2.5inch vs 3inch downpipe

[lucifer666]

Im gettin a custom downpipe section so i can run my stage 2 software.

Question is pro speed in cardiff can only do 2.5inch or 3 inch and not 70mm(2.7inch) like milltek. Which one do i choose. Help?

I dont wana limit gains by having it too small but i also dont want it to go the other way and run into problees with a 3 inch.

 

[InFus1on]

Im gettin a custom downpipe section so i can run my stage 2 software.

Question is pro speed in cardiff can only do 2.5inch or 3 inch and not 70mm(2.7inch) like milltek. Which one do i choose. Help?

I dont wana limit gains by having it too small but i also dont want it to go the other way and run into problees with a 3 inch.

It's not gonna make too much difference mate, but if 3 inch is the same price, just go with that.

I can't imagine it will be worth the extra dosh if it is more expensive.

By the way, when are you having it done? I'd love to pop along and have a quick ride in your car to see how a remapped one feels

I'm only 25 mins away from Prospeed.

 

[Mark300zx]

Not sure on the ibiza specs but the general rule on downpipes is the bigger the better to get the turbo plenty of breathing space.

 

[InFus1on]

I can't disagree but I wouldn't necessarily agree either.

The downpipe I assume acts as part of the restriction which stops the turbo from overspooling. I had a similar problem on my old Fabia as there was no restriction in the exhaust and I blew 2 turbos in 2 months. So while a 3 inch is better than a 2.5 inch, there is a limit to the effective size I would say.

 

[lucifer666]

I was thinking though if it was too wide then it would limit low down torque and actually have a slight negitive effect low down. Although it might be necessary for a big turbo upgrade in the future

Im getting a decat btw.

 

[lucifer666]

It's not gonna make too much difference mate, but if 3 inch is the same price, just go with that.

I can't imagine it will be worth the extra dosh if it is more expensive.

By the way, when are you having it done? I'd love to pop along and have a quick ride in your car to see how a remapped one feels

I'm only 25 mins away from Prospeed.

Cwmbran is towards newport. Yeah no worries, be happy to. They dont do weekends so need to find a way around that cz i work

 

[Mark300zx]

I can't disagree but I wouldn't necessarily agree either.

The downpipe I assume acts as part of the restriction which stops the turbo from overspooling. I had a similar problem on my old Fabia as there was no restriction in the exhaust and I blew 2 turbos in 2 months. So while a 3 inch is better than a 2.5 inch, there is a limit to the effective size I would say.

Downpipe helps to reduce lag and improve response and top end, the turbos you blew up were they new or used, as sometimes the removal of a cat can cause the bearings to go on older turbos, at the end of the day tuning a car causes pressure on most components!

 

[VRSLOZ]

Would there be enough pressure from the turbo, being small, for a 3" system?

 

[lucifer666]

It's not gonna make too much difference mate, but if 3 inch is the same price, just go with that.

I can't imagine it will be worth the extra dosh if it is more expensive.

By the way, when are you having it done? I'd love to pop along and have a quick ride in your car to see how a remapped one feels

I'm only 25 mins away from Prospeed.

Cwmbran is towards newport. Yeah no worries, be happy to. They dont do weekends so need to find a way around that cz i work in colchester

 

[Mark300zx]

Would there be enough pressure from the turbo, being small, for a 3" system?

I used to muck about with 300zx's which are basically a 1500cc turbo vee engine, and there were gains to be made with a 3 inch downpipe, over a 2.5 inch.

If you regard the downpipe as an empty chamber which as it fills up air, holds back the turbo's ability to increase spooling, with a 3 inch chamber there is more room to fill and the turbo will spool quicker and more easily, with less build up of exhaust pressure.

Unless there is recognised problem with a 3 inch over a 2.5, I would go 3!

 

[lucifer666]

Spoke to revo earlyer and they said 2.5 to make sure its gt enough back preassure. And a decat 2.5 is like a 3" with sportcat or the milltek 2.7". Will fone miltek 2mz and ask about their testing.

Found this http://www.jetex.co.uk/website/jete...lkswagen&mod=Polo+GTi+10+&mat=Stainless+Steel

 

[VRSfab]

a complete 3" downpipe doesnt work on the polo/fabia/ibiza due to space problems and IC piping . usualy they start 3" and going into 2.7 /2.5 inch after the Kat.

Individual intercooler piping should fix that i guess...

 

[lucifer666]

Let me get this correct. The start of the downpipe can b 3 until where the cat ends. From then 2.5 for remainder

 

[VRSfab]

right.

mine looks like this .

 

[lucifer666]

Can you label which parts are 3" and which are 2.5? Thank you

 

[Mark300zx]

Spoke to revo earlyer and they said 2.5 to make sure its gt enough back preassure. And a decat 2.5 is like a 3" with sportcat or the milltek 2.7". Will fone miltek 2mz and ask about their testing.

Found this http://www.jetex.co.uk/website/jete...lkswagen&mod=Polo+GTi+10+&mat=Stainless+Steel

Back pressure for what, to save the turbo or to keep an extra microsecond of torque?

 

[lucifer666]

Both. They said safer to go 2.5 decat
They said unknown territory

 

[Mark300zx]

Usually the bearings go if the turbo is a bit old, the torque blip is hardly noticeable.

 

[lucifer666]

Mines 35k old? How old is old. Am i right in saying that a 2.5 will protect the turbo more?

 

[Mark300zx]

To be honest these things are very car specific, if there is a history of the tub bearings going after a decat and three inch dp then don't do it, but it is usually the decat that causes the bearing failure.