Razor2001

Hi all,

I was going to post this in the "decat sti-7" thread, but decided it may need its own......

I noticed that most here are going the 2.5" pipe route when decatting their STI-7......any particular reason why we don't go 3" ??? is it just a cost factor ??? won't one get less back pressure and hence more power with a 3" or will the lack of back pressure affect the low down torque in a negative way ???

Cheers,
Ray

Deep Singh

Exactly what you said razor.3" system will give better top end gains and hence better BHP reading on RR.I was told by someone who knows much better than me that the STi turbo is actually better suited to a 3" system,whereas the WRX(uk) as being smaller is better suited to 2.5" system.For me though Scoobysport are close by and since I'm always bothering them with questions I think I should give them some business! Also I got most of my SS system 2nd hand at a very good price.

Razor2001

Come on all you exhuast experts out there....post your opinions.....don't want to go through the expense of putting on a 2.5" only to find out that I would have achieved better results with a 3"......BretMan, Deep, Pete, Dave T-S please post your respected opinions

Cheers,
Ray

Razor2001

bttt

Razor2001

bttt

Jamie Whitfield

It is certainly a lot louder with 3" but also our Blitz NUR Spec R is the most free flowing exhaust Ive come across.

Jamie

www.j-w-racing.com

Deep Singh

Razor its a bit of extrapolation but you will notice that most of the big BHP cars on this bbs seem to run HKS Hiper exhausts.It is thought to be the least restrictive.This is not just because of the internal design but because it comes out at an angle which is the natural angle from the turbo hence gas does'nt have to go around a corner if you see what I mean.Bloody loud though.If you are after big gains and d'ont mind the decibels definately consider the Hiper.
ps all the ****e I've just spouted is just second hand opinions from other people,some of whom do seem to know what they are talking about though!

mutant_matt

But how many people are really after big Bhp? After all, on the road it's torque that counts......

Perhaps the question should be, which exhaust will give the biggest torque gains?

Matt

P.S I don't know the answer....

Razor2001

Can anyone suggest which turbo back exhuast may offer the best torque gains..???

Basically my whole objective is to try and get rid of that lag and sluggish feeling below 4,000 rpms on the JDM STI-7.

Noise is not an issue, can be loud as needed to achieve my goal of better torque; however, the overboosting is an issue so the system would have needed to be tested and proper restrictor size sorted to match the system. (Scooby sport has accomplished this and I am leaning this way; however, I think their system is a 2.5" system and I am curious if a 3" system will give better results)

I am ready to buy a full turbo back system, just trying to decide on the system that will offer best low down gain and torque improvments

Cheers,
Ray

IanW

The HKS Hiper probably has the beest flow, as its amost striaght!

I've seen some REALLY high powered scoobs running this exhaust.

Razor2001

Does the HKS Hiper mount easily, ie: the ScoobySport etc are direct replacements and no mods to mounts etc needed ?

What downpipe have you guys been using with the HKS hiper and any CEL problems noted ?

If you have gone the downpipe decat route what restrictor size have you used with deacatted downpipe and hks hiper ?


Cheers,
Ray

Razor2001

bttt

mutant_matt

Razor,

Seeing as you're going to have to buy overseas whatever you get, I would get a full APS system. They do a full turbo back system which is tried and tested on the STi and I'm pretty certain they will gaurantee no spiking with this system.

Check out the APS STi High Power Systems URL.

They could probably provide you with standard vs APS system dyno graphs too if you ask nicely....

Matt

Pete Croney

Razor

For the record, the Scoobysport exhaust is 3" after the turbo and tapers to 2.5" at the end of the downpipe. The gas is around 200 degrees cooler here, so has much less volume.

Also, the standard system is 2.5" OD, ours is 2.5" ID and it maintains this diameter all the way back, through the silencer, to the tailpipe.

Some 3" systems are considerably less than 3" inside the silencer

Razor2001

Hi guys,

Very interesting PC, thx for the info :-)

Without trying to start some sort of mine is better than yours war between manufacturers and related companies....is there any dyno proof from the diff exhuasts (hks, scoobysport, aps etc) which produces the most lower down torque gains etc...for a JDM STi-7 ??

As stated before my goal is roughly 20 - 30 bhp increase, 20 - 30 ft. lbs. of torque increase as low down as possible, basically I am trying to get rid of some of the below 4,000 rpm lag and weak power feel.
It should also be noted that I want a 100% safe system that will not boost spike and will not cuase any fueling/ ecu potential engine damage issues. So far the only system I think that has confirmed this is the ScoobySport full turbo back decat with a 1.25mm restrictor used. I have been looking at other companies based on the fact that the SS pipe is 2.5" vs. 3" and I thought I may achieve some better gains with a 3" system. However, maybe there has been some inner diameter compared to outer diameter comparisons ???

Any info provided will be a big help. Like I have said I am ready to do this thing, just trying to get all the info so when this system arrives all the way down to Nassau, Bahamas I will be happy

Thanks again all involved in helping me make the right decision.
Ray

Mike Tuckwood

Our system is being worked on at the moment and will be free flowing mandrel bent all the way through.

It is a myth about larger exhausts having lower torque as I will prove when our new system has been tested and dyno'd (we already have OEM baseline figures for my car which were less than 1% from factory figures).
I will test this on my own car before release (not customers').

RAZOR
You will need to consider how you handle the (guaranteed) overboost issues you will have, make sure whichever system you get has been developed/tested on a new age STi, as that is the most extreme environment. (OEM STi 7's will overboost to 1.5bar in standard form).

NB
===
Although gas volume may be down by the bottom of the downpipe, don't be mislead; gas density increases greatly at cooler temperatures and that is what is bad. This is then compounded by the reduction in pipe size greatly increasing (Evil) back pressure.


Mike.
Scooby Mania

Razor2001

Thx for the response Mike


Our system is being worked on at the moment and will be free flowing mandrel bent all the way through.

Rough time of completion....a week, 3 weeks, month or more ??




It is a myth about larger exhausts having lower torque as I will prove when our new system has been tested and dyno'd (we already have OEM baseline figures for my car which were less than 1% from factory figures).


I assume you have a STi-7 ??? is it UK or JDM spec ?? and when you got the 'baseline figures' it was 100% stock when dyn'd, meaning that the STI does only pump out 276 bhp as stated ??


I will test this on my own car before release (not customers').

RAZOR
You will need to consider how you handle the (guaranteed) overboost issues you will have, make sure whichever system you get has been developed/tested on a new age STi, as that is the most extreme environment. (OEM STi 7's will overboost to 1.5bar in standard form).


You are saying that 100% stock STi-7's overboost to 1.5 bar sometimes and this is completely normal ???


NB
===
Although gas volume may be down by the bottom of the downpipe, don't be mislead; gas density increases greatly at cooler temperatures and that is what is bad. This is then compounded by the reduction in pipe size greatly increasing (Evil) back pressure.

Ok, so I guess a 3" all the way from turbo to exhuast tip is the way to go ??


Mike.
Scooby Mania


Thanks again Mike and all, huge help

Deep Singh

Razor,I'm not saying that a 3" system may not be better,my technical knowledge expires way beyond this.But let me say this..whem I first bought my STi7 I was really depressed having spent loads of money and having a car that just did'nt feel like a bomb.The scoobysport exhaust really has changed that,its now a different beast, low down pull and general revability are improved greatly.I know look forward to driving my car to work again every morning ie the grin factor is back.All I'm saying is that I d'ont think you will be disappointed.

Razor2001

Excellent Deep

We are on the same wavelength....

I am sure the ScoobySport 2.5" system increases performance very nicely and the best thing about it is that they have sorted all boost spiking issues etc...so in the worst case I can get the ScoobySport system and know that I will be getting some nice gains and safely (ie: no boost spike or air/fuel issues). However,
all I am trying to figure out is that if possibly a 3" system will be better and offer more improvements over the ScoobySport 2.5" system....no doubt the ScoobySport shows great gains etc, just curious if there is a 'better' system out there with the same safety as ScoobySport......fair enough, no ?? I am not a millionaire and when I am about to hand over a big chunk of change for a mod I want to make sure I am getting the best one possible within my price range....(not to mention I have to ship it to Nassau, Bahamas and pay a nice fat duty percentage on it

Just trying to get some information for myself and other JDM and UK STi-7 'ers looking to go the full turbo back decat route

Thanks again
Ray

Deep Singh

Understand where you are coming from completely matey.

Mike Tuckwood

Razor, approx 3 weeks dependant upon results.


Yes, JDM spec STi 7. BHP was 272 on SUL + Millers Octane+ so around 99RON fuel (which is what most people run on).


Yes, 1.5 bar overboost is "normal" on an oem STi 7.

Yep, I'm certain that 3" is the way to go, even the baffles in our system are 3".

Mike.
Scooby Mania

Razor2001

Superb,

Can't wait for the finished product and your dyno results

Keep us informed,
Ray

MorayMackenzie

Mike,

Is your new system going to keep noise levels down at a similar level to your previous one? I hope so, because the likes of BPM etc are simply too loud for use on cars that need to maintain a level of civility whilst creeping through urban areas after midnight.

Moray
bbs.22b.com Now with added RX7'ness!

Mike Tuckwood

Moray.

Yes. (sort of)

There will be (at least) 2 options with it, straight through 3" centre pipe and the same pipe with a long resonator to knock the volume down without too much detriment to gas flow. (Got to keep the neighbours and/or partners happy)

There will also be 3 different back box tip options.

Stainless Steel
Carbon Fibre
Anodised Titanium (Rainbow effect).


Mike
Scooby Mania