Dual exhaust

[rexload]

I was just thinking.... why don't people run dual exhaust on highly modded 4cyl engines?

Most high horsepower N/A and turbo guys run 2.5" or 3" exhaust on the street. But why not run dual 1.5"?

My logic is that it will not be any more restrictive than a single 3" pipe... but at the same time it will help velocity, which in turn should = better response for a street car.

I see a "dual exhaust" thread every once in a while.... and most people say that "it's pointless" on a 4 cyl... To me it seems like it would actually be a good idea for a street car. Some 4cyl cars come with dual exhaust from factory, I mean they can't be doing it just for looks, right?

Thoughts?

[93blackcb7]

the only one it looks good on is like the s2ki others with dual exhaust looks dumb

[rexload]

Whether it looks dumb or not is in the eye of the beholder. Not to mention that it doesn't have to be visible (I don't even run the exhaust all the way back on my cars, no point in it)

I was asking more about the functionality.

[prNonVtec4u]

if functionality is the reason... then drop a v8 and run true duals. if an i4 is there... 2.5" - 3" does the job flawlessly.

[GenDBlade]

it would really only be worth it if you run one exhaust per 2cyl.

[Shag Wagon]

Uh oh somebody has some ricer tendencies!!!!! lmao jk. I knew a guy that had a CB who had duals coming out of a flowmaster made for a V8. With the fact he had no cat it sounded like shit and looked like total hell. Something along the lines of 2 pebbles rattling around in a coffee can.

[92accordcb7ex]

i just stick with my dual tipped muffler. the space for it usually isnt right so one side is where it should be and the other is usually hanging lower and looks like complete ass.

[bcjammerx]

IS there a stock TRUE dual exhaust 4 cyl...even 6cyl? The only ones I've seen were always one pipe all the way back then it splits right at the back end...so not dual. Doesn't mean they don't exist...I just haven't seen any.

I think you would spend more time getting two 1.5" pipes to fit under the car than one 3" pipe. Also I'm sure there is some fluid dynamics reason why that wouldn't work...maybe not...something to do with exhaust pulses, pipe cross section...interesting stuff...I just haven't researched it enough.

Like I have this idea of getting a > 3" exhaust but making it mostly oval instead of round so it would fit and allow for a lower ride and no scraping

However I'm pretty sure the flow velocity has something to do with the cross section of the pipe...larger cross section would have better "flow" (I use flow loosely here as a generic term that encompasses several things)

interesting idea though...peaked my curiosity

[sulimed]

why add the weight.

[WilliamW]

Pros for dual exhaust:
Look
cheaper pipe / foot cost


Con's for dual exhaust:
Double the pipe needed
requires 2 mufflers
lots of fabricating to get both fitted properly
weight
exhaust pulse incorrect for "system"

The key is NO back pressure. That's for turbo applications AND N/A. It just happens that when you decrease the diameter of the pipe, the exhaust gas has a higher velocity. Velocity can help your exhaust by adding a scavenger effect to your cylinders. However, it doesn't mean you can run .75 " pipe and have a crazy scavenger effect. You want to have as little back pressure as you can while still maintaining a scavenger effect that will benefit your HP / torque numbers.

There are some really good articles out there on how to tune an exhaust system. I'll have to see if I can dig them up. But performance wise, (true) dual exhaust is pointless and would only hurt you.

[bcjammerx]

all that was the stuff I was alluding too

[WilliamW]

Hey, I found it. It came off a DSM forum. Hope you enjoy.

http://www.dsmtuners.com/forums/freq...kpressure.html

[rexload]

Pros for dual exhaust:
Look
cheaper pipe / foot cost


Con's for dual exhaust:
Double the pipe needed
requires 2 mufflers
lots of fabricating to get both fitted properly
weight
exhaust pulse incorrect for "system"

The key is NO back pressure. That's for turbo applications AND N/A. It just happens that when you decrease the diameter of the pipe, the exhaust gas has a higher velocity. Velocity can help your exhaust by adding a scavenger effect to your cylinders. However, it doesn't mean you can run .75 " pipe and have a crazy scavenger effect. You want to have as little back pressure as you can while still maintaining a scavenger effect that will benefit your HP / torque numbers.

There are some really good articles out there on how to tune an exhaust system. I'll have to see if I can dig them up. But performance wise, (true) dual exhaust is pointless and would only hurt you.

Yes, that is exactly what I was saying.

Smaller diameter pipe = higher velocity = better throttle response when driving on the street.

It seems that you are saying running dual exhaust would increase back pressure. But why? Running two 1.5" pipes would be the same diameter as a 3" pipe which is plenty for most street builds.

Running two mufflers is needed on an N/A car. But a lot of turbo setups are VERY quiet with just a short resonator, and sometimes with no mufflers at all.

Also, theoretically it should be possible to run two pipes together, that way there would be very little fabrication.



Every single time I put an aftermarket exhaust on a car, I notice right away the loss of throttle response below 3K rpm. A lot of people say it's not that much and I want to believe that BUT it's simply not true. You lose a LOT of response.

[WilliamW]

From what I understand is if you run smaller diameter pipes, the velocity is increased. The down side is that back pressure is also made. If you want to make two exhaust pipes and run dual exhaust, your going to have to use small pipes like 1 inch to keep the velocity you want.

Think of it like this, you can run a 2.25 exhaust system or even a 2" system and have a scavenging effect across all 4 cylinders. If you only want to run two cylinders through one system then you'll have to decrease the size by 1/2 and run 1" pipe twice. It would be better for the engine if you ran all the cylinders together and used a smaller diameter pipe like 2" or something rather than two separate pipes and changing the effects on the engine.

I know people like bisi make headers and what not with a science so that the pulses help the engine breath. It just seems like a lot of work and research and science (figuring out which cylinders to group together and where) that can be avoided with technology that's already out there that's been proven to work. If dual exhaust had an obvious plus side to it that a single exhaust system didn't have, I would like to believe that we would all be running dual exhaust.

If we take the same dual exhaust theory and apply it to turbochargers, we could run two smaller 14b turbo chargers on a four cylinder. Would it work the same as a single T3/T4 turbo? Again I wouldn't think so just because the exhaust gas pulses are messed up.

[AccordFan_18]

Hey, I found it. It came off a DSM forum. Hope you enjoy.

http://www.dsmtuners.com/forums/freq...kpressure.html

this is a really good article