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Discussion Starter #1
Currently I'm running Miltek non-res catback which is a 2.5" system on my 07 FN2.
After getting my car ECUtek mapped at TDI North, they suggested that I should really consider changing it to a 3" because it will provide optimal power.

However, I've read and heard a lot of people saying how the 3" drones at higher speeds, especially on motorways and also unnecessarily loud on cold start / revs.
I've even heard some people changing their 3" to a 2.7" Tegiwa catback system because of those reasons and seemingly its the happy median.

My question is, between the current system I got now (2.5") and the Tegiwa catback (2.7"); is there enough of a noticeable power difference for me to switch the system?
Half an inch is quite a difference but not too sure about 0.2 of an inch 馃ぃ
 

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2008 Civic Type R
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I'm not sure how the rear silencer is designed on a Milltek, but I switched from one to the 2.5" Tegiwa (version before their latest) and saw pretty large changes to fuelling, running a lot leaner. Never got my map updated, though I should have. I think the single exit design is a significant part of the improvement to flow.

70 mm and 3" single exits will flow even better than 2.5" - 70 mm is 21% increase in flow area, 3" is 44% so there are significant jumps between each. I can't comment on drone for the bigger systems though I suspect they will. 2.5" exhausts have droned on mine since having a 4-2-1 manifold.
 
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Discussion Starter #3
@SilverCider Thank for the reply. Really appreciate the insight!

Yeah, that definitely seems like a noticeable difference; especially the air flow part on paper.
I also have the 4-2-1 and it already drones when I hit around the 3k - 4k rev mark at 75mph on the motorway in 6th gear.
Luckily its not THAT loud, I can still hear myself think and the music being played in the car.
However, between 4.5k - 5k...the droning stops but youre hitting 80mph+ but it starts back up again if you go any faster.

I can only imagine it will be a lot more louder if I decided to go for the 3".
Yeah, you get optimal power but is that worth not being able to hear the music in your car or yourself think whilst going for a 1hr+ drive?
That is definitely left to be debated 馃し鈥嶁檪锔

One thing I dnt get is the price differentiation:

Miltek non-res (2.5") = 拢715
Tegiwa 70mm (2.7") = 拢500
TDI north (3") = 拢690.

It is the most expensive yet the Miltek is the worst in terms of air flow and power gain due to its diameter 馃
Makes 0 sense to me really.
 

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I've had a teg catback earlier this year I found it quite droney. That was with the OEM manifold aswell ! The FD2 oil pump made it more pronounced

Currently I'm running a Scorpio exhaust it's got a nice rasp and not to intrusive on motorway cruise
 
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