I've searched around a little and, unless I didn't use the right terms, couldn't really come up with a definitive answer to this. I've got a 2012 Grand Sport and I don't want to do a whole lot to it but I do want to make it sound better and possibly a little faster at the same time. I just installed a Corsa Xtreme and it isn't loud enough (I'm guessing because of the factory secondary cats) but I had originally planned on headers anyway I just spent more money than I had planned buying the car. Hopefully within the next few months I can spring for some ARH headers and be able to drive the car like that for a while. I wouldn't mind putting a cam in it down the road but nothing crazy but I would like a nice power bump and some idle lope if I do so, probably something in the midrange as far as aggressiveness. I'm just not sure which header size I should go with that will maximize what I have now and not cost me power but still not be a bottle neck down the road if I cam it. I had a Trailblazer SS before and everyone said the 1 7/8" headers would cost power on those unless doing something like heads, nitrous, etc. Now the Corvette has an LS3 vs. an LS2 and is also significantly lighter and the LS3 flows better stock for stock, so I don't know how much of a difference that makes. I would like it a little faster if that's possible since it's neck and neck with my DD $15k Cobalt SS! I would probably go for a tune after the headers if possible. Any advise for me?

 

Since you aren't planning for a stroker or a forced induction engine I would stick with the 1 3/4". They tend to produce better torque down lown where you need it the most while daily driving. That's just me. Ive been as fast as 11.32@124 with nothing but full exhaust including the 1 3/4 headers, a decent cam, a ported tb, tune and drag radials and a clutch that wants to melt after each pass lol

 

1 3/4

 

That'll work then! You had to be around 500hp, no? I figured I'd need the 1 3/4" again but I wasn't sure once I noticed they offered up to 2" primaries for these cars.

And just to clarify, the Cobalt is only neck and neck from a roll.

 

I have not dyno'd mine. It was street tuned, but Im guesstimating around 475rwhp.

 

1-3/4 is all you need. More important to get a good custom tune once the headers are on.

 

Yeah, that's what I figured as well. I was going to do a tune in a little while anyway but I was also thinking about going catless to save a little money so I'd definitely need a tune as quickly as possible so I don't get a check engine light. Then I have to decide to do a dyno tune or mail order. I've had great luck with PCMofNC in the past with my Trailblazers (one I6 and then the SS) but Vengeance Racing is also local to me and they do good work.

 

Is there a rule of thumb when selecting headers, such as

Stock Exhaust System
500-700 1 3/4 Headers
700-1000+ 1 7/8 Headers

etc.

 

Custom dyno tune is absolutely the way to go regardless of cost. The best tuner in the world would be severely limited if he only has one tune/one chance to get it right.

Proper tuning is data collection, adjustments based on that data, then more data collection, then more adjustments, then more data collection, etc.

The simple and easiest data collection is the info of mods then it has to be datalogged and tweaked multiple times.

With a mail order tune, you have limited that process to just the very first step.

And don't wait on the tune, do them together. If you can't swing it, save the headers for when you have the funds for the tune. And I wouldn't go catless on your combo, no extra power, more noise, not emissions compliant (if you have emissions) and dirtier exhaust.

I've heard great things about Vengeance, good luck!

 

That would be a good way to look at it.

Pretty much stock cubes and stock RPMs with no boost should stick with 1-3/4".
There is more to it than just size. Bigger is not always better and Peak power at the highest rpms doesn't tell the whole story, torque is just as important!

 

Larger headers will give you more HP. Might be slightly higher in the RPM band than smaller diameter but the HP will be higher.

The engine is an air pump, easier in (intake) and easier out (exhaust) makes for more HP.

Cracks me up that the same guys that demand a BIG (3") mid pipe will claim that a smaller pipe (1 3/4") is better for headers. That mid pipe is carrying FOUR exhaust ports. Four X 1 3/4" is smaller than Four X 1 7/8" and still a lot bigger than ONE 3" pipe.

 

Torque may even be more important for street driving. There is a great tendency on the forum to believe that bigger is always better...this is not the case and certainly not with headers. Stick with the smaller ones.

 

Yeah, I thought about that after I posted. I want it a lot louder than it is with just the Xtreme but catless might just be too loud.

 

I would go with 1 7/8 or 2". I know 2" quality headers do not show any tq/hp loss anywhere compared to a 1 3/4 and 1 7/8 headers in an LS3 Camaro. It shows hp gains mid to top.

I didnt have time to check for Corvette dyno sheets, but I would go with 1 7/8 To be sure.

 

Your car will be much louder with any header and hi flow cats. Careful what you wish for. The car will smell without cats too but will be even louder. As posted already, unless you plan FI, stay with 1 3/4".
Jeff

 

I'm not building a race car so I'm not really worried about horsepower up top. I would much rather have the low end torque.

 

I'm very well aware of that. I've driven an 06 with headers and the Corsa Xtreme years ago when I used to work on Corvettes and it was fantastic. I have decided to go ahead and go catted; however, just in case I have emission problems in the future and because I liked that other car the way it was and it was catted (and still had plenty of burble and pops from the exhaust).

 

Unless you are going to put a blower on it, or try to make over 500rwhp I would do 1 3/4", and a long primary version at that. You will make far more total power under the curve and more torque which is what it is all about in a street car anyway.

 

Exactly what I'm looking for. Thanks!