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Explain 3" exhaust system advantage.

WD Pro

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Why do the stock post cat connections neck down to like 2 1/4, does anyone know? Seems like it will make any 3 inch system kind of pointless.
Well the GT350 and I believe the GT500 are 63mm (2.375) and the 5.0 is 2.25”.
It was explained to me the sizes are more than adequate within the designed requirements by the Ford engineers.
Personally I’m still on the fence that the reduction is similar to a header collector choke but that’s going down a deep rabbit hole.
There is a (easily removed) 2.0” restriction in the GT (and Mach) :

Standard GT resonator does a similar thing :
  • 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).
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WD Pro

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15-17 only
Gen3 18+ received a size increase in that area.
I'm a 2020 ... ?

I know I'm a euro, but we get the active exhaust which is a single piece (so defo a facelift part).

The mufflers are identical to a USDM as I checked the stamped part numbers to other photos I had found on here.

I still have the resonator, so we can cross check that part number with a USDM car (if it's important) :like:

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WD Pro

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I’m referencing the diameter of the front flex joint. Are you referring to another area reduced to 2.0” ?
Yes, from my post above :

"Diameter at resonator outlet joint = 2.00" (removed with resonator delete)"

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K4fxd

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I agree 100% about a BB 426 hemi. But a SB 305 with a 3.64 bore/3.62 stroke doesn't move as much air as a 426 with a 4.24 bore/3.75 stroke.
It has nothing to do with the valve diameter or engine size. It is the amount of HP the engine can make. 450 HP from a small block is the same airflow as 450HP from a big block.
 

WildHorse

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450 HP from a small block is the same airflow as 450HP from a big block.
no. cause your not making the same horsepower at the same rpm.
 

K4fxd

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no. cause your not making the same horsepower at the same rpm.
It's still the same airflow at whatever RPM it makes the 450 HP
 

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It's still the same airflow at whatever RPM it makes the 450 HP
I'll add that the flow rate is the same but the frequency of the pulses is different, which will do weird stuff in an exhaust. This may explain why there is some different "tribal wisdom" coming from the guys used to running older motors.
 

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In the air compressor industry HP and CFM are directly proportional.
An internal combustion reciprocating piston engine has far too many variables for HP and CFM to be directly proportional and constant.
 

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I'm old school as in 60s and 70s muscle cars. Majority of people feel that 3"+ pipes are only good for Hemi's and big block strokers because there isn't enough restriction (velocity) for smaller engines for the exhaust system to work properly. Please explain why they work on these engines.
On these s550 coyote motors they make all their power in the upper rpm they naturally lack torque. Going to a 3" will help increase that upper rpm flow for HP. The factory 2.5" piping creates more back pressure resulting in more torque feel. Felt this on my personal car. Car felt quick with the factory exhaust. Once I put a 3" I felt the slight torque loss but the car felt stronger in the upper rpms.
 
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It has nothing to do with the valve diameter or engine size. It is the amount of HP the engine can make. 450 HP from a small block is the same airflow as 450HP from a big block.
Ever seen the headers on a 900hp Indycar or 1,500hp Pro Stock ?
 
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K4fxd

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furdfan2018

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I agree 100% about a BB 426 hemi. But a SB 305 with a 3.64 bore/3.62 stroke doesn't move as much air as a 426 with a 4.24 bore/3.75 stroke.

A 1970 Hemi barracuda made 426 horsepower, trapped 107 mph in the quarter mile and weighed, what... 3300 lbs?


A 2018 Mustang GT makes 460 horsepower, weighs several hundred pounds MORE than the Hemi car, and traps 112-115mph more regularly than a 0700 bowel movement.

I can promise you, the tiny 302 moves more air.
 
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K4fxd

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Stock file pic of Cosworth V8
Ford_Cosw_HB4_3.5_V8_1991_DSC_3494.jpg
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