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I would like to expose my opinion about the exhaust on the 2.0 LSJ. By some theorical calculations I've made and personal experience ... here is also a good web site which helps me a lot.

http://popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index.html

Firstly, most stock Cobalt SS / SC have been dynoed (on a Dynojet) to an average of 208 WHP (on 4th gear), which equals to roughly 245 BHP (brake horsepower; power of the engine) (due to the drivetrain loss).

According to the web site, a section of 2,5" pipe will flows 560 CFM. To be sure there isn't any HP loss due to unwanted backpressure of a too small pipe, your engine needs 2.2 CFM per brake horsepower. So 560 CFM divided by 2.2 is good for 254 BHP. It simply means that a 2,5" catback on a stock Cobalt won't cause any HP loss (versus a 3" one), unless other modifications arrives.

If you plan to go up to 300 BHP (roughly 255 WHP) but not more, the 2,5" catback (flowing a max of 560 CFM) will allow the engine to breath a maximum of 1,9 CFM per BHP. At 1,9 CFM per HP, the HP loss due to backpressure is roughly 2 % only, which won't affect the engine too much (5 WHP or less). Personnaly, since I don't plan to go higher than 300 BHP (or roughly 255 WHP), I won't go larger than a 2,5" catback.

About the stock catback, there is a rear section which is 2,25" in diameter. This section is already maxed for the stock 245 BHP. About the stock rear muffler, it doesn't flow enough too. Those two parts together cause a HP loss of 8 to 10 WHP on a stock SS / SC. A very simple thing to do is to buy the 2,5" Magnaflow catback (available from Modern Performance). But for those like me who want to make a custom one, here is a how-to link which will give roughly the same results than replacing the entire catback.

http://www.cobaltss.net/forums/showthread.php?t=5478

About the stock LSJ header : It has roughly the same inside dimensions than the 2,2 header, so GM has voluntarily got the car detuned the. It is the most restrictive part on this very car (2.0 SS / SC's and Ion Redlines). For those who are replacing the stock catback, but don't plan to replace the stock restrictive header : The stock header inside diameter (where it meet the downpipe) is less than 2 inch; it totally kills the car and cause several HP loss. You will be able thus to get some HP gains with good kits (like the PSI-FI one), but won't be able to achieve maximum results. Also, the stock header stresses the engine a lot.

Have a nice day ! More to come ...
 

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makes sense, worth an experiment if only i had money >.<
 

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Cant flaw much of what you are saying here, other than reminding you to read the fine print in the Hot Rodding article that states the calculations and numbers given are for NATURALLY ASPIRATED engines as these "rules of thumb" change quite a bit depending on the amount of boost, head flow throughput and even cam grind (overlap). But that being said, I will agree that a 2.5" is probably "good enough" to see some improvement from the stock setup.

I also agree that the manifold is a serious bottle neck, but if you think it's not A LOT different from the 2.2 - you need to look at them side by side (as I have) :D
Here's a couple of pics of the stock L61 manifold that I took. Looks to me like they (GM) have seriously (and intentionally) pinched it off.The LSJ has both larger primaries AND a lot bigger (and ROUND!) collector too...
Regards
WopOnTour
 

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WopOnTour said:
Here's a pic of the stock L61 manifold. Looks to me like they have seriously pinched it off intentionally.

Nice invisible pic ;) (sorry couldn't resist)
 

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It's there. I see it. There's a tape measure and everything...beautiful crescent moon opening on the header.
 

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Cynic said:
It's there. I see it. There's a tape measure and everything...beautiful crescent moon opening on the header.
He cheated :eek:

06:38 PM post time by me, 06:41 PM edit by wop
 

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That's awesome. Sometimes you gotta hand it to GM. Way to keep my insurance down. This car seems more and more like a combination lock every day.
 

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Freakazoid said:
He cheated :eek:

06:38 PM post time by me, 06:41 PM edit by wop
LOL I was getiing there!!....
I often post in the "quick reply" box and then edit my posts and add pics after.WOT
 

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dazednconfused75 said:
That's awesome. Sometimes you gotta hand it to GM. Way to keep my insurance down. This car seems more and more like a combination lock every day.
Dazed, you live in HOCKEYTOWN??? You mean Edmonton??? :p
 

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LOL Yup, you'll know too soon enough (Nov 3rd)
I've been an Oilers fan since the old WHA days when a young 17 year old future super-star moved to Edmonton when the Indianapolis Pacers folded.The rest is history.:D
WOT
 

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I too live near hockeytown aka Detroit
p.s. wings are 6and1 :D
 

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MMM I love it when he eludes to things.
 

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Discussion Starter #14
WopOnTour said:
Cant flaw much of what you are saying here, other than reminding you to read the fine print in the Hot Rodding article that states the calculations and numbers given are for NATURALLY ASPIRATED engines as these "rules of thumb" change quite a bit depending on the amount of boost, head flow throughput and even cam grind (overlap). But that being said, I will agree that a 2.5" is probably "good enough" to see some improvement from the stock setup.

I also agree that the manifold is a serious bottle neck, but if you think it's not A LOT different from the 2.2 - you need to look at them side by side (as I have) :D
Here's a couple of pics of the stock L61 manifold that I took. Looks to me like they (GM) have seriously (and intentionally) pinched it off.The LSJ has both larger primaries AND a lot bigger (and ROUND!) collector too...
Regards
WopOnTour
WopOnTour thanks for the pic. I realise that the Ion Redline manifold end (the hole you show on the pic) isn't the same than the Cobalt SS. You can see this on the TOG dyno thread done by selfinfiction.
 

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Discussion Starter #15
With your picture, I have done the calculation (with a CAD software) of the area of the manifold's "inside hole". The area equals to a round pipe of 1,67" !!! LOL. The Cobalt SS / SC is roughly the same area too ...
 

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so the header is the real restriction here huh. ikinda figured when i was boreing the collector just to see if it made a difference. which it didnt so i gotta buy a header but they are so expensive but ill start saving my pennies
 

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jmc007 said:
With your picture, I have done the calculation (with a CAD software) of the area of the manifold's "inside hole". The area equals to a round pipe of 1,67" !!! LOL. The Cobalt SS / SC is roughly the same area too ...

sorry but ive noticed this alot. does your computer not like to use (.) or do you just keep hitting the wrong key?
 

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pclear9061 said:
sorry but ive noticed this alot. does your computer not like to use (.) or do you just keep hitting the wrong key?
In other countries (that use the metric system) (,) is interchangable with (.) both are decimal points in the end. Besides you knew what he meant anyways...

On the main topic all very good information, remember the smallest diameter along the system will be the deciding factor on flowrate. Sounds to me like a bigger (higher flowing) header would be a good HP booster.
 

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ReaL ION said:
In other countries (that use the metric system) (,) is interchangable with (.) both are decimal points in the end. Besides you knew what he meant anyways...

On the main topic all very good information, remember the smallest diameter along the system will be the deciding factor on flowrate. Sounds to me like a bigger (higher flowing) header would be a good HP booster.

but your not in another country ur in NJ, last i knew that was the US of A :D
 
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