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True duals...anyone else have this problem?

No offense to anyone here, but if anyone says that you can get just as much overall power and torque from a single 3" as compared to true dual 2.5 inches they are just plain wrong, so consider this before putting in new exhaust. Now before anyone flips out, yer stock exhaust manifold and a big 3" system may give you equivalent or a maybe even a little more torque numbers from idle to maybe 2000 rpm on a typical 350 cid motor. But headers with a modest primary tube dimaeter into a 2 1/2" system..... for the overall rpm range will walk all over a 3" system. Some on here disagree. Well if so, then why does every race car, sponsered off road truck etc run true duals. Pick up any hot rod, performance truck or car magazine and read the exhaust articles they have and dual systems with headers......dual systems always out flow singles in most all RPM above 1000 rpms. Rule of thumb for every high performance builder is the #1 most cost effective power increase for any ride is a free flowing dual system.

With that being said if you have to inspect your truck every year at the state you live in and they not only check emissions, but also the physically check the exhaust then you are stuck with single if it is your daily driver.

If not, then I suggest looking into every after market distributor including JC WHitney. On a 72 Jimmy I had I bought a 2 1/2" after market system minus the mufflers for under 200 buck and with the addition of a few hanger bolted it up in my driveway in about 2 hours. If your truck is newer than lets say 88-92 when GM went from the squared box type body to a more rounded body of the 90's then I dont think there are any after market systems that are true dual available.

If you must stay with single 3" ( which is what I have on my 93 burb as it is my daily) then I would still go over to a shorty header for more power if you can get away with it...Most a 50 state emissions legal. Summit sells a Shorty header with 16 gauge tubing that is emissions legal for about 170 buck in a painted version.
 
30-A rider said:
No offense to anyone here, but if anyone says that you can get just as much overall power and torque from a single 3" as compared to true dual 2.5 inches they are just plain wrong, so consider this before putting in new exhaust. Now before anyone flips out, yer stock exhaust manifold and a big 3" system may give you equivalent or a maybe even a little more torque numbers from idle to maybe 2000 rpm on a typical 350 cid motor. But headers with a modest primary tube dimaeter into a 2 1/2" system..... for the overall rpm range will walk all over a 3" system. Some on here disagree. Well if so, then why does every race car, sponsered off road truck etc run true duals. Pick up any hot rod, performance truck or car magazine and read the exhaust articles they have and dual systems with headers......dual systems always out flow singles in most all RPM above 1000 rpms. Rule of thumb for every high performance builder is the #1 most cost effective power increase for any ride is a free flowing dual system.

With that being said if you have to inspect your truck every year at the state you live in and they not only check emissions, but also the physically check the exhaust then you are stuck with single if it is your daily driver.

If not, then I suggest looking into every after market distributor including JC WHitney. On a 72 Jimmy I had I bought a 2 1/2" after market system minus the mufflers for under 200 buck and with the addition of a few hanger bolted it up in my driveway in about 2 hours. If your truck is newer than lets say 88-92 when GM went from the squared box type body to a more rounded body of the 90's then I dont think there are any after market systems that are true dual available.

If you must stay with single 3" ( which is what I have on my 93 burb as it is my daily) then I would still go over to a shorty header for more power if you can get away with it...Most a 50 state emissions legal. Summit sells a Shorty header with 16 gauge tubing that is emissions legal for about 170 buck in a painted version.
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First off i am not offended.
second i agree with you to some degree in a hot rod situation i will go duals any day of the week but it seems that most folks want more off idle torque rather than 7500 RPM horse power for their K5 or pickup in a 4x4 situation other than in a mud bogger . my truck came with duals and i changed to the single 3" and noticed a huge increase in seat of the pants power but this is one of those opinionated postes so run what you like im totaly cool with that
 
30-A rider said:
No offense to anyone here, but if anyone says that you can get just as much overall power and torque from a single 3" as compared to true dual 2.5 inches they are just plain wrong, so consider this before putting in new exhaust. Now before anyone flips out, yer stock exhaust manifold and a big 3" system may give you equivalent or a maybe even a little more torque numbers from idle to maybe 2000 rpm on a typical 350 cid motor. But headers with a modest primary tube dimaeter into a 2 1/2" system..... for the overall rpm range will walk all over a 3" system. Some on here disagree. Well if so, then why does every race car, sponsered off road truck etc run true duals. Pick up any hot rod, performance truck or car magazine and read the exhaust articles they have and dual systems with headers......dual systems always out flow singles in most all RPM above 1000 rpms. Rule of thumb for every high performance builder is the #1 most cost effective power increase for any ride is a free flowing dual system.
Click to expand...
Every race car, offroad sponsored truck, big hot rods, etc run are making 700HP and don't have your average stock and mild build SBC. Air is Air, the more HP you make, the more air that engine pumps to make that HP. A 550HP 350SBC sucks and blows more air than if it was making 300HP. With moderate power levels a 3" pipe is large enough to happily flow all the air that little 175HP-275HP SBC that is in the average Joe truck. If you are running stock exhaust manifolds on a built motor than I think it would be overkil for duals, a 3" pipe is not the restriction, it's the manifolds.

If duals are so great than why does every Desiel truck racer run a single exhaust? 4" and 5" are the norm, and 4" doesn't get restrictive until about 750-800HP.

Dual exhaust goes along with "V8"..... when someone says "yeah, and it's got a V8" everyone goes "ooohh" ...."yeah, it's got dual exhaust"...."ooh".

I have duals, with long tube hooker headers. but if I was doing it over again I would reconsider a single 3".
 
Potionmaker,

I encountered the same problem here in California a few years back. A single exhaust just wasn't going to happen and dual exhaust is what I was GOING to have.

I shopped around....and found an exhaust shop that both, cut my cat out for me when I was still running a single, and later built my complete dual exhaust with no cats.

had to do it on Saturdays, paid cash, and no receipt.
 
Woo hoo...love to see all the opinions:D . Well, I already have the new headers (Dynomax full length) so I'm going with those. I wasn't about to purchase new manifolds (305sbc manifolds wont fit 400sbc). They are more expensive than decent headers and I figured I might get a little extra performance from the headers. Im just gonna "Y" into a 3" single from there. Just trying to decide on the right muffler to give me a semi-semi-semi-kinda-sorta-halfway-maybe-aggresive sound. I dont want it too loud, but I love that low GROWWWLLLL!:D

Thanks everyone for posting. Keep the suggestions coming!
Didn't mean to start an argument between "dual" and "Single" exhaust guys. You'd think I would be able to offer up an opinion in my own post, wouldnt ya?:rolleyes:
 
you think the emissions people will really pick-up on it, with 2 cats instead of one?
 
Keeping it really simple, the cross sectional area of the follwing pipes is indicative of their flow characteristics.

CRA
2" - 3.14 in^2
2.5" - 4.9 in^2
3" - 7.07 in^2
4' - 12.56 in^2

Factoring boundary layers, bends, heat rejection etc the single 3" could approach the flow characteristics of a 2.5" dual system and would outflow a 2" dual system hands down.

A mandrel bent 3" single system (headers and free flow muffler) with minimum bends would most probably meet the needs 99% of the motors that reside in a 4wd engine bay. The top end restriction, if any, would be imperceptible.
 
muddybuddy said:
you think the emissions people will really pick-up on it, with 2 cats instead of one?
Click to expand...

Do we even have "emissions testing" here in Va. (other than state inspection)? I've never had it done before.
 
well ive got "truck perminant" plates on mine, so i dont think i have to worry bout it, but im not sure.
 
Drey said:
ya...i feel for you guys...emissions must suck:D
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I'm one state to the West of you, and agree completely.

A moment of silence for our suffering brethren in the smog-testing states - may we never join them in that misery, though some of those states do offer other benefits, for a sniffer up the tailpipe just isn't worth it.
 
muddybuddy said:
you think the emissions people will really pick-up on it, with 2 cats instead of one?
Click to expand...

Just depends on how thorough they are. None* of the trucks with cat converters got true dual exhaust, so it would be easy for an inspector to notice IF they were up on that, or felt like checking. Most of the time, those inspections just seem to turn out how they do based on who's looking.

*=There might be some one off's that used dual cats, I've not bothered to look through every exhaust option used every year, but the K5's most certainly did not.
 
buy some stainless steel tuding and mock up ur own exuast and tack it all together and then bring it to a muffler shop and get them to fully weld it up


Jason

"keep on truckin"
 
Again not trying to get into a pissing match with anyone. But pick up any chevrolet based magazine when exhaust comparisons are performed. The numbers dont lie, and on even stock 350 motors true dual exhause always out performs single. Even when test are done adding one component at a time; with each new component to the exhaust is added you get increased Tq and HP. On top of that gas milage for those of us that use our 4x4 for daily drivers it always helps. For example: a standard 70 chevelle 2 bbls 250 hp bone stock 3.08:1 rear gared automatice car came with duals; cause it flows better. Todays high performance cars like mustangs, camaro, firebird, vette, viper etc,,,,,always benefit over stock systems.

Far as deisels go they run 4" and 5" systems aftermarket. Thats a huge difference from a single 3"; And deisels run max rpms of 3500 and cruise at 1800-2500 approx etc. You cant compare a deisel to a gas motor.

Considering even the SBC motor that is running the mildest stock cam peak torque is usually in the 22-3200 rpm range. Any time you get into that range more free flowing air is gonna benefit most. Now if you had a rig that is pure off road and steep climbs, rock and significantly rough terrain is 90% of your driving then I will go with the fact that stock exhaust manifold and any single exhaust will do just as well as a dual system. In any other case which I beleive 99% of people on here are in that category I still stand by a dual system is most bang for your buck. I do appretiate the conflicting opinion though as I can always learn, Especially the flow #s chart someone put up here comparing pipe diameter and flow.
 
So you think 99% of the people on here run high reving motors and also 99% of the people on here dont do rock? Have you looked at anything on this site before you decided to shoot your wad on this one thread:rolleyes: . Yes there are people that use or need a high reving motor however I would propose to you that 70%-75% of this site care more about what there engine does from idle-3000 rpm. Also a quick search will let you see that this horse has been beat to death several times over the years.

To the poster. Run what YOU want. If you can find someone to do true dual for you, good for you. If not, it is my BELIEF, that you will not see significant gains over a single 3" system.

Ira
 
I wasn't going to get into this one, but isn't 3" pipe a relatively new "invention", if you will?

I can't recall one factory vehicle using 3" anywhere in the past when true dual exhaust was the "performance" norm. Even now, clearance issues and cost might make smaller pipes more applicable in car applications. I know 4" exhaust pipe is insanely expensive, no idea what 3" costs compared to 2.5".

Anyone got links to a back to back single 3" vs. 2.5" dual exhaust test on a "normal" motor? You can dig up all sorts of header testing, but I don't recall seeing pipe size dynoed.

Most magazine testing (although getting better) typically throws away every stock component from the head to the tailpipe at once and claims such wondrous gains, when in fact the gains could be huge fom one component and negligible from another.

From a cost/install standpoint, I'd think single 3" would come out the winner, (especially if dealing with 2 mufflers and cats) but that would have to be weighed against any ACTUAL performance difference.

We can still keep this educational, even if a tad bit argumentative. :)
 
whats a cat? haha just kidding, i installed headers on my truck to find out not 1 exaust shop in town would touch it to tie them into the exaust system since the po had the cats removed, so i ended up buying a dual 2-1/4 kit from jegs for alittle over a bill, then i added a couple 40 series and i was in business, something you might want to look into if you dont have smog checks, if this has already been mentioned, sorry i didnt read all 4 pages, thanks

justin
 
AussieK5 said:
Keeping it really simple, the cross sectional area of the follwing pipes is indicative of their flow characteristics.

CRA
2" - 3.14 in^2
2.5" - 4.9 in^2
3" - 7.07 in^2
4' - 12.56 in^2

Factoring boundary layers, bends, heat rejection etc the single 3" could approach the flow characteristics of a 2.5" dual system and would outflow a 2" dual system hands down.

A mandrel bent 3" single system (headers and free flow muffler) with minimum bends would most probably meet the needs 99% of the motors that reside in a 4wd engine bay. The top end restriction, if any, would be imperceptible.
Click to expand...

This is exactly what I was going to post.

With regards to the so called "tests" another poster mentioned, I would like to know the true details of the different exhaust systems involved. Sure, take an old factory restrictive single exhaust using 2.5" pipe and replace it with dual 2.5" pipes and good mufflers and it will be a huge improvement. Now take a good 3" system and compare it to the dual 2.5's and see what happens. I doubt there is any huge difference.

In general dual exhaust on a V-8 was cheaper and easier to run, and that's why they are so popular. As mentioned, back in the day try to find a shop bending up 3" pipe and also willing to make a Y-pipe that fits around everything.
 
When I lived in Va. Bch in the late 80's early 90's I had to get an inspection every year.
I don't recall any emissions testing but they used to be pretty anal about the visual.
I had bought a 78 T/A in Kentucky and brought it back to va. bch.
It had true duals on it and it failed.
I had to take it to an exhaust shop and have the factory style system put back on to pass inspection.

Same thing with an 80 3/4 ton Chevy that I brought back from Main.
Had to go back to the factory style system to pass.
 
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