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Discussion Starter #1
I bought my zx3 with 2 inch exhaust piping installed already, my engines fixed up quite a bit I wanna cut restriction and go at least 2.5 in is itpossible to cut the piping at the connection fron flex to pipe and weld on 2.5 in piping? I am running a 380 dollarr greddy muffler so wanna keep it is this possible? Lmk
 

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Thats What She Said
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I think you need to phrase your question better...

you want to know if you can go 2.5" from the flex pipe back? Yes, you can how much do you want to spend? If your fancy muffler is still 2" inlet/outlet then going 2.5" for a section and going back down to 2" does not make much sense.

Any thing is possible with exhaust work it all depends on how much you want to spend at the exhaust shop...
 

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Discussion Starter #3
Ya your right would it make a difference in power? Sound restriction?
 

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A good muffler shop could make that Greedy 2.5" inlet and exhaust. Still the best, exhaust option. IMO. Full SVT exhaust. Header, Cat/off road pipe, flex. At that point you are 2.5 ". Lots of options for cat back ...
 

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your best bet is to match the exhaust pipe diameter to the diameter of the header outlet. Reason being (and this is all theroy) is that if you have a 2 in outlet on the header going into the 2.5 exhaust tubing, the exhaust coming out of the header has room to expand, and starts to swirl, thus slowing down the flow. if you have a matching diameter tubing exhaust will find its way out sooner.

Now if you were going from 2in to 2.5in back to 2in that would cause all sorts of airflow interuption.

I don't have my focus anymore, but on my cobalt I have a OBX header 4-1 race style 1.5in primaries to a 2.5 outlet conected to a 2.5in XTC catless downpipe, to a 2.5 megan exhaust. Its the closest I can get to having a 2.5 straight pipe.
 

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Thats What She Said
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^^^ I dont know how much your statement is true. Yes any change in size will cause disturbances but the exhaust is a tricky model to use Fluid dynamics on. First you are pushing the air through a valve in the head which will cause "turbulence" at the very start. Then you have the turbulence from the junctions in the header, Then the Flex section of pipe is ribbed so you have all sorts of things with that. And to mentioned all of this there are "burs" from welds and unless Mandrel bent you have size variations in all the bends from the head to the flex.

It will be best to stick with what ever size you choose for as long as you can.

Will you see any performance change, by changing a 3-4 foot section from 2" to 2.5? Most likely not, you may get a different sound because you have changed the resonance of the cavity.

Exhaust gas will move slower in a larger area, that's why most people only go with 2.5" if NA and 3" if FI. IIRC 2" single exhaust can support up to 200 HP with out restriction, 2.5" can do up to 300-350 and over that 3"... meaning if your at 200HP, you will not see any noticeable change if you upgrade from 2" to 2.5".

If it was my Foci, I would cal shops and see what shops could do with your muffler, and if they can make the opening 2.5". If they can then its up to you how you want them to proceed, either have the shop do all the bends out of their stock, or get a tube kit from a place like TruBendz, have been a lot of discussion as of late with them...
 

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^^^ I dont know how much your statement is true. Yes any change in size will cause disturbances but the exhaust is a tricky model to use Fluid dynamics on. First you are pushing the air through a valve in the head which will cause "turbulence" at the very start. Then you have the turbulence from the junctions in the header, Then the Flex section of pipe is ribbed so you have all sorts of things with that. And to mentioned all of this there are "burs" from welds and unless Mandrel bent you have size variations in all the bends from the head to the flex.

It will be best to stick with what ever size you choose for as long as you can.

Will you see any performance change, by changing a 3-4 foot section from 2" to 2.5? Most likely not, you may get a different sound because you have changed the resonance of the cavity.

Exhaust gas will move slower in a larger area, that's why most people only go with 2.5" if NA and 3" if FI. IIRC 2" single exhaust can support up to 200 HP with out restriction, 2.5" can do up to 300-350 and over that 3"... meaning if your at 200HP, you will not see any noticeable change if you upgrade from 2" to 2.5".

If it was my Foci, I would cal shops and see what shops could do with your muffler, and if they can make the opening 2.5". If they can then its up to you how you want them to proceed, either have the shop do all the bends out of their stock, or get a tube kit from a place like TruBendz, have been a lot of discussion as of late with them...
I didn't even think to mention about the bending, but that is very true as well, if its not mendrel bent, its crush bent. In a 2 inch diameter mendrel bent pipe the pipe will remain 2 inches through the bend. In a 2 inch crush bent pipe, its not uncommon for the pipe diameter do get as low as 1/3 the original diameter.

here is a link to a 2.5 inch mendrel bent pipe vs a 2.5 inch crush bent pipe, you'll notice the difference.
http://warpspeedperformance.com/huth7.jpg
 
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