I would like to expose my opinion about the exhaust on Cobalt SS / SC. 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.*************/forums/showthread.php?t=5478

About the stock header on the Cobalt SS / SC: 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 ...

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.*************/forums/showthread.php?t=5478

About the stock header on the Cobalt SS / SC: 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 ...

Pure speculation about the muffler. No one has actually measured how much restriction it actually has. Large bodied chambered mufflers tend to have good flow and good sound attenuation properties. A compromise yes but a good one.

I have to take issue with your assesment of the stock exhaust manifold also. My personal feeling is a good porting job on it in the area of the collector would be a benifit. The size of the runners and the smooth turns suggests to me that it's a good piece to start with. Headers also are a maintenence item and will not give the service life of the stock piece.

I have yet to see a dyno test where a header actually improved the power but have seen one where power was lost. Yes there were problems with that dyno test and it's just one data point but it was a negative gain. I prefer to see proof instead of "It has to be better".

Regards
Pierre

Good write-up!!

I think its a safe bet to say that the stock muffler is a little restrictive, just as jmc007 said. While not very restrictive, it was designed to keep the car quiet, not make power.

And I thought there were some dynos of the header making like ~15whp. With the rest of the exhaust stock. And it really is that small on the exit of the exhaust manifold. So OBVIOUSLY it is restrictive at less than 2". Its barely bigger than the primaries, so just can't accomadate the flow from 4 primaries. Naturally, porting it some will help, but you just can't make the exit large enough to have a well balanced manifold.

Not a bad write up. Someone needs to dyno their car back to back with 2.5 inch and 3 inch and varying mods to actually test when the 2.5 inch begains to lose HP over the 3 inch. It was done with the SRT-4 and it wasn't til about 300 FWHP, not BHP, that it started to show more power with a 3 inch over 2.5 inch exhaust. I guess there would have to be an aftermarket to be able to do that though. :rolleyes:

First of all Pierre I have high respect for older dudes, but sorry to tell you I didn't speculate on nothing. We got 2 Cobalt SS / SC dynoed on a Mustang dyno, both stock but the stock restrictive muffler replace, both gaves 8 to 10 WHP gain, period.

Secondly, the effective size of the runners is for sure the inside area, which equals roughly to a 1" diamter tubing on bended section. It is not enough for the supercharged LSJ. But yes you got some good points relative to the porting, it will help a lot, but not with the stock manifold. Plus the fact that the inside diameter of the manifold's collector is less than 2"; I am sure you also know it's not enough. This is the less restrictive section of the entire exhaust.

Thirdly, if you do some search on other forums, there has been some dyno posted with increased HP (for sure i'm not talking about other car but the SS / SC or Ion Redline) with a replaced header. 5 at the very less on bad conditions and 15 to 20 at the maximum on good conditions, most on totally stock car.

A few guys which posted some dyno loss (with a replaced header) got their car dynoed on a different day than their base pulls, that's not ideal.

Have a nice day !

First of all Pierre I have high respect for older dudes, but sorry to tell you I didn't speculate on nothing. We got 2 Cobalt SS / SC dynoed on a Mustang dyno, both stock but the stock restrictive muffler replace, both gaves 8 to 10 WHP gain, period.

No worries JeanMark

I just like to play devils advocate :-) don't take offense.

Your 8-10 WHP gain was made with both the muffler and changing the stock 2 1/4" od press bent pipe to 2 1/2" od mandrel bent pipe.

Did the HP gain come completely from the muffler of was it from the combination of the two?


[/QUOTE]Secondly, the effective size of the runners is for sure the inside area, which equals roughly to a 1" diamter tubing on bended section. It is not enough for the supercharged LSJ. But yes you got some good points relative to the porting, it will help a lot, but not with the stock manifold. Plus the fact that the inside diameter of the manifold's collector is less than 2"; I am sure you also know it's not enough. This is the less restrictive section of the entire exhaust.[/QUOTE]

Sorry about the confusion. I was actually talking about porting the exhaust manifold itself specificaly in the collector area. When you look at equivalent resistance in a piping system you do take diameter into account. You also need to factor in the length at that diameter. A 2" ID pipe 3" long will flow more than a 2" ID pipe 5 ft long. The stock collector is fairly short and the equivalent restriction may not be that high. I have not gotten to inspect the stock manifold myself but I'd guess that the primary tubes on the manifold have the equivalent cross section area of the exhaust port of the head. Yes large cross section primary tubes will flow better but given the rather low rev limiter setting on the LSJ the engine may not be able to make full use of that increase. Perhaps you can take some detailed measurements when you get a chance?

[/QUOTE]Thirdly, if you do some search on other forums, there has been some dyno posted with increased HP (for sure i'm not talking about other car but the SS / SC or Ion Redline) with a replaced header. 5 at the very less on bad conditions and 15 to 20 at the maximum on good conditions, most on totally stock car.

A few guys which posted some dyno loss (with a replaced header) got their car dynoed on a different day than their base pulls, that's not ideal.
QUOTE]

I did look yesterday and found 1 gain of 10WHP and 5 WTorque. 15-20 I have not seen. My point is you could probably get half of that ( 5 WHP ) by porting the stock manifold and put your money to better use somplace else with a mildly (<245WHP dynojet, mustang would be lower) built up engine with the stock rev limiter.

Regards
Pierre

I did look yesterday and found 1 gain of 10WHP and 5 WTorque. 15-20 I have not seen. My point is you could probably get half of that ( 5 WHP ) by porting the stock manifold and put your money to better use somplace else with a mildly (<245WHP dynojet, mustang would be lower) built up engine with the stock rev limiter.


that 10whp and 5 wtq was with the tog header, not the scdyne. and i can pretty much gaurantee you will get that 10whp, because those are real numbers, tested by me and not by the company that made them. you would see more of a gain if you're on a dynojet, but definitely not 20hp gains like scdyne claims. and porting the stock manifold would be a waste of time and money. the primaries are much larger, and the collector is atleast 2 times larger on the tog. but hey...if you want to spend the time porting out this thing and not getting anywhere near the capabilities of the tog setup go ahead :D

http://www.ricermath.com/sspics/manifold.jpg
http://www.ricermath.com/sspics/header002.jpg

Pierre the 8 to 10 whp gain was from the combination of the two parts (stock 2,25" rear crushed bent section and stock muffler) replaced by a 2,5" mandrel bent section and straight through Magnaflow oval muffler.

that 10whp and 5 wtq was with the tog header, not the scdyne. and i can pretty much gaurantee you will get that 10whp, because those are real numbers, tested by me and not by the company that made them. you would see more of a gain if you're on a dynojet, but definitely not 20hp gains like scdyne claims. and porting the stock manifold would be a waste of time and money. the primaries are much larger, and the collector is atleast 2 times larger on the tog. but hey...if you want to spend the time porting out this thing and not getting anywhere near the capabilities of the tog setup go ahead :D

In your opinion, and anyone elses.....which header do you think is better? The TOG or the Scdyne?

In your opinion, and anyone elses.....which header do you think is better? The TOG or the Scdyne?

i'll let you decide. this picture of the TOG header is the prototype header... the welds are rough on it.. since it is the prototype the rough welds are expected. the TOG has a 3" collector and will be coated inside and out. but even though this is the prototype the welds are ten times much cleaner than the scdyne product.
http://www.ricermath.com/sspics/header002.jpg
TOG above
-----------------------------------------------------------------
scdyne below
http://*************/gallery/files/2/7/3/6/225820.JPG
http://*************/gallery/files/2/7/3/6/225830.JPG

this scdyne is a completed production uint and look how crappy the quality is. my personal opinion is that it looks like pewter metal with cheap coating and extremely horrible welds. i am a novice welder and those looks about the quality of what i can do..... and this is supposed to be the final product that people are paying for? this one only has a 2.5" flange, but doesn't even appear to have a real collector. and it is only coated on the outside, you can see the coating starts to fade as you look into the flange.

these pictures speak for themselves.

<edit> the TOG header in the picture is not coated, it should have the silver ceramic high temp coating on it and will have a similar color finish as the scdyne. the TOG in the picture just has some high-temp paint on it.

Selfinfiction

1 : I agree the welds are a bit ugly ... but what is the most important for a header, the look (since he is mainly invisible even with the hood opened) or the HP gain ? I think both one will give some good results with a 2,5" or 3" catback.

2 : The collector is a merged one, it is done this way.

3 : It is available right now, it is why i bought one, and I am satisfied with it, it was my choice. You aren't supposed to say it's pure crap just because you don't like it.

Thanks for the posts ...

i'll let you decide. this picture of the TOG header is the prototype header... the welds are rough on it.. since it is the prototype the rough welds are expected. the TOG has a 3" collector and will be coated inside and out. but even though this is the prototype the welds are ten times much cleaner than the scdyne product.

-----------------------------------------------------------------
this scdyne is a completed production uint and look how crappy the quality is. my personal opinion is that it looks like pewter metal with cheap coating and extremely horrible welds. i am a novice welder and those looks about the quality of what i can do..... and this is supposed to be the final product that people are paying for? this one only has a 2.5" flange, but doesn't even appear to have a real collector. and it is only coated on the outside, you can see the coating starts to fade as you look into the flange.

these pictures speak for themselves.

<edit> the TOG header in the picture is not coated, it should have the silver ceramic high temp coating on it and will have a similar color finish as the scdyne. the TOG in the picture just has some high-temp paint on it.

Thanks! Yea I noticed that the Scdyne collector looked a little smaller, but didnt want to say anything just incase I was wrong.....So the best bet would be the TOG header, then to add that downpipe would be a great combo... Also another question for you would be how do you like Magnaflows new catback? I dont like the sound at all...I was thinking of just replacing the stock muffler with a borla XS or Turbo and even possibly eliminating that resonator right after the cat...any thoughts on that?

Selfinfiction

1 : I agree the welds are a bit ugly ... but what is the most important for a header, the look (since he is mainly invisible even with the hood opened) or the HP gain ? I think both one will give some good results with a 2,5" or 3" catback.

2 : The collector is a merged one, it is done this way.

3 : It is available right now, it is why i bought one, and I am satisfied with it, it was my choice. You aren't supposed to say it's pure crap just because you don't like it.

Thanks for the posts ...

VERY TRUE, not to mention it is $100 cheaper.....But I can afford to wait for the TOG. Honestly I dont think HP gains are comprable enough to even make a difference between the two...

jmc,

The article you refer to was written by David Vizard. He is a genius at exhaust system design. He first penned a predecessor to this article many years ago in Super Stock and Drag Illustrated.
I have followed his advice ever since with excellent results.
Few folks know about or understand the 2.2cfm/hp rule of thumb!
From that I knew the SS/SC 2.5" system was quite adequate.

Question. What exactly is inside the resonator on the SS/SC? How big is the internal pass tube? 2.5" all the way through?

About the stock manifold. Although I haven't seen one off the car in person, I agree with Pierre that it just might be possible to hand port it for a performance gain. Or....one could have it Extrudehoned. I PM'd Selfinfliction asking if he might like to sell his stocker so I could investigte that....but got no reply.

The stock muffler could be ok......but w/o cutting one apart and looking inside, hard to tell what GM attempted. If it's the same part for the non SS cars, then I imagine GM figured most of us would remove it anyway.
Replacing it along with the 2.25" section, is probably a smart move. And easy to do. Even with stainless.

About those "headers". Neither has much of a collector. Sorry, but compared to a real header, they just don't. The portion of tubing leading to the cat ends up becoming the collector. I'll say this again, a real header would have longer tubes, a real collector and the stock cat would have to be relocated.
Not to say that either of these don't make more hp than stock. As time goes by, other companies will make headers and the dyno will tell the story. But don't expect anyone to buy all of them and do a shootout!
The welds on both of those are typical wire feed welds, they might not look perfect, but they don't need to be.

Good discussion, thanks.

Ron (another old guy)

About those "headers". Neither has much of a collector. Sorry, but compared to a real header, they just don't. The portion of tubing leading to the cat ends up becoming the collector. I'll say this again, a real header would have longer tubes, a real collector and the stock cat would have to be relocated.

They are made that way because with a supercharged motor, you don't really benefit from equal length headers like a N/A motor does. I think that header is just about perfect for this motor. Assuming, naturally, that the quality is good, primaries have smoothe bends, etc...

I just wish someone would hurry up and by the TOG header, PSFiwhatever pulley kit, intake, and get to 300whp (wihout nitrous). That would impress me.

[QUOTE=Drewfu$]They are made that way because with a supercharged motor, you don't really benefit from equal length headers like a N/A motor does.

Oh really,
Show me a technical article or real evidence that proves this?
They are made short because with the stock cat arrangement, there isn't enough room to do anything more than a shorty header. Period.
Ron

Pierre the 8 to 10 whp gain was from the combination of the two parts (stock 2,25" rear crushed bent section and stock muffler) replaced by a 2,5" mandrel bent section and straight through Magnaflow oval muffler.

Then I would conclude that the stock muffler itself is not worth the whole 8-10 WHP loss. Ball park guess 5-7 with the piping upgrade providing the remainder.

Good luck today on your header tests.

Pierre

jmc,

The article you refer to was written by David Vizard. He is a genius at exhaust system design. He first penned a predecessor to this article many years ago in Super Stock and Drag Illustrated.
I have followed his advice ever since with excellent results.
Few folks know about or understand the 2.2cfm/hp rule of thumb!
From that I knew the SS/SC 2.5" system was quite adequate.

Question. What exactly is inside the resonator on the SS/SC? How big is the internal pass tube? 2.5" all the way through?

About the stock manifold. Although I haven't seen one off the car in person, I agree with Pierre that it just might be possible to hand port it for a performance gain. Or....one could have it Extrudehoned. I PM'd Selfinfliction asking if he might like to sell his stocker so I could investigte that....but got no reply.

The stock muffler could be ok......but w/o cutting one apart and looking inside, hard to tell what GM attempted. If it's the same part for the non SS cars, then I imagine GM figured most of us would remove it anyway.
Replacing it along with the 2.25" section, is probably a smart move. And easy to do. Even with stainless.

About those "headers". Neither has much of a collector. Sorry, but compared to a real header, they just don't. The portion of tubing leading to the cat ends up becoming the collector. I'll say this again, a real header would have longer tubes, a real collector and the stock cat would have to be relocated.
Not to say that either of these don't make more hp than stock. As time goes by, other companies will make headers and the dyno will tell the story. But don't expect anyone to buy all of them and do a shootout!
The welds on both of those are typical wire feed welds, they might not look perfect, but they don't need to be.

Good discussion, thanks.

Ron (another old guy)


HI ron, the stock Cobalt SS/SC resonator is totally empty in the inside. I didn't measure it exactly on the outside, but it seems to be roughly 3,5". We look inside and saw it was empty through. At the beginning and the exit, it is smaller to 2,25", but just for a one inch long section (on both side).

Thanks jmc!
Good info.
Almost sounds like GM duplicated Vizards "expansion chamber".
Ron

do you guys know anything about the GMPP header?

It allows only 30 more CFM than stock, not a good gain in my point of view. Maybe 5 hp ...

Thanks! Yea I noticed that the Scdyne collector looked a little smaller, but didnt want to say anything just incase I was wrong.....So the best bet would be the TOG header, then to add that downpipe would be a great combo... Also another question for you would be how do you like Magnaflows new catback? I dont like the sound at all...I was thinking of just replacing the stock muffler with a borla XS or Turbo and even possibly eliminating that resonator right after the cat...any thoughts on that?

Yes that is what I did. I cut out the resonator and the rest of the exhaust and did a 2.5" pipe with a Magnaflow Turbo muffler and a 4" tip to help fill the huge cut-out in the rear bumper. It is not too big but not small but I think and many others think it looks awesome compared to the stock 3" tip. It also sounds very good! I get a lot of complements and will soon be doing the TOG header and probably a high-flow car or a cut-out or both...