To 3" or not 3" ?

[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

[GT3]

..worked out that the original polo exhaust was the bomb (perfect).

..really? bugger me - well that settles that!

[mitch_gti]

You are all a bunch of school girls.


Part of owning your own car is the pleasure of being able to make your own decisions as to what you do and dont do to the car.

I think this thread should be locked up.

[RhysQ]

i dunno if anyone knows guy harding

guy harding? nope, never heard of him.....oh wait, is he the guy that posts on here all the bloody time

personally, i like the sound of the stocko exhaust so i will be sticking with that. if i was to upgrade however, it would be to a Milltek 2.5" cat back.....mmmmmm

[mazgtr]

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.

I have the REVO Tune on my Polo GTI like Timbo. I also have had a custom 3inch DP installed by Castle Hill Exhausts.

From driving my car since the DP mod, it has not lost any power down low.

The car now comes on boost harder and faster than before.

The improvement in the cars midrange is fantastic, the extra torque overpowers the front tyres far more reguarly.

The REVO tune's most impressive improvement IMO was the cars increased mid-range torque. With the 3inch DP it simply has even more.

Tims results of around 10-12kw at the wheels is accurate IMO.

[Blitzen]

At the end of the day, it comes donw to your own hard earned cash...If your happy with the mods you have dine ti your own car, then so be it...Add a 2.5inch, 3 inch, 15.55327 inch pipe...as long as you are happy with it, go for it, cos at at the end of the day, unless you are a really sad case that relies on your parents for your spending money, you don't deserve to have a car...

[Sharkie]

Guy himself did tell me when I looked at the prototype of the full APR Polo GTI exhaust, almost 2 years ago now, that it made all of 1kw difference on the dyno.

I was very keen on buying one and loved the sound. But to me $2000+ for 1kw was not worth it.

I did love taking the K04 red beast for a drive though and plan on doing the K04 next year for sure.

As to an exhaust, I'll take my time and also try both a 2.5" and a 3.0" dowpipe before committing. Even if it means driving to Newcastle ....

Mmmm, maybe I should ask Guy if I can do a trial ..... on the dowpipe that is....

[GT3]

Guy himself did tell me when I looked at the prototype of the full APR Polo GTI exhaust, almost 2 years ago now, that it made all of 1kw difference on the dyno.

Sharkie, keep in mind that when I bolted the same full 2.5" exhaust on my Polo GTI, it gave another 12.5 kw atw. ..and I think your approach is right, go with what works, test it (not just on a dyno) and see for yourself.

[thestu]

guy harding? nope, never heard of him.....oh wait, is he the guy that posts on here all the bloody time

personally, i like the sound of the stocko exhaust so i will be sticking with that. if i was to upgrade however, it would be to a Milltek 2.5" cat back.....mmmmmm

haha ohhh sorry guy i used to work at volkspower you have probably seen me around.

but it is true yes the apr exhaust lost power?

[Guy_H]

I suppose the only real way to tell is to get the same car & try two downpipes on it, back to back

When we did it back in 06' our exhaust developer built 3" reducing to 2.5 catback & 2.5" all the way through. He ran dynos on both (back then) and there was power from both, and he found significantly more low & mid range from the 2.5, but the 3" passed it at (from memory) 5000rpm & provided more up top. The torque dropped off in the 3" around 4200rpm, where the 2.5" held it until after 5000. Then he put the standard rear exhaust on & we found little difference in the power output. We have not use him since 2006 ( He exclusively does off road 4WD systems now), but I sent him an email to see if he had the original dyno's from testing & if I can go pick them up.

We also did a heap of testing on the MKIV Golf back in 05' with 3" & 2.5" & found pretty much the same results - one thing on the MKIV though was the internal cabin noise almost doubled with the 3" piping!

If anyone has a 3" system, it will be interesting to overlay the curves of where it makes it's power compared to 2.5" when we do the polo dyno day in August.

[GT3]

If anyone has a 3" system, it will be interesting to overlay the curves of where it makes it's power compared to 2.5"

I've done just that - overlayed all runs with each respective DP modification:

- Base dyno/stock exhaust (Blue)
- 3" DP (Red)
- 2.5"/3"DP combo (Pink)
- 2.5" DP (Black)

There were three runs each time. Rather than use runs that simply spiked or peaked, we selected the most representative (average) run of each three and charted them.

While the figures may appear low, it's coming from an average base dyno of 116 kw atw. I won't comment on the chart other than to say that (with my car) the 2.5" DP provides as much power as the 2.5"/3"DP combo, with the difference being (on the street) it has much more usable power down low and mid-range.