Not trying to be insulting or anything, but is it possible you like the sound so much that you are "sticking your foot in it" more than usual? A mod such as you did should have had little to no effect on fuel mileage.

 

lol, the first couple of weeks i was a little heavy on the foot, but I want to get a real feel for what its doing, so I have really been very easy on it. My biggest concern is the loss of power. this weekend we took a trip up north, no load, no towing. on minor hills it would drop into passing gear just to get over it, my f150 5.4 has never done that on the same trip, even with light load in the box. I only have 3,000 miles on my 2012 f250 6.2, but something just isnt right since i put that y pipe on.

 

I do like the sound of a big V8 laboring through the gears,….yes I do, but when you are lucky to get 13 mpg and lose 2 of that just to the hear the rapacity of the exhaust,…..I think I will pass until it is figured out.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>

 

Your loss of power is not due to too little back pressure; keep in mind you still have a catalytic converter in each head pipe. I'm wondering if something got stuck in a pipe during installation, since you also report a LOSS in power, which should not be the case! Even with the loss of mileage, you should still have gained power. Something is definitely wrong here....

 

Your loss of fuel mileage is understandable with the loss of power. In my opinion, your exhaust system is too big. You lost exhaust velocity which enables the scavaging effect. Your engine is using power just to pump out the exhaust gases, thus eating up power and fuel.

You said this happenened when you added the dynomax y pipe to your mbrp system. The muffler is what is determining the performance and what size and type of pipe to use. Perhaps mrbp left the stock resonator because it worked well with their muffler design. I would bet they tried eliminating the big stock resonator, but their testing proved (just as your experience has) it would be a performance loss, so rather than redesign the muffler to work with out the stock resonator, they left it and took whatever performance gains came from just using the muffler.

On the other hand the big stock resonator hindered the performance gain potential of the Dynomax muffler, so rather than redesigning the muffler to work with the stock resonator, they eliminated it. It appears testing the Dynomax muffer with new piping eliminating the resonator produced better performance gains rather than leaving it.

Your experience proves that today's computer controlled engines are very finely tuned machines and any slight change can have noticeable effects on performance - good or bad. In my opinion, it is best to use a system that has been tested rather than going out on your own and putting one together.

 

If the Y-pipe would have been sized right, there would have been no problems. After looking into it(and Dynomax's website), I found that the pipe ends at 4" dia., which I feel is too big. 3-1/2", while sounding like not much of a difference, is actually quite different in area @ 9.62 sq. in. while the 4" pipe is 12.57 sq. in., enough to disrupt the flow velocity(which is really what you need to maintain) to a degree that low-end torque plummets, causing the need for more throttle (along with more fuel...) to do the same job. Even though the owner did neck the pipe down to the 3" orig. pipe size, the flow was probably disrupted enough to cause the problems experienced.
Sounds like a lot of theorizing, but I THINK I got it right.........







'

 

I think you got it right too Gary, but what is the best solution for his ptoblem(s)

 

That is what I was thinking all along, From where the 2, 2-3/4" pipes dump into the 4", the 4" pipe runs 40" before it reduces to the 3" pipe. My question now is if I shorten the 4" pipe....what would be a good length to get the back pressure i need, but still give it the flow. I'm tempted to just reduce it after about 6" and see how that works. its got the flow thru muffler so nothing else would disrupt it. Thank you for all your input by the way!!

 

It's not back pressure you're after; it's flow velocity. What you might try is to cut the Y-pipe RIGHT behind where the two headpipes join, and weld the reducer to that and continue the system with the 3" pipe to the mufffler. Actual backpressure should NOT increase; flow velocity WILL be maintained in a more continuous manner thruout the system, or at least that is my "theory". Try it; it can only help.

 

ok, I will be attempting this on sunday, I will keep you posted.

 

Just keep in mind to keep the flow path smooth; you want it to transition from the headpipes into a smooth joint that transitions into the 3" pipe to the muffler, minimizing the large "collector effect" that would slow the flow, or add turbulence. This, if done right, SHOULD be an improvement over the stock resonator in power and mileage. The operative word being "should"........
Good luck!

 

it's sunday ..I think. Let's hear how that 'theory' worked out?

My question is the dynomax site advertises 12 HP 14 ft/lbs of power gained with the system;so low-end is sacrificed for more power at top end?

 

It is, and I agree; I too am curious!
I think you make a good point- I'd be curious to see the dyno chart to see if, indeed, it's all at the top end, while losing some power AND efficiency at the low-to-mid range. If Dynomax claims gains thruout the range, they must do some kinda magic in the muffler because their system is 4" from Y-pipe to the end of the tailpipe.

 

another thing we have to consider is the stock tune on our new 6.2 2valves is only tuned,at WOT, for the plate to open 100% at 4500 RPM. they are designed this way from ford.

Another question about the tranny shifting from the dude,for sure not an exhaust issue. think we all experience this. I just hit 3000 miles yesterday and these transmissions are of new design ; CPUs recognize different gears at different speeds.. not all sure how its programmed or how it works ..somethin to look into tho.. sure we've all caught ourselves in 6th gear at 30MPH ! drives me a lil crazy too , my 2010 and 2001 always shifted at the same speed and throttle position! these things just love to shift.

 

I think these trannies are better than ever at being in exactly the right gear at the right time, and that may not always cooincide with what YOU think that "right" gear is at the time. We've come a loooong way, baby!