frayz

iTrader: (7)

Hey all,

Ive got a Hayward & Scott 2.5" system fitted to my 02 STI.
I called respected tuner today regarding mapping etc and i said i wanted to achieve approx 330bhp with 330+lbsft

I was told that this will not be possible with my exhaust system and that i would need at least 3 maybe 3.5" bore exhaust.

I found this a little odd, ive not long had the exhaust and really like it,

So have i bought the wrong item and my power is unacheveable or is he talking @rse?

If it is acheveable, what will i need to do inorder to get the performance i want.

Opinion please

Cheers

Ben WRX Bug-Eye

I personally don't agree with that. I've heard that a 2.5" system is only a real constraint when going for over 400'odd bhp. I am sure you'd gain a few horses at the top end with a 3" system, but don't believe that 330bhp is a problem with a 2.5" bore.

frayz

iTrader: (7)

Thats what i thought mate but he seems adamant that id be lucky to get above 310bhp with pants torque.

highlander68k

I believe H&S suppliers are basing their information on back-to-back tests H&S have done with their systems.

Are you sure it wasn't just a recommendation rather than a requirement? Although the 2.5" system will enable you to achieve the figure, it will be easier (cheaper) to achieve with a 3" exhaust system.

The information I've seen show a considerable increases in peak figures with the 3" system on the same car (without remapping), compared to both the 65mm and 70mm systems.

However, the fact that the testing was carried out on one particular vehicle and not a number of vehicles does not take into consideration the hugely variable set-ups that are available. Nor does it take into consideration different ECU settings, fuel types or blah blah blah.

ZEN Performance

I have personally got over 400hp from a 2.5 inch exhaust (well, 2.5" up to the 3" backbox) and others (John banks and Andy.f at the very least) have done it with full 2.5" systems mated to a 3" downpipe.

It sounds like someone wants to sell you something. Perhaps the 3" or 3.5" system (the 3.5" APS is about the most expensive system available) will give you a gain, but at the 350hp level I am confident the 2.5" system isn't going to limit power excessively.

Paul

frayz

iTrader: (7)

cheers mate,

do you recomend having the 3" downpipe over the 2.5" downpipe even though the rest of the system is 2.5"

frayz

ZEN Performance

The 3" downpipe is probably worth it.

frayz

iTrader: (7)

Even though the rest of the system is 2.5"?

what gians will the 3" give over the 2.5" mate

sorry for all the q's just trying to do my homework

easyrider

Surely a 2.5 downpipe mated to a 2.5 system is going to flow better than a 3" d.pipe mated to a 2.5" system due to there being no steps to cause a restriction/turbulance.

Nick Read

It's true that the system is basically restricted to the narrowest part, but keeping this narrow section as far back from the turbo as possible does improve things. There are gains to be had from say keeping a 2.5" backbox section because you like the sound or whatever, and then replacing the rest with 3". But essentially it's best to make a decision. Stick with your existing system or dump in and go bigger.

I would say that in general 2.5" is easily adequate for a 300 bhp system or just over, but as someone else mentioned, it's a lot EASIER to acheive your target with a bigger system - less back pressure for the turbo to fight, in simple terms.

If you're never going to want more than say 350bhp, keep the 2.5".

Woody1

My car and my mates are both STI uk's unmodded apart from cat back exhausts and panel filters. On the rolling road, bhp was virtually same (1hp dif) but torque on mine was 13lb/ft up at the wheels. Mine is a 2.5" nija backbox with afterburner mid pipe, his a DC sports 3". Not sure how they would compare with Remaps or such.

neil

frayz

iTrader: (7)

this is all interesting stuff lads.

Im not really sure what to do now, i didnt think a 2.5" exhaust system would really be restrictive at all

ZEN Performance

The exhaust gas in the downpipe is much hotter than in the rest of the system, typically around 650ºC compared to maybe 300 at the backbox. The hotter gas travels faster and more restricted by the smaller pipe (ideal gas law). So it pays to have additional size near the turbo, although the biggest gain by far is to remove the cat or fit a much less restrictive one. A good 3" to 2.5" downpipe will have a gradual decrease at the exhaust flange rather than a step.

frayz

iTrader: (7)

so should i ask hayward n scott to make me a 3" downpipe or do you recomend another one?

SPIKE LIKE MIKE

I have a 2.5" H&S system with tmic and ind kit, i run 352 bhp and 338 torque, with the 3" system i would acheive maybe 10 torque and a few bhp.hope this helps.
If in doubt call WRC technologies mate,really helpful with any questions and i cant fault the work.

goodluck

DBY

I bet it is them that are telling him to junk the 2.5 inch in favour of their 3 inch system.

SPIKE LIKE MIKE

lol, didnt encourage me to change mine

frayz

iTrader: (7)

DBY

Actually mate youre spot on, Why are they telling me this?

_Meridian_

iTrader: (1)

Because they want to sell you £800+ worth of APS 3" piping...


M

frayz

iTrader: (7)

Hey all,

sorry to drag this post back up again , but having spoken to another very respected tuner today regarding a remap,

Since starting this thread my car has been fitted with a 3" big bellmouth full decat pipe that replaces both cats already fitted was a 2.5" resonator replacement section and 2.5" rear box.

After telling the tuner this, they too have told me id be lucky to get 310bhp out of my car.

Please bear in mind that its a UK STI7 with a decent pannel filter, uprated fuel pump and the exhaust.

Is there anything else i should get before the car is mapped? or is my exhaust really junk?

Please help

Neilo

who is telling you that? its certainly not true that 310 "if your lucky", utter rubbish, if the exhaust is good then it will be good for getting up to near 400.....as was advised earlier, unless its got a weird U-bend somewhere or it goes down to the size of a 5p at a join

Id relax, get it remapped and see what happens....have you asked other mappers opinions? feel free to pm

Turbotits

iTrader: (2)

I have a 2.5in h&s and am seeing 330ish no problem on a 2002 sti .Someone wanted to sell an exhaust

willy

I`ll add my experiences about this.
My old scoob, my95 tdo5 turbo 2.52 downpipe and system.
289 bhp and same torque.The exhaust wasnt the limiting factor here, more the intercooler.
Dales spec c, 2.5" system made 367bhp, etc.Exhaust was limiting it a bit.
He did change his to 3" and alter boost settings etc, just made 396bhp.
Both cars mapped by Andy F, by the way.
There are the facts.
*****

ZEN Performance

I think over 350hp a 3" is preferable. However, a good 2.5" system can do better than a poor 3" system.

Paul

DIPSY

See the twin scroll turbo on the newage sti .Does hayward and scott make one for the twin scroll turbo .Milltek and janspeed make them i am on about the down pipe

paulmcnally

Hi All,

I've got a 52 plate STI V8, totally standard. After emailing my local specialist regarding upgrades I was quoted...

Power can be increased up to 350bhp for around £1500 Stage 3, this includes ECU Upgrade, Fuel Pump, Full Stainless Steel Exhaust System Inc Cat re-placement pipes.

Does this sound like a reasonable figure for the upgrades? Obviously there are no manufacturers mentioned which will make it hard to "compare" the quote, but does this list sound right for achieving 350'ish?

Thanks Paul

frayz

iTrader: (7)

So what do you guys think i should expect for a

2002 wrx sti prodrive type uk
Full 3" Decat bellmouth downpipe
2.5" resonator replacement pipe and rear box.
Group N pannel filter
Walboro 255 fuel pump
HKS SSQV

Ecutek mapping of this little lot

willy

Some where around 330bhp maybe more.

*****

scooby-tc

iTrader: (2)

Sorry to jump in here but ive got a 3" H&S downpipe that tapers into 2.5 at the flange then 3" centre and back box,are there any major restrictive problems with the 2.5 flange end bearing in mind the rest of the system is 3" or is it better to get a 3" d/p with 3" flange end

Just trying to work out the implications before shelling out again

Budgie

iTrader: (4)

just a thought for anyone
i have a 3.5 inch APS system for sale
half rrp

budgie