Help find my missing power.

[Guest]

 Wiretap said:

The carbon ring will not seal properly if you attach it to the wrong sized exhaust, it might work but it doesn't make it a good idea.

Strong For Subaru may have some downpipes available. Give them a ring and speak to Gerald.

thats the point of the gasket true its not a good idea i was meaning until he gets a downpipe.

that system i found is hell cheap if its a complete rage exhaust not just tip.

[Wiretap]

 evowrx']

[quote name='Wiretap said:

The carbon ring will not seal properly if you attach it to the wrong sized exhaust, it might work but it doesn't make it a good idea.

Strong For Subaru may have some downpipes available. Give them a ring and speak to Gerald.

/quote]

thats the point of the gasket true its not a good idea i was meaning until he gets a downpipe.

that system i found is hell cheap if its a complete rage exhaust not just tip.

Seems the guy can't measure though, it's a 2.5" system. And rage stuff is often over the noise limit.

[Guest]

just take a tape and check it, they do make 3" systems too. i sell rage, the 63mm has resonators in same location as tm pic.

if its got 2 resonators and a tip it shouldnt be too loud. mines quieter with 3", 2 res and same tip than it was with standard dp with cat and 2.5" freeflow cat back.

[Stoffa]

my fujitsubo 3 inch system bolted onto a factory downpipe and a rage 2.5 inch downpipe. Just stepped up after the first smal resonator

[AdamOst]

So going to a full 3inch system wont lose me too much low down/mid range power?

[Wiretap]

 AdamOst said:

So going to a full 3inch system wont lose me too much low down/mid range power?

None. That's a myth that belongs to speed-density computed non-turbos.

[Guest]

 Wiretap']

[quote name='AdamOst said:

So going to a full 3inch system wont lose me too much low down/mid range power?

/quote]

None. That's a myth that belongs to speed-density computed non-turbos.

I definitly noticed the difference and loss in back preasure when I wnt from the factory system to a 3" TBE, before the ECU was retuned.

[Wiretap]

 NO BOS!']

[quote name='AdamOst said:

So going to a full 3inch system wont lose me too much low down/mid range power?

/quote]

None. That's a myth that belongs to speed-density computed non-turbos.

I definitly noticed the difference and loss in back preasure when I wnt from the factory system to a 3" TBE, before the ECU was retuned.

http://en.wikipedia.org/wiki/Back_pressure

http://www.thumpertalk.com/topic/571594-exhaust-backpressure-the-myth/

Worth pointing out that in terms of flow velocity as mentioned in the latter article. In a turbo engine this only matters before the turbo. You want as much pressure differential across the turbo as possible to improve turbine efficiency and spool rate.

[funkytown]

 

Worth pointing out that in terms of flow velocity as mentioned in the latter article. In a turbo engine this (back pressure) only matters before the turbo. You want as much pressure differential across the turbo as possible to improve turbine efficiency and spool rate.

I think your statements are a little confused / dont tell the whole picture.

what you fail to acknowledge in the its full completeness of the working system, in that exhaust back pressure (or EGBP) post turbo definitely affects power and delivery. This is at odds with you're statement about pre turbo only matters. This then is at odds to the statement that you're looking for the max pressure differential across the turbo (which i believe is correct). Why is only one side important if you want the net across both sides?

Smaller exhaust systems can cause a bottle neck in evacuating the gases once they have exited a turbine housing on medium to higher HP systems. This reduces your pressure differential and drops top end potential. This i am to prove just shortly going from a 2.5" mid to rear section (generating 7-9psi back pressure post turbo) to a 3" mid to rear freer flowing section - results of EGBP and power will follow.

I'm openly not totally sure on pre turbo back pressure theory, but im also fairly confident you want maximum flow through the exhaust pre turbo (velocity) but nil pressure.. (But then in my head the 'pressure across the turbo' statement wouldn't make sense.) - I need to do some more reading.

*note this discussion is applicable for turbo applications, NA is different!

[Wiretap]

 funkytown said:

 

Worth pointing out that in terms of flow velocity as mentioned in the latter article. In a turbo engine this (back pressure) only matters before the turbo. You want as much pressure differential across the turbo as possible to improve turbine efficiency and spool rate.

I think your statements are a little confused / dont tell the whole picture.

what you fail to acknowledge in the its full completeness of the working system, in that exhaust back pressure (or EGBP) post turbo definitely affects power and delivery. This is at odds with you're statement about pre turbo only matters. This then is at odds to the statement that you're looking for the max pressure differential across the turbo (which i believe is correct). Why is only one side important if you want the net across both sides?

Smaller exhaust systems can cause a bottle neck in evacuating the gases once they have exited a turbine housing on medium to higher HP systems. This reduces your pressure differential and drops top end potential. This i am to prove just shortly going from a 2.5" mid to rear section (generating 7-9psi back pressure post turbo) to a 3" mid to rear freer flowing section - results of EGBP and power will follow.

I'm openly not totally sure on pre turbo back pressure theory, but im also fairly confident you want maximum flow through the exhaust pre turbo (velocity) but nil pressure.. (But then in my head the 'pressure across the turbo' statement wouldn't make sense.) - I need to do some more reading.

*note this discussion is applicable for turbo applications, NA is different!

At no point did I discuss 'back pressure' in my response. Don't add words I didn't use.

[AdamOst]

I love internet discussions, ive learnt about exhausts but no closer to discovering whether i should be getting 2.5 or 3inch

[Wiretap]

 AdamOst said:

I love internet discussions, ive learnt about exhausts but no closer to discovering whether i should be getting 2.5 or 3inch

My personal feeling is that 2.5" is the 'sweet spot', though I've seen good results on 2.75" systems on NAs also. As, on a turbo, a larger (assumedly better flowing) exhaust will create a larger pressure differential across the exhaust housing of the turbo it should result in a faster spool.

In reference to before, the thing that makes the turbine on a turbo spin is primarily the pressure differential across the turbo, velocity will have some effect (which is why you don't want to run a bigger up-pipe) but that is primarily before the turbo starts producing positive pressure in the intake system.

[Guest]

 AdamOst said:

I love internet discussions, ive learnt about exhausts but no closer to discovering whether i should be getting 2.5 or 3inch

up to you lol. people make good power with a open downpipe and 2.5" cat back and also with 3" free flow...

[AdamOst]

So 3inch downpipe into 2.5inch downpipe back is what i want? Im not massivly fussed on top end as its not a race car, but I will be doing trackdays so i guess midrange is whats important?

Im going to be hitting 200wkw max at elast for the next couple of years.

[Wiretap]

That would be exactly what you don't want. 2.5" downpipe into 3" catback, 3" into 3" or 2.5" into 2.5". You don't want your exhaust diameter getting smaller towards the tail end.

[Stoffa]

2.5 catless downpipe and 3 inch for the rest is my vote. A rage 2.5 will fit a factory exhaust without mods which means its easier to find an exhaust to match secondhand that just bolts on

[AdamOst]

Where do i purchase said rage downpipe.

[Guest]

doesnt exhaust gas cool as it gets further down the tube? heated air expands.

personally id run 3" the whole way no biggie theyre the same price secondhand.

[Timmah]

 AdamOst said:

Where do i purchase said rage downpipe.

http://lmgtfy.com/?q=rage+downpipe+new+zealand

and Trademe

[Wiretap]

 evowrx said:

doesnt exhaust gas cool as it gets further down the tube? heated air expands.

personally id run 3" the whole way no biggie theyre the same price secondhand.

Yep, it does cool down, but any sudden step-down will add a restriction, if the stepdown has a sharp edge (such as the rim of a flange) the effect is squared.

[slystiguy]

as I said before. Jap race sells them for a good price. And be sure to get one with an oxy sensor port in the correct place.....

IMO - 3inch is to noisey and you will have issues at wof

[Guest]

 Wiretap']

[quote name='evowrx said:

doesnt exhaust gas cool as it gets further down the tube? heated air expands.

personally id run 3" the whole way no biggie theyre the same price secondhand.

/quote]

Yep, it does cool down, but any sudden step-down will add a restriction, if the stepdown has a sharp edge (such as the rim of a flange) the effect is squared.

just doesnt sound right to restrict it at the turbo where the gas is hottest where it needs to flow best. if youre gonna run 3" go turbo back and if noise is a problem use resonators and a quiet tip. just looking at it logically i know nothing about back pressure.

ring autobend they make rage

[sultan]

i had a 3 inch downpipe to 2.5 exh. made 205kw with vf23 limited to 16psi by injectors. this a good setup for most cars, why would any one build an exhaust with sharp edges? moving to higher hp build, this setup restricted power to around 230kw, moving to a full 3" with some strange baffles in it (zerosports system!!!), power was still restricted to around 240kw... full 3" from redline for $600 allowed over 280kw. only one reso, and not too overly loud. borderline legal i'd say, another reso and it'd be easily well under. sounds awesome, best exhaust i've ever had, and i've had a lot of them

[Stoffa]

 AdamOst said:

Where do i purchase said rage downpipe.

http://www.trademe.co.nz/motors/car-parts-accessories/subaru/accessories/auction-473305810.htm

This is a rage downpipe, the guy doesn't know exactly what he's selling, its not custom, just after market

2.5 inch ones have a wastegate seperator that sits right inside the turbo exhaust housing keeps the wastegate from disturbing the exhaust flow as much, the 3 inch version doesn't have this

same guy is selling a quality exhaust system as well 5zigen which is japanese after market http://www.trademe.co.nz/motors/car-parts-accessories/subaru/accessories/auction-473305721.htm

makes for a pretty cheap setup

[Guest]

 Wiretap']

[quote name='funkytown said:

quote]Worth pointing out that in terms of flow velocity as mentioned in the latter article. In a turbo engine this (back pressure) only matters before the turbo. You want as much pressure differential across the turbo as possible to improve turbine efficiency and spool rate.

I think your statements are a little confused / dont tell the whole picture.

what you fail to acknowledge in the its full completeness of the working system, in that exhaust back pressure (or EGBP) post turbo definitely affects power and delivery. This is at odds with you're statement about pre turbo only matters. This then is at odds to the statement that you're looking for the max pressure differential across the turbo (which i believe is correct). Why is only one side important if you want the net across both sides?

Smaller exhaust systems can cause a bottle neck in evacuating the gases once they have exited a turbine housing on medium to higher HP systems. This reduces your pressure differential and drops top end potential. This i am to prove just shortly going from a 2.5" mid to rear section (generating 7-9psi back pressure post turbo) to a 3" mid to rear freer flowing section - results of EGBP and power will follow.

I'm openly not totally sure on pre turbo back pressure theory, but im also fairly confident you want maximum flow through the exhaust pre turbo (velocity) but nil pressure.. (But then in my head the 'pressure across the turbo' statement wouldn't make sense.) - I need to do some more reading.

*note this discussion is applicable for turbo applications, NA is different!

At no point did I discuss 'back pressure' in my response. Don't add words I didn't use.

Umm true... but you did link two articles about it and also quoted directly from one of them hahahaha

Look I'm not questioning your knowledge, I certainly don't know alot ... I'm just stating an observation from when I did the upgrade on my V7 STI... I didn't get it tuned for a day or two and the bum o'meter could definitly tell the difference.

If I understand the situation, the OP has a Rex.. I'm not sure what he wants out of the car.. but if no other major mods as you mentioned before, I would probably look at going 2.5" or even just chopping out the cat on the standard system (cheaper) hahaha.

But if he has aspirations for more modifications in the future (i.e. turbo swap)... then a 3" would make sense. I used to own a V7 rex before I got this car, which had some minor mods done to it (boost, exhaust system, headers (extractors), it had the boost turned up it had a bit of torque

EDIT: just read that OP wants 200wkw from his car