My 4" Flo Pro exhaust system will arrive soon. I had somebody lined up to install it but it's not going to work out now. How much of a bear is it to get these things installed? 2006 F350 Crew Cab 6.0. Do I need to modify anything to get the 4" downpipe to fit?

 

Is your truck lifted? If it is it's actually not a bad job at all. Especially if you just sawzall the old exhaust system when removing it. Toughest part will be getting up-pipe clamped loosely to the turbo with only one person. But if I can do it (didn't take too long) you can

 

and you may have to dent the pipe or the firewall to get the clearance.

 

If the pipe truly is a 4" and not a 3.5 to 4 then dent the firewall from the get go. mine still rubs when I get the truck articulated at weird angles.

 

When researching this I find people referring to the 2006 and 2007 models having more room for the 4" up pipe than the earlier models. Is this true?

 

No, nothing changed.

 

I have an 06 and it was a B with the 4"

 

So seriously, dent the firewall? No harm?

 

Sorry to bear the news, give it a good dent the first time.
just make sure you give it enough room or face the rub/vibration... there's always the option to remove it and dent it a little more.

but seriously, the 3.5" down leading into a 4" exhaust is the way to go. I know, you already bought the pipe. Members report that the 4" takes a little more time to spool up, potentially gives better power. Your giving away low end torque, spool time and moving the power into a higher RPM range.

There's been a bunch of posts (older posts reporting the issue) on the effects of a 4" down pipe. Search doesn't really do a good job.

 

I just installed the 4" on my 07 last weekend, with a little help from my son it wasn't a problem. The kit I purchased already had the down pipe 'dented' to clear the firewall AFTER it was in place, it still took a little finesse to get it into place. I pulled from the top while my son tapped on it from underneath.. ....It came up through without any issues, after it was in place it didn't hit anywhere. The rest of it was easy to puzzle together.
Oh, and a sawzall was they only easy way we found to get the old downpipe out.

...My new kit was a Diamond Eye, I'm not sure if others have the pipe predented or not.

 

You DO NOT have to dent anything for it to fit. I found a thread on here, somewhere, that a guy gave some hints on how to do it. I remember removing the transmission dip stick tube (or at least just disconnecting it and moving it a few inches) was the key. I installed mine in less than 4 hours, by my self from pulling into the garage to pulling out. The down pipe was one of the easiest parts of the whole install. What took time, was lining everything up to keep it from rubbing on bolts and cross members. Once I got the tranny tube out of the way, the down pipe "fell" into place (from underneath).

 

That doesn't make sense to me...being turbocharged we're not dealing with exhaust scavenging like on a normally aspirated engine. A larger exhaust post-turbo should allow faster spool up.

 

Haven't we discussed this at length in other threads?

 

You mean, like, with me? I don't think so...but I'm pretty forgetful, so it's a possibility.

From what I understand the turbo provides any back pressure needed, allowing the exhaust to escape post-turbo allows more efficient spool up.

 

I had the serious lag our friend here is talking about. I had a full 4inch Flo-Pro exhaust and had two problems with it:

1. Lag was absolutely dreadful (Simon Cowell)

2. It constantly vibrated against the shackle for the front leaf spring.

The lag even with the Atlas 40 was the worst part of it. It would think....think....think some more, then BAM! Take off like a raped ape. No matter how they adjusted my tunes or even backdated me to something earlier, nothing fixed it.

When I went to a 3.5 inch downpipe, both those problems went away and my mileage even got better. Keep in mind I ditched the Atlas 40, went back to my stock FICM and still have better spool times as well as mileage than before.

Of course it doesn't make sense, you're thinking about it backwards...

What takes longer to completely fill with air?

A 4 inch cylinder? OR A 3.5 inch cylinder?

The correct answer is the smaller of the two or 3.5 inch cylinder.

When Ford originally designed the exhaust for the 6.0, they designed it with a 3 inch down pipe and 3.5 inches after the cat. This helps spool the turbo, but helps the truck breathe some as opposed to having 3 inches from downpipe to exhaust tip.

Also, contrary to what's been previously posted, the 6.0 does indeed require a reasonable amount of backpressure to run properly. Again, this is why the exhaust was designed the way it was:

1. To help spool the turbo and allow it to respond reasonably quickly.

2. Maintain the required back pressure to spool the turbo.

3. Provide the good low end torque you paid for.

When you add a 4 inch downpipe, yes you're eliminating back pressure, but you're also increasing spool time because the truck has to dump more fuel than it usually did to get the truck moving and now the torque you paid for, is now at a higher RPM. Which is exactly why I was told by the Engineer who wrote the programming for the 6.0, that : "Unless you plan on racing the truck, leave the exhaust alone".

Keep in mind that if you were running 175, 190, or 225 cc injectors, I could see a 4 inch exhaust making sense because those injectors would dump more than enough fuel for it to make sense. Otherwise, if you feel you have to upgrade with stock injectors, stick with the 3.5 inch downpipe.