So I was thinking (weird I know right). our exhausts are 2.5 inches for the most part, with the exception of the kinks in the header and around the axle which are 2.25. But we only have 171 horsepower from stock. Isn't 2.25 inches more than adequate for 171 N/A horsepower? IF you were to go to a full 2.5 inch or even a 3 inch exhaust wouldn't you be doing more harm than good if you aren't modified further in other areas? Boost, aggressive tune etc. Would it not be better for performance (not to mention the pocket book) to just throw a superturbo (or similar) muffler on and call it square? Just one of my musings this morning, looking forward to the replies.

 

You are correct.

There was a test done involving a 2.4 SS back in the day.

The car gained around 2hp or so from a GMPP 2.25" catback.

The guys running the test mention how the stock catback exhaust seems to flow well enough for the 2.4L.

 

All you need to do is get the cti 2.5 inch axel back kit and add a muffler of your choice. doing this will probably add about 5 hp. the main thing is its alot cheaper than buying a gmpp exhaust. I did a custom setup with a dynomax turbo muffler and i'm pleased with the sound of it and did notice extra throttle responsive. Remember a catback is mainly for sound not hp.

 

I'm pretty interested in the Dynomax VT and just bolt it straight onto the to stock pipes. If I'm running a CAI already am I going to throw CEL codes from the increased airflow?

 

The increase in airflow from just a muffler shouldn't cause any problems.

 

Aren't most of the increases in power seen from getting a mid/long-tube header and a 2.5in downpipe? If this is the case, then I'll be saving alot of money!

 

yeah you won't get a cel from a cai or just a exhaust. the header and downpipe will cause the cel. however you wont get the true hp potential without adding those mods plus a tune.

 

This sounds about right. Thats why I keep sayin the stock cat back is actually very good for N/A.

Though the op said the stock pipe is 2.5. I thought it was 2.25. I measured mine with a caliper at 2.25 and I had bends that measured 1.9"od. Even then that is ok. Its the header and downpipe that are restrictive.

If you keep the stock cat back you won't get a cel. I did header/downpipe for a year with no cel on the stock cat back.

 

This is true and why the vibrant header/downpipe kit is so popular!

 

2.2/2.4

2.0 LSJ



2.0 LNF


CAT BACK FLANGES.

 

John it was always to my understanding that the 2.4's had the same exact catback as the LSJ's.

To add to these photos so people don't get confused on exhaust system sizes.... John is showing everyone the size of the inlets. The catback exhaust systems are not the same size I.D. as the inlet flanges. This is why when people say "I'm going to just replace the over axle section" I tell them about the restriction at the resonator.

 

I didn't get any cel's and I have a full exhaust (zzp lt header, dp, hf cat, 3 inch all the way back to borla xr1).

 

Small problem with the measurments shown - rigid tube (like exhaust pipe) is spec'ed on the OUTSIDE diameter. Hoses and the like are spec'ed on the inside diameter. You should know that John
Does show where the choke point really is though

To the op's question though, the stock setup on the 2.4's is more than enough, header with appropriate downpipe will help with scavanging more than anything (a good thing btw) but it will be louder and a different tone than the stock manifold and downpipe.
You will also get a better hp per dollar return on your investment with the header / downpipe than you will with a catback imho.

 

Ok. A lot of people are saying a header/downpipe is loud. With the stock cat back the noise difference is marginal. Way less noise than a straight through cat back style like a magnaflow. Honestly I think a header/downpipe/stock catback has the best sound.

I surely agree with you though on hp per dollar though. When I was N/A, header and downpipe was my first mod and the power was instantly noticeable above 4k.

 

I think most people get the point. Thank good ness. With a n/a car like you all have said, header and downpipe with stock cat back is best bang for the buck, and ZZP do the best least expensive long tube well made, imho. But based on what I have measured, a gmpp exhaust cat back would be a good addition. and not too noisy.

On an SC just a header and downpipe by Vibrant (all I have tested in this combination) on a stock cat back is very very raspy. Quiet but raspy.

 

wow thanks for all the feedback guys! I'm just thinking of a little extra volume from the back end. I don't think it really pays for me to go for a power monster, this is just my daily driver. It'll never keep up to my old firebird anyway. Once I'm done with my marketing degree I would like to see a 'vette in the the driveway.

 

Good choice these cars really don't make alot of power unless you add a turbo or supercharger. I would just add a cai and a muffler and call it a day.

 

^^^ that's the plan, like I said if I want excitement I'll get something with more cylinders and power going to the right end

 

My first setup that worked was a zzp mid length with a catted downpipe on the stock catback it worked well but honestly I hated the sound of it. With the SLP catback it did seem to pull slightly better but was MASSIVELY louder!

Will be going back and getting the zzp longtube John mentioned soon enough.

 

i have a CA V2 header to zzp 2.5 catted dp to 2.5 magnaflow resonator to stock piping to 2.5 magnaflow muffler. should i or should i not change the over axle to 2.5? will it make any improvement? or should i just leave it stock? This was never really fully made clear.

 

Leave stock. Even with boost it would be ok to still have.

 

K thanks. Saves me some money lol