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(Post Link) post #1 of 8 Old 17-05-09 Thread Starter
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Q for you exhaust experts & engineers

Does anyone know why the front pipes of 3.2 GTA are inconsistent in diameter?

1. The Longer front pipe is 50mm at connection to manifold, than 60mm to about half-way, then 50mm to connection to the cats
2. The Shorter front pipe is 50mm all the way to the cats.

What is the reason for this? Why only one?
Is there any benefit of having larger diameter front pipes, when the manifold exit diameter is 50mm?

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Re: Q for you exhaust experts & engineers

I reckon its just a sleeve over the normal section of pipe, maybe with some insulating material in there. Can't be sure though.
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Re: Q for you exhaust experts & engineers

That never crossed my mind, but you could be right.

Has anyone looked at it more closely?
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Re: Q for you exhaust experts & engineers

Anyone have a picture of this front downpipe?
But basicly it could be done to gain the same resonance as rear downpipe. Also remember that most of standard exhausts are not resonance type so different pipe lenghts are not so unusual.
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Re: Q for you exhaust experts & engineers

Quote:
Originally Posted by Yaninnya View Post
Anyone have a picture of this front downpipe?
But basicly it could be done to gain the same resonance as rear downpipe. Also remember that most of standard exhausts are not resonance type so different pipe lenghts are not so unusual.
Jan
I dont know what you mean by gaining resonance. Isn't the point always to reduce it?
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Re: Q for you exhaust experts & engineers

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Originally Posted by Lemi View Post
I dont know what you mean by gaining resonance. Isn't the point always to reduce it?
You mean back pressure. The resonace can be used to reduce back pressure. Thats why tubular manifolds are exist.
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Re: Q for you exhaust experts & engineers

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Originally Posted by Lemi View Post
I dont know what you mean by gaining resonance. Isn't the point always to reduce it?
I suppose where the two manifolds join into one pipe it's more desirable to have equivalent pressure waves, rather than two different ones merging together. I'm not an engines man though so just an educated guess!
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Re: Q for you exhaust experts & engineers

I'm going to be replacing the front pipes soon, so hence my Q's.

I was going to for a 50mm (non equal length) FP to replace the original ones but know I feel a little confused by the above and by the choices I got.

1. According to this thread I should use 76mm front pipes: https://www.alfaowner.com/Forum/alfa-...-system-4.html
Now, is there any benefit with this, as the manifold exits are restricted to 50mm? To me it does not make since. I always thought if you have a 'bottleneck' in the system (50mm) there is no point having bigger pipe afterwards...

2. Others swear by equal length front pipes...

3. And then, the longer front pipe of the factory setup goes 50mm - 60mm -50 mm…
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