bainsy

I know the physical differences..

Can someone advise what the potential power/performance/noise differences are if any?

Thanks

Harps

bainsy

Would it be safe to assume a Twin-Dump and Open Neck Downpipe allows turbo to spool up quicker than a closed neck?

Is a Closed Neck downpipe restrictive?

Anyone?

Boyakasha

iTrader: (2)

I was wondering this as well

I am about to take my car (03 STi) up to 380-400bhp and was wondering what DP I should use.

scoobyDAZZA

u want an open neck 3" down
check out the group buy

bainsy

Hi dazza1802,

why would I want a open neck over a closed neck or twin dump?

I have seen the group buy, but need to know before I buy one..

Probably a simple explanation..

Harps

Comper100

As far as i am aware

Closed Neck - Same as standard downpipe, with flate plate covering the wastegate side of the turbo outlet, thus at high revs the exhaust gassed are forced to hit a 90 degree bend in order to flow out and down the neck, which causes disturbance to the laminar flow of the gas - which in turn creates resistance which the exhaust gases hence engine have to work against = Power Loss.

Open Neck - Has the wastegate side and turbo side funneled down into the neck so that the gasses can escape easiler without resistance, prodrive use this design woth a long funnel neck to aid gas flow = more power. A good Type.

Twin Dump - Uses the same downpipe neck as the closed type but has a smaller diameter pipe that runs parralell for X amount of distance to the main neck, that allows the wastegate side to "breathe" more easily. Some argue that this design is not as effiecent as the open neck type but the difference will be neglegable certainly for a road car.

Does this help?

Comper100

scoobyDAZZA

cuz bob rawle told me
lol
i had the magnex twin dump originally.
received my open neck H+S 3 hours ago
been busy lagging it,got halfway and had used 20 foot ffs
need some of that heat resistent spray
halfrauds here i come

scoobyDAZZA

ps
agree with comper100

bainsy

Nice one Comper100 and dazza... that settles it..

Open neck or twindump first choice...

Closed neck second choice...

But price has big part to play also...

Thanks

Harps

bainsy

Does this mean you have a magnex twin dump for sale?

Thx again

Harps

Joth

Open neck best with the with a splitter plate to give a few inches of gas separation

BuRR

Just out of interest, why do most of the Jap exhausts (such as HKS) use the "closed neck"?

jasonius

iTrader: (1)

Are u fitting it yourself..?

If so keep us posted on how it went.

Jason

hades

Burr - I know HKS use the closed neck, wasn't aware of any of the others doing so? It does seem to be the case that closed neck generally gives noticeably lower power and worse spool-up than the other two types. Very few people make closed neck anyway.

Regards the twin-dump vs open neck debate - I've seen arguments either way. One key design point seems to be to not allow the gas flowing out of the wastegate to interfere with the gas flow as it leaves the turbo - this is where the "splitter" comes in.

RoRu

Hades,
I'd have to disagree with you on the power a closed neck design can make, i've have a HKS closed neck on my car for four and a half years, and last weekend it made 383bhp,

The main problem with the closed neck is boost creep,(due to the wastegate being covered) when i was running the std VF24 at 1.4 bar it was not an issue and for most people using small(ish) turbo's it would'nt be either, but since i have uprated to a Td05/06 and mapped for 1.45bar i have noticed it creeping upto 1.61bar on the road.

These are just my own findings.

Andy.

hades

Andy - I didn't say closed neck can't make big power, I'm suggesting that (by most accounts and intuitively by physics), a well designed open neck/twin dump is less restrictive so will make a little more power with a given set-up. Several people have made a little over 400bhp (on the right rollers, at least) with the TD05/06 and e.g. the H&S open neck d/pipe. Have you tried an open-neck ot twin-dump on your car; if not, who's to say you won't make more power (and/or torque) with one? Or less, come to that?

The problem with most of this is that most people have a solution that works to a fair degree, and unsuprisingly due to cost/hassle won't go and try 15 other versions to see if there is a small improvement! The only way to give a 100% answer is to test the same car on the same rollers with different downpipes (and map adjusted to suit, perhaps) but everything else the same. Problem is, you'd probably find that even then, some downpipes will work better with certain turbos, or other supportinf bits.

Having said all that, well done on the 383, anyway!

RoRu

Hades,
I know what your saying, and may be an open neck on a given setup may produce slightly more power, but for most people running faily std cars as far as i can see there is nothing wrong with a closed neck pipe, a company like HKS who as far as i know do alot of R&D work must of made it that way for a reason.
I would be interested to konw if any one has tried the two different design and can say what the difference was power wise.

Andy.

Andy.F

Stay tuned....work in progress to do exactly that on a series of turbos, initial findings suggest the choice of header is far more critical, certainly on the smaller turbos.

Andy

Floyd

iTrader: (9)

Have you tried the Megan headers yet Andy in your comparison?

F

Andy.F

Yes, but only on a smaller turbo, they were not the best. Due to their larger bore I would expect them to do better as the turbos get larger

Andy

Floyd

iTrader: (9)

I've been offered a set of equal length scooby sport headers to try and I'm dithering on which turbo to use with it (Hybrid TD04 or 'many' ported VF35) or I could use the ported std headers? Any ideas?

F