2.75" V's 3" - what do you think?..

[A80Avant]

would an increase of the cat back system from 2.75 to 3inch tubes have any marginal effect on backpressure?

will it become quite louder or is that something that has to do with the boxes anyway?

If the boxes are already 3inch internally,will changing to 3inch tubes have bigger effect in noise ?

Im going to go shortly to a shop nearby to have my downpipe slightly modified and i was wondering if it was worthwhile going to 3inch catback tubing from 2.75 . previous exhaust guy told me that the boxes were 3inch internally and in the future if i was going for more hp,he could just swap them for 3inch ones,but left the 2.75 for less noise. I dont really believe everything he said,especially about the boxes,but i was wondering if it was going to be worth having that done as well or not.

[GazzaG60]

id say no.

gas speed is at its greatest at the downpipe. then you have a restriction.

basically after the cat the gases are a lot cooler.

look at a performance cat ideally in a removable pipe. just after the downpipe. you then have the option to remove and refit once a year for a "track day"

there no doubt on your car a 3" system would be a benifit if yoyu can handle vibration and noise.

there is another option. make the system from mild steel. this would cut noise quite heavily.

[Rusty]

id say no.

gas speed is at its greatest at the downpipe. then you have a restriction.

basically after the cat the gases are a lot cooler.

look at a performance cat ideally in a removable pipe. just after the downpipe. you then have the option to remove and refit once a year for a "track day"

there no doubt on your car a 3" system would be a benifit if yoyu can handle vibration and noise.

there is another option. make the system from mild steel. this would cut noise quite heavily.

This is the reason I am happy with my system even though it drops to 2.5" for the rear section, the gas density will be much higher at this point so a drop in bore will maintain gas velocity although there will be more restriction...

[GazzaG60]

density is lower and velocity is infact lower hence the reason a smaller pipe is not a restriction. otherwise you would have a jet of gas from the tail pipe. more heat, more velocity hence the reason for the use of wrap.

the 3" over the axle is a pain. i have 3" straight through, no cats, 1 box, the 034 2 pipe one.

ideal for a big power setup thats road legal would be i think. 3.5" downpipe, 3" middle, 2.75 rear.

[A80Avant]

right,
i had a talk at that place and basically they aggreed that there is no immediate need to go to 3inch at the moment.On the other hand he wouldnt like to just change the tubing anyway,so im not going to spend more money on a 4th!!! catback anyway.I may try it on in Greece on the same place i go this one,and see how it goes.Otherwise i may just go for the new turbo at some point and i find it that im having to add too much fuel to get the EGTs down,i may try something.

I may even go at a 80mm downpipe and nothing more. My cats are 200cpi race cats from BN pipes and since there are 2 of them with more than 100mm diameter,they are not causing that much of a restriction to the whole system. If it was just one,then i would think of a possible restriction there.

Anyway i got booked early March to have the downpipe modified starting from a small cone to a 76mm as close as possible to the turbo,add an EGT and a wideband plug as well,so that i can therefore get my hands on the VEMS thereafter!!

[madpugger]

how much was it out of interest?

£830 i think, there or there abouts.

[europeanme]

aaarrgghhh......

still no nearer making a decision....

[Jamo]

downpipe 3" rest of the system 2.75 to reduce noise with centre and rear box.

[Rusty]

Drove mine a bit the last couple of days and it's perfect. Not loud at all (in fact a lot quieter than the BM) apart from WOT where it howls. Will get some in nad out car video this week hopefully.

[Bram]

Yeah!

[europeanme]

cheers andy that would be great...

[Ross]

Only go for a 3" downpipe if you want total hell when it comes to fitting it

[QuattroFever]

boom can be induced by having outlet too short in relation to body, been there and seen that also. Yes, it's much nicer looking when nicely tucked with bumper cover, but reality is, 1-2" longer outlet and presto, welcome silence

Just had the tailpipe extended out on mine and it's made the world of difference.

I've got a stock downpipe modded to a single pipe instead of that dodgy looking y-peice, into a 2.75 inch sport cat then 3" from there right out the back and one 5" round box at the rear about 10" long.

used to have a big 10 x 8 box on the rear but it was too quiet for me.
I found the bigger box made the deeper tones more boomy too.

If you're keeping the standard cats I think 2.75 and one box would suffice, but using a sport cat and/or downpipe I would go with a 3" and two boxes both as close to the rear as poss. to cut out most of the resonance.

If you're quite reserved and not chav like me

[merlin's S4]

Only go for a 3" downpipe if you want total hell when it comes to fitting it

Sounds like you're speaking from experience!! Just read about your's on your thread.

[S2central.net]

Very timely this one... My zorst is just starting to blow a little and it looks dreadful underneath - more rust than the titanic.

What options - off the shelf (not custom build) do I have on an S2 Coupe for a 76mm (3") downpipe and 70mm system - probably with two boxes. I can run without the cats and wish to delete the stupid Y sections ???