Just looking for an update. There was a thread some time back on header. Seems there were only 2.2 owners with them. The cobalt ss 2.4 header is supposed to fit the 2lt hhr. So if you have one was it worth the money? Did it increase performance and/or mpg? Butt dyno is fine.
Thanks

 

A header will definitly help performance and mileage but at a cost. Headers are notoriously bad about leaking, burning plug wires, cracking etc. Welding and porting a factory exhaust may have the same cracking and leaking issues.
A good header with stock restrictive cat and exhaust will make little if any difference. Removing the cat is illegal and will make it start throwing codes requireing a tune which may void warranty.
Even a good complete header with high flow cat and better flowing exhaust will make considerably more noise (and performance) than stock. The stock system is not too bad but certainly not as free flowing as a complete system where noise or warranty is not a concern.
A cat back system with stock exhaust manifold and cat will make little difference in performance and mileage. It may sound better but not much more unless all restriction from header to tail pipe is eliminated. Then it may need a tune to recalibrate the fuel and timing to match the improved flow.
I have a friend that put a header, removed cat and put on dual exhaust. He is getting about 5 MPG better in the city according to him. I am not sure how much faster his car (probably faster) is as I have not raced him. But his car is much louder than I would want and I do not know what he is going to do to get it inspected or if there is a warranty issue. So Yes, it can help but at a cost. And to do it right creates other issues.
There are many compromises from the factory and even with our mods to meet noise regs, performance and mileage goals and durability requirements.
What I did to my 2.2 is to put a complete 2.4 exhaust including downtube and cat on the car. Then I removed the Turdle muffler and put on the Cherry Bomb Vortex muffler. Now it flows much better than stock. I am considering a header but just do not want the problems or noise that come with a header.
Right now my car sounds very good and is not loud but a header would make worse and I do not want that.
There is a very interesting thread on the different factory exhaust manifolds, porting them and headers in the 2.2 section of this forum. The same things apply to your 2.4.
The 2.2 has more options but you are better off just starting with the 2.4.
I believe a small tube header (or modified factory manifold)to keep the air velocity up with a large exhaust system to reduce restriction is best. There is no good restriction or backpressure but good air velocity is important in drawing out the air from the other cylinders. If there is backpressure then the header simply will not draw the air out like it is supposed to.
Sorry for the long winded response but there is no simple answer to the question and there is drawbacks to which ever way you decide.

 

Don't worry about the long post. The longer it is the more we all learn. Noise increase isn't a problem for me. I went to the muffler shop and told them I wanted the deepest sound I could get without being ricey. We decided on a straight through magnaflow. Another muffler came in. Don't recall brand. It worked out very well. It has a little interior drone, but sounds like a v8. No high pitched metalic whine. It would be too loud for most. But I like the sound.
We wont get into the catalytic converter. I do have one, I have seen posts on jbody or cobalt ss on how to kick the o2 sensor out of the exhaust path so you wont get codes. There is no emmisions check here.

What's the deal with a header loosening up? I do not have the patience or welding ability to build up and re-port a stock manifold. Are aftermarket headers prone to coming loose from the head? Or do they come loose at the connecting flange? I was wondering this because they have the flexible exhaust coupler off the stock manifold. Thanks for the redirect to the 2.2 I will check it out when I get time.

Thank you very much for the help.

 

If you are not concerned about noise or cat then a header could definatly help. It can make your car much faster than similar cars and probably 5 MPG better mileage. You may have to do a Trifecta tune to calibrate it and keep it from throwing codes. A header has tubes that should be fairly small diameter and a certain lenght. Then they all dump into one collector. The idea is that when one cylinder pumps the air out as it goes past the other tubes it sucks or draws the air out of the other tubes creating a low pressure or suction effect. There must not be any restriction in the exhaust system for a header to work right. The better the system the less problems you will have with leaks etc.
There are several reasons why headers come loose at the head. Most have thinner flanges. Some use bolts with smaller heads for clearance from tubes and some use thicker gaskets. As things heat up it expands compressing the gaskets more and when it cools the bolts are not as tight as they were before. Flanges to thin warping or the smaller bolt heads sinking into flange.
Some headers are better than others but I do not know which ones work good and which ones do not.

An engine is an air pump and the more good clean air at the correct fuel mixture you can get into and out of your engine the more effecient and powerful it will be. More effecient means you can use a smaller engine and or less throttle to do the same work. Or if performance is what you are after it will be faster than a similar car with out the mods.

 

i don't see how doing away with the o2 sensor could help mpg or performance, that is where computer gets its info in order to calibrate air/fuel mix.

 

I agree with you there. I think the best way is to get good clean air in and out as effeciently as possible and then do a Trifecta Tune to customise your fuel and timing curves to your needs.

 

A little input on the second O2 sensor guys, it is purely for emmisions. The first one controls the air fuel mixture for good mileage. The second is to make sure the cat is working correctly, burning the left overs. Even though new cats are less restrictive than the old styles. They still have restriction. The o2 eliminators or kicking them out of the flow path is just a trick to make them think there is a properly functioning cat. The power improvement comes from eliminating the cat's restriction. Since no more fuel is used the side effect if improved gas mileage.

 

One HHR has the Hahn header
the other Cobalt Addictions... I prefer the Hahn header..

 

One of yours I assume? What are you using for a downpipe and catback? How does it sound?

 

I bought a obx race header with down pipe, muffler shop redid the downpipe and installed a high flow cat. I still had to space out the rear o2 to keep the cel out. Does have more power and sounds great up to 3500 when the cams change, then it has the tuner car sound. I like it.