downpipe question: siamese vs normal

[nickch]

What's the difference between your run-of-the-mill aftermarket downpipe versus a siamese aftermarket downpipe?

Have been looking at the RAGE catalogues here: http://www.autobend.co.nz/rage/New%20Site/web-content/bigbore%20pages/subaru.html

And am curious about the differences between parts BB3089 and BB3056?

Performance gains and sound wise..

Thanks.. ;P

[Guest DMSREX]

Read this it'll tell what a well designed down pipe should look like.

http://www.msengineering.com.au/exhaustsystems.html

[Scoobydoo]

Yes having the divider in the centre is the best result, but not many do that. Although that one can be improved on again by having the wastegate gases flow seperately until further down the pipe, instead of combining right at the top. That would be the best of both worlds.

[Guest DMSREX]

Hmmm......When i was researching for my downpipe i was told Siamese designs were prone to causing boost spikes and to stay away. Anyway i have bellmouth with splitter welded in and i'm happy.

[Scoobydoo]

Any downpipe replacement will cause some amount of boost spike due to the free-er flow and less restrictions. If you have a boost controller though, that's not a problem, even a manual tap.

[nickch]

 DMSREX said:

Hmmm......When i was researching for my downpipe i was told Siamese designs were prone to causing boost spikes and to stay away. Anyway i have bellmouth with splitter welded in and i'm happy.

surely the length and position of the splitter must be carefully calculated in order for it to be optimum?

and it is rather hard to find a split bellmouth in NZ aye..

[funkytown]

 nickch']

[quote name='DMSREX said:

Hmmm......When i was researching for my downpipe i was told Siamese designs were prone to causing boost spikes and to stay away. Anyway i have bellmouth with splitter welded in and i'm happy.

/quote]

surely the length and position of the splitter must be carefully calculated in order for it to be optimum?

and it is rather hard to find a split bellmouth in NZ aye..

for a stock VF turbo you arent going to notice bugger all difference honestly. Sure going from a factory CAT DP to an aftermarket one yes. but not between bellmouth or split, or 'special length' split.

you would be better off finding a turbo like the vf34 which spools earlier than a vf30 or 22 as apposed to worrying about the length or split of the divider in the DP.

[Guest DMSREX]

Yep i ended up getting a Hi-Tech dump pipe from Oz and had MSR Engineering mod it...and yes your right splitter length is critical. Probably not the cheapest alternative but i'm happy.

I think you'll find its the entire exhaust design that has an effect not just the dump. MSR told me to have mine tapered down to 2.5 inch at the rear for good midrange torque delivery along with the correct tune.

[nickch]

 funkytown said:

for a stock VF turbo you arent going to notice bugger all difference honestly. Sure going from a factory CAT DP to an aftermarket one yes. but not between bellmouth or split, or 'special length' split.

you would be better off finding a turbo like the vf34 which spools earlier than a vf30 or 22 as apposed to worrying about the length or split of the divider in the DP.

cool..

current plan is to get the basic stuff done before i get my hands too dirty..

It has got a Blitz Realize TT cat back on the factory downpipe..

am just keen to free up the exhaust a little.. just to get the basics covered.

[bubblz]

a few mths ago redline had a bellmouth dump pipe for sale...maybe they still got it?