and gain even a few more hp. its all the little gains that add up. plus if you plan on further modding the engine in the future, you've already got a good size exhaust to support those mods.

as for forced induction, you want the biggest piping possible. the pressurized intake charge pushes the exhaust out of the cylinder during valve overlap so you dont have to worry about the scavenging velocity to draw it out. you just have to worry about free flow and no restriction, especially with turbos. any restriction or backpressure what so ever could slow down the turbine wheel and cause excessive turbo lag. 3" piping is a must for boosted applications. anything bigger would be better, but you'd have a tough time fitting it under the car and going over speed bumps without scraping anything.
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Old 05-02-2005, 04:28 AM   #22
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so the moral of this story: the bigger piping you go on a NA car, the higher in the rpm band the peak power output is. in my opinion, 2.5" header back without a cat is ideal for a lightly modded 3400 v6. so you sacrafice maybe a little low end grunt for that top end power, but the engine puts out enough torque to make up for it. 2.5" piping will give decent power gains and leave room for further mods in the future.

mike2002, nothing against you here at all. just stating what i think would work better and how it makes sense to me.
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Old 05-02-2005, 04:03 PM   #23
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borla is stainless steel, but it is expensive. very few shops bend stainless steel, most have aluminum. the stainless steel pipes are pretty expensive compared to aluminum.

headers dont give you more power because they're 2.5" they give you more power for a few reasons. 1 there are no ridges, it a completly smooth setup. on the stock exhaust manifolds the exhaust comes out and hits a basically 90* wall, and has a very rough path to make its way back to the cat. lots of sharp corners, which is bad for backpressure AND velocity, which is why headers designed correctly give you power through the whole power band.

also, they help from scavanging. if all the pipes come together in circular kind of twist motion, what happens is the exhaust comming out of one cylinder gets to this point right when the next cylinder is venting out, if made correctly (by varying pipe size and length) the exhaust passing through will actually help to suck the exhuast comming out of the next cylinder, THATS what makes a good header(s)

edit: the bigger pipe does help, but its not as significant as its made out to be. you have alot more velocity by the engine then you do at the tailpipe, which is why its more benifical to have bigger pipes at the engine than the end of the exhaust

people are so happy with there 2.5" because they see how big it is and now they can brag to there friends that they have "2.5" catback" for a stock car like mine, intake/exhaust/dhp/pully is the most i had ever planned to get for it, so for me it was more benifical to keep the stock pipe. if your planning on headers, 2.25" is your best bet. you may be able to pick up a used borla kit of here, or grandamgt.com. since its stainless steel it will last forever. the grandam borla kit is dual exhaust, the alero kit was twin tip
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Old 05-02-2005, 04:46 PM   #24
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hmmm well, considering i didnt even ask for a definition of what headers do....im gonna still have to ask you.... why would you go from 2.5 in piping (headers) and then downgrade to 2.25 from the cat back?

and at first i could of sworn borla wasnt stainless, it was just normal steel or something, i forget. but anyways aluminum piping will work just as good as stainless. people say it rusts, when it actually just corrodes, but that takes years/abuse.
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Old 05-02-2005, 10:59 PM   #25
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Quote:
Originally posted by -Alero-@May 2 2005, 02:46 PM
hmmm well, considering i didnt even ask for a definition of what headers do....im gonna still have to ask you.... why would you go from 2.5 in piping (headers) and then downgrade to 2.25 from the cat back?

and at first i could of sworn borla wasnt stainless, it was just normal steel or something, i forget. but anyways aluminum piping will work just as good as stainless. people say it rusts, when it actually just corrodes, but that takes years/abuse.

i give up, put 2.5" on your car. then you can brag to the kid at checkers you have 2.5" exhaust. you need the 2.25 to maintain decent velocity, the headers are 2.5" for different reasons, and your going to have more exhaust pressure at the headers because of all the exhaust combining/scavanging and whatnot, hence another reason why the headers piping should be a little bigger than the rest of the exhaust. your car is also lightly modded, the s&s is also made to accomadate more heavily modified cars, they arn't going to make 2 series of headers for a low demand car. if you were running cams, heads, intake mani's, tb blah blah, then you'd want 2.5" back

and the aluminum does rust, maybe its from the reaction of the weld, whatever it is, mine rusted through. and it does take years, as in 3, thats how long it took mine to rust through. my aurora was lowered, which helped to speed the process, since it was in more contact with snow/water than if it hadent been lowered i guess.
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Old 05-03-2005, 02:22 AM   #26
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Quote:
Originally posted by -Alero-@May 2 2005, 03:46 PM
hmmm well, considering i didnt even ask for a definition of what headers do....im gonna still have to ask you.... why would you go from 2.5 in piping (headers) and then downgrade to 2.25 from the cat back?

yeah i have no idea where headers came into this conversation. going big to small from the engine back? good question. doesnt make much sense to me. if you have 2.5" going into 2.25" towards the back its just going to cause restriction trying to squeeze the amount of exhaust in the bigger pipe down into the small one. restriction is bad.

depending on mods 2.25" is good for small 4 cylinders, 2.25-2.5" for larger 4's and small 6's, and 2.5" for larger 6's. 3400's are decent sized v6 engines. you need room to flow that much exhaust. you'll be happy with 2.5". and trust me, 2.5" piping will do you more good than just being able to brag to 12 year old girls that you have a big exhaust. and if you decide that you do want headers, you'll even gain a little more. like i said before, its all about the little gains here and there that add up.
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Old 05-03-2005, 08:53 AM   #27
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Just buy a kit :rolleyes:
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Old 05-03-2005, 05:03 PM   #28
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Quote:
Originally posted by mike2002+May 2 2005, 10:59 PM--><div class='quotetop'>QUOTE(mike2002 @ May 2 2005, 10:59 PM)</div><div class='quotemain'>
Quote:
Originally posted by -Alero-@May 2 2005, 02:46 PM
hmmm well, considering i didnt even ask for a definition of what headers do....im gonna still have to ask you.... why would you go from 2.5 in piping (headers) and then downgrade to 2.25 from the cat back?

and at first i could of sworn borla wasnt stainless, it was just normal steel or something, i forget. but anyways aluminum piping will work just as good as stainless. people say it rusts, when it actually just corrodes, but that takes years/abuse.

i give up, put 2.5" on your car. then you can brag to the kid at checkers you have 2.5" exhaust. you need the 2.25 to maintain decent velocity, the headers are 2.5" for different reasons, and your going to have more exhaust pressure at the headers because of all the exhaust combining/scavanging and whatnot, hence another reason why the headers piping should be a little bigger than the rest of the exhaust. your car is also lightly modded, the s&s is also made to accomadate more heavily modified cars, they arn't going to make 2 series of headers for a low demand car. if you were running cams, heads, intake mani's, tb blah blah, then you'd want 2.5" back

and the aluminum does rust, maybe its from the reaction of the weld, whatever it is, mine rusted through. and it does take years, as in 3, thats how long it took mine to rust through. my aurora was lowered, which helped to speed the process, since it was in more contact with snow/water than if it hadent been lowered i guess.
[/b]


uh, trust me aluminum does not rust....i am a welder. it corrodes and the welds can rust yes. but anyways light mods or not, a cat back exhaust is a basic/light mod anyway, but i just dont see why you would go from 2.5 then to 2.25.....makes no sense. im not getting the biggest piping just to brag at checkers. im getting whats best for my car in the future, im pretty confident i will dump more money into the car further down the road, its just maybe taking care of exhaust once and only once is better than redoing it twice.

Quote:
Originally posted by Spilner521@May 3 2005, 02:22 AM
<!--QuoteBegin--Alero-
Quote:
@May 2 2005, 03:46 PM
hmmm well, considering i didnt even ask for a definition of what headers do....im gonna still have to ask you.... why would you go from 2.5 in piping (headers) and then downgrade to 2.25 from the cat back?


yeah i have no idea where headers came into this conversation. going big to small from the engine back? good question. doesnt make much sense to me. if you have 2.5" going into 2.25" towards the back its just going to cause restriction trying to squeeze the amount of exhaust in the bigger pipe down into the small one. restriction is bad.

depending on mods 2.25" is good for small 4 cylinders, 2.25-2.5" for larger 4's and small 6's, and 2.5" for larger 6's. 3400's are decent sized v6 engines. you need room to flow that much exhaust. you'll be happy with 2.5". and trust me, 2.5" piping will do you more good than just being able to brag to 12 year old girls that you have a big exhaust. and if you decide that you do want headers, you'll even gain a little more. like i said before, its all about the little gains here and there that add up.
[/quote]

yeah going 2.5 isnt gonna hurt. the 2.5 from headers all the way back just seems to make more sense
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Old 05-03-2005, 05:04 PM   #29
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Quote:
Originally posted by Redog@May 3 2005, 08:53 AM
Just buy a kit :rolleyes:

you dont tell me how to live my life! lol ...............................
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Old 05-03-2005, 07:29 PM   #30
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[/quote]

yeah i have no idea where headers came into this conversation.
[/quote]

headers came into the conversation because someone said "why would i go from a 2.5" header to a 2.25" exhaust" well i explained how/why headers are the way they are because a explanation was obviously needed if you think you need 2.5" exhaust because the header has a 2.5" outlet.

[/quote]
going big to small from the engine back? good question. doesnt make much sense to me. if you have 2.5" going into 2.25" towards the back its just going to cause restriction trying to squeeze the amount of exhaust in the bigger pipe down into the small one. restriction is bad.

depending on mods 2.25" is good for small 4 cylinders, 2.25-2.5" for larger 4's and small 6's, and 2.5" for larger 6's. 3400's are decent sized v6 engines. you need room to flow that much exhaust. you'll be happy with 2.5". and trust me, 2.5" piping will do you more good than just being able to brag to 12 year old girls that you have a big exhaust. and if you decide that you do want headers, you'll even gain a little more. like i said before, its all about the little gains here and there that add up.
[/quote]

i didn't think i had to explain the reason why you wouldn't want 2.5" AGAIN, but for kicks, i guess i do. with 2.5" you dont have enough veloicty to get good torque from the engine. the headers are 2.5" to accomadate such things as heavy mods, which you dont have. the larger size of the headers IS NOT NEEDED in your application, your car is NOT benifiting from 2.5" over 2.25" in the header. its benifiting from the other things i already explained in a previous post, which is why i explained them. please read this again, and again

a 170hp pushrod v6 does not benifit from 2.5", it hurts it. my friend just ordered a borla exhaust kit for his CORVETTE and its 2.5", its a 99ls1. so do you think if this 5.7L 345hp car needed only 2.5, you also need it? LMAO. you dont need 2.5" unless you were running at least 300hp. i dont really car if you put it on your car, but im just trying to prove a point

[/quote]
uh, trust me aluminum does not rust....i am a welder. it corrodes and the welds can rust yes.[/quote]

UH trust me, ive had aftermarket aluminum exhaust and the person i sold it to just told me it rusted through, and then i saw it (sold the car to a family member)corrodes or rusted, the whole thing is shot, and not just at the welds, the pipe is all brown with what looks like rust, but i guess its somthing else.
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Old 05-03-2005, 07:34 PM   #31
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im done ranting
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Old 05-03-2005, 08:41 PM   #32
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mike! ask anyone here, aluminum does not rust! if yours rusted, then it wasnt aluminum. like i said it will corrode and only corrode.

also back the 2.5 thing. you know im not trying to get 2.5 just to brag to 12 year olds or be cool like a corvette or try to be something im not.

its just, with that 2.5 headers and 2.5 cat back exhaust it just seemed so much more reasonable to have. in fact i forget who it was exactly (he's on this board), but all he had was "light mods" including a CAI or WAI i forget, and SLP cat back exhaust, once he got headers he dynoed a 27 whp gain. so im pretty possitive it doesnt matter if you have heavy or light mods, headers will benefit no matter what. offcourse with the teamwork of a cat back exhaust.

but yeah i know for a fact you will loose some low end with the bigger the pipe, but what i was trying to say earlier was, the 3.4 has plenty of low end torque, and not enough high end. but yeah
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Old 05-03-2005, 11:18 PM   #33
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