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Discussion Starter #1
Hi All,

I have a 2002 GTV V6 which as I understand will adhear to Euro 3 specifications which means it has two catalytic converters in each of the manifolds. My tuning insticts suggest that a manifold which instantly dives into a cat is actually going to really hinder performance and so there should be some significant gains to be had by removing them (15-20BHP?).

First question... is the 15-20BHP realistic? I'm not going to bother doing this for any less to be honest...

Second question... what do people know about the emissions situation? From what I can see there is little difference between Euro 2 and Euro 3 in terms of measured emissions, so as long as I keep the main under car cat do you think I will pass a UK MOT?

I know that I can use the manifolds off of many of the V6's in terms of them mating to the head, but, what I am concerned about is mating them up to the downpipes! I have seen a thread which shows the use of 164 or 166 manifolds but these had to be extended with some fiddly welding to mate up with the std downpipes. Needless to say, I would like to avoid this!

Third question... are there any options out there that would mate up exactly with the Euro 3 GTV downpipes - i.e. a straight swap of the manifolds?

Fourth question... last one... failing the above, could I use both the manifolds and the downpipes from an early GTV V6 (i.e. pre '99)? Even if they didn't mate exactly with the under car cat at least that would be an easier join to make...

Any thoughts or experience much appreciated guys!

Cheers,

Chris
 

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I think there is only 2bhp difference between the CF2 V6 cars and the later CF3 cars (218bhp v's 220bhp), so removing the manifold cats won't make much difference IMO.

If you were to remove them the car would still pass the MOT however, as they are there to reduce emissions as the main cat warms up, so as long as the main cat is hot you will be fine.


I cannot answer the third and 4th questions.
 

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Hehe you mean my thread, well as i searched, all manifolds without cats have only 2 holes on the flange, where original have 3 holes.
It's not so hard to weld new flanges in an exhaust shop, i did it myself that's why it's not the best by the looks.

I think you can use secondary pipes from the car that you will take the manifolds, then it should go together without the problem.

About HP gains, anyone who knows how the catted manifold looks, will see that there is great benefit with manifolds that are originally withouth cats.
 

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I think there is only 2bhp difference between the CF2 V6 cars and the later CF3 cars (218bhp v's 220bhp), so removing the manifold cats won't make much difference IMO.

If you were to remove them the car would still pass the MOT however, as they are there to reduce emissions as the main cat warms up, so as long as the main cat is hot you will be fine.


I cannot answer the third and 4th questions.
Have to agree. Also the joining and bodging together puts me off. I did a thread a while back regarding manifolds for the GTV. I got in contact with a company called Mario Designs in Hong Kong but worked out VERY ££££ (about 3k) Alfaholics offered to make some but I don't think it's worth it IMHO and will kick the sensors off for sure. Just decating the floor pan cats makes a hell of a difference to the CF3 engines (4 cats) and
C02's are bob on :thumbs:
 

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Discussion Starter #5
I know the difference in the production engines is only 2BHP, but Alfa could have made any number of little tweaks to up the power elsewhere to make up for the cat losses... Logic just says to me that they must significantly impeed gas flow which at the manifold is critical to performance...

I'm also not keen on welding extensions to the manifolds, mostly due to the time it would take to get the right pattern hence the question about using different downpipes as well...

Anyone else have any thoughts on potential power increase + how difficult it actually is to remove the manifolds?

Cheers!

Chris
 

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Discussion Starter #6
Hehe you mean my thread, well as i searched, all manifolds without cats have only 2 holes on the flange, where original have 3 holes.
It's not so hard to weld new flanges in an exhaust shop, i did it myself that's why it's not the best by the looks.

I think you can use secondary pipes from the car that you will take the manifolds, then it should go together without the problem.

About HP gains, anyone who knows how the catted manifold looks, will see that there is great benefit with manifolds that are originally withouth cats.

Thanks for that, that's helped to confirm I think that the best route would be manifolds and down pipes off a pre 2000 GTV...

Any plans to get yours on a rolling road to see the numbers?
 

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Discussion Starter #7
Guys... found some really good info which only seems to confirm that this is worth doing performance wise and works in terms of MOT and ECU... but...

... I now have some reservations about how easy it is to actually remove the manifolds with the engine in the car?

The manual suggests it's pretty easy, whip off the strut brace at the front and the inlet plenum at the back, undo all bolts and simply lift the manifolds upwards and out through the engine bay. Is it really this simple? I can sense horror stories here...
 

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I think the 2hp difference could be a pie in the sky number, plucked out of the ether. By the looks fo the photos of the insides posted recently they look very restrictive
 

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Discussion Starter #10
I think the 2hp difference could be a pie in the sky number, plucked out of the ether. By the looks fo the photos of the insides posted recently they look very restrictive
They certainly do! I wouldn't be supprised if Alfa revised the mapping or even the cylinder head porting a little in order to keep the outputs broadly similar...

I know from tuning older engines that when binning the std cast manifold for decent tubular items you could easily realise 10BHP, and that was on a really small capacity engine so it just show how critical they are...

@ ChrisH

I'm not planing any rolling road session yet, because i'm gonna make a few more mods to the car.
But i easely beaten an alfa 156 gta sw, and my car has 1460kg.
Just looked at your videos again, you're crazy! The drive up that hill the car is sideways more than straight! Great vids though... can I ask one more question, the noise of your car now, have you also changed the silencer configuration? It would be a little too noisy for me day to day and whilst Im happy to get a slightly raspier exhaust note by loosing the pre cats I don't want it booming... I also notice your engine warning light was on in one of the vids?

P.S. was that track a karting track? looks small...
 

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Some nice video clips there .............looks like some of the local truck drivers must get the occasional scare :p
 

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I have the Alfaholics De-Cat front pipe on my Twinnie with a sport main cat.No problems at all when MOT'd. Although i dont notice it so much now, the car felt much more responsive with more torque when i first picked it up. Sounds much better also:cool:
 
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