Originally Posted by JimAllen

In fact, I did some dyno-testing on my '05 F-150HD, stock pipes with a 2.5-inch straight thru muffler added vs a full 3-inch cat back. The muffler change gave 3/4 the performance gain of the full system for about a third the cost. Stick a nice tip on the stock tailpipe for window dressing and you get a great performance/dollar ratio.

Originally Posted by Trilandun

Jim,

Thanks for all the great info in this thread

Do you have an example of a straight through muffler that won't add too much roar such as a MagnaFlow?

Also, did you leave the stock cats in for your testing?

Thanks!

Originally Posted by Yogi.kudos

Ok so when I was taking off my old side steps I took a look at my muffler and what I thought was a Super 44 is a knock off, probably a Flopro. Throwing that thing out and getting either some bullets or 14" Magnapacks. I live in CA so I will be keeping the stock cats.
I love 4.6 Punishers (with stock cats), mblouir, and rudaay's (Youtube name, idk his name on here if hes a member) exhaust. I have a few questions since they are a little different then what I would have.
4.6Punishers is my favorite but I was wondering how much of a difference there would be with a 5.4 and x pipe? I know that the 5.4s are a little bit quieter.
Do the high-flows just make it louder or do they change the tone too? I love the sound of mblouirs and if its a little quieter thats ok.
Any performance differences between Magnapacks an bullets?

I actually like drone so theres no problem there and I know its gunna be loud inside.

I won't be getting this done for a while, but I will be ordering my Gryphon this week. I would have to have the custom tunes rewritten if I went from single to dual muffler correct? By the time hes done with the tunes I should have my exhaust done

Originally Posted by DarrenWS6

Hi-flow cats increase the flowpath a bit enhancing performance, and with no resonation inside the cats it lets out a much louder volume.
And in Mblouir's video, he has hi-flow cats, just mentioning if you didn't know that, otherwse the other guys did have stock cats in those videos.

Originally Posted by Yogi.kudos

Thanks. I was listening to the difference between the hiflows and stock on Punisher's videos, but didnt really notice much. I relistened to them more closely and now I can definitely tell the difference.

At this point I think I'm leaning more towards the Magnapacks, but I got a while to decide.

I drive about 50/50 highway/city. True duals are better for highway and WOT(correct?) so would it be better for me to go 2.25" piping. Don't tow often, but if I did it wouldn't be more then 5000lbs.

Originally Posted by JimAllen

Phil:In my experience, what you get from an exhaust change depends on how good or bad the system you are replacing is versus the system you are replacing it with.

I was very surprised that the the headers and true duals on the Tahoe we tested didn't do more on the stock tune, however when the truck was custom tuned later, of course, it was uncorked and didn't lose anything due to exhaust restriction. It had primary header tubes that were large (1-3/4 IIRC) and dual 2.5 inch pipes.

You made some interesting points, the first being that the 5.4L vans have OE 3-inch exhaust systems. The F-150s have only 2.5-inch systems and I feel hosed!

Second interesting thing is that the Magnaflow system uses dual 2.25s. That's about the equivalent amount of "raw" flow as a 3-inch system but the smaller pipes will help a little more with velocity at low speeds, so it sounds like a well designed system. Many of the dual setups are 2.5 or 3-inch systems which, IMO, are too large for a stockish truck. How do I know about the flow? Here are the flow rates for different sizes of pipes (6-foot lengths) gleaned from the engineering department at Walker muffler.

5-inch: 2200 cfm +
4-inch: 1800 cfm
3.5-inch: 1400 cfm
3-inch: 1200 cfm
2.5-inch: 900 cfm
2.25-inch: 600 cfm


The only exhaust formula I've found that translates well to the "home user"
is this one:

exhaust temp in Fahrenheit + 460
___________________________ x intake airflow cfm = exhaust flow
540

This will give you a static flow rate, which you can compare to the published flow rates of mufflers. Problem is, there are a whole lot of variables. It's difficult to find the flow rates for pipes, for example. I finally got some for length of straight pipe (you saw them above), but they don't account for bends which change the flow rate.

Flow also changes according to exhaust temp. My truck cruises at highway speeds at around 1250 degrees EGT at the exhaust manifolds. At WOT I can see 2000 easy. If you run the calc above for both those temps, you will see greatly different flow numbers.

The other thing, as you alluded, is velocity, which is part of the equation. Given the same volume, smaller pipes have more velocity than larger. As you know, velocity downstream creates inertia, just like a siphon. That delivers a result commonly known as "scavenging" which helps clear the cylinder better. The problem is that it's relative to flow versus pipe sizes, so with every given setup, it's going to be strongest in a certain rpm range. With a big pipe, it will be stronger at the higher rpms. With a smaller pipe, it's stronger at lower speeds. If the pipe is too small, it won't have the flow at the high speed WOT and that reduces upper end power.

But here's the kicker to me! From what I've seen and read, the loss of low rpm performance with with a system that's too large (within reason) is less than the higher rpm loss, or midrange loss, of a system is too small. I think that's why you see so many aftermarket systems that are a little larger for more or less stock trucks than they need to be.

On the other hand, fuel economy is better the closer you can optimize that scavenging to the rpm range in which the truck most often operates. That means smaller pipes and in fooling around with various calculations, the 2.5 diameter is about right in that regard for the 5.4L. The stock muffler is pretty restrictive, but that's easy to change out. Below are the dyno tests results in testing the two systems I mention in the earlier post, plus fuel economy.

Test Data: 2005 Ford F-150 XL 4x4
5.4L 3V V8, automatic, 8,200 GVWR, 4.10:1 axle ratio

Performance Test Data

Condition 0-60(sec.) RWP (hp) RWT(lbs-ft)
(best/av.) (best/av.) (best/av.)

Stock 8.31/8.43 206.6/202.6 252.5/251.5
Muffler Only 8.10/8.15 215.6/215.1 276.4/266.9
Catback 7.89/7.91 224.8/222.6 283.7/278.3


Fuel Economy Test Data

Condition Steady 55 Steady 65 Steady 70 Overall
MPG MPG MPG Average MPG (1)

Stock 17.0 16.5 16.3 15.2
Muffler Only 17.2 16.7 16.5 15.7
Cat Back 17.3 16.7 16.6 15.7

Notes:
1) Mixed situations, approx. 35 percent city, 65 percent rural roads at 60 mph.


In any case, I'm going to have to give that Magnaflow 2.25 true dual system a look! It sound like a way to have a little of both... velocity and high flow.

Sorry, I can't get the chart to stay formatted when I post it.