Pipes

[ocnblu]

Locally, we have an exhaust shop with a very good rep for workmanship and reasonable prices. They have stainless pipe and a mandrel bender, with a choice of muffler designs. I want to get them to make a dual cat-back system for my truck, but I don't know if I want 3" pipe, or 2 1/2". I have heard that there is such a thing as too little back pressure. Is this something I should be concerned with if I go with 3" pipe? Will 3" pipe have any advantage over 2 1/2? Will the sound be any different with the same mufflers through the bigger pipe? I think I'd like the looks of the 3" pipes doing a side exit behind my wheels. Thanks to anyone who can point me in the right direction.

[the_yellow_dart]

Big pipes? Kinda gross, IMO.

:AH-HA_wink:

[Northstar]

The bigger the pipes, the louder it's going to be, generally. I know there are people on LS1GTO that have 5 inch (yes 5), pipes that totally fill up the holes in the bumper and they're loud as hell. It looks kind of dumb to me, as i think 4" would be plenty, but 5" is louder...

[capriceman]

2 1/2 to 3 wont have much difference in sound. but mufflers will. I recommend Flowmaster's since they sound great on the caprice with 2 1/2 pipes.

As long as you dont mess with anything before the cat I don't think you will have any problems with back pressure and sensor issues. Although you will see a decrease in fuel efficiency if there is loss of back pressure. because The O2 sensor will not have enough of a sample and will force the computer to run a richer safe mode type deal. This Accordingy to the guy when i had a exhaust put on my 01 silverado.

[balthazar]

Northie- those are 5" tips, right?

I have a Flowmaster poster in my shop of a '68 Chevelle standing on it's rear bumper- I believe that car had a 4" system and a stupid amount of power (1200?? I don't remember). 5" pipes under cars with under --say-- AT LEAST 1500-HP is a complete waste of money, not to mention a gross weight penalty- with no benefit whatsoever. You need to be putting out enough power... pushing enough air to justify the weight of such a system. 3" true dual systems behind 700-hp have been proven countless times. N/A street cars just don't need that much flow. 750-hp would do just as well power-wise with 5-in pipes as it would with 10-in, which is to say it would do measurably worse than with 3-in.

How the hell anyone could even FIT 5-in pipes under a GTO- I have no idea.

Ocn : I could give a better opinion if I knew what was on there now: it's a circa 310-hp 5.3 with a single pipe, right? What's the pipe measure in diameter both before and after the cat?

If it's a single pipe after the cat and you are going to a dual after-cat system, you need to maintain the same cfm over 2 pipes- I would not go larger than the pre-cat pipe or you may encounter scavenging / backpressure issues.

[capriceman]

I think i have only seen a 5 inch exhaust on a twin turbo diesel.

[76ChevyTrucker]

Normally you're not going to find a 3-1/2" plus exhaust system on anything shorter than a diesel powered application. If I remember right the stock exhaust on a Silverado is 2-1/4 inches both before and after the cat, so if you go to 3, you shouldn't have any trouble. And really and truly as long as you're not changing exhaust diameter in front of the cat, you're not going to be hurting backpressure since most of your backpressure is made in front of the cat. Like everyone has said, the biggest difference between a 2-1/2 and a 3 inch system is going to be noise. Actually you may be able to buy an aftercat system for cheaper than having someone build you on at an exhaust shop. I'd do some digging around online and see what you could come up with on an after cat system.

[ocnblu]

I was quoted a price on the phone for a full stainless system with Flowmaster mufflers for $435. That sounds like a bargain to me after doing a quick check for systems off the 'net from the big names. Not sure what diameter pipes that was for, I didn't ask at that point.

Thanks for all the input, guys.

Edited February 22, 2007 by ocnblu

[balthazar]

Jeg's lists a DynoMax aluminized, mandrel-bent cat-back system with Super Turbo or UltraFlo mufflers for a RC/SB Silvie 4.8 or 5.3 for $247. Doesn't list diameter. Now, this listing is for a 1999-2004MY, but should be indicative of a '07 system's price. And I like the engineering behind a dedicated exhaust company vs. that of the corner mandrel jockey.

When I bought my F-150, I thought "When the exhaust rots thru, I can put a big DynoMax muffler on". 145,000 miles and 12.5 years later and I'm still waiting for the first hole in the factory aluminized system. A few of the hangers got thin enough to warrant me replacing them, but the pipes themselves are still solid.

If you're wanting stainless for looks, fine, but if it's for longevity, you likely needn't bother.

My brother ran Flowmasters on more than one truck and blew the packing out (behind a 350) in frustratingly short timespans- to the point he won't buy Flowmaster anymore. They get really loud over time. I can tell you that the big block Buick crowd prefers Dynomax mufflers about..... oh; 8:1 over Flowmasters, based on sound, performance & longevity. They have a number of excellent products- check 'em out.

Edited February 22, 2007 by balthazar

[Northstar]

Northie- those are 5" tips, right?

I have a Flowmaster poster in my shop of a '68 Chevelle standing on it's rear bumper- I believe that car had a 4" system and a stupid amount of power (1200?? I don't remember). 5" pipes under cars with under --say-- AT LEAST 1500-HP is a complete waste of money, not to mention a gross weight penalty- with no benefit whatsoever. You need to be putting out enough power... pushing enough air to justify the weight of such a system. 3" true dual systems behind 700-hp have been proven countless times. N/A street cars just don't need that much flow. 750-hp would do just as well power-wise with 5-in pipes as it would with 10-in, which is to say it would do measurably worse than with 3-in.

How the hell anyone could even FIT 5-in pipes under a GTO- I have no idea.

Ocn : I could give a better opinion if I knew what was on there now: it's a circa 310-hp 5.3 with a single pipe, right? What's the pipe measure in diameter both before and after the cat?

If it's a single pipe after the cat and you are going to a dual after-cat system, you need to maintain the same cfm over 2 pipes- I would not go larger than the pre-cat pipe or you may encounter scavenging / backpressure issues.

Whoops, yeah, they were the tips.

[NOS2006]

FWIW, bigger pipes are always better for sound and flow. Better flow equals better performance and efficiency. However, the engine needs to get a certain amount of backpressure or it won't run properly. So, therefore, if you go too big it's not good for your vehicle. For a better sounding exhaust, I'd open her up to 2.5" all the way back. I would only reccommend 3" to higher performance vehicles. I know of a lot of LS1/LT1 Camaro owners going to 3", but almost all of the 3.8L owners go to 2.5" because of the size and output of the engines.

[ocnblu]

But...but... my 5.3L, 315 hp V8 needs to breathe...speaking of which, GM Accessories has an intake kit available for my truck...

[NOS2006]

Hey man, I'm not saying it couldn't use that three incher! But, hey, between you and I, don't go with the 5" tips.

Oh, and I'm going with the GMPP CAI for my car too. And the exhaust.

[balthazar]

Not dissin' yer steed, ocn, but 5.3L is not pushing that much air N/A. It's good, it's very good; but it doesn't need 3". I am still curious: you have a single pipe from the Y-pipe to a single cat, right- what is it: 2.5" there? That's the 'bulkhead' in the flow- jumping to 3" after the cat doesn't address that.

Will you please indulge & describe the factory system.

[mightymouse]

Not dissin' yer steed, ocn, but 5.3L is not pushing that much air N/A. It's good, it's very good; but it doesn't need 3". I am still curious: you have a single pipe from the Y-pipe to a single cat, right- what is it: 2.5" there? That's the 'bulkhead' in the flow- jumping to 3" after the cat doesn't address that.

Will you please indulge & describe the factory system.

Exactly. Too little backpressure will sacrifice low-mid range torque, and provide more burble or popping on deceleration...

2.5 is best for 327/350... it's been proven in the car mags over the years..

[the_yellow_dart]

Exactly. Too little backpressure will sacrifice low-mid range torque, and provide more burble or popping on deceleration...

2.5 is best for 327/350... it's been proven in the car mags over the years..

I've noticed some burbling and popping from time to time on my Cobalt. Is this normal for newer cars? I've never heard it until this car. My Sunfire (which was also a 5-speed and I think even had the same engine) never did that.

[ocnblu]

Of course, the stock system is 2 1/2". It comes back from the Y to a cat with about a foot and a half pipe before it goes into the muffler. With my fuel tank taking up all the space inside the frame rail on the left side, it appears I could only do a split aft of the muffler (or maybe put two mufflers side by side after the cat) if I want the look and sound of dual exhaust. I might just do a free-flow single system, like I did with my '02, but dammit, the stainless Gibson system I put on that truck just didn't speak loud enough. All this brings to mind the first late model Camaro SSs with the big single pipe. It had plenty of flow and the shortest distance to dump gases, but people whined and cried, so they went to a dual tailpipe system. Not sure if those two pipes did anything to improve horsepower or sound, but they did look cool.

Speaking of burble and pop, I consider those bad traits. I know the V8 F-bodies did it, and even my Colorado would do it. I didn't like that.

Edited February 24, 2007 by ocnblu