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what is the max RWKW out of a 2.5inch exhaust 

 

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 Post subject: what is the max RWKW out of a 2.5inch exhaust
Posted: Fri May 13, 2011 12:52 am 
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hi all i have a lukey 2.5 inch sports exhaust fitted to my turbo setup. Whats the rough max figure i can get with that? Ive almost finished making my 3inch exhaust but im gettin a J3 chip tuned with my 42lb injectors an wondering whether it will be worth puttin the 3inch on or could i just stick with the 2.5inch for now? Reason i ask is that the 3inch exhaust is far loud so would rather use the 2.5inch exhaust, but if its gonna restrict it to much will just use the 3inch. Thanks
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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Fri May 13, 2011 12:53 am 
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It's a rather subjective question, depends on how well your 2.5 flows. Some flow better than others.

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Fri May 13, 2011 12:59 am 
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As Toranaguy said it is really up to what the system is. A good 2.5" could possibly outflow a s**t 3" system.
All the good 4.0 turbos I have seen run a 3" system so I would look at that. Yobbofords 3" on his ED was nice and quiet and flowed well.

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Fri May 13, 2011 9:28 am 
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Best i ran was 225rwkw, ceramic high flow cat and a single muffler.

just installed a 3" and it deffinately feels like its picked up some top end.

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Fri May 13, 2011 1:06 pm 
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if your making your own exhuast then why not add another muffler, or change the existing muffler setup to quieten the 3" system down a bit?

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Wed May 18, 2011 5:05 pm 
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I have similar concerns as the OP.

I too would maintain the 2.5" for the quiet note alone if it meant I could still make more power. But am willing to opt for a 3" system that had maximum flow with minimum noise.

The hardest part is getting the balance right and I guess only an exhaust technician can provide solid help in that regard.

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Wed May 18, 2011 5:53 pm 
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I think you should be asking what people have generally seen out of a 2.5" system with decent boost rather than what is the absolute max. So many factors in play its too hard to work them all out unless you are a rocket scientist.

For a start you have:

Number of bends
Angles of bends
type of bend (mandrel or press)
internal pipe roughness
texture of internal weld beads
thermal conductivity of pipe material
wall thickness
muffler flow rates
cat flow rates
length of pipe
surface coatings

Change any one of those and your target changes, that's why its too hard to accurately predict unless you tell us every single one of those details.
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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Wed May 18, 2011 6:22 pm 
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800rwkws.

Its an answer. might not be right though.

Forced on 2½" I would suggest high 200's though. alot of factors as Cabbi has suggested.

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Thu May 19, 2011 11:46 am 
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I personally doubt high 200's but i could be wrong. As a guess I would have to say at best about 230rwkw if all of xcabbi's list were taken into consideration.

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Thu May 19, 2011 12:04 pm 
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some NA e series have been resticted by 2.5" exhuasts and they were only making 180rwkw...

if you have the 3" then use it, there is no need to make the turbo work so much harder than what it needs to... if you only have one muffler and its too loud, then add another one.

by releaving the back pressure youll be able to make the same power on less boost, this then means lower discharge temps from your turbo, intercooler has less heat to reject, so cold side temps will drop and be more consistant. Boost control will also be improved.

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Sat Dec 24, 2011 1:36 am 
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john is on the money.
when it comes to a boosted setup you need to get rid of a certain amount of exhaust gas to produce the desired boost level, and in tern, if the exhaust flows free enough, then the power is subjective to things like cam, head work etc etc.

with a restrictive exhaust, you will be limited to around 220rwkw and whatever boost is required to get there.
on the dyno sheet the boost line will rise the even out almost as if your gate has opened at the desired boost level.
it will act the same as if the cat had collapsed for obvious reasons...

theres a guy on the boosted forums with a really efficient top end (good port work, well matched cam etc) but is using a 2.5" exhaust and think he managed around 230rwkw but couldn't get anymore than 4psi.
some other cars might get to 5-6psi yet will still make 200-220rwkw.

moral of the story, just don't use a 2.5" exhaust :)

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Sat Dec 24, 2011 7:54 pm 
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On my 330 TT v8 it had single 3" exhaust with 2.5 dump pipes up front..
I couldn't make over 350 / 370 RWKW..
So I would assume a 4.0 with 2.5 exhaust with no baffle mufflers
would be about 250 / 280 rwkw...[debatable guess ??]
I could make power in lower rpm with boost but as rpm increased...
Power levels would full off big time...
Depending on tune / boost levels can change things around...
I DID find though going to twin 3" the turbo's spooled way faster and at lower rpm..
I would run a larger dump pipe by 1/2 inch over the rest of exhaust..
This allows wastegate and circular flow from turbine housing exhaust to change better into flowing down exhaust
with out much turbulence...
yes it goes against what we think N/A...

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Tue Dec 27, 2011 10:26 am 
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Just run the 3" exhaust. Two mufflers and it will be fine,Will be more quite then an n/a i6 with a 2.5" exhaust.

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Tue Jan 03, 2012 11:10 am 
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I assume this theory would be the same for a centri blower setup too?

 

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 Post subject: Re: what is the max RWKW out of a 2.5inch exhaust
Posted: Tue Jan 03, 2012 11:25 am 
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if your responding to Michael (HYPOEB)
its the turbo that acts as a muffler to take some noise out of the system....

 

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