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Old 07-16-2004, 05:17 PM   #1
StillDriver72
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Default Single exhaust vs. dual exhaust??

Maybe I'm missing something, but here's something I've never quite gotten.

A car like the Mazda 3 with the 2.3 liter I4 is rated at 160 hp and has a little single exhaust pipe coming out the rear.
The Mazda 6 with the 2.3 liter I4 is also rated at 160 hp, but has a dual exhaust system?

How is this?
Many people in the aftermarket change their exhaust systems, or add dual exhaust with the promise and reward of getting more horsepower. But why is it then that so many manufacturers use different exhaust systems on different cars, with the exact same engine, but supposedly they are rated as the same power?

And sometimes a manufacturer will change their exhaust system a bit, then re-rate the power of the engine. But isn't the power rating at the crank?
How exactly does a vehicle with a different exhaust system (especially one from the cat back) give an engine more power at the crank? Wouldn't it NEED a more efficient INTAKE first?
If the engine is taking in the EXACT same amount of air, how does giving it a slightly better exhaust system benefit, if the engine isn't taking in more air?

Thanks for the anticipated thoughts and answers.
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Old 07-16-2004, 05:19 PM   #2
Brad Pittiful
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lots of duals are a single that splits into duals after the cat
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Old 07-16-2004, 05:21 PM   #3
sneeky
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Default Re: Single exhaust vs. dual exhaust??

Quote:
Originally posted by StillDriver72
Maybe I'm missing something, but here's something I've never quite gotten.

A car like the Mazda 3 with the 2.3 liter I4 is rated at 160 hp and has a little single exhaust pipe coming out the rear.
The Mazda 6 with the 2.3 liter I4 is also rated at 160 hp, but has a dual exhaust system?

How is this?
Many people in the aftermarket change their exhaust systems, or add dual exhaust with the promise and reward of getting more horsepower. But why is it then that so many manufacturers use different exhaust systems on different cars, with the exact same engine, but supposedly they are rated as the same power?

And sometimes a manufacturer will change their exhaust system a bit, then re-rate the power of the engine. But isn't the power rating at the crank?
How exactly does a vehicle with a different exhaust system (especially one from the cat back) give an engine more power at the crank? Wouldn't it NEED a more efficient INTAKE first?
If the engine is taking in the EXACT same amount of air, how does giving it a slightly better exhaust system benefit, if the engine isn't taking in more air?

Thanks for the anticipated thoughts and answers.

i'm guessing it's still the same exhaust manifold but the axelback is split into two, giving you two pipes in the rear. and another reason... looks. car manufacturers don't want all their cars looking the same.

just my guess


chris
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Old 07-16-2004, 05:22 PM   #4
AaronWRX
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why didnt you poll this kn0b?

edit: nm. im the kn00b
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Old 07-16-2004, 05:25 PM   #5
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Quote:
Originally posted by StillDriver72
If the engine is taking in the EXACT same amount of air, how does giving it a slightly better exhaust system benefit, if the engine isn't taking in more air?
If the exhaust is the bottleneck, then opening it up will make the engine breath more. Look a the WRX, you can make 400hp with the stock airbox because the intake isn't a limiting factor.
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Old 07-16-2004, 05:27 PM   #6
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Quote:
Originally posted by StillDriver72
Maybe I'm missing something, but here's something I've never quite gotten.

A car like the Mazda 3 with the 2.3 liter I4 is rated at 160 hp and has a little single exhaust pipe coming out the rear.
The Mazda 6 with the 2.3 liter I4 is also rated at 160 hp, but has a dual exhaust system?

How is this?
The dual exhaust on the 6 is for appearance purposes and flows approxiamtely equally as well as the single outlet system. That or the HP of that car is limited by the intake side rather than the exhaust.

Quote:
Originally posted by StillDriver72
Many people in the aftermarket change their exhaust systems, or add dual exhaust with the promise and reward of getting more horsepower. But why is it then that so many manufacturers use different exhaust systems on different cars, with the exact same engine, but supposedly they are rated as the same power?

And sometimes a manufacturer will change their exhaust system a bit, then re-rate the power of the engine. But isn't the power rating at the crank?
How exactly does a vehicle with a different exhaust system (especially one from the cat back) give an engine more power at the crank? Wouldn't it NEED a more efficient INTAKE first?
If the engine is taking in the EXACT same amount of air, how does giving it a slightly better exhaust system benefit, if the engine isn't taking in more air?

Thanks for the anticipated thoughts and answers.
If you think of an engine as an air pump, (a useful analogy for this discussion) then it becomes clear. You have to cram air in on the intake side and get it out on the exhaust side. Cars that gain power from exhaust only changes are fitted with slightly better flowing intakes than their exhausts in stock form, this is why the air pump flows more air with the change of the exhaust only. If the intake is the "bottleneck" then changing the exhaust will have no appreciable effect.

When you hear about bolt-on modifications we are typically trying to increase the efficiency of the air pump up to the point where the bottleneck is in the heads or cylinders rather than in the intake or exhaust manifolds.
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Old 07-16-2004, 05:43 PM   #7
wrigh003
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Note what you see dual exhausts on most often: Trucks and rear-drive cars, generally with a V8 or V6. The reason for that is that those engines have exhaust manifolds on both sides, vs. an inline-4 or inline 6 where all the exhaust comes out one manifold on one side of the block. It just makes more sense to have duals go all the way back than to try to get it all collected together somewhere up in the engine bay or under the passenger compartment (especially in the case of a rear-drive vehicle where thereís a driveshaft to think about). A lot of these kinds of exhaust systems will have a crossover pipe somewhere, either for purposes of noise cancellation or increasing exhaust efficiency (or both).

So, for the purposes of sweeping generalization, true dual exhausts are mostly used on V6 or V8, rear drive vehicles. (Still, there are V6 Accords and other front drive cars with dual exhausts, but Iím betting they have a collector and then split again after the catalytic converter, and as such are not true dual exhaust designs. Or maybe not, thatís just conjecture.)

I think the use of a dual exhaust on a typical 4-cylinder car is, as Mr. Pittiful said, more about form than function. I see a car that Iím not completely familiar with rolling down the road with two exhaust pipes sticking out from under the rear, and I almost automatically think ďHmm. That carís got a V6/8 in it. Cool.Ē Though it may increase the efficiency of the exhaust a little, on an inline4 or 6 engine, dual exhausts are generally unnecessary and just something to use as a bullet point on the window sticker of the car at the dealership.

Edit: Sigh. All that typing and still coming back to edit.
Everybodyís right about engine as air pump, etc. A more efficient exhaust (generally more open) will create power by increasing the amount of air/fuel the engine is able to consume on each stroke. (Note that race cars are real freaking loud, as they pretty much have little/no exhaust restriction beyond whatever would create useful backpressure.) A more efficient exhaust will increase power output at the crank by x%, then after driveline losses are deducted, the figure is what power you are putting out at the wheels. If the engineís rated at 160hp, and the driveline losses are 26%, then the wheel hp figure is 118.4. If you were to bolt on an exhaust (or intake, or header, or combination of the three, and donít forget the catalytic converter) that allowed enough extra air to flow to create 12 crank hp:
172hp x .74 (for the minus 26% driveline loss), then you would then get 127.28hp at the wheels.

And the 26% figure I just pulled out of the air. Iím sure you can google automatic/manual driveline power loss percentage or something and get a more accuarate guesstimate.

And Iím spent. Bored at work, so I figured Iíd type a huge post. Time to go home now!

Last edited by wrigh003; 07-16-2004 at 05:53 PM.
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Old 07-16-2004, 05:44 PM   #8
Nightwing
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Old 07-16-2004, 11:57 PM   #9
StillDriver72
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Some guys just HAVE to get off this "noob" thing.
As for this forum, I registered nearly two years ago, just recently changed name because my usual name of "Driver72"
couldn't be accessed with my new computer (lost my password and my old email address is closed).

As for cars...think of me as Tom Cruise's character in Days of Thunder.
Can drive, knows little of the tech stuff.

I always get a kick out of people who call others "noobs"
Many of the people they were calling that were probably driving when they were still breast feeding.

Don't judge a book by it's cover, and don't judge a person based on how NEW they are to a particular forum.

Thanks to the guys for the serious answer. I always thought it strange that manufactuers would do that just for looks, but I guess it works.
A car with dual exhausts most certainly does LOOK like it's faster or has a bigger engine then one with a single exhaust, even though the car with the single exhaust may in fact be the FASTER car.

I personally prefer the "sleeper" look.
I'm not into all the show, but no go that the "kids" these days seem to think makes their cars faster....slap on a Type R sticker and it must be fast right?

Thanks again.
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Old 07-17-2004, 01:06 AM   #10
well_armed
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Quote:
Originally posted by StillDriver72
Some guys just HAVE to get off this "noob" thing.
As for this forum, I registered nearly two years ago, just recently changed name because my usual name of "Driver72"
couldn't be accessed with my new computer (lost my password and my old email address is closed).

As for cars...think of me as Tom Cruise's character in Days of Thunder.
Can drive, knows little of the tech stuff.

I always get a kick out of people who call others "noobs"
Many of the people they were calling that were probably driving when they were still breast feeding.

Don't judge a book by it's cover, and don't judge a person based on how NEW they are to a particular forum.

Thanks to the guys for the serious answer. I always thought it strange that manufactuers would do that just for looks, but I guess it works.
A car with dual exhausts most certainly does LOOK like it's faster or has a bigger engine then one with a single exhaust, even though the car with the single exhaust may in fact be the FASTER car.

I personally prefer the "sleeper" look.
I'm not into all the show, but no go that the "kids" these days seem to think makes their cars faster....slap on a Type R sticker and it must be fast right?

Thanks again.
n00b
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Old 07-17-2004, 01:09 AM   #11
Brad Nely
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Old 07-17-2004, 01:38 AM   #12
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Dual exhaust is pointless unless you have more than one cylinder head.
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Old 07-17-2004, 01:45 AM   #13
wyn525i
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My car has full dual exhaust, and only one muffler.
Its an I6, but if you look at the engine, you will see that there are two exhuast manifolds and the two pipes runn parallel all the way back to the muffler.





As you see, two in, two out.

as for the Accord V6 with its dual mufflers, its basically a single exhuast setup that is split near the rear axl to make it look as if its a true dual exhuast.
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Old 07-17-2004, 03:21 AM   #14
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