MK5 Golf GTI
All Things Mk5 => Modifications & Technical Area => Technical Workshop => Topic started by: sm17hy on January 23, 2009, 09:23:21 pm
-
been lookin all over the net. few different exhaust to choose from but the bores range from 2.5" to 3"
am stuck to think which is best?!
i've always thought it better to get rid of gases quick but its back pressure u have to watch out for as well.
so would like all your opinions please :P
-
the way ive always been led to believe is the hose pipe theory
basically when the water is running slowly to remove it from the pipe as fast as possible you need to pinch the end of the hose, therefore saying that at low speeds you need your zorst pipes small. that said, when you increase the water in the hose you no longer need to pinch the end to release the higher flow, indicating that at speed you need a bigger bore.
the answer lies in the happy medium, which itself can be a grey area as it can also depend on the mods you have. too big a pipe and you will lose power, to small a pipe and you will restrict it.
summary, unless you decat i wouldnt stray any further than 3" which should accomodate most mods, give better performance (assuming you upgrade your cars intake at the same time as improving the exhaust gas removal combined with an ECU remap to knit it all together)
3" sounds nice too :wink:
-
oh...and back pressure isnt a relevent issue with a modern car such as the golf, doesnt exist :happy2:
-
thanks for the info! :happy2:
-
what car you got sm17hy ??
2.5 normally on the GTI
3 on the ED30
however at least two members on here have deliberately chosen a 2.5 downpipe as there have been some great dyno results indicating the ed30's work well in this config. This does however fly in convention, and EGT's have never been measured to see if its a problem. Needless to say the cars run brilliantly :happy2:
do lots of forum research, also depends on the level of tune you want to run (std / remapped etc)
Milltek most popular, but APR have the RSC and Matt has just had a custom 3' fitted by Bluflame too
not so sure about the no back pressure thing Very Cherry tbh
-
not so sure about the no back pressure thing Very Cherry tbh
maybe i should put it into context a bit more, the backpressure isnt really influenced when you talking about a modern automotive exhaust as such, as any pressure wont particularly come from the bore of the tube but from any resistence such as bends or obstructions. so not really a concern from a modern day car, in the case of the golf this will only really happen with over complex exhausts that have to move through the length of the car utilise series of complex bends for clearance over undercarraige 'furniture'. the standard route is normally the most direct to avoid these complications.
this means that as long as the shape of the exhaust and route hasnt changed dramatically and no dramatic additions are made to it from the factory design, then the bore when talking in 0.5"s in difference wont come into play
theres more risk of back pressure from running to small a bore rather than too big as the engine cylinders fire at different times, which mean exhaust leaves them at different times thus creating waves of gas. the wave from one cylinder may not completely vacate if the pipe is too small before the next pressure wave makes its way into the mix, in the same way that overcomplicated bends and obstructions can create back pressure so does this and a restriction in the engine's exhaust system can restrict the engine's true performance possibilities
happy mediums, but depends on how much modding you have planned as to how serious you make it, if its just for a bit of noise and hopefully a few horses then its nothing to worry about in that sense
-
Both the standard GTI and ED30 have exactly the same 2.5" exhaust system..
Some of the guys on here are running 70mm (2.75") Milltek downpipes, designed for the K03 GTI, with good results..
Still, the results would be even better with a 76mm (3") downpipe, as I have on my car, you can get away with a 2.5" system on a k03 turbo car, but 2.75 downpipe and 2.5" cat-back is the best IMO.
For K04 you need a 3" full system to see the best results :happy2:
-
As jonny says 3"" system sounds :evilgrin: and you should see better gains if you have that :happy2:
-
Some say that having a 3" with a stock ECU car results in some low-down torque loss - due to the increased air mass required to be moved, however I experienced no loss when mine was fitted. I ran the 3" system with the stock car for three days before I put the remap on.
Not that answers your question, but it may help a little.
Chris.
-
Backpressure? Who needs it when you've got a big turbo in the way :wink: bigger the better on a turbocharged car, if you can stand the noise go for a front exit exhaust :jumping:
-
Both the standard GTI and ED30 have exactly the same 2.5" exhaust system..
Some of the guys on here are running 70mm (2.75") Milltek downpipes, designed for the K03 GTI, with good results..
Still, the results would be even better with a 76mm (3") downpipe, as I have on my car, you can get away with a 2.5" system on a k03 turbo car, but 2.75 downpipe and 2.5" cat-back is the best IMO.
For K04 you need a 3" full system to see the best results :happy2:
I am getting a bit confused with this guys. Is 3" system ok on a KO3 or will it be too big. :rolleye:
-
^ That's my thinking TC, I think 2.75 is best???
-
^ That's my thinking TC, I think 2.75 is best???
For a K03 car I would say no bigger than 2.75" really.. Guys in the US would disagree though, I find the best way is to just try it..
Its going to be a trade off for top end power when you go smaller, as the K03 runs out of boost at about 5k revs its pretty pointless going large on the bore size.. For a K04 which still makes power at 7k its well worth it..
If I go big turbo on mine (GT3071R) then im going to go with an 80mm downpipe and 76mm system..
-
The Yanks think bigger is better by default.
So, a 2.5 will benefit low down torque and a 2.75 will loose a touch of this torque in trade off for a better release at the top of the revs??
-
^ That's my thinking TC, I think 2.75 is best???
For a K03 car I would say no bigger than 2.75" really.. Guys in the US would disagree though, I find the best way is to just try it..
Its going to be a trade off for top end power when you go smaller, as the K03 runs out of boost at about 5k revs its pretty pointless going large on the bore size.. For a K04 which still makes power at 7k its well worth it..
If I go big turbo on mine (GT3071R) then im going to go with an 80mm downpipe and 76mm system..
I understand the logic in 3" being pointless. :smiley: but would it cause any loss in power. :chicken:
-
^ That's my thinking TC, I think 2.75 is best???
For a K03 car I would say no bigger than 2.75" really.. Guys in the US would disagree though, I find the best way is to just try it..
Its going to be a trade off for top end power when you go smaller, as the K03 runs out of boost at about 5k revs its pretty pointless going large on the bore size.. For a K04 which still makes power at 7k its well worth it..
If I go big turbo on mine (GT3071R) then im going to go with an 80mm downpipe and 76mm system..
I understand the logic in 3" being pointless. :smiley: but would it cause any loss in power. :chicken:
It wouldn't loose power, but it would loose bottom end torque, so really its a trade off..
The best set up on a K03 car in my experience is a 2.75" downpipe with no cat, and a 2.5" cat back..
-
Thanks. :happy2:
-
Hmmm, no cat you say?
Do they bring up any warning lights/error codes that need fudging with VAGCOM etc.?
-
....
Milltek's full system is 2.75" on the GTI K03 and 3.00" on the Ed30 K04.
My assumption/expectation is that these sizes will be the result of their development and testing and will also take the established tuners remaps into account.
-
Can someone confirm for sure that the ED30 system from the cat back is the same as the standard GTI system?
-
Just to add my two pence worth:
In simplistic terms, with a smaller diameter zorst pipe, top-end outputs will be resticted, but low-range torque will be increased or enhanced. At the other extreme, a large diameter pipe will have the opposite effect - much better at the top end, but also noticeably worse torque at the bottom end (and also mid-range on a normally aspirated car too).
The 'happy medium' will be to find an exhaust diameter which maintains a decent low- to mid-range torque, whilst not overly limiting top-end power.
Standard discaimers also apply - in that there may be other limiting factors too. If you bolt on a 6" dia zorst, on sommat with a teeny weeny turbo - not only will you look like a chav, but it wont give you any of the 'expected' increases top-end.
And back-pressure - virtually all engines, including our beloved GTI mota, all need some back-pressure - for very teccy/nerdy reasons.
-
Can someone confirm for sure that the ED30 system from the cat back is the same as the standard GTI system?
I have sold one of my catbacks, but to answer your question, here are pictures of a stock gti downpipe and a stock ed30 downpipe, can you tell me which is which?? :laugh:
(https://www.mk5golfgti.co.uk/forum/proxy.php?request=http%3A%2F%2Fi715.photobucket.com%2Falbums%2Fww160%2Fjakethemoss%2FIMG_4909.jpg&hash=93092a2d1a8d6356caf5ccde195e2c2ce2935894)
(https://www.mk5golfgti.co.uk/forum/proxy.php?request=http%3A%2F%2Fi715.photobucket.com%2Falbums%2Fww160%2Fjakethemoss%2FIMG_4910.jpg&hash=ffa127e76b4a1f6a0952f13d6058cbdd30f1f1d8)
And the catbacks were just as similar to eachother.
Buttom line the GTI and ED30 has exactly the same exhaustsystems.
-
Buttom line the GTI and ED30 has exactly the same exhaustsystems.
....No wonder fitting an aftermarket downpipe, such as Milltek TBE, releases more performance from the Ed30's K04 turbo etc.
[TT will correct me if I'm wrong]
-
miltek i think do a 3" for the Ed 30 where as i think its 2.75" for the gti
-
milly dp is 3 inch, cat back is 2.75 inch for the k04 cars. Blueflame and apr do true full 3 inch tbe's.
-
milly dp is 3 inch, cat back is 2.75 inch for the k04 cars. Blueflame and apr do true full 3 inch tbe's.
....I think there's a reason why Milltek do what they do but I've forgotten it! Could be back-pressure related.
-
Since i have it and are over the moon with it APR RSC 3" TBE, then you're ready to go K04 also :wink:
-
k03 the miltek is 2.75" bore straight through aprt from where they join as it reduces there to std 2.5 inch. RR is right it is to do with back pressure, as it will give you a bit more torque from lower down the rev range than a 3" DP will. But a 3" should have its bonus's too. it should achieve slightly more at top revs,
-
milly dp is 3 inch, cat back is 2.75 inch for the k04 cars. Blueflame and apr do true full 3 inch tbe's.
....I think there's a reason why Milltek do what they do but I've forgotten it! Could be back-pressure related.
Would be interested to know why, especially seeing as milly are doing a full 3" system for the focus rs.
-
milly dp is 3 inch, cat back is 2.75 inch for the k04 cars. Blueflame and apr do true full 3 inch tbe's.
....I think there's a reason why Milltek do what they do but I've forgotten it! Could be back-pressure related.
Would be interested to know why, especially seeing as milly are doing a full 3" system for the focus rs.
Almost certainly it's £££ related.. 3" turbo back is the way to go on the KO4 cars but Milltek have already developed a system for the GTi back when it was all KO3 and 2.75" was perfect for them..
The 3" Milltek downpipe for the ED30 / Cupra etc also fits the S3 so that's always a consideration when developing a new part as they only need to produce one jig
-
Since i have it and are over the moon with it APR RSC 3" TBE, then you're ready to go K04 also :wink:
I concur that the AP 3 inch RSC system is superb. Quiet when you want and a belter when your on it.
Definately livens up the top end on stage 2.
-
milly dp is 3 inch, cat back is 2.75 inch for the k04 cars. Blueflame and apr do true full 3 inch tbe's.
....I think there's a reason why Milltek do what they do but I've forgotten it! Could be back-pressure related.
Would be interested to know why, especially seeing as milly are doing a full 3" system for the focus rs.
Isn't the focus RS a 2.5 litre five pot engine? If it is, then the extra half litre displacement may well account for the 3" zorst.