Open Neck and Closed neck Decat Downpipes, your opinion.
 

Hello Guys,

When i had my Terzo, i bought a scorpion full de-cat system, and it had a closed neck downpipe (e.g half of it was blanked off)

Whats the main difference between the open neck one,
in terms of performance, and mainly SOUND.

Obviously a open one would give the gas an easy time at getting out, but is it really necessarry ? Surely a closed neck one would be fine for the road ?
and cheaper ! :luxhello:

Let me know your opinions.

IMHO:
A 'closed' one on a stock engine will be fine.
Start tuning and the 'open' kneck allows the waste gate gasses to flow into the main turbo gas stream more gracefully.

My Sti v3 made about 400bhp on a very old semi open kneck D/P and drove great.
I really doubt it makes much difference.

As to the noise? No difference at all in my experience.

Change the induction to a cone filter and you will certainly get a very different soundtrack.
Graham.

I have a scorpion on my rb5 are they all closed neck!?

Bet is runs well too.

So what about open neck and a twin dump down pipe?

Think mine is either miltek or magnex and has a little 2nd pipe leading into the main pipe further down.

Guess it would make an easy mod to a screamer pipe :)

I did have a closed neck HKS downpipe on my STi v3. I managed a respectable 326bhp with this and a 2.5 " decat system and k&n filter.
I have recently fitted a 3" Megan racing open neck downpipe and although I haven't had it on the RR yet but I would say I'm getting much more low down power.
On greasy roads it seems much easier to lose traction in a big way in 2nd gear while accelerating. It never used to be this bad, largely because of the lag with the big turbo on the V3 meant you were travelling at a decent rate before the power cut in.

The Megan downpipe is very shiny:) and well made - bought off ebay for £129 from the US. But be careful as although the ad says it fits all models, it actually is designed for the newage cars. Only difference is that the rear section is 3" longer than the classic pipe. I just shortened it and refitted the flange and it's fine.

Now looking for a 3" centre and rear to complete the upgrade;)