To 3" or not 3" ?

[Timbo]

Neil, that doesn't really make sense. AFAIK, Milltek only makes a full system for the Pog (am not sure one has ever been delivered in Australia -- or a DP, if they do in fact do one) and the line about making a bigger pipe only for a bigger turbo is supported more by the desire of marketing people to segment the market (in the same way VAG does) than actual data relating the DP to the stock turbo.

I'm still scratching my head to understand how the primary cat works as a stand-in resonator when it's basically filled with catalyst.

Regardless, my stock exhaust was flow tested before I had a DP built. The biggest restriction in my stock system (which still includes the middle resonator) was the stock turbo to cat pipe. The exhaust tech then explained the maths to me about going to 3" rather than 2.5".

Why go to 3"? Because even a 2.5" will restrict flow at its bends. So, having 2.5" full system from the cat back will still suffer from the bend restriction prior to that, and thus reduces the benefit of the 2.5" system. Wa a a y back, Guy did his initial work on a custom Pog 2.5" exhaust, and found little to be gained. Has this changed?

As far as I am concerned, the proof of the 3" DP is on the table and I'm not sure why people argue against it, without putting forward alternative evidence

[Blitzen]

Is it just me, or do the storm clouds seem to be forming(tongue firmly in cheek)

[VW GTI]

As far as I am concerned, the proof of the 3" DP is on the table and I'm not sure why people argue against it, without putting forward alternative evidence

Have you got a link to your dyno graphs somewhere?

[GT3]

As far as I am concerned, the proof of the 3" DP is on the table and I'm not sure why people argue against it, without putting forward alternative evidence

Ok I guess I got it wrong, what would I know.

For those who think Tim's isolated anomaly is compelling evidence, then go ahead with a 3" DP, it's your choice. I've tried to do the right thing and caution against it.

[Timbo]

Have you got a link to your dyno graphs somewhere?

Here's the first time I posted them, and this is the second time.

For those who think Tim's isolated anomaly is compelling evidence, then go ahead with a 3" DP, it's your choice. I've tried to do the right thing and caution against it.

Caution against what?

Neil, I would simply observe -- even though you seem to think deleting posts changes history -- that you have been singularly negative towards the whole idea of a 3" DP since I first posted, challenging the results, the dyno etc, etc. For what reason I don't know ?:

Yes, it is up to people to make their own minds up, based on the evidence they are able to see. Equally, as I have repeatedly maintained, it is important to get this mod done by an experienced and well-qualified exhaust technician. I certainly would avoid any chop shop that also suggests removing any part of the catalytic converter

[Spec83]

VW designed that specific section to be quiet, that's why they added the primary cat, which functions as a stand-in resonator. This was a counter-balance for having no resonator between the cat and rear muffler

My stock exhaust (or what I thought was stock) has a resonator between the cat and rear muffler... I am confused??

[VW GTI]

My stock exhaust (or what I thought was stock) has a resonator between the cat and rear muffler... I am confused??

Old Polos had this.

Timbo: I don't believe the downpipe can make 13kw atw on its own, but I do agree it's made an improvement. There are still way too many variables to say it makes 12-13kw atw, even using the same dyno.

[thestu]

well for power right through the power band i would say 2.5" because the 3" would loose a lil down low as you said but for the exhaust note and for driving at full noise 3" depends is it a daily?

[GT3]

..even though you seem to think deleting posts changes history -- that you have been singularly negative towards the whole idea of a 3" DP since I first posted, challenging the results, the dyno etc, etc. For what reason I don't know ?:

Yes I've come to realise you don't appreciate anyone questioning the merits of this mod, me in particular. ..which is consistent with your views on other mods, eg air intake. ..and why resort to phrases such as "AFIK", "I observe"? ...bc it's just another way of saying "I'm not really sure" - which is nothing more than prejudiced opinion.

When someone else can reproduce the results you got with a 3" DP on a stock Polo GTI, then that would make it two substantiated cases, which is better than one! Even then, peak power figures on a dyno are meaningless on their own. The loss of low-end, loss of boost, distorted power bands, poor AFR etc etc are all equally important.

..and yes, again, you're right, I've been singularly negative and hostile to the mod. In fact, I was so opposed to it, I actually tried it.

[thestu]

wait this is for a polo isn't it? i dunno if anyone knows guy harding he does apr for aus he had a polo gti got it dynoed with and without an exhaust it actually lost power with the after market apr exhaust. worked out that the original polo exhaust was the bomb (perfect).

this polo also had a K04 and went past the gti golfs with 4 people in it