2.5" vs. 3.0" Cat Back system [Archive] - SaabCentral Forums

: 2.5" vs. 3.0" Cat Back system


WallySaab
2nd March 2004, 05:02 PM
Hey Guys,
I'm considering installing a cat back system. What are the relative merits/disadvantages of using a 3.0" system versus the available 2.5" systems? What will be the performance advantage? Will there be a difference in sound quality? I have installed the PPC system on my 2.0T and it has turned this fun car into a very serious one. I am assuming that stage 2,3 and so forth will include a cat back system. Any thoughts you guy's might have would be greatly appreciated.

joshd2012
2nd March 2004, 05:46 PM
This will bring about serious debate. Some will point to documentation that shows that a 2.5" system is all you need on a system that is producing less than 350HP. Others will tell you that the 3" is the only way to go and that 2.5" is a waste of money when there is bigger available.

My thought is, the freeing flowing the exhaust system is, the better it is for the system. I would say go with the 3" if you have that option. Some will say that you will see no difference between the 2.5" and 3.0" performance wise. I don't think that this fact has sucessfully been proven.

You are also going to want to think about switching to a cone filer for the intake instead of the standard box. It will give you the extra flow you need to utilize your new system.

This leads me to my question for you: where are you getting such a system? I not seen any 2.5" or 3.0" systems used on the SS yet. Who makes this, JT? Or are you getting this custom made?

CallipNCSUsaab
2nd March 2004, 06:14 PM
dont you think you will need some backpressure to spool up the turbo though?

the BSR and saab sport exhaust are both 2.5'' arent they? I know the BSR one is unless I am going crazy

joshd2012
2nd March 2004, 06:20 PM
dont you think you will need some backpressure to spool up the turbo though?

the BSR and saab sport exhaust are both 2.5'' arent they? I know the BSR one is unless I am going crazy

The Saab Sport Exhaust is 2.25" and the BSR is 2.5".

As for your first question, I direct you read this quote from another Saab forum by a member named Dean:


With less back pressure there is less residual exhaust gas in the cylinders, so the volumetric efficiently should increase, so less boost will be required to jam the ECU controlled air mass flow into the cylinders. And then the turbo does not have to make as much boost then, so the wastegate is a bit more open and the turbine is working less to turn the compressor. So the turbine back pressure is lower. So there is another example of the synergy of flow restriction removal in a turbo application.

With the lower boost, I assume the air mass flow is as it was before, but there will be more power as their is less parasitic losses from the turbine back pressure. More responsive too.

That was in responce to the addition of a 3" DP to a T7, but the application to a T8 should be similar. Hope that helps explain why it is better.

Johnken
2nd March 2004, 06:40 PM
Just a pointer, if you don't change the pipings before and incl the cat, the difference between a 2.5" and a 3" cat-back system is, well, slim too none. The cat-back isn't the week point of the exhaust, but mote likely the downpipe from the turbo, and the catalyst. If you are planing on changing the cat and the downpipe in the future, it might be worth going for the 3" system though.

WallySaab
2nd March 2004, 06:42 PM
Joshd2012: here is an old inquiry I made to Group 9 and Maptun. They are coming out with a 3" cat back and I am seriously considering it.

Hi Walt,

It is a brand new piece, so I don't have pics yet. The install is easy,
just unbolt the old one and put in ours. You are best off getting new
hangers as it is easier to cut them off then try to remove them.
The pricing will be about $749 as the cat back is most of the system.
If you want one now, I will have the exhaust guy make one up for your
ahead of the production run.

Thanks!

James


James T. Dale
Group 9 Performance, LLC
401-421-4876 Phone
401-633-6091 Fax
james@group9performance.com
www.group9performance.com


-----Original Message-----
From: Walt Smith
Sent: 2/12/2004 9:50 PM
To: James Dale
Subject: Re: FW:_SV:_Formulär_Maptun


Hi James,
I am very interested in the cat-back exhaust system.
please send me info, pictures, pricing and install
requirements.
Thanks,
Walt
--- James Dale <james@group9performance.com> wrote:
> Hi Walt,
>
> Just to follow up. We have a cat-back exhaust in 3"
> 304 SS for your car as well as an improved
> intercooler.
>
> Do you still want to play with the car?
>
> Thanks!
>
> James
>
>
> James T. Dale
> Group 9 Performance, LLC
> 401-421-4876 Phone
> 401-633-6091 Fax
> james@group9performance.com
> www.group9performance.com
>
>
> -----Original Message-----
> From: MAPTUN
> Sent: 1/5/2004 5:45 AM
> To: walt_a_s@yahoo.com
> Cc: US ÅF
> Subject: SV: Formulär Maptun
>
>
> MaptunHi sir,
>
> So far, we only have an updated intercooler for the
> SS model.
>
> Our US supplier will contact you about it.
>
> Best regads Johnny
> Maptun
> -----Ursprungligt meddelande-----
> Från: Walt Smith [mailto:walt_a_s@yahoo.com]
> Skickat: den 1 januari 2004 01:49
> Till: info@maptun.com
> Ämne: Formulär Maptun
>
>
>
>
>
> Namn: Walt Smith
> Epost: walt_a_s@yahoo.com
> Telefon: 406-363-5303
> Meddelande: Dear Sirs, I am the proud owner of the
> new Saab 9-3 ss w/210
> Hp engine. I am very interested in upgrading the
> ECU. I would like any
> information you have on upgrading the new 9-3 and
> its suitability for
> performance modifications to the motor. I have read
> some posts at Saab
> Central that say the motor is to weak for upgrading.
> Any light you could
> shed on the topic would be greatly appreciated. I
> would also like any
> details you can give me on any performance products
> that you are developing
> for the new 9-3. Thank You Walt Smith

joshd2012
2nd March 2004, 06:56 PM
WallySaab: That is quite interesting. I had heard about MapTun working on some stuff, but not Group 9. I wonder if a 3" DP is also in the works? I would like to replace the entire system at once if at all possible. It is good to hear that it uses the same hangers as the stock system, its just remove old and replace with new. That is key. Thanks for the info.

Cayman1
2nd March 2004, 07:44 PM
I don't believe our level of HP will warrant a 3", a 2.5 should be fine.

And yes, some back pressure is good. I was told that you will loose some top end power with too little back pressure.

moz
2nd March 2004, 07:46 PM
Very interesting, another option to consider :)