I was looking at some exhaust systems and noticed that some come with two mufflers as opposed to one. Will this make any difference as far as backpressure, performance, noise etc. Thank you....

 

A dual exhaust setup on a weak 4-cyl car isn't very beneficial. There is less exhaust velocity, and will lead to a loss of torque and horsepower at lower RPMs, but you would gain some horsepower on the high-end.

But on a 4 cylinder, where do you want the power? At lower RPMs, or do you want to rev high to get anywhere?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hondaracin24 &raquo;</TD></TR><TR><TD CLASS="quote">I was looking at some exhaust systems and noticed that some come with two mufflers as opposed to one. Will this make any difference as far as backpressure, performance, noise etc. Thank you....</TD></TR></TABLE>


thats a negative


you need to get 7 mufflers for it to actually do anything....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Beach Accord &raquo;</TD></TR><TR><TD CLASS="quote">thats a negative


you need to get 7 mufflers for it to actually do anything....</TD></TR></TABLE>

i thought thats why my accord was so slow... damn single muffler system!

 

Na, just run some scag pipe back and then put a dummy muffler. Maybe even a spark plug and see if you can do those Fast and Fer. flames?

LMAO

Na the straight pipe is good, but the engine does want some back pressure or it will not run right.

 

if a 6cyl TT supra can go with one exhaust "system" then im more then positive a 4cyl N/A motor can handle it, the whole dual exhaust is more for looks then anything, lots of times the cars running around with these (aftermarket) have a muffler thats not even attached to anything, its just hung from the bumper... rice

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Se7ens Travels &raquo;</TD></TR><TR><TD CLASS="quote">lots of times the cars running around with these (aftermarket) have a muffler thats not even attached to anything, its just hung from the bumper... rice</TD></TR></TABLE>

haha. its funny in the winters up here when u can see one working and one just dead. ahaha.

 

Backpressure is a theory and basically does nothing

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JakeIsCool &raquo;</TD></TR><TR><TD CLASS="quote">Backpressure is a theory and basically does nothing</TD></TR></TABLE>

ok so then why is the ECU programmed to use it as a test to help the engine run properly????

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JakeIsCool &raquo;</TD></TR><TR><TD CLASS="quote">Backpressure is a theory and basically does nothing</TD></TR></TABLE>

just like internal combustion

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by biggs2.2 &raquo;</TD></TR><TR><TD CLASS="quote">

just like internal combustion</TD></TR></TABLE>

there is no such thing as internal combustion....just internal running hampsters

 

dual exhaust is beneficial in 1 situation......a NA V configuration engine (v6, v8, v16, etc...), where each bank of cylinders goes to one manifold, and out one system of piping....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fw190bvi &raquo;</TD></TR><TR><TD CLASS="quote">dual exhaust is beneficial in 1 situation......a NA V configuration engine (v6, v8, v16, etc...), where each bank of cylinders goes to one manifold, and out one system of piping....</TD></TR></TABLE>

Yeah, a TRUE dual exhaust. But that means you need 2 cats...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pyrojeff &raquo;</TD></TR><TR><TD CLASS="quote">

Yeah, a TRUE dual exhaust. But that means you need 2 cats...</TD></TR></TABLE>

If you live in a smog tested state....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ACC0RD22 &raquo;</TD></TR><TR><TD CLASS="quote">

ok so then why is the ECU programmed to use it as a test to help the engine run properly???? </TD></TR></TABLE>

Theoretically backpressure would decrease engine power.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JakeIsCool &raquo;</TD></TR><TR><TD CLASS="quote">Backpressure is a theory and basically does nothing</TD></TR></TABLE><TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JakeIsCool &raquo;</TD></TR><TR><TD CLASS="quote">Theoretically backpressure would decrease engine power. </TD></TR></TABLE>Backpressure is a simplified explanation for someone who doesn't understand the difference between steady-state vs. pulsating flow.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">Backpressure is a simplified explanation for someone who doesn't understand the difference between steady-state vs. pulsating flow.</TD></TR></TABLE>

so explain it for some of us that dont know please

 

somewhere along your exhaust pipe...your flow capacity will change tremendously as one pipe seperates into two. i doubt this is a good thing; you want the least amount of change in your flow capacity (diameter) and you never want to start from a big pipe at the downpipe and end up with a smaller pipe at the end of the exhaust; this will cause backpressure.

now here's something about backpressure.

backpressure in a pipe occurs when there is a restriction of flow. If more air goes into the engine than the exhaust can expel, then restriction occurs. you need to have enough flow capacity in your exhaust system. however, the purpose of the exhaust system is to evacuate gases from the combustion chamber as quick and efficient as possible. therefore gas velocity is also important. the higher the gas velocity, the quicker the gases will move through the pipe.
so...your exhaust system needs to have enough flow capacity (big pipe) to ensure that there is less restriction to airflow yet have a high gas velocity (small pipe) to expel the gases quicker. you also want the least amount of restrictions in your exhaust system as possible. gutting your cat creates turbulance in your exhaust and slows the gases.
there's a little more to backpressure though...after your combustion process, the exhaust valve is opened and the gases exit the chamber. at this time, there is a period when the exhaust valve and the intake valve are both opened. this is known as the overlap period. high velocity exhaust has more overlap while low velocity has less overlap.
lets first look at the low velocity with less overlap. at low RPM, you will have lost the least amount of intake compression due to overlap. this means you will have more torque at low RPM. but at higher RPM, more exhaust gases will be left in the chamber and the motor becomes less efficient.
next is a system with a high velocity exhaust and more overlap. at low RPM, there is sufficient time to suck the intake charge right out of the cylinder, which will generate less torque. also your O2 sensor might read a rich condition in this case. but at higher RPM, the high velocity sucks in more intake charge and the exhaust valve closes much quicker, making the engine more efficient at higher RPM.

so.....a "smaller pipe" will result in a lower flow capacity and higher gas velocity, less efficient combustion at low RPM and more efficient combustion at high rpm
a "bigger pipe" will result in higher flow capacity and a lower gas velocity, more efficient combustion at low RPM and less effiecient combustion at high rpm

 

you've have this much information and you've only made 4 posts in over a year?????!!! dude, keep talking!!

 

that was great, you should make a seperate thread for that so everyone can do a little learning! thanks lots

 

Backpressure is an explanation that's based on most people's understanding of steady incompressible flow. Like in a garden hose. But the exhaust doesn't flow continuously, it pulses. Not only that, the cylinder pressure when the exhaust valve opens is way higher than the exhaust manifold pressure, so there's a sharp pulse. In the manifold & A-pipe it's sort of an acoustics problem, where the pressure wave reflects back from different features. Like where the tubes join in the manifold or A-pipe, the wave travels back up to another cylinder. Just in time to help suck the exhaust out from there.

Scavenging would work best with the lowest exhaust port pressure that you can get. Thing is, with these reflected pulses, that's lower than what you'd measure if you put a simple pressure gauge in your cat.

If you only ever operated the engine at one rpm, it'd be easy. You want the lowest backpressure you can get, then choose the exhaust manifold runner length based on that rpm.

But speed of sound changes with temperature, & exhaust temperature changes with pressure. Backpressure can broaden the torque peak that's caused by these reflected pulses.

 

Along with the info from typhoonk, the temperature variations across the whole system play into it too. As the exhaust cools, it gets denser and tends to slow. It is the reheated in the cat due to the reaction which speeds things up once again and cools down again throughout the remaining pipe. Along with the pulsing caused by the valves, this additional pulsing causes increases and decreases in pressure along the flow path. This in turn creates turbulance causing more friction in the pipe. This friction caused turbulence also slows the flow. The slowed flow in the cooler sections gets hit from behind by the faster moving hot gases causing an increase in pressure(backpressure). Isn't fluid dynamics fun.

 

It's kind of funny but I had this same question when I first started.

Dual exhaust (2 mufflers and piping) will do nothing but decrease performance on your already slow car.