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Disappointed with my Apexi catback
Topic Started: Apr 19 2010, 09:21 PM (283 Views)
Deleted User
Deleted User

Been having a look at my Apex catback, where it bolts to the cat it's a small bore, goes into the 1st box and then it's bigger from there back.

Why would Apexi make a section of it (quite small, about 10 inches) smaller than the rest?

It's a good half inch smaller than the rest of the exhaust (even the stock cat)
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TRUENOSAM
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Stage 6
That doesnt sound right. My Apexi N1 was one size pipe (was the same bore all the way)

Difficult to see but this was mine

Posted Image
Edited by TRUENOSAM, Apr 19 2010, 09:46 PM.
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Deleted User
Deleted User

Maybe mine isn't an N1. It has the front box like yours but no middle box.

I'll try and get pictures tomorrow.
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TRUENOSAM
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Stage 6
Unless its a universal backbox with custom pipework and scilencers
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Deleted User
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It's an original Apexi and it's not been cut up, etc. Do they do any models other than the N1?
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TRUENOSAM
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N1 and N1 evolution is all I know of. Not entirley sure off the difference
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Deleted User
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Just been looking on Apexi's website, they do 2 systems for the AE111, N1 evo and a Bomber III. There is a PDF on thier website which says 54mm - 60mm for the internal diameter of both systems. http://www.apexi.co.jp/products/exhaust/pdf/exhaust.pdf

So all of them are the same. It's not obvious when fitted to the car but I noticed how much narrower the flange was when I removed my de-cat. When I put on the vernier calipers on them, it became obvious.

6mm isn't a huge difference I know but I can't work out why they are designed like it?
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DreadAngel
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Han Lue
AE111 also had available to it other Apexi models that are now discontinued... There was the original Apexi N1 that was a straight through blaster, I think 2 other models I forgot the name though
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Deleted User
Deleted User

I found out that the smaller diameter going to larger is part of their 'Megaphone' design.
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Megaphone piping is based upon the law of physics stating that exhaust gases travel along the OUTSIDE of the pipes. Sudden changes in piping diameter actually HURT the performance of the vehicle due to turbulence created inside of the pipes. Since exhaust gases travel at close to the speed of sound, a pocket of turbulence inside the pipes closes off the pipe leaving only a small diameter to pass through. This effect is similar to the movement of a shutter in a camera. The hole fills up with turbulent gases as impenetrable as steel. This is why apexi engineers introduces the MEGAPHONE piping system where the piping is GRADUALLY enlarged to provide smooth exhaust gas flow. No abrupt piping diameter changes are present in any of our systems. This allows for a velocity piping effect and allows exhaust gases to exit the vehicle faster than with a single piping diameter system. Another benefit to the MEGAPHONE piping design is the achievement of the perfect balance between the highest air flow and, where necessary, the proper amount of low-end torque. In addition, the Megaphone Series mufflers use little, if any, steel wool packing to preserve the canister from deterioration or prevent "blowing out." The amount of packing used in each muffler varies specifically on the sound deadening requirements of the application vehicle, i.e. rotary motors, turbo-charged engines, etc.


That sounds great but I can't see how it works when you take into account the internal size of the flange on the factory cat (or aftermarket decat in my case). It's a huge bottle neck.
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BZR4AGE
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JDM TODA
can you take a picture of your system so we can understand it better. A picture is worth a thousand words
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Deleted User
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I think I have a blow going from my cat so will take some photos when I sort that out.

Not alot to look at really, just a smaller diameter pipe leading into a box, then getting bigger after the box.

It seems to me that the 54mm might actually be smaller than what Toyota use originally.
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