Straight pipe instead of catalist - Alfa Romeo Forum
You are currently unregistered, register for more features.    
Tuning & Upgrades Discuss performance enhancements for your Alfa Romeo

 
Thread Tools
(Post Link) post #1 of 17 Old 11-07-14 Thread Starter
Status: Trying to make sense of it all...
AO Member
 
bernas68's Avatar
 
Join Date: Feb 2011
Location: Portugal
County: Cascais
Posts: 212

Member car:

2000 156 3.0 v6

Straight pipe instead of catalist

Hi guys,

Ok, so what kind of gains should I expect if on my CF2 156 Selespeed I would remove the cat and put a straight pipe in its place?
Please bear in mind that on the CF2 the (only) lambda sensor is before the cat, so the ECU wouldn't notice the absence of the cat...

PS - I have a pipercross air filter (the foammy type) a GTA pipe for the v6 mod and am expecting the arrival of a set of Denso Iridium Power IU22 and IK20.

Thanks for your input!

Cheers,
Bernardo
bernas68 is offline  
Sponsored Links
Advertisement
 
Status: Race cars in progress
AO Silver Member
 
Gertie's Avatar
 
Join Date: Oct 2007
Location: South Africa
County: Gauteng
Posts: 5,993
Garage
If you let the exhaust breath better, your intake mod will come more to life too It is well worth the effort. You will get gains yes, but not 10% more power. ECU won't notice the lack of cat. Even in 3 lambda V6 motors we successfully remove cat's without errors.

Hope you have a nice taper to match the throttle to the intake pipe - any step decrease in diameter will slow down airspeed and thus loose power

As for the special Iridium Spark plugs - don't expect the world of difference - only if your current sparks plugs are TOTALLY fouled will you FEEL a difference. Those spark plugs will most probably just last longer.
Gertie is offline  
(Post Link) post #3 of 17 Old 15-07-14 Thread Starter
Status: Trying to make sense of it all...
AO Member
 
bernas68's Avatar
 
Join Date: Feb 2011
Location: Portugal
County: Cascais
Posts: 212

Member car:

2000 156 3.0 v6

Thanks Gertie!

I think I'm going to get a straight pipe in that case and I'll let you guys know how it turns out.

Gertie, sorry but what exactly do you mean when you say "Hope you have a nice taper to match the throttle to the intake pipe - any step decrease in diameter will slow down airspeed and thus loose power"?
Basically, what's a "taper"? (doh!)
(Sorry, me no speak very good English, very difficult language for me to understand, yes. )
bernas68 is offline  
Status: Roarrrrrrrr!!!!!
AO Member
 
lewrot's Avatar
 
Join Date: Apr 2014
Location: United Kingdom
County: Kent
Posts: 173
Sorry to hike your thread, I have a 97 gtv. Am I legally allowed to permanently remove the cat and I stall a decat pipe. I can't remember what year the 'shut off' was.
lewrot is offline  
Status: -
AO Platinum Member
 
David C's Avatar
 
Join Date: Aug 2003
Location: London, England
Posts: 29,952
Quote:
Originally Posted by lewrot View Post
Sorry to hike your thread, I have a 97 gtv. Am I legally allowed to permanently remove the cat and I stall a decat pipe. I can't remember what year the 'shut off' was.
No.

Cats became compulsory in 1992.
David C is offline  
Status: Race cars in progress
AO Silver Member
 
Gertie's Avatar
 
Join Date: Oct 2007
Location: South Africa
County: Gauteng
Posts: 5,993
Garage
Quote:
Originally Posted by bernas68 View Post
Gertie, sorry but what exactly do you mean when you say "Hope you have a nice taper to match the throttle to the intake pipe - any step decrease in diameter will slow down airspeed and thus loose power"?
Basically, what's a "taper"? (doh!)
(Sorry, me no speak very good English, very difficult language for me to understand, yes. )
A taper changes slowly.
I am just worried that you have GTA pipe (80mm??) and mating that to the 72mm?? throttle That lip will cause the air flow to slow down.
If you change diameter it must be smooth:
Straight Reducing Silicone Hoses - AutoSiliconeHoses.com - Silicone Hose Store - Buy Silicon Direct
Gertie is offline  
Status: -
AO Platinum Member
 
David C's Avatar
 
Join Date: Aug 2003
Location: London, England
Posts: 29,952
Quote:
Originally Posted by Gertie View Post
I am just worried that you have GTA pipe (80mm??) and mating that to the 72mm?? throttle That lip will cause the air flow to slow down.
You've misunderstood.
The pipe he is talking about is the feed INTO the air filter housing.
David C is offline  
Status: Race cars in progress
AO Silver Member
 
Gertie's Avatar
 
Join Date: Oct 2007
Location: South Africa
County: Gauteng
Posts: 5,993
Garage
Quote:
Originally Posted by David C View Post
You've misunderstood.
The pipe he is talking about is the feed INTO the air filter housing.
Aha - ok cool that makes sense. Thanks
Gertie is offline  
(Post Link) post #9 of 17 Old 16-07-14 Thread Starter
Status: Trying to make sense of it all...
AO Member
 
bernas68's Avatar
 
Join Date: Feb 2011
Location: Portugal
County: Cascais
Posts: 212

Member car:

2000 156 3.0 v6

Like DavidC said!

Anyway, thanks for all the advise guys, I'll keep you posted.

Cheers,
Bernardo
bernas68 is offline  
Status: Medication time!
Unregistered
 
Join Date: Jun 2014
Location: United Kingdom
County: Devon
Posts: 299
Quote:
Originally Posted by bernas68 View Post
Hi guys,

Ok, so what kind of gains should I expect if on my CF2 156 Selespeed I would remove the cat and put a straight pipe in its place?
Please bear in mind that on the CF2 the (only) lambda sensor is before the cat, so the ECU wouldn't notice the absence of the cat...

PS - I have a pipercross air filter (the foammy type) a GTA pipe for the v6 mod and am expecting the arrival of a set of Denso Iridium Power IU22 and IK20.

Thanks for your input!

Cheers,
Bernardo
Hi Bernado,

Perhaps I am missing something here, but how about a sport cat?

Jetex Performance Exhausts - Suppliers of Sports Exhaust Systems, Custom Exhaust Parts, Sports Catalytic Converters and Replacement Aftermarket Catalytic Converters, Air Filters and Induction Kits

ATB, Ray.
Mista Smiff is offline  
(Post Link) post #11 of 17 Old 16-07-14 Thread Starter
Status: Trying to make sense of it all...
AO Member
 
bernas68's Avatar
 
Join Date: Feb 2011
Location: Portugal
County: Cascais
Posts: 212

Member car:

2000 156 3.0 v6

Thanks Ray,

But I'm really trying to obtain the best possible flow without spending too much money for now. And if I don't like the sound it will make (too noisy or too metallic), I can always go back.

Cheers,
Bernardo
bernas68 is offline  
Status: Medication time!
Unregistered
 
Join Date: Jun 2014
Location: United Kingdom
County: Devon
Posts: 299
Quote:
Originally Posted by bernas68 View Post
Thanks Ray,

But I'm really trying to obtain the best possible flow without spending too much money for now. And if I don't like the sound it will make (too noisy or too metallic), I can always go back.

Cheers,
Bernardo
Hi Bernado,

I understand, well slip a bit of suitably sized pipe in place and give it a try, nothing ventured nothing gained as they say?

ATB, Ray.
Mista Smiff is offline  
Status: -
AO Member
 
Join Date: May 2012
Location: United Kingdom
County: Hampshire
Posts: 517

Member car:

1.9CDTI 16v

I don't think you'll see any gains at all, it will just help with EGTs. The Pipercross filters gave no more power than a standard paper filter when I tested them back to back but the K&N cotton filter gave a noticeable difference.
nutron is offline  
Status: Medication time!
Unregistered
 
Join Date: Jun 2014
Location: United Kingdom
County: Devon
Posts: 299
Quote:
Originally Posted by nutron View Post
I don't think you'll see any gains at all, it will just help with EGTs. The Pipercross filters gave no more power than a standard paper filter when I tested them back to back but the K&N cotton filter gave a noticeable difference.
I fitted my Hyundai Tucson with a K&N a couple of years ago and so far quite pleased with it, I have been thinking of doing it to my Spider, basically cos it's a fit and forget in real terms for me.

Could you expand a bit on what you found?
Mista Smiff is offline  
Status: Race cars in progress
AO Silver Member
 
Gertie's Avatar
 
Join Date: Oct 2007
Location: South Africa
County: Gauteng
Posts: 5,993
Garage
Quote:
Originally Posted by nutron View Post
The Pipercross filters gave no more power than a standard paper filter when I tested them back to back but the K&N cotton filter gave a noticeable difference.
Air Filtration Test

He says something similar. Found this yesterday
Gertie is offline  
Status: -
AO Member
 
Join Date: May 2012
Location: United Kingdom
County: Hampshire
Posts: 517

Member car:

1.9CDTI 16v

I just put my car on the rollers, ran with standard panel for a bench mark, then fitted the pipercross and got actually a few hp less but it would have been warmer from sitting a few minute. Then I swapped to the K&N and ran again straight away and got about 8hp more than the standard filter. This was with a standard GT1749 turbo at the time, so I would expect effects to be higher with boost raised on a larger unit.

It should be noted that both the pipercross and K&N are oiled filters and I've had to change MAF once for the oil killing it. I now just refresh a standard paper filter more often.
nutron is offline  
(Post Link) post #17 of 17 Old 23-07-14 Thread Starter
Status: Trying to make sense of it all...
AO Member
 
bernas68's Avatar
 
Join Date: Feb 2011
Location: Portugal
County: Cascais
Posts: 212

Member car:

2000 156 3.0 v6

It has been done!

I must tell you my first impressions: much quicker response below 3,000 rpm and the noise isn't too loud.
I think I'm keeping it like this!

Next up: new spark plugs (Denso Iridium IK20 and IU22 - or vice-versa)

Cheers,
Bernardo
bernas68 is offline  
Reply

Go Back   Alfa Romeo Forum > Supported Alfa Romeo Models > Technical & Vehicle Assistance > Tuning & Upgrades

Tags
catalist , pipe , straight

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome