Fg Twin 2.5" Vs Single 3.5"

[discostig]

2x2.5 has slightly (like a few %) more flow area than single 3.5. We all remember how to calculate area of a circle right? Pi * r^2?

As mentioned there is more surface area though. I think the actual design of the system as a whole will make the difference, eg mufflers, again as already mentioned.

[Paulie2256]

Doesn't the twin 2.5" tuck up better under the car?

I <3 Bananas ye it does. If it wasn't for the massive cat it would almost be the same as stock.

[Kosij]

I remember reading this!

hey guys there is another factor u gotta think about the frictional area of the pipe

Example one : 2.5" pipe 1 foot long frictional area = 94.24" square

Example two : dual 2.5" 1 foot long frictional area = 188.48" square

Example three: 3.5" pipe 1 foot long frictional area = 131.94" square

if u compare a dual 2.5" (9.818 square inches) agains a single 3.5" (9.622 square inches) system the cross section is nearly the same but in a single 3.5" the exhaust gas got less area to " rub " on compared to the dual 2.5" so it will flow better than a dual 2.5"

[Paulie2256]

You are just trying to justify a whole new exhaust system instead of just getting a muffler replaced under warranty. Hey, you may have not heard they are doing that so I understand.

480 has been made and a 9 sec pass on a twin 2.5" so tell me again how it doesn't flow.

Edited 06/03/13 08:20 PM by Paulie2256

[Never had any say Panda]

Also in pipe flow you need to consider a roughness coefficient of the material the pipe is made from.. To determine how much impact the additional surface area has on the flow..

Say concrete pipes have a roughness values of 0.028n.. I can bet polished stainless steel pipe is probably 0.0000000000001n..

[unclewal]

I have twin 2.5 and making 455+ no problems, but in saying that back pressure was tested to be 7psi. For noise it is perfect, nice and quite but still a little bit of noise. In all honesty all you can hear is the intake, the exhaust rarely draws attention and I have been through 3 breathalysers this week alone and the cops are more intrigued by the buzzing of my twin pumps as opposed to the exhaust. It all depends on what you want your car to do and how you will drive it and how much attention you wish to draw.

To answer your questions regarding noise it will depend on the material you use either stainless or mild and what mufflers are incorporated into the system, I have found that

3.5 is louder as opposed to 2.5. That is comparing my car to the workshops car that had a 3.5inch and mine running a 2.5. Again all comes down to system and muffler setup.

As for a tune being required, some say yes some say no, personal I would say yes unless you want your investment on an exhaust to give you a headache later on when your car runs poorly or has poor fuel economy and continues to throw engine lights. There will be some people that will say "nope had an exhaust for 10 years never got it tuned, runs fine". From my point of view, anything that changes flow or intake/exhaust velocity will require atleast a AFR check to make sure its behaving and not going to harm your car.

Hope this helps you.

[rednose]

That sounds about right, not sure how Kosij had more back pressure with less power but may be due to different muffler as SDP pointed out.

[cam69]

I have an FG auto, I have heard (well from google) that the XForce can drone with an automatic. Anyone know if that's true or not?

I am facing the exact same dilemma, wanting a catback, not sure if DiFillipo, Redback, XForce or HiTech is the way to go. Wanting a nice deep note without sounding like a bogan doing laps with NO drone - preferably a twin system as I like the look but the key is the deep note and lack of drone...

[Bonjaz]

xforce 4" on a sedan auto and I dont think it drones at all, my old 3.5" on my bf droned more

[Kosij]

My 3.5" xforce doesn't drone on my ba at all! If anything it's way to quiet