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I replaced the factory single exhaust on my 85 EC with dual exhaust with dual catalysts when I bought my EC 8 years ago. The performance improvement was substantial including higher RPM range, faster acceleration, more low range power with a little improvement in gas mileage. The guy I bought my EC from sold it to me because he felt that my EC (with single exhaust when he owned) could hardly pull itself let alone his 4000 pound boat and trailer. Have others experienced the same increase in performance. Have others compared the performance with and without catalysts. If so, how much difference did the catalysts make.
 

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Unfortunately, a lot of the improvement you felt could have been because you wanted to feel it. If dual exhaust did make substantial improvement in performance and mileage, we'd see them on everything. The 5th Gens came out right after a fuel crisis and were downsized to meet a high priced fuel market. That's why we had things like the 267 available and no big blocks, even though the chassis was big enough for them to drop right in. If an exhaust system is overly restrictive, it can hurt performance and mileage, but mufflers have come a long ways in the past 20 years. You'll notice that new cars are almost silent, yet the gas mileage is a primary target in the design. Loud is not always good, especially with things like glasspacks with the baffles hanging down in the wind. Buy a muffler that was designed for flow, not for noise. the Walker turbo mufflers are a good choice. A true 2 1/2 inch single exhaust on a 305 is going to handle everything the engine can put out.

Cats can be restrictive if they are clogged, but I just dropped a nicely cammed 383 into a 1978 and even it is running just fine with the original Y shaped single exhaust. I am going to have a better head pipe made for it, but I will retain the cat and the turbo muffler that is there now. I honestly don't feel there is any real gain in going to duals with a 305, unless the car is faster because your wallet is lighter.

I'm sure there are those who will feel differently, but like they say: "Your mileage may vary".
 

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Unfortunately, a lot of the improvement you felt could have been because you wanted to feel it. If dual exhaust did make substantial improvement in performance and mileage, we'd see them on everything....
I disagree with thhat logic. Duals cost considerably more than a single system so to keep costs down on lower priced cars the factory will only install a single exhaust. Same applies to the consumer, the cost of installing one isn't trivial.


When I installed mine my performance absolutely increased with improved 0-60 times. My mileage improved quite a bit. I went from 18 highway to 22+, that's nothing to sneeze at.
 

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i just recently installed dual exhaust i did notice a power increase, my motor is not stock so i think it helped i still have to check mileage .:smileyb:
 

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Not a good source of info or your experiance with single to dual was not measured with anything but feeling. Dual will almost improve any combustion engine that can get and needs more flow. I have read and seen the improvements and done it to three 1966,67,69 new el Camino going from single to dual is a + on power usually about 6 to 12 HP, fuel MPG is 2 to 4 MPG and is more often readable on NONE CAT cars (this I read). Now going to duals with to much diameter is not good and is done very often thinking bigger is better not so. If I was doing a stock 305 it would be done with 2" pipe and maybe with no cross over or install a cross with th ability to take out easily. The other side of this is is the cost worth it and if so do what you wish its your car to plug and play.
 

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An internal combustion engine is basically just a fancy air pump anytime you can improve air flow i.e. intake and exhaust you make the engine work less which increases performance. On a stock engine there is a tendency to go overboard with exhaust where too big can actually hurt performance. Almost any engine will improve performance with a true dual system but as Leo said there is a cost factor involved. The factory "bean counters" take this into consideration on every model produced. It is a fact that one of the best "bang for the buck" improvements you can make to a stock motor is the exhaust. Over the years there has been alot of work done on cats to the point now where they may not help the exhaust flow they certainly don't hurt much.
I am by no means an expert but I did stay at a Holiday Inn Express last nite.:nanawrench:
 

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well i have a question: you who went to duals; did you keep your cast iron exhaust manifolds or go to headers? my exhaust shop will do duals "on any car" for $275, no h- or crossover, cherry bomb turbos. would be closer to $450 if i took him a set of headers to put on, more yet if i buy from him. About hp increase: isn't it relative to what you start with? Catalogs and manufacturers claim hp gains on a 350, already starting at more hp than my 85 150 hp lg4. so if they claim 15, i might only see 7 or 8. So then what would duals do for a stock 85 elky with the 150 horse LG4 and then what would be the addition with headers. then cost benefit could be determined.
 

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When I installed mine my performance absolutely increased with improved 0-60 times. My mileage improved quite a bit. I went from 18 highway to 22+, that's nothing to sneeze at.

You are talking about an increase in mileage of 25 percent. If such a simple change could be accomplished and documented, I suspect we'd soon see a federally mandated program to start retro fitting vehicles with dual exhausts as the best way to quickly reduce our dependence on foreign oil as well as reducing carbon emissions. If you look at the loops and spins the manufacturers are going through to comply with C.A.F.E. requirements, the cost of a dual exhaust system would be trivial in the face of an increase in mileage of over 25 percent.

Most of the LG-4 came with tiny exhaust manifolds and 2 bolt flanges which were then plumbed to 2 inch piping. Installing a set of the three bolt manifolds which were found on some early gen 5's and more common on Camaros will allow the use of 2 1/2 inch tubing. A 2 1/2 inch exhaust is not much more expensive to produce than a 2 inch exhaust, yet it will flow over 50 percent more, while fitting within the confines of the chassis and crossmember.
 

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I have never known headers to hurts an engine, with your engine I would go to duals using stock manifolds and no cross over (cross is a choice) You have no HP and are looking to make things breath better and they will, you will see a small improvement unless your engine is not in good shape inside then all bets are off.
 

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i went with headers but i'm running a 350 with a .525 lift cam with ported heads and i'm using two and a half inch tubing:smileyb:
 

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yeah, relativity is key. my 85 exhaust was rotten. LG4, 150 horse, as i said. kept cast iron exhaust manifolds and had a new gm y-pipe, magnaflow high flow cat, and single cherry bomb put on because i had it in my head to keep it as close to stock as possible. i am happy with it but the factory y-pipe and magnaflow cat drove the price of the single exhaust to $371. So if i had a do over, i'd have gone straight duals, no cat, saved $90 and maybe got 5 more horse and 1 more mpg. there is no vehicle exhaust testing here.
 

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You are talking about an increase in mileage of 25 percent. If such a simple change could be accomplished and documented, I suspect we'd soon see a federally mandated program...
So you doubt my word? Really? I can't remember the last time someone called me a liar. The mileage increase absolutely went from 18 to 22 and if you don't believe me well that's not really my problem now is it?

Your math logic is way off however. The increases in mileage will vary proportionatley depending on the engine set up. Some cars with already good mileage may see only a small % increase, others which don't have good flow will see better. That is, a car getting 25mpg may see an increase to only 26 or 27 while another that gets 15 with cats may see 20+ with dual and no cats.

Also, the gov't won't mandate that you retrofit your vehicle, that's insane. They are already mandating that new vehicles get better mileage and because of this you'll see more with dual and better tuned exhausts and higher sale prices.
 

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Sweet Thunder makes a true dual exhaust that fits the stock crossmember. :texas:

When I first got my El it was completely stock.....added duals without the cat and got nada, nothing, zip. Did make some noise tho.
 

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So I spend all weekend watching these car/truck shows where they do different tips and tricks to increase fuel economy. I have seen 25% percent increases in fuel economy by changing the exhaust. But in addition to the exhaust, they changed the rear gears, the timing (or programming on ECM equipped engines), installed and monitored a vacuum guage when shifting, etc. Do I doubt the 25% increase? Nope. But maybe there was more to it than just changing the exhaust.

And if you don't think the govt will regulate anything that can be written down on a piece of paper, just pair any word with regulation in a Google search and you'l see some off the wall stuff that is on the books. I just found a link with nine pages of regulations on what it takes to be considered a sweet potato in Georgia.
 

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The gains in performance and fuel mileage depend on how much restriction was in the old system and whether or not you picked the exhaust volume that fits your engine output now.
You can go to big and lose exhaust scavaging without the scavaging you get a lot of sound and no go with it.Headers generally 1 3/4" for the street is good with 2 1/2" pipes.If your running more horsepower say 500HP headers with a 1 7/8" primary pipe
and 2 1/2"- 2 3/4" pipe ,if you have 600-750 increasing the pipe and mufflers from 2 3/4" to 3 1/4" should still hold scavaging for use on the street.
If you going all out race exhaust scavaging is not as big of a deal as you're looking for performance in the 5000 RPM and up rangeand you'll probably be using 2" primary headers on a small block and 2 1/8" big block with 3 1/2" open collector or racing muffler.
 

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I just found a link with nine pages of regulations on what it takes to be considered a sweet potato in Georgia.
Is "drive a pink el camino" on that list?

:texas:
 

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Greetings!
In 40 years of vehicle ownership, I have only had the personal experience of 1 vehicle that made any noticeable difference with a dual exhaust. I bought a new 1979 F250 4x4 and it would not come close to touching the mandated 85mph speedo mark. I installed a dual exhaust on it and it easily touched the top speed marker. No other changes. Other than that, I have only noticed whatever sound change (not an improvement to everyone around me) that I wanted at that time in life. Most of my vehicles have either had duals as factory stock or have been resto-mod vehicles that were barely driveable at purchase so I have no clue as to what they performed like with an engine that worked properly at purchase time. All those vehicles ended up with duals (although the mufflers have definitely gotten quieter as time marched on) and a few had headers also. My current El Camino had a dual exhaust when I bought it, but I don't think that I would have done duals given the choice. I don't think that the low revving 305 has any trouble breathing at the rpm range that I drive. I really love the mileage that it demonstrates now on the highway, but I have no single exhaust reference point. I live in the Land of Pickup Echo Chambers so most folks must feel that 2 is better than 1.
Craig
 
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