Dual exhaust benefits

[bdcardinal]

I have an x-pipe on the 14 Mustang that came with the catback from Borla, it retains the factory cats because they are not part of the X pipe on that year Mustang. It does have the factory tri-y headers on it still. I did it purely for sound. My 95 that I am slowly rebuilding will have an offroad X but I made the decision to pull it off road permanently and have it be a track rat car.

 

[ragtoplvr]

Most exhausts now are a lower grade of stainless steel. They last the normal life of the vehicle. Some lower grade cars use aluminum killed steel, it is usually good for 5 to 10 years most places. The good ole days they used mild steel with no coating, or galvanized, which will burn off after a while, sometime OE lasted just 2 years.

The best sounding IMHO old time exhausts used chambered mufflers. There used to be a big chambered side pipe that was the best of all, burns on your leg getting in and out of the car were a learning experience. Thrush was the cheapest and were quite loud, Best et. Constant announcing your presence to the local law enforcement is not my thing. Chevy had a 36" (I think) 3 chamber muffler that was quite expensive but great sound, quieter than thrush that advertised your presence everywhere . Never owned one to run on the strip. Glass packs were a little quieter but the heavily louvered cores were somewhat restrictive higher ET. When fresh had a nice deep tone. Still announced your actions to the law. On those days, a huge caddy muffler with 2 ½ inlet and outlet for the old 500 CI V8 had the same or slightly better ET than most glass packs, and was quiet enough not to attract law enforcement attention. Had a nice lower sound, on the caddies they had resonators to get rid of the last little bit of noise. They were expensive, oddly the caddie dealer was the cheapest place to buy them. They were huge though. The famous turbo muffler was much smaller, and moderately louder, unless you liked stealth mode they were a good option. Again convincing people that even though they were quieter, the Caddie muffler had less restriction and a lower et was impossible.

 

[benjy]

duals can be a benefit when you cant get a big enough single system to support your power level. todays cars + trucks are surely choked to meet EPA rules, with cats + resonators as well as mufflers + undersized pipes. exhaust is surely a science + what works + what fits can be different. the most gains are on turbocharged engines + today they are many + the downpipe just off the turbo is most important. on my 1.8T 2001 jetta i could see on the boost gauge i installed about 3 lbs more + quicker boost everything else stock after upsizing from an sickly 1 5/8 twisted system to a 2.5" still catted + no check lites + on really powerful engines gains can be even better as they need more breathing in + out. prolly for about 10 yrs all OE exhausts are 400 grades of stainless, they corrode + look ugly but don't rot thru + some like my 2001 jetta used non-magnetic 300 grades of stainless that only discolors + outlasts your car. there are surely benefits but noise levels will increase + depending on your state regulations modifications may not pass inspections. even catted pipes that are bigger + higher flow can trip a check lite. as i often reference check the gains on goapr a top line audi, vw, etc tuner, not cheap but good stuff that works!!

 

[nthach]

I think my understanding with true dual exhaust(not the faux-duals used by Subaru and Honda) is that the X/H-pipe is there to "tune" the exhaust for efficient scavenging, with the X-pipe providing a little less backpressure for more top-end and the way the exhaust manifolds are made affect how the system is "tuned".

My parent's Lexus LS430 has a true system - if it wasn't for the center pipe assembly that branches into a Y-pipe into a cat and then back out to separate resonators and mufflers. The car does have a slight rumble to it if you listen very, very very closely. Probably the same deal on the Tundra, the Lexus system was designed not to disturb the peace. Toyota V8s do sound good with an exhaust on them. Almost like a Ford Mod motor.

 

[4WD]

Given a choice I'll take dual drive shafts any day

 

[Malo83]

I'll stick with single drive shafts

 

[4WD]

But you have two now … a driver side and a passenger side … 🤔
(On the car, not the pickup) …

 

[eljefino]

Originally Posted by WyrTwister
But back in the day , they tended to rust out twice as fast , especially when short tripped . Did not get hot enough to evaporate the water / moisture form the inside of the system .



Leaded gas had scavengers so the lead wouldn't stay in the combustion chamber, but it wound up in the exhaust pipe where it corroded the heck out of things.

Today's faux-duels have packaging advantages and allow adequate flow with less noise or more flow at the same noise. You can do more with more cubic inches of baffles and things.

 

[DoubleWasp]

Let's get one misconception out of the way. Back pressure does not help an exhaust do anything at all. Zero, zip, zilch.

When testing an exhaust for blockage, anything greater than 1.25 PSI at idle is a fail, and anything greater than 3 psi at 2000 rpm is a fail. Mind you, this is on a factory OEM exhaust with cats, mufflers, and all. A catless exhaust will generate almost 0 psi unless fitted with a grandpa-car "can't hear it running at all" muffler.

There is no specific minimum for back pressure. If an exhaust were to have 0 psi at both speeds it would be considered a pass with flying colors.

Pipes that are too big, or exhausts that are made wrong cost low end power due to a lack of or incorrect exhaust velocity or scavenging.

The back pressure theory has been tested in a million different ways and is a solid failure every time.

The gains of an OEM dual exhaust system over a single is simple. Take an OEM muffler. Designed to flow as much as it can while maintaining a certain sound level. Let's just use some arbitrary numbers here and say that "OEM Muffler X" flows 400cfm and emits 69 decibels. "OEM Muffler Y" flows 500 cfm and emits 75 decibels. Let's say the target noise level is 70 decibels. What's an engineer to do? Just split the exhaust, put two of the "X" mufflers in, and now you still have 69 decibels (or maybe less) and 800 cfm flow.

Of course, sometimes the OEM will decide that their "aggressive" dual exhaust should also sound different, and will be louder despite being a dual. Complete style issue there.

But anyone in the know is aware of the fact that a single exhaust with a big single muffler makes the most power. This is mostly due to the Dynamics of combining dual banks without splitting the exhaust again. Let's call this "OEM muffler Z". Why use two "X" mufflers rather than a single "Z"? Packaging and styling.

 

[Skippy722]

Originally Posted by DoubleWasp
Let's get one misconception out of the way. Back pressure does not help an exhaust do anything at all. Zero, zip, zilch.

When testing an exhaust for blockage, anything greater than 1.25 PSI at idle is a fail, and anything greater than 3 psi at 2000 rpm is a fail. Mind you, this is on a factory OEM exhaust with cats, mufflers, and all. A catless exhaust will generate almost 0 psi unless fitted with a grandpa-car "can't hear it running at all" muffler.

There is no specific minimum for back pressure. If an exhaust were to have 0 psi at both speeds it would be considered a pass with flying colors.

Pipes that are too big, or exhausts that are made wrong cost low end power due to a lack of or incorrect exhaust velocity or scavenging.

The back pressure theory has been tested in a million different ways and is a solid failure every time.

The gains of an OEM dual exhaust system over a single is simple. Take an OEM muffler. Designed to flow as much as it can while maintaining a certain sound level. Let's just use some arbitrary numbers here and say that "OEM Muffler X" flows 400cfm and emits 69 decibels. "OEM Muffler Y" flows 500 cfm and emits 75 decibels. Let's say the target noise level is 70 decibels. What's an engineer to do? Just split the exhaust, put two of the "X" mufflers in, and now you still have 69 decibels (or maybe less) and 800 cfm flow.

Of course, sometimes the OEM will decide that their "aggressive" dual exhaust should also sound different, and will be louder despite being a dual. Complete style issue there.

But anyone in the know is aware of the fact that a single exhaust with a big single muffler makes the most power. This is mostly due to the Dynamics of combining dual banks without splitting the exhaust again. Let's call this "OEM muffler Z". Why use two "X" mufflers rather than a single "Z"? Packaging and styling.


Thank you! I was waiting for someone to post this!

Also, in regards to different mufflers, here's some OEM ones from a Charger. One is an R/T or v6, the other from an SRT. SRT is a lot more open and free flowing while being louder.

 

[ka9mnx]

Originally Posted by NGRhodes

For a specific reciprocal engine power = torque x revolutions per unit of time.
By that definition you need torque to make power at any RPM high or low, therefore it is always factor.

Where does the torque come from? Once HP and torque cross on the dyno curves, torque drops like a rock.

 

[DoubleWasp]

Depends on the engine, mostly the Volumetric Efficiency. How much air and fuel gets into the cylinder per pump of the piston at WOT. Engines that have high VE above 5252 rpm will continue to increase torque past that limit. This is seriously uncommon in street engines, but the Honda S2000 is one exception that I believe does this.

There is always torque. Think of horsepower as the effect of torque causing rpm. Torque can exist with or without rpm, but because there is nothing locking a crankshaft in place, it spins in response to the actions of explosions acting on the Pistons and rods.

So why is the torque dropping after 5252 say on your typical V8? That's because of the design of the engine. The engine is designed for best cylinder filling of air and fuel (through tuning of the intake/exhaust velocity) at lower rpms, for most torque where it will be used the most. The smaller and longer tracts are great at doing at this at lower rpms. The smaller and shorter camshaft durations and lifts are also great at doing this. But there is a limit.

At higher rpms, the engine starts to choke a little. Intake runners are too small to flow the air the cylinder wants, long enough that restriction is increasing, and those valves are too small and aren't open big enough or long enough to meet demand. VE at that speed begins to suffer. Torque past the limit of greatest VE begins to drop. But guess what? The engine is still increasing in rpm. It's doing a bad job of processing air and fuel efficiently, but it's still getting by. It's getting less air and fuel per pump of piston but it's doing a lot more pumping.

Less force of torque, but still more actions are being performed by the torque that is being produced, and hence the horsepower number is still above the torque number.

If you look at those dyno sheets, you will see that horsepower takes a dump not long after torque takes a dump as VE becomes so bad that the engine is literally hitting a wall, or the electronic or mechanical rpm limit just shuts the whole thing down before the engine flings into pieces.

 

[DoubleWasp]

Look at the stock S2000 dyno chart. This is a high VE engine. Low end torque is low due to big and short intake tract and big valves. Low rpm VE is less than perfect, but it has a cute cheat. It has two cam profiles via the VTEC system. See what happens when it switches to it's secondary cam profile? VE is restored and torque and horsepower both come back with a vengeance.

Now look at the Corvette dyno chart. More typical situation, but notice how slightly less than 1000 rpm after torque begins departing, horsepower starts bowing out as well. Engine reaches mechanical limits and Rev limiter steps in before we can see how much worse it would get.

The whole story is infinitely more complex than what I have described, but that is the largest part of it.

 

[supton]

Very interesting. I've thought a couple of times of getting duals for my truck, but I guess there isn't much gain. It's not like the old days when uncorking the exhaust really did something (30 years ago plus).

 

[Dinoburner]

Lots of good and interesting info in this thread.

 

[OilUzer]

Originally Posted by Dinoburner
Lots of good and interesting info in this thread.

 

[ARCOgraphite]

ka9mnx -Where does the torque come from? Once HP and torque cross on the dyno curves, torque drops like a rock


Engine makes torque. HP is a calculation using torque and time - as in how fast can you perform work?

. In the I.C. Engine formula, torque (twisting force) and HP are the same at 5252 rpm.

I say Ignore the HP numbers and just look at the torque.

I say this as i drive my new VW with a dinky 85 cu. in. engine with the torque of a 3.0L tuned V6 from 2000-4500 rpm! Right where you want it in a passenger car! Yes i got the 6 speed manual. Thank somebody - no more AT woes! I am back in control.

 

[SubieRubyRoo]

Originally Posted by DoubleWasp
Depends on the engine, mostly the Volumetric Efficiency. How much air and fuel gets into the cylinder per pump of the piston at WOT. Engines that have high VE above 5252 rpm will continue to increase torque past that limit. This is seriously uncommon in street engines, but the Honda S2000 is one exception that I believe does this.

There is always torque. Think of horsepower as the effect of torque causing rpm. Torque can exist with or without rpm, but because there is nothing locking a crankshaft in place, it spins in response to the actions of explosions acting on the Pistons and rods.

So why is the torque dropping after 5252 say on your typical V8? That's because of the design of the engine. The engine is designed for best cylinder filling of air and fuel (through tuning of the intake/exhaust velocity) at lower rpms, for most torque where it will be used the most. The smaller and longer tracts are great at doing at this at lower rpms. The smaller and shorter camshaft durations and lifts are also great at doing this. But there is a limit.

At higher rpms, the engine starts to choke a little. Intake runners are too small to flow the air the cylinder wants, long enough that restriction is increasing, and those valves are too small and aren't open big enough or long enough to meet demand. VE at that speed begins to suffer. Torque past the limit of greatest VE begins to drop. But guess what? The engine is still increasing in rpm. It's doing a bad job of processing air and fuel efficiently, but it's still getting by. It's getting less air and fuel per pump of piston but it's doing a lot more pumping.

Less force of torque, but still more actions are being performed by the torque that is being produced, and hence the horsepower number is still above the torque number.

If you look at those dyno sheets, you will see that horsepower takes a dump not long after torque takes a dump as VE becomes so bad that the engine is literally hitting a wall, or the electronic or mechanical rpm limit just shuts the whole thing down before the engine flings into pieces.


It's been quite some time since I've seen anything as blatantly false as the garbage you spewed here. HP and torque crossing at 5252rpm has nothing whatsoever to do with the design of the engine, and has absolutely everything to do with the way HP is calculated.

The truth about TQ and HP

 

[clinebarger]

Originally Posted by SubieRubyRoo

It's been quite some time since I've seen anything as blatantly false as the garbage you spewed here. HP and torque crossing at 5252rpm has nothing whatsoever to do with the design of the engine, and has absolutely everything to do with the way HP is calculated.


Not to put words in DW's mouth......But, I believe he was discussing VE vs RPM using a Scale/Media most of us can easily understand. You start using Newton meters & Kilowatts or scaling the HP different from Torque......I have a hard time myself.

 

[ARCOgraphite]

Originally Posted by SubieRubyRoo


It's been quite some time since I've seen anything as blatantly false as the garbage you spewed here. HP and torque crossing at 5252rpm has nothing whatsoever to do with the design of the engine, and has absolutely everything to do with the way HP is calculated.
Originally Posted by clinebarger

It's been quite some time since I've seen anything as blatantly false as the garbage you spewed here. HP and torque crossing at 5252rpm has nothing whatsoever to do with the design of the engine, and has absolutely everything to do with the way HP is calculated.


Not to put words in DW's mouth......But, I believe he was discussing VE vs RPM using a Scale/Media most of us can easily understand. You start using Newton meters & Kilowatts or scaling the HP different from Torque......I have a hard time myself.



As a M.E. I dont have a problem with Doublewasp's logic above; he is explaining to the layperson how V.E typically affects torque and thus HP above 5000 rpm. -Ken