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2.5 or 3 inch exhaust 

 

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 Post subject: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 5:07 pm 
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hey guys

any thoughts which would be better system 2.5 or a 3 inch for my bf mont

cheers
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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 5:15 pm 
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you should describe your car a bit more for people to give there opinion, such as 6 or 8 cylinders, auto or manual

 

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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 6:01 pm 
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sorry its a 4spd auto, 4ltr inline6
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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 6:01 pm 
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go for the 2.5, only time you need to go to 3' is if its an V8 or got forced induction, if you put 3' on a stock car you lose back pressure hurting your performance and fuel economy.
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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 6:49 pm 
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cheers for the info mate!
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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 6:59 pm 
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ranio wrote:
go for the 2.5, only time you need to go to 3' is if its an V8 or got forced induction, if you put 3' on a stock car you lose back pressure hurting your performance and fuel economy.


dont listen to him, if thats the only modification your going to do then go 2.5, if your eventually doing to go extractors cai, tune etc go the three inch..

either way on a stock i6 you will realize the same difference between a 2.5 and a 3..
i dont think i need to mention what the difference is

 

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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 7:46 pm 
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ranio wrote:
go for the 2.5, only time you need to go to 3' is if its an V8 or got forced induction, if you put 3' on a stock car you lose back pressure hurting your performance and fuel economy.




the whole point of fitting a larger exhaust is to reduce back pressure. The myth of engines 'need' back pressure was disproven years ago.


that said, there is more to it then having a 3 inch collect outlet and 3 inch system.

you get a better torque spread if you have a 2.5 collector with 2inch long section of 2.5 inch straight pipe with a 6 inch long tapered expander to 3 inch and then your full three inch system.

the size, length and shape of the collector is very important. needless to say mass produced extractors dont get this right. although pacemaker gets it 'less wrong' then the others

 

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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 8:37 pm 
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jerrytorry wrote:
you should describe your car a bit more for people to give there opinion, such as 6 or 8 cylinders, auto or manual


you relise this is the 6 cylinder workshop? lol.

MontyCarlos35 wrote:
hey guys

any thoughts which would be better system 2.5 or a 3 inch for my bf mont

cheers
it really depends what your plans are for it and whats been done.
2.5's good for most, but people that have used 3" has had some gains with there moded car

Last edited by Troy on Thu Feb 11, 2010 8:52 pm, edited 1 time in total.

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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 8:40 pm 
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Troy wrote:
jerrytorry wrote:
you should describe your car a bit more for people to give there opinion, such as 6 or 8 cylinders, auto or manual


you relise this is the 6 cylinder workshop? lol.

oops, forgot to check that

 

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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 8:59 pm 
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tickford_6 wrote:
ranio wrote:
go for the 2.5, only time you need to go to 3' is if its an V8 or got forced induction, if you put 3' on a stock car you lose back pressure hurting your performance and fuel economy.


the whole point of fitting a larger exhaust is to reduce back pressure. The myth of engines 'need' back pressure was disproven years ago.


really? i only went 2.5 for that reason! the 3 different exhaust workshop i talked to all gave me that exact reason, so i thought it had to be right, and this was only 6 months ago... well being toowoomba workshop i wouldnt expect much more haha
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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 9:31 pm 
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ranio wrote:
tickford_6 wrote:
ranio wrote:
go for the 2.5, only time you need to go to 3' is if its an V8 or got forced induction, if you put 3' on a stock car you lose back pressure hurting your performance and fuel economy.


the whole point of fitting a larger exhaust is to reduce back pressure. The myth of engines 'need' back pressure was disproven years ago.


really? i only went 2.5 for that reason! the 3 different exhaust workshop i talked to all gave me that exact reason, so i thought it had to be right, and this was only 6 months ago... well being toowoomba workshop i wouldnt expect much more haha


It doesn't take a genius to operate a pipe bender and mig welder.

Done poorly yes a 3 inch system is not good, and that is why these general exhaust places make the claims they do. because all they are doing is fitting off the shelf headers and slapping some pipe behind them. For the average guy that wants some noise a few extra HP this an acceptable practice.

If you are really chasing HP it's not good enough, BUT for well designed, hand built system from head to tail pipe you'll pay AT LEAST double what the general exhaust shop is charging for 'off the shelf systems'

 

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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 9:54 pm 
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yeah i only paid 265 for a straight flow catback with a redback muffler
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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 10:26 pm 
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ranio wrote:
yeah i only paid 265 for a straight flow catback with a redback muffler



you'd be looking $2000 plus for complete system that was designed build specifically for your engine combo. I've seen guys pay over $1200 for set custom 4cyl headers

 

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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Thu Feb 11, 2010 11:00 pm 
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tickford_6 wrote:
ranio wrote:
yeah i only paid 265 for a straight flow catback with a redback muffler



you'd be looking $2000 plus for complete system that was designed build specifically for your engine combo. I've seen guys pay over $1200 for set custom 4cyl headers



1200 on 4cyl headers! why the hell would you put that much money into a headers for a bloody 4cyl...
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 Post subject: Re: 2.5 or 3 inch exhaust
Posted: Fri Feb 12, 2010 7:44 am 
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ranio wrote:
tickford_6 wrote:
ranio wrote:
yeah i only paid 265 for a straight flow catback with a redback muffler



you'd be looking $2000 plus for complete system that was designed build specifically for your engine combo. I've seen guys pay over $1200 for set custom 4cyl headers



1200 on 4cyl headers! why the hell would you put that much money into a headers for a bloody 4cyl...


because thats how you make real HP, one off custom headers specifically designed and built for the engine they going on. None of this one size fits all crap.
The one i mention was cosworth YB engine that was making about 270hp (that's like your 4L making 540HP)

like i've said hundreds of time before. the only reason people aren't making 400hp out of these engines is because they all want to use off the shelf parts and stock intake manifolds.

 

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