3" or 2.5" is there a big difference
#22933
March 04, 2002 02:57 pm UTC
March 04, 2002 02:57 pm UTC
|
Joined: Dec 2001
Posts: 979 Ottawa
Yasar Issa
OP
Serious Member
|
OP
Serious Member
Joined: Dec 2001
Posts: 979
Ottawa
|
Hi Guys
It me agine .... Ok for my Down pipe does it really matter if I get a 3" or a 2.5" down pipe
I have a 16g that I plan on turning up the boost on this year. I have a High flow Cat (3") and 3" Thermal Cat back all the way to the back.
Thanks Yasar
96GST --> Sold 97TSI 13.00@104 <--Sadly SOLD 2003 Mustang New Project
|
|
|
Re: 3" or 2.5" is there a big difference
#22934
March 04, 2002 07:32 pm UTC
March 04, 2002 07:32 pm UTC
|
Joined: Jul 2000
Posts: 1,131 Kingston,Ont
Ryan Hutchins
Member
|
Member
Joined: Jul 2000
Posts: 1,131
Kingston,Ont
|
Now I don't know a lot about this since I haven't got my Apexi N1 yet, but you'd think 2.5" would be better, less chance of getting boost creap. And I know that RRE sells the downpipe that starts at 2.5" then goes to 3" at the cat.
Question for ya Yasar, how do you like your Thermal? I'm most likley getting a N1, but is the Thermal loud at all? annoying loud I mean...thanks
Black '92 Talon TSi AWD - SOLD
|
|
|
Re: 3" or 2.5" is there a big difference
#22936
March 04, 2002 08:02 pm UTC
March 04, 2002 08:02 pm UTC
|
Joined: Sep 1998
Posts: 7,944 Halifax, NS
Troy Jollimore
Senior Member, with Far TOO Much Time on Their Hands
|
Senior Member, with Far TOO Much Time on Their Hands
Joined: Sep 1998
Posts: 7,944
Halifax, NS
|
The 3" would give you slightly better top-end, but I'd be surprised if it's enough to notice. If you want a real-world comparison, put a 2.5" pipe up next to, say, a stock Honda exhaust. (:
Even my 2.25" exhaust seems to produce decent power, and I know that setup has seen 11's with a 16g (years ago).
|
|
|
Re: 3" or 2.5" is there a big difference
#22937
March 04, 2002 09:19 pm UTC
March 04, 2002 09:19 pm UTC
|
Joined: Feb 2002
Posts: 1,958 London, Ontario
Jon Arnett
Serious Member
|
Serious Member
Joined: Feb 2002
Posts: 1,958
London, Ontario
|
2.5" is fine for a 16g. I don't think you need 3" turbo-back until you're pushing big boost with an 11sec goal.
According to Buschur, 2.5 crush bent piping will take you right into the 12s.
True...but, bigger is always better in turbo exhaust land. I'm in the process of building a 3" turbo-back for mine, and I've still got the 14B. Mind you, I'll be running 19psi...but if you want high boost, you want big pipes.
*2002 Porsche 911 Silver *2006 BMW 325XIT Black *2003 BMW 325i Silver
|
|
|
Re: 3" or 2.5" is there a big difference
#22938
March 04, 2002 09:28 pm UTC
March 04, 2002 09:28 pm UTC
|
Joined: Nov 2001
Posts: 3,720 Toronto
Darko Miodrag
ok wait, maybe I am
|
ok wait, maybe I am
Joined: Nov 2001
Posts: 3,720
Toronto
|
Well yeah ideally you wouldn't want an exhaust at all on our cars, but when it comes to comparing 2.5" and 3" there really isn't that much difference on smaller turbos, especially on the stocker.
19psi on a 14b is nothing compared to the same boost on a 20g or bigger turbo. By going to a larger exhaust you're losing more bottom-end too, so that's something to consider.
It's not a question of which is better... it's about what you need or don't need. 3" is a lot more expensive than 2.5" and it's not necessary for a stock or slightly bigger turbo, no matter how much boost you're running on them.
|
|
|
Re: 3" or 2.5" is there a big difference
#22939
March 05, 2002 12:53 am UTC
March 05, 2002 12:53 am UTC
|
Joined: Dec 2001
Posts: 979 Ottawa
Yasar Issa
OP
Serious Member
|
OP
Serious Member
Joined: Dec 2001
Posts: 979
Ottawa
|
Hey Ryan
My Thermal has a deep sound not wimpy...But keep in mind I still have the Stock Cat and Down pipe I'm sure it going to get a bit louder... A lot of the guys say my car sound nice ... I would buy Thermal gain if I had to
96GST --> Sold 97TSI 13.00@104 <--Sadly SOLD 2003 Mustang New Project
|
|
|
Re: 3" or 2.5" is there a big difference
#22940
March 05, 2002 01:03 am UTC
March 05, 2002 01:03 am UTC
|
Joined: Dec 2001
Posts: 979 Ottawa
Yasar Issa
OP
Serious Member
|
OP
Serious Member
Joined: Dec 2001
Posts: 979
Ottawa
|
So far what I got is It's not worth it to go to a 3" unless you have a 20G or bigger. I will also be slower off the line? If I go with the 2.5 I should be OK... and not lose to much on the bottom end?
96GST --> Sold 97TSI 13.00@104 <--Sadly SOLD 2003 Mustang New Project
|
|
|
Re: 3" or 2.5" is there a big difference
#22941
March 05, 2002 01:13 am UTC
March 05, 2002 01:13 am UTC
|
Joined: Dec 2001
Posts: 896 Ottawa
Tom Whelan
Member
|
Member
Joined: Dec 2001
Posts: 896
Ottawa
|
Yasar, I have 3" all the way. You want to take a look, have a listen and go for a ride (drive) in my car to see what the 3" Thermal etc is like, let me know. We can meet somewhere and you can see if you like it. Personally, I understand what everyone is saying about low end power etc but frankly, I am not sure if I would be able to tell the difference.
Like Darko says, not alot of difference with smaller turbo applications BUT, in years to come, pick up a used 20g for alot less, you will not be kicking yourself having a smaller exhaust. That is why I went 3". I have a 16g now, hopefully, in a few years, I can bolt the 20g on because all the fuel upgrades etc will be done already. That is why I went 3". Planning for the future. Send me an email if you want to have a listen. I would buy the Thermal again.
|
|
|
Re: 3" or 2.5" is there a big difference
#22943
March 06, 2002 07:04 pm UTC
March 06, 2002 07:04 pm UTC
|
Joined: Nov 2001
Posts: 35 Snohomish, WA
Darryl Lang
Member
|
Member
Joined: Nov 2001
Posts: 35
Snohomish, WA
|
The first couple feet of exhaust after the turbo is the most important part. Most turbocharged engines will make more power with a 3" downpipe and 2.5" exhaust, than they will with a 2.5" downpipe and 3" exhaust.
On the small turbos, there probably isn't as much of an advantage, but the larger pipe generally will help spool the turbo quicker in all cases...it may not give any more power than the 2.5" if the flow isn't needed. The general idea to using a large downpipe is that it causes turbulence in the exhaust to reduce the swirling effect of exhaust leaving the turbine. Swirling exhaust doesn't travel (linearly) as fast as the turbulent exhaust.
Lastly, behind a turbo, there is not a problem going with too large of pipe for the engine. The backpressure that's necessary for low end torque is provided by the turbo. Anything after the turbo just slows the turbo down. No exhaust would be preferred.
Darryl Lang '96 Eclipse GST, auto @ 18psi '78 Mustang II T-Top, 351W 5spd, 310rwhp & 353rwtq '78 Mustang II Coupe, 2.3L Turbo, 174rwhp & 201rwtq (old engine, no I/C) '77 Mustang II Mach 1, 5.0L 5spd
|
|
|
Re: 3" or 2.5" is there a big difference
#22944
March 07, 2002 04:14 am UTC
March 07, 2002 04:14 am UTC
|
Joined: Sep 1998
Posts: 6,079 Mississauga, Ontario
Jeff Mitchell
Senior Member, with Far TOO Much Time on Their Hands
|
Senior Member, with Far TOO Much Time on Their Hands
Joined: Sep 1998
Posts: 6,079
Mississauga, Ontario
|
Originally posted by Darryl Lang: The first couple feet of exhaust after the turbo is the most important part. Most turbocharged engines will make more power with a 3" downpipe and 2.5" exhaust, than they will with a 2.5" downpipe and 3" exhaust. This is backwards from everything I've ever heard, and seems contradictory to your assertion that the best exhaust is no exhaust. You want the smaller pipe where the exhaust is hot and the velocity is high (i.e. at the turbo side) and the larger pipe where the exhaust is cooler and the velocity is lower. Think of blowing into the small end of a cone, then blowing into the large end of a cone. Which one is harder? Besides, putting the smaller pipe downstream will cause a major flow problem when the pipe suddenly reduces from 3" to 2.5" and some of that exhaust smacks into "the wall" and slows eveything down.
|
|
|
Re: 3" or 2.5" is there a big difference
#22945
March 07, 2002 03:56 pm UTC
March 07, 2002 03:56 pm UTC
|
Joined: Nov 2001
Posts: 35 Snohomish, WA
Darryl Lang
Member
|
Member
Joined: Nov 2001
Posts: 35
Snohomish, WA
|
Except you forgot what I said about the exhaust swirling on it's way out of the turbo...
All you need is one book...Turbocharging by Hugh McKinnes. Plenty of other books on turbocharging also discuss this same behavior with exhaust.
What you're saying about small pipe keeping the velocity up by keeping the temperature up right after the turbo really only applies to N/A engines. Also, I'm not saying a 3" downpipe to 2.5" catback is preferred. 3" all the way back would be better still, but the first upgrade to exhaust should be the downpipe.
Darryl Lang '96 Eclipse GST, auto @ 18psi '78 Mustang II T-Top, 351W 5spd, 310rwhp & 353rwtq '78 Mustang II Coupe, 2.3L Turbo, 174rwhp & 201rwtq (old engine, no I/C) '77 Mustang II Mach 1, 5.0L 5spd
|
|
|
Re: 3" or 2.5" is there a big difference
#22946
March 07, 2002 04:31 pm UTC
March 07, 2002 04:31 pm UTC
|
Joined: Sep 1998
Posts: 7,944 Halifax, NS
Troy Jollimore
Senior Member, with Far TOO Much Time on Their Hands
|
Senior Member, with Far TOO Much Time on Their Hands
Joined: Sep 1998
Posts: 7,944
Halifax, NS
|
You're also forgetting the Combined Gas Law. A high temperature gas takes up more space, and 'contracts' as it cools. So the big pipe right after the turbo still makes sense.
My 2.5" necks down to 2.25". Can't say I really notice any loss of power, but we'll see what I get with a 3" exhaust. (:
|
|
|
|
|