Power Restriction?

[Rolls]

I think because the diameter of the turbo is that size, why they don't smoothly taper out to the bigger size I do not know, perhaps it introduces turbulence which is a good thing for flow?

[bj0rn]

ok guys got under it today,

hks dump ID - just under 69 mm

dodgy tasmanian backyard exhaust ID - 59mm

plus the welds are f**ked on the inside so i guess that would choke it a bit more.

ill get it fixed and retuned as soon as i can.

one final question, would it be worthwhile losing one of the mufflers while i get a new front pipe made? i actually enjoy how quiet it is, but i dont really have any idea of how much power they leach.

[MrStabby]

I think because the diameter of the turbo is that size,

Makes sense.

why they don't smoothly taper out to the bigger size I do not know, perhaps it introduces turbulence which is a good thing for flow?

No, that's not it. I'd say it would be manufacturing cost of having a taper of the right length blend into the pipe bend which is quite close after the diameter change.

[skylinecouple]

The only reason Greddy or others make those pipes is due to fitting up to stock or almost stock turbo combinations. Still no excuse though, The quicker the hot air expands into a larger pipe the better off you will be. I have spent considerable time confirming the differences between a 3" pipe and 3.5" pipe and there is definately power and more importantly quicker boost to be had in a larger pipe.

I will also tell you I am running a Garrett 3071 .82 housing which is considered the equivalent of the HKS turbo you have. If it were me I would replace the whole front pipe with 3.5" and know it won't be held back. I have seen other results where the cat back was changed to 3.5 from 3" and power increased. The whole idea of exhaust gas cooling after the cat is rediculous from a heat perspective. True, the exhaust manifold can glow red with heat while the exhaust doesn't while under load but the fact is, the exhaust is on it's way to glowing if the revs and load on the engine are kept up. And just because the exhaust itself isn't glowing doesn't mean it isn't bloody hot. That's how the cat works, by holding the various poisonous gasses a little longer and burning the shit out of them till there is less of it going into the atmosphere.

Get into the big Ford turbo forums and see the warning on exhaust size after 260rwkws. It must be 3.5" or better. Get this right, you will still do well with a 3" but best efficientcy is at 3.5". In the States especially there are so many bigger power cars having to go to 3.5" exhausts.

P.S: your dump pipe is crap, no, I mean it is really crap. Like whoa, that is sooooo........CRAP.

Edited January 31, 2011 by skylinecouple

[Harey]

The only reason Greddy or others make those pipes is due to fitting up to stock or almost stock turbo combinations. Still no excuse though, The quicker the hot air expands into a larger pipe the better off you will be. I have spent considerable time confirming the differences between a 3" pipe and 3.5" pipe and there is definately power and more importantly quicker boost to be had in a larger pipe.

I will also tell you I am running a Garrett 3071 .82 housing which is considered the equivalent of the HKS turbo you have. If it were me I would replace the whole front pipe with 3.5" and know it won't be held back. I have seen other results where the cat back was changed to 3.5 from 3" and power increased. The whole idea of exhaust gas cooling after the cat is rediculous from a heat perspective. True, the exhaust manifold can glow red with heat while the exhaust doesn't while under load but the fact is, the exhaust is on it's way to glowing if the revs and load on the engine are kept up. And just because the exhaust itself isn't glowing doesn't mean it isn't bloody hot. That's how the cat works, by holding the various poisonous gasses a little longer and burning the shit out of them till there is less of it going into the atmosphere.

Get into the big Ford turbo forums and see the warning on exhaust size after 260rwkws. It must be 3.5" or better. Get this right, you will still do well with a 3" but best efficientcy is at 3.5". In the States especially there are so many bigger power cars having to go to 3.5" exhausts.

P.S: your dump pipe is crap, no, I mean it is really crap. Like whoa, that is sooooo........CRAP.

Your post confuses me. Firstly you recommend a 3.5" front pipe, then say people have gained power by going back from a 3.5" to a 3" catback exhaust and then completely deny the exhaust cooling idea. If you dont believe in this what do you think it is the reason?

Surely the exhaust is hotter at the start and cooler by the time it exits the rear tip?

Then after saying people have gained power by going back from a 3.5" to a 3" catback exhaust you quote many cars needing to go to 3.5" exhausts??

I value your opinion as your suspension experience helped me solve my axle tramp so I am interested to understand what you are trying to say.

[NSNPWR]

Untie your panties and actually read what he wrote mate.....

cat back was changed to 3.5 from 3"

So it was changed TO a 3.5" FROM a 3"....................capeche?

Edited February 1, 2011 by NSNPWR

[Harey]

Untie your panties and actually read what he wrote mate.....

So it was changed TO a 3.5" FROM a 3"....................capeche?

HAHAHAHAHAHA woops, yup I did misread. So hes just saying bigger is better.

Its a pity that all off the shelf products for the RB25 I have found only come in 3".

EDIT: I lie, XForce sell a 3.5" catback option but nothing for the front half which I think is more important.

We dropped my 3" fujitsubo catback and it only made less than 5kw difference on the 280rwkw it normally makes.

[simpletool]

We dropped my 3" fujitsubo catback and it only made less than 5kw difference on the 280rwkw it normally makes.

Yep...but that was a fujitsubo

[bj0rn]

yeh i know the front pipe is likely the problem, i said that i'll get it fixed in the last post (i.e a new one made up).

is there any benefit of having a 3.5" front pipe, if the outlet of the dump is only 69mm ?

heres a pic of the dump

[SLYDA]

well, i realise dyno's are only a means of measurement, but i'm convinced that my setup has seemingly less power than almost everybody elses thats similar, so im just trying to figure out what the restriction could possibly be.

here's a list of what's been done:

unopened s1 rb25det

ems stinger ecu

hks gt2835 pro-s

3" flexi pipe intake hose

nismo 740cc injectors

walbro pump

hybrid cooler

stock coils

exhaust that goes from 2.5" to 3", 2 mufflers no cat

18psi - 315rwhp

13.1 @ 109mph on 205 rubber

compression test came up as 150psi across all 6 cylinders

it holds boost through to redline, and im assuming the coilpacks are working as it doesnt miss. it has a stock fuel pressure regulator.

the most obvious thing i can think of is either the exhaust is restricting it, or my tuner isn't putting any timing into it?

any thoughts please punt them at me

cheers in advance

Same setup with stock manifold running a Z32 and PFC got me 350HP at the wheels at 18PSI, Same Injectors, Same Turbo, Same Fuel Pump, Splitfire Coils, howecer had a 3" front pipe comming from the HKS Split Dump, to a High Flow Cat into a 3" Exhaust.

Hope that helps.

[r32-25t]

Get a 3in bellmouth dump and front pipe in one, I'm not a fan of hks dump pipes and that front pipe is horrible, me and a few people I know are all getting rid of the hks dump pipes on our Gtrs due to us believing they are a restriction