Ozz1967

iTrader: (4)

I'm just curious, I've looked through the threads but can't find a really strait answer to my question.

I am wondering,

For those of us with Auto transmissions, it really isn't practical to run a dual exhaust past the transmission.

Since the y-pipe is essentially a dual exhaust until it mates with the cat, is there enough room to do a dual exhaust following the y-pipe routing, coming together at the cat, using it as an "X" pipe of a sorts, then back to then after the cat go back to a dual exhaust out the back of the car?

Would it gain anything? Is it even worth considering other than be a novelty?

robertfrank

iTrader: (27)

I'm actually in the process of doing a true dual set up on my car. I already have an x pipe and dual 16 inch classic chambered mufflers. I'm going to run mine just before the rear axle.

MoJoe

iTrader: (5)

The N10 dual cat system merges into a single intermediate pipe to go over the axle. You could duplicate that to get past the transmission. With or without cats is up to you. From behind the trans, over the axle and mufflers is up to you...

Thanks to Dyno Don from this thread...


And more help from Google, select the images...

InfernalVortex

iTrader: (4)

What's the benefit of doing duals along the stock route vs doing a larger single pipe? The only one I can think of is MAYBE sound. But you're going to get more airflow through a single pipe because you're going to have a lot less bends and restrictions and friction. A single pipe will have less interior surface area with the same or more interior volume.

So again... what's the benefit?

MrBrooks

Once you combine the the two flow paths into one cat, there will be zero advantage to re-dividing the flow.
I think ALOT of people do not understand the purpose of an x pipe. It does not.........or rather, should not, combine the two flow paths. It is there to equalize pressure between the two, and assist with scavenge.
If it allows the two paths to mix then it is nothing more than a glorified y-merge. Which if sized properly, a y-merged single can perform as well as a properly sized dual system, and most definatly out perform a poorly sized dual setup.

MrBrooks

And that is a whole other VERY good point.............and there is only 1 muffler to buy.........

skinny z

What's easier to run over the axle? Two at 2.5" or one at 3.5"? Probably the single pipe but when it comes to mufflers, you have to consider the flow needed for the horsepower produced. It's tough to find a reasonably quiet muffler that'll flow enough on it's own. You're talking 800+cfm for a 400chp engine. That's easier with two mufflers.
There are some clever installations with side by side bullet mufflers in the OEM location feed by a pair of pipes over the axle or alternately by a single pipe that splits into two after the axle.
The y-pipe after a set of long tube headers has been many times, automatic or stick. A cross-member modification is generally needed to keep it tight to the floor.
Either way it's a lot of work.
If I had a drag only car and it was at stock height, the simplicity of a couple of collector extensions and some bullets that dump before the axle would be way I'd go. Then you could into a little header tuning too.

MoJoe

iTrader: (5)

Packaging, price, saying you have "true duals". 2x 2.5" might be easier than 1x 3.5" to install. All things being equal, it is 1" better ground clearance. 2.5" parts are cheaper, but I don't know if 50% cheaper. 3.5"+ isn't so easy to come by, and not many choices in cats and mufflers. 2.5" parts you can find all day long. 2x 2.5" mufflers should be quieter than 1x3.5". Loud is fine for a race car, but can get old in a DD, and can attract unwanted attention (cue the polizei .

Based on this, 2x2.5" = 1x3.5" in horsepower potential.

Of course, adding Mufflex to the argument, and their offering 3.5" and 4" cat backs makes this a less obvious choice. Before Mufflex, anything bigger than 3" was full on custom and very expensive.

InfernalVortex

iTrader: (4)

All very good points.... but friction against the inside of the exhaust pipe is a problem also. 2 pipes will have far more interior surface area. A single pipe has far less. How big of a difference is that? I really don't know.

I run a dual 2.5 into a single 3.5.... and it's kinda loud. It's mostly my muffler choice, but Hooker makes an aerochamber in that size that I'd like to put on it.

I'd say do whichever is easier. I dont think you're going to notice any major differences in performance, not sure about cost.

skinny z

The difference in performance will come down to how much restriction your muffler introduces into the system.
It seems though that nobody considers the flow of the muffler as being anything significant. In reality even the best efforts of a large single ande two medium sized pipes will go to waste if the muffler only flows 350 cfm.
Fact: 2.2 cfm of muffler flow per crankshaft horsepower is required before backpressure starts to limit power output.

Orr89RocZ

iTrader: (20)

Depends on area of pipe but on our cars the best you will beable to do down factory location without major ground clearance issues is a single exhaust system. Single 5" is the biggest you can go and it does fit
3.5" single works well for most 300-400whp cars. Gm 400 hp 6.2 trucks come with 3.5" exhaust. You can make 500+ thru 3.5 but starts to become restriction.

Dual 2.5" will flow as much as a 3.5 single but weigh slightly more. There is a tradeoff. As others mention big advantage to duals is more choices in mufflers and ability to add more mufflers to a system for sound reduction without killing flow to much. I had dual 3" with x and 4 mufflers overall. Car was quiet and made 1000hp. They can support alot even as restriction increases.

If you have shorty headers duals down factory location side by side works extremely well. Longtubes you still have to get pipes around cross member to make a y pipe or run duals, so it doesnt matter what you do at that point

Ozz1967

iTrader: (4)

Thanks guys for the awsome discussion on this topic! This is exactly what I was hoping for.

I have shorty headers, and I see how the dual cat set up runs and then combines into one pipe to go over the axle. that's exactly what I was thinking of but keeping it dual all the way back to the mufflers.

I would be concerned about having enough rom for dual 2.5" exhaust going over the axle on the same side...but again I've seen it done by some members here.

I would not go back past the transmission on each side as that's not really feasable for me without quite a bit of work that I'm not really willing to do at this point.

I have never heard of "interior wall resistance" before, so that was fun to read about.

Now, I just need to find someone here in Utah who does mandrel bent exhaust work.

bdle

Just about the only true dual exhaust you can run on third gens without doing any frame/ cross member modifications and still having alright ground clearance is the Dynomax Header-Back Dual Exhaust kit(http://www.summitracing.com/parts/wl...t/model/camaro). It follows the factory exhaust set up but its not a 2.5", its 2.25" and there will still be modifications needed in order to make it fit perfect

Orr89RocZ

iTrader: (20)

Run like a y then put in an x like this







Right down the tunnel. Thats 3" dual

MoJoe

iTrader: (5)

I don't know either, however, to beat the math to death: 2.5" pipe diameter = 4.9 square inches of cross section area and 7.8" of wall surface (circumference).
Double that, and 2x 2.5" = 9.8"" area and 15.6" wall.
3.5" pipe diameter = 9.6"" area and 11" wall.

Therefore, 2x2.5" has 2% more area but 41% more wall than 1x3.5". Again, using this, they are "rated" at 463 and 468hp, respectively, with just a 1% benefit to the 3.5" pipe.

So, the additional friction from the additional surface area does have a negative effect to flow. But, comparing 2x2.5" against 1x3.5" is apples to apples as far as performance goes. Which leaves the choice between the two up to other factors: price, packaging, mufflers, general preference.

Ozz1967

iTrader: (4)

So the question then begs, and I can't see the photos Orr89 posted here on the work computer, is which muffler, since yo're supposed to have roughly 2.2cfm of flow per hp...running 300hp, means I need 660cfm of flow of which my current Hooker Aerochamber only gives me about half of. Every muffler comparison I've seen so far is running about 6 years old, and nothing with good flow numbers.

InfernalVortex

iTrader: (4)

Have you guys seen this?

http://www.mustangandfords.com/parts...mparison-test/

Doesnt seem like mufflers really make THAT big of a difference. Everything stays within about the same 5-10hp range. They do affect the power curve, though, which makes me think that even the best muffler for a given engine will not be the best muffler for a different engine.... Probably still within the same deviation range as this test, though.

Interesting thing is, people bash the Spintechs all the time for poor flow... but the spintech made more hp than the Borla XR-1, which is really almost nothing more than a glasspack.

Borla:

redneckjoe

pretty much any straight-through muffler design will flow good, especially if you step the muffler up to the next size bigger pipe.

skinny z

I guess that depends on what you consider big.
Here's a published test I came across.



On a personal note, I can tell you that without any other changes other than uncapping my exhaust just ahead on my nonflowmaster went from 8.124 @ 83.82 to 8.070 @ 85.14 in back to back tests. That tells me something right there. That's in a 3700 lb 12.5 second all street car too. It may not mean much to some but close to 20 rwhp gain because of a muffler is something to think about.

InfernalVortex

iTrader: (4)

And I see things like this all the time... so how come that dyno on that site shows on average a 5hp variation from muffler to muffler? Why the inconsistencies? It's not the first time I've seen big gains from getting rid of the muffler, but it's just surprising how much it varies from build to build. I mean that 365-375hp build on the site I linked made LESS power with the open exhaust than with mufflers... I dont know if that was open headers or just no muffler, but it's just strange to me.

The only thing I can think is that some engines just need a much shorter exhaust pipe than others to suit their RPM ranges? Of course, that test used mostly pretty well-regarded mufflers. Spintechs and Borlas and Bassanis and Aerochambers etc.

mmadden55

Pure performance, Under chasis long tube headers into. Big 3.5 y pipe glass pack and out the passenger side in front of the rear wheel, or you can go big cat and delete the pack.

I have run this set up on several cars including non f bodies and it always makes more powerr than dual 2.5 s with or without an x or h pipe. Cheaper and lighter too. Look at a NASCAR set up some time

InfernalVortex

iTrader: (4)

skinny z

If you examine the test results in the article posted, you'll see that there are a couple of mufflers that actually produce MORE power than with an open exhaust (as you've observed). There's are indication right there that the open exhaust isn't as well suited as it could be so any muffler test demonstrating the effects on back pressure vs output is already skewed.
That said, without any flow numbers for the mufflers tested we're unable to draw any conclusions regarding how much any one muffler impacts performance. It may well be that all of the mufflers tested were within a few percent of each other in the cfm department.
You made a valid point earlier and closer examination of the chart I posted reinforces it. As an example using a 400 hp engine (because the math is easy), a muffler that flows 700 cfm will allow power output to be within about 5% of a muffler that flows the target 880 cfm. That's 20 hp. It's once you get into the really crappy muffler territory (read that as what's installed on my car) where muffler flow is less than 70% of the ideal ,that's 600 cfm, and you get output reduced to less than 330 hp or a drop of 70 hp. That's not even the extreme given that there are mufflers out there that don't flow 500 cfm (or worse) so you can see where this is going. Just to qualify the example on my car, that's with an already restrictive 2 into 1 system so the potential for an uncorked exhaust allowing the engine to realize it's full output isn't there.
Keep in mind that this is all predicated on having an exhaust system ahead of the muffler that doesn't introduce any back pressure into the system in the first place.
I think that's the intent of this thread isn't it?
Now with all due respect to Orr and his beast with 1100 rwhp (good lord!) then there's so much power being produced that dropping 100 hp or more is hardly going to be noticed. Plus it's a turbo and I have no idea what the dynamics are involving exhaust pulses or back pressure. But it is possible to muffle even a Pro Stock engine and be within a few percent of open header performance. (tuned open headers that is).

Ozz1967

iTrader: (4)

Just based on what you have said here, even if my set up, with hooker shorties to a Single 3", is big enough for the motor, it's saying in every chart I can find that my Aero Chamber only flows around 340cfm...a little more than 50% of what's needed for the motor. If you you say here is true, i'm leaving 20+hp on the table?

Just for kicks, I dynoed 262 at the wheels last fall. FIguring 15% drive line loss, that puts me just over 310hp from the motor. Add in the 20hp your saying im' giving up, that kicks me all the way up to 330hp from the motor, with the correct muffler?

skinny z

Not exactly.
Put your car on the dyno and tune the engine with open headers. Chances are your short headers won't do a very good job of scavenging but back pressure shouldn't be an issue. So there's your baseline. Let's say you managed 330 at the crank and have optimized the tune. Now add your exhaust and a muffler. If you restrict the flow to the point were your system develops more than 2 psi of back pressure then output will drop about to about 80%. That's about 265 hp. Also realize that 2 psi of back pressure is quite a bit. Keep in mind this isn't so much for a stockers as it is for an engine that's more dependent on adequate flow but the principle is the same.
If all of the restriction introduced is due to the muffler then a change in mufflers to one with enough cfm will result in a gain. Been there, done that. With time slips.
Think of it in engineering terms. If you put a total blockage in the exhaust, then output would be zero. Gradually decrease that restriction and power output will increase up to the point where the restriction has no effect on output. Simple.