Okay, here goes my 2 cents worth. Everybody wants to change your exhaust for all this magical power, then they complain the truck loses its low end grunt. Ive been doing custom exhaust for 15 years now- on everything you can imagine, and Ive heard this before. Lets look at what you are driving, a 4500 plus pound vehicle with an engine designed to move it, and a heavy load down the highway. Most Triton v-8s have a peak hp. and torque curve down low, usually3500 rpms or less. This is why most of us bought a Ford truck, remember? Changing an exhaust system ALTERS THE HORSEPOWER AND TORQUE BAND. Its that simple. If your tuck peaked at 3000 rpm, for example, true duals are gonna move that peak up sometimes 1000 rpm, even more. Just think about what you are trying to achieve: more hp. and torque. Totally possible, but you have to change operating perameters to do it. Is one way better than the rest? Hmm, I have done nearly every conceivable configuration on a 97-up f-150, and my happiest customers are the people who just change a muffler, or muffler and tailpipe. Brand? Your call, depending on the noise you want. I have flowbench tested everybodys mufflers myself, and compared to a stock unit, ANYBODYS is an improvement in flow. The factory muffler is your bad guy here, dualing out after the cats will cut the bottom end torque, I promise. Sometimes you wont notice on a lighter truck with a 5.4, but if were talking 4x4, youre gonna notice. Research this stuff yourself, grab a flowmaster catalog and see what they recommend for an engine your size, guarantee it isnt a pair of 3 inch tailpipes. In fact, too big a tailpipe cuts power as well. How, atmospheric pressure will fill a large tailpipe between exhaust pulses, so then the engine is working to force that out too! Sounds crazy, but Ive shared a few beers with some exhaust engineers. Theres more to this stuff than a couple tailpipes hanging out the back. Just think about what you want- a good cat-back kit is a decent investment, as long as you are paying attention to what you get. Have the company send ck peaked at 3000 rpm, for example, true duals are gonna move that peak up sometimes 1000 rpm, even more. Just think about what you are trying to achieve: more hp. and torque. Totally possible, but you have to change operating perameters to do it. Is one way better than the rest? Hmm, I have done nearly every conceivable configuration on a 97-up f-150, and my happiest customers are the people who just change a muffler, or muffler and tailpipe. Brand? Your call, depending on the noise you want. I have flowbench tested everybodys mufflers myself, and compared to a stock unit, ANYBODYS is an improvement in flow. The factory muffler is your bad guy here, dualing out after the cats will cut the bottom end torque, I promise. Sometimes you wont notice on a lighter truck with a 5.4, but if were talking 4x4, youre gonna notice. Research this stuff yourself, grab a flowmaster catalog and see what they recommend for an engine your size, guarantee it isnt a pair of 3 inch tailpipes. In fact, too big a tailpipe cuts power as well. How, atmospheric pressure will fill a large tailpipe between exhaust pulses, so then the engine is working to force that out too! Sounds crazy, but Ive shared a few beers with some exhaust engineers. Theres more to this stuff than a couple tailpipes hanging out the back. Just think about what you want- a good cat-back kit is a decent investment, as long as you are paying attention to what you get. Have the company send you a dyno chart- or hunt the net for one. So many say 15, 20 horsepower gain, etc, etc. Ok, but where, 1500 rpm? 2500 rpm? Do you drive around in second gear turning 3000 rpm all day just to feel that 15 hp? Probably not. Ford engineers arent stupid, sure they have cost considerations, and NVH isuues to work with, but the bottom line is that system that came on your truck is pretty optimized for horsepower and torque where most people drive. Look under a 2004, still a single 2.5 inch tailpipe, even with 300 hp. Anyway, Im rambling now, but after doing this all these years and having so many people call the next day complaining how much power they lost, it gets old .
My advice and 2 cents worth is to just change the muffler, if you must change anything. Any Flowmaster, any Dynomax, any spintech, whatever, they all help the higher rpm flow without killing low end torque. As far as bang for the buck, another muffler which flows great and sounds like a flowmaster is the cherry bomb Vortex. These used to be junk, because the old design would come apart at the welds. They are redesigned now and built like a flowmaster with the baffles placed in a different configuration. Noise is somewhere between a 40 and 70 series. Anyway, thats my vent. Hope I helped somebody.

 

wow you got me answered! except for this one. i got my flowmaster second hand with 3 inch in's and out's. i run 2.5. any suggsetions?

 

Good post, but half of it is repeated. You might want to edit out the duplicate.

 

I don't agree with everything (heck, I don't have the attention span to read such a long-winded repetitive paragraph). THere is soem evidence (at least to me) that you don't fully understand what you are talking about either. Horsepower is a fucntion of torque over time which means it is relative to torqu and engine speed. No production gasoline engine I can think of has its peak horsepower below 3000rpm. Anyway, there have been dyno proven exhaust mods than increase torque from 2500RPM and up. Chassis dyno testing below that is impossible/unreliable with automatic trannies in F-150's. Butt dynos give favorable results in the 1500-2500 range by many people who modify their exhaust too. BTW, the Superduty with 5.4L comes with a 3" exhaust. Although the flywheel power ratings are the same as the F-150 with its 2.5" exhaust, there may be a reason why Ford did that (other than reducing build complexity).

While your 15years of custom exhaust work is nice, I doubt you are the one who takes the vehicles to the dynos to confirm/deny the results. Most manufacurters of systems (cat-back) dyno tune them before releasing to the public. Not all aftermarket exhausts are bunk or only move the powerband.

 

excellent post but i have a couple questions, if you dont mind answering them:

I cut out the stock muffler and putin a Y pipe with dual tips. (stock cats and Y pipe by the motor) If i want to put on hi flo cats, how much louder would it be? Should i keep the same tailpipes -both- Y pipes, or should i run true duals out the back, with 2.25" or 2.5" pipe? Would true duals be louder than non-true duals?
By the way, im running a pretty much stock 98 4.6. Thanks, and great article

 

91SMD,

I appreciate your candor. I understand exactly what you mean. I previously had a 96 Thunderbird LX with the 4.6L V8. I removed the stock mufflers(resonators) that were mounted directly below the bumper. I then removed the exhaust from the cats back and went with 2.5" pipe and a single glasspack muffler. From the muffler I went with 2.5" pipe that 'Y' ed out from there into 2 single 2" stainless steel tailpipes. The car sounded great, but I did notice a loss in bottom end torque. I have recently purchased a 00' XLT extended cab Flareside with the 4.6L. I was looking to change the exhaust to give it some note. I was thinking about leaving everything alone, except installin a Flomaster single in-dual outlet muffler with tips. Do you think this would cause me the same loss I noticed with my T-bird. I'm not increasing the pipe size, just adding a different muffler with dual tailpipes.

Good idea or not? or should I just put on a single in - single out and put on stainless tip for jewellery??

 

I agree with the fact that bigger pipes do cause the loss of some low end torque, otherwise the Detroit 3 would have every truck outfitted with F-350 pwrstrk exhaust! And no most engines don't peak hp at 3000rpm's, but they come close on the torque side. And most people buy trucks to tow/pull/haul things. And it's no secret that torque get's you going and hp keeps you going. So you want your peak torque as low as you can get it, but in good hp range.

 

Have had some major mods done to my engine & trans. Still don't have it back but only dynoed at 303 HP, which was very disappointing. I have heard that you add anywhere from 20% to 28% to this figure which would bring it closer to 375 to 380 HP. I am running JBA shorty headers and Flowmaster 50 muffler. The shop pulled the 02 sensors and it increased 47 HP on the dyno with the same set up. Ordered Dynotech Long Tube Headers and the shop is going to make some special X pipes and wants to still use Flowmaster mufflers. Was told this will decrease the boost, but should increase the HP considerably. Remember this is all being dynoed as it is tested. Anxious to see what the results will be myself.

 

The factory PSD exhaust uses the same as the 5.4L in the same SuperDuty truck. The 5.4L in the SD is the same as the LD. Compromise is why the F-150's all have 2.5" exhausts.

 

So you're saying the f150 SD and LD have the same exhaust as an F250 PSD?

 

No, I'll clarify. Same engine, different exhaust. All Super Duties have a 3" exhaust which joins after the cats, regardless of the motor. 5.4L V8, 6.8L V10, or 7.3/6.0L PSD, all 3" from the factory. All LD (F-150 and F-250 LD) have 2.5" joined after the cats. The 5.4L used in the F-150 is the same as the 5.4L used in the SD (well, 2004 3V is different). If Ford thought there would be a torque loss using 3" on the 5.4L in SuperDuty applciation, they would not have used it.

 

so as to answer my question which got lost in the mix, will i be safe to use the 3inch flowmaster and just use a 2.5 to 3 inch couplings to make up for the size difference?. OR, should i just use 3inch pipe out the back of the muffler all the way out to the tip, which is 3 inches as well?

 

It really doesn't matter what you use because the restriction is the OEM y-pipe which takes two 2.5" into a single 2.5" ( or smaller - poor design) tube. You'll still have the 2.5" from the y-pipe to the front of the muffler so having 3" after doesn't matter much.

 

so APT, what is your inputs? i heard going three all the way might be better but now thinking about it, i would have to retro fit the cat and all that jazz! maybe not, anyway, do you think that it will affect any pony power? thanks for getrting back with me on that!

 

IMO, just have a shop throw your 3" muffler on in place of the OEM and see how it sounds. $25-50 is all you should pay to have that done.

Also IMHO, this is what the optimal exhaust setup is for near-stock naturally aspirated 5.4L's. Replace the OEM y-pipe with a 90degree mandrel bent elbow. Then use a better designed y-pipe, dual 2.5" in and single 3" out. Then 3" mandrel tubing bent out to the tip. Pick the muffler of your choice for sound level control and tone. I recommend straight throw designs over baffles.