3inch all the way back?

[robmustang201528]

I have the ARH 1 7/8 header with a 3inch ARH X pipe with the stock mufflers. I've herd that having 3inch all the way back to the muffler can rob horsepower and torque(no back pressure) unless your have a super charger on your car. Im all motor.Is that true? I was looking at Corsa but i noticed their axle backs are 3inchs. Thinking about just getting a Ford racing borla muffler, cut the factory muffler off and clamp the borla on. Its also a lot cheaper. $1000+ for sound and no gain is a lot.

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[z06psi]

So I would ask you. The engine is basically a pump. How would back pressure help its operation?

 

[craigsix]

might help low end torque but not high rpm horsepower.

 

[Laztug]

Gains (if any) should be minimal. I would say a good +/- 2hp.
Here is a quote from a tuner in another forum.

I get this question all the time, or more accurately I repeatedly talk customers out of going 'too large' with primary size.

Figured perhaps a thread is a better way to educate a little bit.

When it comes to headers, bigger is not always better. The easiest way to visualize this when it comes flow potential we can use math to see which primary size is best for a given exhaust diameter.
For the purpose of standardizing the math we will assume all headers have .050" wall thickness

Calculating the volume of exhaust flow is not easy, so we will focus on the area of the pipes for ease of comparison as volume is directly related.

Factory 2.75" OD exhaust has an area of 5.51 square inches
3.0" OD exhaust has an area of 6.60 square inches

Now it's time to calculate the area of the primaries.
Since these are V8 engines with dual exhaust the calculation for total area of the primaries would be 4x the primary size.

4 - 1 & 1/2" Primaries have a toal area of 6.15 square inches (Yes, larger than factory 2.75" exhaust)
4 - 1 & 5/8th" Primaries have an area of 7.30 square inches (A perfect size for dual 3" exhaust IMO)
4 - 1 & 3/4" Primaries have an area of 8.55 square inches
4 - 1 & 7/8th" Primaries have an area of 9.89 square inches

Given this information you can see unless you are running 3.5" + exhaust, there is no reason to run large primary headers.

However, there are good reasons to run smaller primary headers, not the least of which is heat and volume of exhaust in the system. The more volume you have in the primaries, the longer it takes the exhaust to reach the O2 sensors and the colder it will be when it gets there. Velocity will be lower with larger primaries, O2 data will not be as accurate, the exhaust will have lost more heat energy, and the blow-down pulse will have less energy to pull exhaust out of the next cylinder. The result is lower power output until RPM's are high along with poor O2 readings which causes driveability and idle issues.

Food for thought. You CAN go 'Too Big'.

 

[GSLSE20B]

I have the ARH 1 7/8 header with a 3inch ARH X pipe with the stock mufflers. I've herd that having 3inch all the way back to the muffler can rob horsepower and torque(no back pressure) unless your have a super charger on your car. Im all motor.Is that true? I was looking at Corsa but i noticed their axle backs are 3inchs. Thinking about just getting a Ford racing borla muffler, cut the factory muffler off and clamp the borla on. Its also a lot cheaper. $1000+ for sound and no gain is a lot.

as long as you got rid of the 1.8ID factory connect you are fine with the factory mufflers

 

[svtfever]

full arh actually necks down to 2.5 at rear axles. I will trust their judgment

 

[atekido]

something also that is forgotten is most aftermarkets exhausts are ALOT lighter than the stock exhaust/mufflers.

 

[david borla]

We designed this 3" exhaust system exclusively to be used with long tube headers - http://www.borla.com/products/mustang_gt_catback_exhaust_atak_part__140630.html

If you have any questions please let me know. [email protected]

db

 

[craigsix]

i got the low buck at the time gibson with custom 3 inch connecting pipes.

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