Upgrade to factory head pipes, getting rid of the factory restrictions.

[1MeanZ]

I'm about to start on a small project that will likely a be a waste of time and yield no power gains, but I like working with exhaust tubing and I'll be getting rid of some pretty common sense restrictions in the factory exhaust so I'm going to do it anyway.

The main focus area is getting rid of the 1 7/8" restriction on the passenger side head pipe where the flex joint is, and the second goal is just to get everything else sized up to 2.5" like the rest of the exhaust. I'll be keeping the stock tri-y manifolds and cats. I'll be carefully cutting the welds on the outlet of the cats at the bottom to seamlessly match to some stainless 2.5" tubing. I'll be using a Vibrant flex joint on both sides and then routing back into my X pipe per the factory routing. Essentially I'm going to make what the factory should have put on these cars originally.

Pictures below are before, and show the restrictive area where the flex joint is. If anyone has done this before or has any guesses to how much power, if any, might be gained I'd like to hear it.

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[EFI]

Wth is a head pipe?

 

[WD Pro]

Wth is a head pipe?

Moving on ...

Didn't the facelift / 18+ cars get rid of that flex pipe restriction ?

WD

 

[engineermike]

Yes the 2018+ pipes are 2.5” and go oval for the flex joint. Gen2 and 3 are 2.25” at the factory connection at the resonator, though.

Op you’d have a big head start if you found some used gen3 cats to swap in. Then the only spot needing attention is the factory connect.

 

[WD Pro]

Gen2 and 3 are 2.25” at the factory connection at the resonator, though.

And for a small section, the standard resonator actually goes down to 2.00" :

I had mentioned before (multiple times) about the 2” ‘restriction’ in the standard resonator :

• Standard pipe diameter = 2.5"
• Diameter at front manifold clamps = 2.25" (same for standard resonator and resonator deletes).
• Diameter at resonator outlet joint = 2.00" (removed with resonator delete).

Most just seem to accept that it’s a 2.5” system with a 2.25” restriction at the front clamp, ignoring the 2.0” restriction at the back of the resonator ?

Interestingly, someone (thanks @GregO ) questioned me on it, so I went to double check.

Just for those on the other side of the pond :

• 2.00” = 50.80mm
• 2.25” = 57.15mm
• 2.50” = 63.50mm

Inlet :

Outlet :

Outlet, right next to the resonator :

Note that on one of the pipes in particular, the reduced section is quite oval and ranges from 48mm ish to 54mm ish.

You can see the severity of the neck down quite well on this photo:

Now mines a 2020 euro spec, so we wondered if the USDM was any different ?

Then by chance, I came across this in the classifieds from @Ballistica - removed from his USDM 2021 GT PP1 :

This is the 2.0” pipe section (same as my 2020 euro GT) :

Then we wondered about the Mach 1, so after a little search and courtesy of @WCRookie99 :

So they all get it …

I can’t photo it very well, but it’s obvious to see - if you look internally down the length of the resonator the way the gas flows, you can see the step where the tubing necks down and the end of the small section protrudes into the resonator.

I suspect the resonator is made and then placed in a jig, the rear sections inserted, positioned for rotation and overall length, and then welded around the outside.

So the standard resonator is straight through, but don’t be fooled into thinking it doesn’t add a restriction - now how much difference it makes is probably a topic for another thread, and probably also heavily influenced by what other mods you have got going on …

WD

WD

 

[1MeanZ]

Op you’d have a big head start if you found some used gen3 cats to swap in. Then the only spot needing attention is the factory connect.

You sir are correct and that's initially the direction I tried to go, however, I can't get any of the guys that part these cars out to sell me a set of Gen 3 cats. Plus, I have all the stainless pipe left over from the exhaust I built for my truck, so I'll only have about $150 in material with clamps and braided flex joints, no one is going to sell me a pair of Gen 3 cats for $150 shipped, they are probably worth more than that for scrap.

The neck down at the flex joints on Gen 2 cars is really small. I'm measuring a little under 2" OD with calipers on mine. Originally I was just going to cut out the flex joint and put a larger one in but it will hurt my ground clearance(hence why the Gen 3 flex joint is oval). As I got to looking more, I decided I'll just remake everything between the cat body and the X pipe. That way I can keep the flex joints tucked up and actually have 2.5" all the way like Ford should have done in the first place. The fact that Ford spent the time to update this arrangement for 18+ cars tells me that what the 15-17 cars have must be restrictive and worth changing.

I'll post pics once I get started on the project. Again, I like exhaust fabrication so for me this is just a fun way to harvest some low hanging fruit from the horsepower tree.

 

[K4fxd]

I see you are in Indiana, when you get done with yours do you want to do mine?

 

[GregO]

The fact that Ford spent the time to update this arrangement for 18+ cars tells me that what the 15-17 cars have must be restrictive and worth changing.

Keep in mind the Gen3 has a good increase in upper RPM CFM over the Gen2. The Gen3 CFM increase is close to the VooDoo.
Off the cuff Ford didn't miss the Gen2 exhaust sizing by much given the factory designed operating parameters.

 

[1MeanZ]

Keep in mind the Gen3 has a good increase in upper RPM CFM over the Gen2. The Gen3 CFM increase is close to the VooDoo.
Off the cuff Ford didn't miss the Gen2 exhaust sizing by much given the factory designed operating parameters.

I hear you. I have the Ford Performance Power Pack 2 installed on the car. Granted I still have the stock intake, but the new redline is 7150, and I'm sure up there a small increase in exhaust flow won't hurt anything. I've toyed the idea of swapping to the Voodoo intake or even an Gen 3 intake but haven't pulled the trigger yet. Mainly because the car is street driven and midrange power is where I spend most of my time and the Voodoo certainly won't help with that. I have yet to see a good comparison power curve between the 15-17 intake and the 18+ intake.

 

[1MeanZ]

I see you are in Indiana, when you get done with yours do you want to do mine?

Lets see if you're happy with my end result and then we can talk.

 

[GregO]

I've toyed the idea of swapping to the Voodoo intake or even an Gen 3 intake but haven't pulled the trigger yet. Mainly because the car is street driven and midrange power is where I spend most of my time and the Voodoo certainly won't help with that.

I have the Gen2 w/VooDoo intake and 80mm TB on OEM tune.
It’s a misconception that there’s a loss at the low and mid range.
Almost 5 years of urban driving on my setup and never once have I looked back. It just flat out works.

 

[K4fxd]

I've got the GT350 mani and stock 80mm TB. It works great. I do believe it will benefit from larger head pipes.

 

[Brazos609]

Op you’d have a big head start if you found some used gen3 cats to swap in. Then the only spot needing attention is the factory connect.

Is the OD at the exit of the Gen 3 cats a larger diameter than the Gen 2 cats?

 

[engineermike]

Yes I believe the gen3 cat exit is 2.5” and gen2 is 2.25.

 

[GregO]

I'm assuming the factory Gen3 and Gen2 4-2-1 header primary diameter is the same @ 44mm

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