Split Dump Vs Bellmouth Dump

[DaveO74]

My tuner (Unigroup Engineering) says he can squeeze another 20rwkw out of my R33 Hypergear Highflow if I do away with my Batmbl Split Dump/Front pipe and go for a Bellmouth type Dump/Front pipe whilst still retaining the standard 33 housing. I have no reason to disbelieve him as those of you that know him would agree that he is one of the best in the biz.

My question is as this turbo is producing 230rwkw @15psi with all the usual supporting mods and is capable of running approx 20psi is there anybody out there that has acheived this kind of increase changing from split to bellmouth??

I have spoken to Stao and he says that although the compressor should be ok for about 270rwkws at 24psi Im still held back by the standard 33 housing, but I love the response that I have and want to keep it that way if I can so Im not real keen on moving to the .63 rear housing.

Any of you guys think 250rwkw is genuinely acheivable with just a dump pipe change?

GcG have told me that they have pulled it off with the 33 rear but with the tradeoff of a little lag, so Im a little confused.

Im keen to hear your opinions.

[PM-R33]

I had a split dump and went to a bellmouth. My split dump kept causing boost spikes and couldnt hold boost. Solved it with the bellmouth. I think 20rwkw (40ishHP at the engine) is a bit of a stretch. Maybe 5-10rwkw throughout the rev range yes.

[DaveO74]

Funny you say that cause it has been known to spike before.

Will any old bellmouth do (within reason, not sh1t) like a JJR one or should I spend some bigger $$$

I have seen some up to the US $700 mark

[Simon-S14]

most split dumps are pretty poorly designed and cause a restriction for the gate if anything... the only decent one i have seen on the market is from AM Performance.

in saying that, i doubt you'll make more or less power with a bell mouth, just pick up some more response with a well designed split dump.

[STATUS]

My tuner (Unigroup Engineering) says he can squeeze another 20rwkw out of my R33 Hypergear Highflow if I do away with my Batmbl Split Dump/Front pipe and go for a Bellmouth type Dump/Front pipe whilst still retaining the standard 33 housing. I have no reason to disbelieve him as those of you that know him would agree that he is one of the best in the biz.

My question is as this turbo is producing 230rwkw @15psi with all the usual supporting mods and is capable of running approx 20psi is there anybody out there that has acheived this kind of increase changing from split to bellmouth??

I have spoken to Stao and he says that although the compressor should be ok for about 270rwkws at 24psi Im still held back by the standard 33 housing, but I love the response that I have and want to keep it that way if I can so Im not real keen on moving to the .63 rear housing.

Any of you guys think 250rwkw is genuinely acheivable with just a dump pipe change?

GcG have told me that they have pulled it off with the 33 rear but with the tradeoff of a little lag, so Im a little confused.

Im keen to hear your opinions.

ive found the hks style dumps to be the best, the ces split style ones dont seem to offer any benefit other than a lighter wallet. We did back to back testing with the cheap DRIFT (trust/tomei copy) and the CES split on a s15 with gt2871r and found no difference.

[DaveO74]

most split dumps are pretty poorly designed and cause a restriction for the gate if anything... the only decent one i have seen on the market is from AM Performance.

in saying that, i doubt you'll make more or less power with a bell mouth, just pick up some more response with a well designed split dump.

Im pretty sure the AM Perfomance ones are sort of the same design (at the turbo housing flange part anyway) as the Batmbl/Bos Importing ones. Do AM make the full Front/Dumps or just the dumps?

Got a link?

[Pal]

hey Dave,

as long as it is a 3" i dont think it will make much difference. i think i paid $80 on ebay for mine and have had no problems with it. just check the flatness of the face that bolts up to the turbo and square up if out. dont think it will make much difference on the power side but definitely stabilizes boost.

[SLAPS]

If your changing dump try to squeeze a 3.5" in there... Taper it down to 3" if required before the cat.

[SimonR32]

ive found the hks style dumps to be the best, the ces split style ones dont seem to offer any benefit other than a lighter wallet. We did back to back testing with the cheap DRIFT (trust/tomei copy) and the CES split on a s15 with gt2871r and found no difference.

are you talking about the "xs power" hks copies? i have always assumed theses are not the greatest as they have a 2.5" main pipe and a 1" (i think) gate split but then all the flow is guided back into a 2.5" pipe before hitting the front pipe?!?

would you not be better with a bellmouth 3" or a ces style split that the gate pipe runs back into a 3" pipe further down the exhaust?

[DaveO74]

My current setup is exactly like that (1" split into 3" pipe further back) and this is what my tuner believes the restriction is. Boost creep or whatever you want to call it sometimes happens with this setup. I have had a look at nengun and the full hks dump/front is a bellmouth style and they have said it's a good match for my hks exhaust (3.5")

I also like the moonface dump which has a sort of streched out barrel type area but at $700 it's a bit exxy. I'll post pics of the two when I get home

[9krpm]

I changed my bellmouth dumps (Mine) to splits (Greddy) and boost came in a few hundreds rpm earlier without any tuning.

I cant recall the exact rpms, but definitely more than 500 and less than 1500rpms...too long ago to remember.

I did not have a chance to put the car on the dyno to test out so I don't really know if this "positive" pressure means earlier power or more restriction.

[adamskill]

i really dont think 20kw is attainable by swapping from split to bellmouth.

[DaveO74]

So here are the two I am interested in trying out, thisHKS pipe (Is this the one you were talking about Trent?)

And this Moonface one. I know somebody on these forums has one but I cant seem to find the thread about it. I read it a while back.

I am really interested in finding out some user info on the moonface pipe as I am very curious about this design

Has anyone out there had experience with these two pipes?

A better alternative to a Split?

[TALBO]

Im pretty sure the AM Perfomance ones are sort of the same design (at the turbo housing flange part anyway) as the Batmbl/Bos Importing ones. Do AM make the full Front/Dumps or just the dumps?

Got a link?

AM Performance make the full dump/front pipe and they're incredibly well built. I'm pretty sure the BATMBL dumps were in fact made by Andrew at AM Performance.

Andrew - 0401865373