Benefit of open neck down pipe over normal?
 

Can anybody tell me if there are any differences? as i have been offered an HKS down pipe for a great price but it is not the open neck design.....any ideas??

Are open necks more powerful? also, would i need any further modification? I am told that this pipe will replace both the cat in the down pipe and the one in the center......

Thanks,
Neil.

nobody??

If it's not an open neck design, what is it, twin dump, or just a normal single pipe design?

The reason "open neck" downpipes get their name is that the mouth of the pipe is larger than normal, which improves gasflow from the turbo and wastegate into the exhaust. You do get a little more power from this design, but compared with a standard single outlet catless downpipe, the difference isn't huge - a handful of horsepower rather than dozens.

If it's a twin dump pipe, it'll have two separate outlets on it, for the turbine and wastegate, which join back together further down. The reason behind this is the same as the open neck pipes, and there's no widely agreed consensus over which approach is the more effective.

what does allowing the wastegate gases to escape thru the open neck or separate pipe with the twin dump do to the life of the turbo?

if it's a good thing, why weren't they designed with a wastegate pipe in the d/pipe to start with and what happens to the wastegate gases with a std. d/pipe as the outlet is shut off?

by the way neilo, i've got a twin dump magnex d/pipe (on MY99), probably cheaper than an HKS and i can't fault it. as for modifications, my heat shield needed a bit cut out of it to clear the larger diameter pipe and the extra wastegate pipe.

Thanks for that, it is just the single pipe, not twin dump, so it looks like its a bit of a steal :)

I should add that the pipe is not brand new hence the "steal" part. Its about a year old and its from an 01 bugeye, looking to put it on an 03.

If it is just a decat but still has the plate across the wastegate then its not that good compared to the open kneck design however its better than std.

the oem downpipe was designed that way as the whole car was targeted at a performnce level which that hleped them limit to.

bob

HKS is not the best downpipe you could use, (as Bob points out) the wastegate area is blanked by the HKS's design.

If you can picture the back of the turbo.. exhaust turbine wheel on the right, wastegate door on the left.. an open neck d/p will (as it's name suggests) as well as sitting predominantly behind the exhaust wheel but also partly sit behind the wastegate to aid flow from the wastegate. The HKS d/p is not open neck (ie 3" round pipe only) sitting behind exhaust turbine wheel and the d/p's plate that bolts to the exhaust housing covers the wastegate flow.

so why is covering the wastegate bad?

Causes turbulence and backpressure behind the turbo, which isn't good.

Isnt good as in, it could damage it? or isnt good as in, because it produces less power?

Ta,
Neil.

Isn't good as in produces less power.

How about an external wastegate, performance, legalities, life of turbo/wastgate etc
?

Not as good a solution to optimise as much as possble the gas flow out of the turbo, and yes less performance when remapping however levels of modification start to come to bear here.

bob

B hell we are all at it !!!


bob

LOL and why not :)

Its madness!

If i give you a little background then maybe you lot can see if this is good or not. I intend to get myself a full decat, this pipe being the first stage (no im not fitting it until i have ALL the bits, as it would cause probs), this pipe would be solving both of the turbo back cat issues and connect straight to the second section on the system, then to the backbox.

I would intend to get myself an up-pipe from either HKS or scoobysport.

No turbo mod as yet, so it is a stock TD04.

Hey Neilo.

Whilst doing the up pipe get Harvey to port your headers aswell. Alot of people swear by Harveys Headers. Lol and not alot of cost involved.

what does that do then?

ive got a feeling he's at the other end of the country :D

From what I have been told. Its a process which removes the excess material in the manifolds (Headers) to increase flow rate to the turbo from the block. This modification can be carried out on standard manifolds (headers) and should decrease the turbo spool up time. Which means you can get on boost quicker. With the modified up pipe It might also flow more exhaust gases aswell. One of the expert Techies will give you a full low down on the mod.

Harvey is based in Darlington area but I believe he does a mail order system so to speak and I believe he sends you ehaders and you send him your old headers in exchange. You might be aswell contacting Harvey and asking him about this.