Brun

I've noticed a lot of talk of twin dump and single dump downpipes. I will soon be in the market for the said item, so i was just wondering which would be the prefered option and why?
What sort of money should i be expecting to pay for supply and fitting of a d/p.

Moles Dad

You should try a search on this as the pros and cons have been discussed for ages.

Primarily it is all about keeping the wastegate gasses and the exhaust gasses separate as they leave the turbo housing.

Theory is a wonderful thing

PS. In theory, bees cant fly...but they do

Brun

I did a search, but i found it a little inconclusive.

Moles Dad

OK, sorry.

Well I think I have just about summed it up anyway, the 'argument' is that the wastegate 'dump' should be kept separate from the exiting flow of the turbo so a 'twin dump' does exactly that.
The 'open' type just has a large oval which takes all the gasses in the one downpipe entry.

Have a look at Power Engineerings site and the Scoobysport site for comparisons.

Cheers for now.

nom

Another point of view
bell-mouth (single tube, ScoobySport style) technically is not as good (more turbulence, etc.) but seems to have consistently good results.
twin-dump is technically better as there is less turbulence. However, results appear more varied - I have heard that a possible cause of the problem is the wastegate exit joining the exhaust (rather than being seperated all the way) can lead to a pressure drop across the wastegate exhaust pipe, leading to a few little problems (as there is a partial vacuum behind the wastegate the actuator may well open at the wrong pressure). Sounds plausable.
But then again, the difference also seem to be extremely minor unless going for masses of power & so the best solution is one that is the right price and available

AlanG

I think as far as downpipes are concerned, it really depends what your goals are in terms of power and what car you start off with.

If you have, say, a std UK car and just want a to do a couple of mods ( like exhaust, air filter, maybe a slight increase in boost) to free up some power/torque, then go for a 2 1/2" de-cat downpipe along with a suitable system on the back of it.

The problem with doing this, is that the tuning bug bites and you want more......

If you intend to go big power at some point (internal, whatever), then buy a 3" downpipe, again, with a suitable sysytem.

IMHO if i had an Sti as a base, wanted to improve it a bit, but don't see me upgrading all the time to get like 400 brake, i would go for a 3" system.

As far as twin dump, open neck etc etc, yep probably will make a difference between them, but it will depend on how highly tuned the car is going to be.

Around the 300 brake mark, i don't see any benefit from open neck over twin dump.

Before you all say otherwise, I'm not knocking one over the other but everybody has a different view with what they want to do to their cars. You also have to take in to account the cost against the benfits gained.

A

<Probably get flamed but it is only an opinion...>

Brun

Me thinks that, as i have a Magnex 3.5" i may as well complete the trend with the down and centre pipes. Does anyone know off hand if Well lane Turbos do these two pipes? because they are the nearest Magnex dealers to me.

ustolemyname??stevieturbo

iTrader: (1)

3.5" Magnex?? Thats the biggest one of them Ive heard of. They are all usually 2.5"
IMHO, all this twin dump stuff is bollox. I think its mostly just a bandwagon everyone has jumped onto. The Wide neck SS would be the one I would prefer, although the Magnex Twin dmp is very well priced, and as it is cheaper, so Id probably buy it. Ive fitted a couple of twin dumps, which did look very similar to PE T75, although not sure what make they were. They both hit the steering Universal joint. Apparently this only happened on earlier designs of twin dumps, but I would certainly never buy one that looked like it. They are also absolutely ridiculously priced.
Has anyone actually done any back to back tests with the various designs?

Brun

Whoops, i didn't make myself too clear. I have the 3.5" backbox. So has anyone had a decat section fitted by Well Lane? or am i gonna have to ring them to find out? (yup, i'm lazy)

P20SPD

iTrader: (1)

Sure your not talking about the size of the tailpipe there, and not the bore of the tubing, as i thought all magnex was 2.5 inch bore. It certainly is on my decat centre for MY00.

Brun

Do excuse me! Yup, the end is 3.5". Dunno what the rest is but it ain't 3.5" so 2.5" is probably right.