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This is probably a dumb question, but is a bottleneck at the rear of an exhaust just as bad, not as bad, or worse than one much further up?

I figure it is probably the same, but I know that before here I was told that only the header and a little pipe after that is what is really important, the rest after that is just for sound insulation etc. Most likely that doesn't address the bottleneck issue though.
 

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to properly speed up the velocity, you would want an hour-glass shape inside. This acts as a venturi-
as the gasses speed up they create a low pressure area in the center, which aids in "sucking" the higher pressure (slower moving) gasses across the restriction. anything else would actually create a seperation bubble and choke off the flow. the faster the gasses cross the restriction, the bigger the bubbles become and the more the flow is choked.

So as MD said, the closer to the engine it gets the more it will restrict flow.
 

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You wouldn't want a venturi in place of bottlenecks. you would want the venturi at the Merge collectors in the header.

(pics borrowed from this article @carcraft.com)
side by side comparison


Inside with venturi:


Inside straight thru:



Another example would be in a stepped header design, the steps would incorporate a venturi.

anywhere else in the system you should eliminate bottlenecks if possible.
 

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The restriction on the itr exhaust is the muffler not the 2" bottlenecks.

I would think you would want to slow the velocity of the exhaust before it reaches the most restrictive part. The 2" bottlenecks even out the speed in the exhaust system.

It's like everyone running to the exit in a fire drill. lol
 

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Sevendale on Nov/01/08 said:
How come the ITR (2.25") exhaust has a two 2" bottlenecks? one right after the cat, and one right before the muffler? Don't you think Honda's engineers would have figured this out when they designed the USDM ITR?
Maybe because they're a car company like any other car company, and tooling up and using different part numbers constantly in your assembly line increases costs. The ITR is really cobbled together from a few other cars. The head, etc. Spec'ing out, contracting, procuring, and manufacturing specialized parts costs a lot of money.

The ITR was a limited production car, but at the end of the day, it was an Integra. They couldn't do every little thing to squeeze out every little horsepower, or else it would have costed 40 grand, and nobody would have bought it.


Sometimes the simplest answer is the most correct.
 
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