Mister Will

I have a question on exhaust systems. I have largely decided on Magnaflow for my exhaust upgrade.
However, I was thinking of just installing a muffler vice a full cat-back. Muffler is cheaper, but with a cat-back you have a more complete system.

The question I have is which option is preferable performance wise. The main difference between a muffler install and a full cat-back is the intermediate pipe. The intermediate pipe on the cat-back is 3 in. dia. while the stock pipe is 2.75 in. dia. The larger diameter pipe has a larger area providing more flow at high RPMs. However, at low RPMs the exhaust gases will slow down creating back pressure and robbing horsepower. I wonder if this is the reason for loss of low end torque with cat-backs.

Does anyone have any experience comparing the two (3 in. vs 2.75 in.)? Will the 3 in. intermediate pipe of a cat-back really provide a significant increase in performance.

Note: I plan to add shorty headers in the future.

PS. I realize that a simular topic was posted recently. But it didn't result in a clear concensus

Thanks in advance.


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1998 Z28 Mystic Teal Metallic hard top coupe, M6, Hurst Billet shifter, SFC, Hotchkis STB, K&N FIPK, & more to come
Dyno bone stock:
282 rwhp
291 rwtq

[This message has been edited by Mister Will (edited September 12, 2002).]

nikkev

New to the V8 world myself,but I know a little about the V6's.The V6 comes with a 2.25 I-pipe and there was a TON of discussion on this very topic.Dyno's show that on even the V6 that the entire cat-back is the way to go.You don't actually lose torque with a larger I-pipe.You gain torque but it's moved up the RPM band.The V6 shows gains of 12 RWHP and 14 RWLB-FT of torque on a dyno.I'm not 100% about our cars though since they come with a 2.75 I-pipe stock.However,I don't know if it's mandrel bent or not.I know this probably didn't help you much,but in my opinion,you should go the entire cat-back.You don't have to spend a ton of $$$ either.I paid $192 for my Dynomax cat-back without tips.Good luck.
Kevin

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1998 Black Z28 A4
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FCIMAN

I am wondering the same thing..Took my 02 z-28 to have a cat back system put on at a local muffler shop...Everyone there was telling me "why waste your money on a cat back system", all you need is a free flowing muffler??? They were telling me the 2.75 inch pipe was more than enough??
Anyways, they didn't want to fool with the car I guess, unless I just wanted to put the free flowing muffler on....I declined just the muffler bit and am now looking elsewhere.. However this is the second place that has tried to talk me out of using a cat back system???? Whats up??

psychocabbage

I only listen to shops when they know what they are talking about when they give me advise (i.e. they have performance cars and are into modifing them).

Only you really know what your future plans are for a car and a shop that doesnt understand them should just let you make your mistakes. Perhaps there isnt enough markup for them or they cant get the cat backs.

I know a friend of mine had a muffler shop and he wanted $300 for 1 high flow cat installed.. where I can buy the cat for $110 and then have him weld it by slipping him $20 - $40

Makes no sense but they made money going their route.

I say stick with your catback plan.. and be sure to get the one you want.

as for the I pipe. . on an LT1.. it is stock at 2.5", by going to 3" I gained both torque and HP plus my trap speed gained 2-3 mph

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Psycho Cabbage
2002 Camaro Z28
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ratio411

Unless you are doing heads and cam the 2.75" pipe is fine. If you do heads and cam, you will want a system larger than 3". So IMO the .25" larger pipe for 300-1000 bux more is a joke for any LS1 car.
The fact is that the factory system is 2.75" mandrel bent stainless steel. The HP loss behind the cats is almost all in the clogged stock muffler. I have a muffler only (the Dynomouth mod) and my car dynos the same or higher than big $$$ systems on cars with the same mods.
Exhaust manufacturers have brainwashed folks into thinking they need the cat-back... Just get the muffler, you won't regret.
Btw: Shorty headers rarely show any gains on our cars... Either mid length Macs, Bassanis, or long tube Hookers are the ticket for LS1s.
Good luck
Dave

JackZ.Twenty8

You might as well do it right the first time. Get the full 3" or 4" exhaust, and then later, when you do heads, it(exhaust) will really wake up...

RS Dragster

You've got my vote on the muffler only. Exactly what I did. I knew the stock one is pretty restrictive since it's pretty much quite as hell, so I went to the local speed shop and they slapped a Dynomax muffler on there. Sounds MUCH better, plus it wakended the car up enough to notice it. I also think the catback's are jokes. I'd only consider one if I wanted to make the whole car "show", you know- go underneath with some stainless-steel Borla. But no, I got a nice free-flowing muffler, gonna get some nice exhaust tips, maybe Borla, then an Electric cut-out. That right there is the best setup you can have. Choose a muffler that is right for everyday use, have some NICE tips to show things off, then have cut-out exhaust at the push of a button. Ya know?

SLOW_SS

When I bought my car it had SLP dual/dual exhaust, it was pretty quiet, and I was told that Dynomax muffler was bit louder with better flowing numbers. So, I had it installed on my car. Had that same set up for about 15 months, it was alright but still was too quiet for me but at the same time, I didn't want too loud like loudmouth either.

Anyway, I was tired with the exhaust set up so I went ahead and bought B&B TriFlo catback w/Quad tips and had it installed two weeks ago. WOW, what a difference in sound, the sound is very deep tone and it just exactly what I was looking for. The look of the exhaust tips, the pipes, and muffler is awesome.

I don't know if there is any power gain with B&B, but I'm really happy with B&B catback.

Mister Will

Thanks for the replies, everyone. I am still wondering what the affect of a different size intermediate(I) pipe will have on torque.

A larger I-pipe, as on cat-back systems, will provide freer flowing exhaust at high RPMs over the smaller OEM I-pipe.

However I keep hearing about the loss of low end torque with the large dia. I-pipes of the cat-backs. There was another opinion posted in another thread stating that there was no actual low end torque loss. That the loss was simply a psychosomatic response to the louder exhaust.

My car is a daily driver. So I see allot of driving at low RPMs. I don't want to install a cat-back only to turn my chariot into a dog 90% of the time.

Has anyone seen a loss of low end torque from the OEM exhaust to a aftermarket cat-back on a dyno sheet. If so at what RPM ranges and how much?

Thanks again

TireSmoke

First off... that guy is on crack -- there will be a loss of lowend torque because of the loss of back-pressure when you go with a less restrictive exhaust system. However, depending on how efficiently the newer system is compared to the stock one, it is very possible that you will experience enough of an increase in efficiency that you won't see a loss in low end torque.

Secondly... there are more factors at work here than just back-pressure and a bottle neck in the exhaust system. Open headers are always going to make more power however larger diameter pipes are not always going to make more power than smaller ones. How is this possible, you ask? Because when you are running open headers, your exhaust gases are effectively out of the car's exhaust right away. But when you are running big fat pipes, while they provide low backpressure, you are still trying to push gases out of the car. And those huge pipes are moving gas more slowly, allowing it to cool down and get more dense and harder to "push".

The bottom line is that there are a whole lot of variables so it's simply NOT a case of "a little is good so more is better."