If you're planning on doing heavy performance down the road, I cant really suggest going single or dual to start.

Ask any old pro to engines, exhaust should really be the last thing you do. It comes the way it does stock for a reason. Now, with the old 5.0s it was so it would pass California emissions.. this isnt the case anymore. I would do everything to the engine I was possibly going to do, then decide on the exhaust based on that... not try to mold and tune the engine to the exhaust.. especially when they are so dang dependant on backpressure. Does this make sense? Its like trying to find a bottle rocket to fit the pipe you're going to stick it in... not the pipe to fit the bottle rocket you already have in hand.

 

How bout them mustang 4.6's made for cali with 6 cat converters lol. Ive seen a few of those through my shop. Those are the ones where they gain 35rwhp from headers, midpipe, and exhaust. But those days are long gone. Most of the GT owners arent seeing more than 6-10hp gains from exhaust, but thats because for did an incredible job on the mustang gt exhaust.

 

It's strange. I've been looking at the possibility of dualing out my V6 exhaust with the Flowmaster 40's (they seem to be the most widely distributed muffler for the '05s here in Houston) and was wondering about the vaibility of an X-pipe. There's an epic thread over at another major Mustang board (won't say which) where there's all sorts of people swearing that you HAVE to have an X-pipe, whereas true duals (2 straight pipes from the cats to the mufflers) would kill your HP (something about your engine not being able to breathe efficently).

However, 3 different shops here in town have said that the X-pipe wouldn't make any difference. When I brought up the arguments for it, one of them even said, "Well, the people on the internet will say whatever they want to, doesn't mean it's right." So, basically, I'm stuck between the "experts" who install the systems and the online people who seem to have some very well informed assertions of their own.

Any ideas which way I should go? I plan on having this car for a LOOONG time and make it my "mod" car, and don't want to do something that might screw it up.

 

I tend to trust experts over well informed internet experts. Especially if the expert has no reason to lie. If a muffler shop says you don't need, you probably don't need it. If anything, they would want to sell you something if anything. If just an x-pipe gets you more than 3 peak HP on a 4.0L, the end of the world is coming. I read a lot, and I haven't seen a dyno that supports massive HP from just an x-pipe. My opinion is just my opinion. I don't want to sound like an internet expert. If those other guys have a dyno, a good dyno, I'll change my opinion. Even magazines will try to bullpoo readers, so I really look at the details. Did they change just the x-pipe or x-pipe and cats? MM & FF will do a article next month, I'd take a look and see what they say. Look for the Mangaflow thread, they sell this stuff and still recommended against an x-pipe for the 4.0l. Dr. Gas invented the x-pipe so I checked out his site. An x-pipe was a .5 percent increase on a Winston Cup engine. Maybe 1 percent on a stock engine?

 

I'd ask to see those "experts" degree in mufflerology.

They are probably correct about the X, but I wonder if they really know why.

There has been endless discussions of X vs H on Mustang boards for years.
The bottom line is that EVERY proper A - B dyno test of a Forrd V8 has come out with a good X pipe delivering the highest HP and the highest torque over the entire RPM range (not peak, area under the curve, which is more important).

The reason why the X pipe works better on a Ford V8 is that the firng order of the 4.6 is 1-3-7-2-6-5-4-8
This means that 2 cylinders on the same bank fire in succession, which can "over load" one of the pipes. H pipes only provide pressure balancing at low RPM, they do next to nothing (other than effect the sound) >3,000 RPM. X pipes balance exhaust flow better over the entire RPM range.

Now lets look at the Ford 4.0 V6
Its firing order is 1-4-2-5-3-6
So every consectutive cylinder fire is from the opposite cylinder bank.
This means the exhaust flow will be balanced no mattter whether you have NO cross pipe, an H pipe or an X pipe. The primary effect of NO, H or X will have will be on the exhuast sound NOT the HP or torque.

This talk about lowering back pressure reducing HP & torque is complete crap.
If this was true, gutting / removing the cats would cause you to loose HP & torque as cats add back pressure. Ask yourself why people say gutting cats increases HP but adding dual exhaust reduces HP? Doesn't make any sense does it? Of course it doesn't.

I say put duals on your V6, but understand that they will mainly improve HP at the top of the RPM range and affect the sound. HP & torque at lower RPM will be pretty much unaffected.

 

That was easily the best and most informative post I have ever seen on an x-pipe. My only question, are you saying you can never oversize (too big) your exhaust system? From what I've read, you can oversize the exhaust system, this kills low end torque. If your dual exhaust is 2.5" plus, its probably too big for a 4.0L and will hurt you down low.

 

1.) The Cats have an upstream and a downstream sensor (two sides; four total). If you gut the Cats, the sensors may cause a reduction in power because of unexpected values on the sensors. I suspect that optimum fuel ratio could be lost, reducing horsepower. A Cat eliminator plug is available; however, I don't know how well it functions.
2.) Reduced backpressure might allow a very slight loss of fresh fuel charge during the period of valve overlap, but I doubt that it would be noticeable.
3.) Two cycle engines on Motorcycles and Outboard Engines very much do depend upon the correct backpressure in order to properly charge the combustion chamber. As the piston moves down in a two cycle, first the exhaust port is exposed, discharging the high pressure spent gas, and then the intake port is exposed, allowing a fresh charge (previously compressed under the piston) to flush-out the combustion chamber. Banks of three cylinders can have what is called "Loop Charging", wherein one cylinder's exhaust helps pressurize the next cylinder's charging by forcing back into the combustion chamber the fresh charge, which was just starting to escape the combustion chamber.
4.) In my humble opinion, most of the fear of reducing backpressure is from the old stories from the two-cycle world, where backpressure is very much a tuning factor. In four-cycle combustion, pretty much less backpressure is better, providing that your fuel mix stays correct with what your sensors and computer expect.

 

Thank you! I appreciate the straight forward opinions set forth, not the usual hemming and hawing and covering your hiney-ness that sometimes occurs.

Since I'm not very automotively minded, I especially liked V10's breakdown of the firing of a V6. I guess this opens the way to dual it out. Found a small place that'll do it here in town for just the parts cost (and free advertizing by me). As long as they don't screw up cutting a spot for my 2nd muffler, I should be in business.

 

One more quick note on Duals on a V6.
My muffler guy (Randy's in Marysville, WA) advises me that straight duals will be "Poppy" sounding, without a crossover of some sort. He is hooking me up with 2.25" duals, a cross-over, and MagnaFlow mufflers, all for about $400 out the door. Not too bad, right?

 

Thanks for replying. I don't know if backpressure and exhaust velocity are one and the same. Borla and Mangaflow say its important to keep exhaust velocity up, oversized pipes kill that at low rpm. Are you saying this rule only affects older cars?

 

Backpressure is important to anything fuel injected, it wasn't a big deal back then. Exhaust velocity is faster on smaller piping where a hot gas is kept. Bigger pipes would cool down the gases, then require more power to push them out since cool gas doesnt flow as well as a hot gas.

 

Xcal 2 can turn off the O2 sensors. There is the O2 problem remedy.

 

Thanks for replying, so the back pressure issue is important for newer, fuel injected cars? That explains the different in opinions out there. Somebody brought up on carbs will have a different view than somebody brought up with FI. Most of the websites, like Borla and Magnaflow, are probably focused on newer, fuel injected cars.

 

I decided to mock something up to visualise it, but what you are saying would be true if it was a chevy. Ford numbers their cylinders differently. It looks to me the V8 would be more balanced than the V6. Not to mention in a 4 stroke engine the V6 won't always be as balanced as a V8. The X pipe will equalize pressure from both banks to smooth out operation.
Heres what I came up with.

 

These debates have turned into something close to the Ford vs. Chevy debates.. they just go on and on and round and round...

That having said, yes, going with bigger piping will reduce your exhaust velocity and create a popping noise. Flowmaster advises against their 40 series mufflers for this reason alone. Apparently with an Xpipe it eliminates this popping. I havent heard them with an H, but Ive heard people say they're pleased with the sound. I had true dual 40s on, and yes it popped horribly. So I went in and installed resonators. I was brought up on carb theory, and fully believe in the importance of backpressure. If anyone can find a qualified mechanic to tell me differently, and back it up, Id absolutely love to see it (not being sarcastic.)

 

Popping noises. Huh. Well, I can stand the occasional pop but how bad is "popped horribly"? Any other way to get rid of the popping? I could do resonators and one of the installers said he would put on an X "if [I] wanted". I don't want it to sound like some ricer, I want American muscle sound.

 

H-pipe is the traditional muscle car sound, and Im pretty sure it would clear up the popping.

 

Thanks. Found a guy who's recommended by several co-workers. He putting an H-pipe on and dual MagnaFlows at cost because he's been waiting for the opportunity to work on a new Mustang. I took a look at his schedule, and he's bumping like 7 or 8 jobs back to get mine done ASAP. He's even throwing in some 9" stainless steel tips for free (couldn't find the right chrome tips). It's a bit of a drive, but he's coming in almost $80 lower than the next closest estimate.

 

My dealer put duals on V6s for about $450.00. Sounds a little weak to me, plus, when you take you foot off the gas, there is a weak sounding popping noise. The duals on the Lincoln V6 don't make this sound - and, of course, they are OEM duals. what makes the popping sound - sudden change in back pressure? I would like duals on my V6, but I don't want the weak sound! How does changing to a GT muffler help/hinder? Any suggestions?

 

What kind of setup&size for the duals do they use? That alone will have a huge effect in everything.