I putting a new exhaust system on my 04 4.0 and I want the dual exhaust, but ive heard that i'll lose low end power. Whats the reasoning behind this? Any body experienced this lose that i'm talkin about?

 

I don't see where dual exhaust would have any real effect on your torque.

 

By "new exhaust system" are you referring to a complete system or the more common cat-back systems? A complete system with tuned headers into a true dual system will provide more power across the band provided the system is properly engineered. The cat-back starts at the muffler and will increase your performance slightly provided you do not go too big on the tail pipes. The reasoning is that your engine is an air pump and air-in/air-out is a major part not only of power output, but where that power is delivered. The loss you mention was probably caused by the loss of scavenging caused by using pipes that were too big ..... bigger is not always better.

 

To expand on this, some engines by design need some back pressure to deliver their best performance. Overly reducing back pressure can result in performance reductions. Think overlap on the cam, think about backpressure, think intake utilizing that backpressure, and you'll realize what's on my mind.

 

Backpressure is cause by a restriction. You do not want backpressure. Backpressure causes burned exhaust gasses to backup into the combustion chamber. Burned gasses in the combustion chamber do not increase power. The changing of pipe size causes a change in the velocity of the gasses, which has an effect on where the power band is located. jd

 

Yes, but backpressure is necessary to some extent. Not that much at all, but it is necessary. It's more for diesels than anything. However, the larger pipes reduce the scavenging of exhaust gases, as well as putting two of the same size pipes (ie having a stock 2" single exhaust and putting a 4" single pipe or two 2" pipes). I know when I put an aftermarket muffler (no tailpipes, just a muffler) on my truck, I can't rev past 4000 rpms, but when I'm accelerating, I have no problem getting to 6000rpms at all. It has to do with the scavenging of gases.

However, the aftermarket cat back kits are designed to perform, and they will give you more power all accross the rpm band.

 

For what reason?????????

Changing pipe size may reduce "scavenging" at a certain rpm, but may increase it at another. It is all relative. jd

 

I run a pipe from the cat to the muffler and nothing afterwords other than the turndowns I made. I didn't feel any loss of power, nor any gain. With or without tailpipes, seemed the same other than sound. (sound much better with no tailpipes)

I highly doubt you'd lose torque, since most of the manufacturers claim gains.

bigdavesohc, I'm pretty sure something's up with your exhaust, I have no problems going right past 4K, sitting still or under acceleration of any sort.

And I don't believe the exhaust hole is the same with a 4 inch pipe versus two 2 inch pipes...

RP
Zach

 

Nowhere near the same. A=pi rsq. A=pi rsqx2 jd

 

Using that formula I guess they would be the same size, though I sure can't see it by looking at it...hmm. It's been over two months since I've done serious math, so I'm a bit behind lol.

RP
Zach

 

I'm just a hillbilly, so I won't try to get all scientific on you. I will tell you that I put a gibson dual sport catback on my 4.0 ranger, the tone was good, and I didn't notice any decrease in lowend. The kit uses 2.5" pipe to the muffler, with two 2" pipes exiting behind the passenger side rear tire.

 

I'd say bigdave filled in what I somehow didn't clearly explain and the point that was being made. Now if someone thinks that installing a 4" dia exhaust system is the way to go don't let me be the one to try to talk 'em out of it. I'll be delighted to sit on the sidelines and watch .

 

I read an article awhile back that said no amount back presure is good, however the effect that back presure produces is needed, depending on application. So it's the effect, not the back presure it's self. Billy, your an engineer, do you know what they meant ? Cause they lost me.

 

So...from what I understand, and this is purely skeptical and a product of my own mind.

To produce zero backpressure, the area of the inside of the pipe at the smallest point must be equal to or greater than the combined area of the most exhaust valves that would be open at one point. Right?

hijack/ my friend wants to cut the muffler off his Chrysler Sebring. Anybody wanna take a guess at what it will sound like /hijack

RP
Zach

 

From what I've read over the years (multiple articles), some backpressure will, as expected, result in a pressure during the exhaust stroke that is higher that it would be if the exhaust were made from something like 6" pipe (deliberate attempt to have the least possible backpressure). Due to the overlap on the cam, this pressure during the exhaust cycle forces gas/air into the cyl at a more rapid rate, thus producing what designers are trying to achieve. I'd say that would be the best blend of performance, mileage, and driveability. All these things like the cam, combustion chamber, mechanical/effective compression ratio, backpressure, pipe size, intake, etc etc are engineered as a package deal; because auto manufactures spend millions of $ doing this I wouldn't expect them to be very excited about devulging their work. While such work could benefit aftermarket manufactures, it could also benefit a competitor. On the other hand, I could also see an aftermarket manufacturer paying for some needed information and signing a confidentiality agreement (I've done that one b4). Sure would be nice to have a member here that worked for an aftermarket manufacturer confirm this one. While it is true that I am a ME, my emphasis was not on combustion technology. That is a sciencey subject that was, IMO, something that I would use at an employer in some large city. Said another way, limited employment market. I don't like big cities too much, I like smaller ones to no city at all (which is on the horizon).