Downpipe without back box?
#1
Can I decat my downpipe, ie replace it with a down pipe without a decat in, like a scoobysport one without actually changing the back box. I'm keen to get some more power but I dont really want all that noise from a new back box.
Will I still get 20-30hp more with just the downpipe or do I need the noisy backbox too?
Also how does the centre pipe affect this discussion?
Will I still get 20-30hp more with just the downpipe or do I need the noisy backbox too?
Also how does the centre pipe affect this discussion?
#2
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I don't know of anyone who has tried what you suggest, but I can say:
With some downpipes, it will physically fit. Doing so will increase noise a bit anyway as the cat absorbs/blocks some of the exhaust noise.
The centre section has a cat at the front, which also acts as a sound muffler and also restricts power.
The backbox restricts flow a bit (probably less than a cat though), whilst removing some of the noise.
In very basic terms, each time you remove a restriction from the exhaust, you will get more power and more noise. A scoobysport backbox with an OEM centre/downpipe is not as noisy as a full scoobysport system, but gives much less power.
Having said that, some exhausts are much noisier than others - do a search here and you'll find a number of posts about that. From my limited experience, I would put the scoobysport in the medium noise category - eg Blitz will be louder, but several quieter. Quieter systems will often have a sports cat and a resonated centre section, as both of these will absorb noise without having too much effect on power.
With some downpipes, it will physically fit. Doing so will increase noise a bit anyway as the cat absorbs/blocks some of the exhaust noise.
The centre section has a cat at the front, which also acts as a sound muffler and also restricts power.
The backbox restricts flow a bit (probably less than a cat though), whilst removing some of the noise.
In very basic terms, each time you remove a restriction from the exhaust, you will get more power and more noise. A scoobysport backbox with an OEM centre/downpipe is not as noisy as a full scoobysport system, but gives much less power.
Having said that, some exhausts are much noisier than others - do a search here and you'll find a number of posts about that. From my limited experience, I would put the scoobysport in the medium noise category - eg Blitz will be louder, but several quieter. Quieter systems will often have a sports cat and a resonated centre section, as both of these will absorb noise without having too much effect on power.
#3
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That is very do-able, not sure you'll get 'that' much power, BUT you'll be amazed at how different the car drives, it should be a LOT smoother, less on-off!
The downpipe is the one bit on my car that made the best change, I would have considered doing it first if I'd realised.
Ron.
DO IT!!!!
The downpipe is the one bit on my car that made the best change, I would have considered doing it first if I'd realised.
Ron.
DO IT!!!!
#4
I've run all sorts of combinations......
I ran a Scoobysport downpipe with a standard (STi) exhaust for a couple of years.
I'd be surprised if the downpipe ever gave those sort of power increases. What it does do though is get the turbo spinning earlier - it seemed to shift the whole response level down atleast 500rpm. It makes the car much more driveable.
IMHO - the down pipe is the best upgrade - I'd do it before the backbox every time !
BTW I'm now running Scoobysport downpipe, PE catted centre and Magnex back box.
I ran a Scoobysport downpipe with a standard (STi) exhaust for a couple of years.
I'd be surprised if the downpipe ever gave those sort of power increases. What it does do though is get the turbo spinning earlier - it seemed to shift the whole response level down atleast 500rpm. It makes the car much more driveable.
IMHO - the down pipe is the best upgrade - I'd do it before the backbox every time !
BTW I'm now running Scoobysport downpipe, PE catted centre and Magnex back box.
#6
It depends...... my STi failed which is why I've now got a PE catted centre - I just couldn't be arsed with swapping it about every year. I've heard that some UK's still pass if they're hot enough when tested.
#7
I dont want to go through all that hassle, it sounds like a nightmare keep changing stuff to pass an MOT, would a decat downpipe and a better centre section pass?
I think the question I need to ask is whats the most powerful combination that will still enable a flawless MOT pass?
I think the question I need to ask is whats the most powerful combination that will still enable a flawless MOT pass?
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#8
S55 HOT
How do you find your PE centre?
Any noticable power changes when it was fitted?
How about increased noise over your standard STi centre.
I have ordered SS DP & BB so far, but leaving OE centre to try to keep noise down, and pass MOT.
Jules
How do you find your PE centre?
Any noticable power changes when it was fitted?
How about increased noise over your standard STi centre.
I have ordered SS DP & BB so far, but leaving OE centre to try to keep noise down, and pass MOT.
Jules
#9
UHF - as far as I know Power Engineering are the only ones who do a catted center and therefore it is the most powerful one ;-)
Jules - The PE centre feels slightly freer and is only very slightly louder than standard.
Jules - The PE centre feels slightly freer and is only very slightly louder than standard.
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S55Hot - Not true. There's quite a few people who do sports cat systems. PE do, but also Graham Goode, MRT, APS off the top of my head and I think there are others.
Re "most powerful" - I don't know, although IIRC someone did a back to back trial of many exhaust systems which may include several of these systems.
Edit - I believe the someone who did the tests was dalloyd. Haven't found the results yet, though.
[Edited by hades - 10/13/2002 9:17:25 PM]
Re "most powerful" - I don't know, although IIRC someone did a back to back trial of many exhaust systems which may include several of these systems.
Edit - I believe the someone who did the tests was dalloyd. Haven't found the results yet, though.
[Edited by hades - 10/13/2002 9:17:25 PM]
#12
yes, indeed, what I wanna do is de cat down pipe, sports cat centre section and a moderate back box and get some nice power and still pass MOT cos of a decent centre pipe cat!
#13
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Jules - Fair point, I should read more carefully. The other sports cats I mentioned will not fit to a SS dp. If UHF has already got/ordered a SS downpipe, that is the best option.
Re: limiting performance - I'm not convinced. One other variable in the equation is that with SS dp and PE centre, (IIRC) you have a diameter restriction where the two parts meet as they run OEM compatable flanges. I know the APS maintains the larger pipe diameter by having their own centre sections (MRT too I think). Downside is that their cat is a little nearer to the turbo than the PE one, as you said. APS is apparently fine to 360bhp+. Whether it is more or less restrictive than PE, I don't know. Guess we need to find some dyno results to settle that one!
Re: limiting performance - I'm not convinced. One other variable in the equation is that with SS dp and PE centre, (IIRC) you have a diameter restriction where the two parts meet as they run OEM compatable flanges. I know the APS maintains the larger pipe diameter by having their own centre sections (MRT too I think). Downside is that their cat is a little nearer to the turbo than the PE one, as you said. APS is apparently fine to 360bhp+. Whether it is more or less restrictive than PE, I don't know. Guess we need to find some dyno results to settle that one!
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So . . .It roughly boils down to you want MOT legal, not too loud, lots of power? I can see variations on two basic options
1. Decat dp/sports cat centre/fairly quiet backbox. I just found another sports cat centre - Milltek also appear to do one here .
2. Fit a full MRT or APS sports cat system - these are quieter than most systems and give good power gains.
The MRT/APS systems have a centre resonator as well as a sports cat - which makes them quieter than the PE system which just has a cat in the centre and no resonator. A resonator and free flowing backbox is (I'm told) a less restrictive way of reducing noise than no resonator and a more restrictive quieter backbox. Because of what I've said, I recently ordered an APS system, which I believe is right for me.
I would still love to see all the systems proved on a dyno to get a definitive answer about the power output. Without that everyone can express opinions, but we have no proof of who is right.
Does that help?
1. Decat dp/sports cat centre/fairly quiet backbox. I just found another sports cat centre - Milltek also appear to do one here .
2. Fit a full MRT or APS sports cat system - these are quieter than most systems and give good power gains.
The MRT/APS systems have a centre resonator as well as a sports cat - which makes them quieter than the PE system which just has a cat in the centre and no resonator. A resonator and free flowing backbox is (I'm told) a less restrictive way of reducing noise than no resonator and a more restrictive quieter backbox. Because of what I've said, I recently ordered an APS system, which I believe is right for me.
I would still love to see all the systems proved on a dyno to get a definitive answer about the power output. Without that everyone can express opinions, but we have no proof of who is right.
Does that help?
#18
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try here
They are aussie made, so take a couple of weeks to arrive - ordered mine last week, so not here yet
Phone them - Jamie is helpful, and has generally impressed people on here who have used him. If you tell him I pointed you at him, he might even give me a discount - how about it Jamie?
They are aussie made, so take a couple of weeks to arrive - ordered mine last week, so not here yet
Phone them - Jamie is helpful, and has generally impressed people on here who have used him. If you tell him I pointed you at him, he might even give me a discount - how about it Jamie?
#19
Horses for courses I guess.
The problems with the integrated solution are
a) you have to buy it all at once
b) if you don't like it you can't tweak/experiment a bit
I noticed the most performance increase from the downpipe and practically none from the backbox - though the increase in sound makes it feel faster.
AFAIK I was the first person to actually test a backbox back to back (before & after) on a rolling road on the same day! The results are here.
Pete Croney didn't seem particularly keen on me doing it - he was there that day and was very interested in the results. The Power Engineering boys were very surprised - in something like 15 years of tuning, they'd never seen a backbox deliver any gains before let alone meaningful ones.
When I swapped my Scoobysport backbox back to the regular STi one, I noticed no performance degredation, but it was a lot quieter !
I'm thinking of going back to the STi one again as I find even the Magnex one quite loud and that's supposed to be quiet......
The problems with the integrated solution are
a) you have to buy it all at once
b) if you don't like it you can't tweak/experiment a bit
I noticed the most performance increase from the downpipe and practically none from the backbox - though the increase in sound makes it feel faster.
AFAIK I was the first person to actually test a backbox back to back (before & after) on a rolling road on the same day! The results are here.
Pete Croney didn't seem particularly keen on me doing it - he was there that day and was very interested in the results. The Power Engineering boys were very surprised - in something like 15 years of tuning, they'd never seen a backbox deliver any gains before let alone meaningful ones.
When I swapped my Scoobysport backbox back to the regular STi one, I noticed no performance degredation, but it was a lot quieter !
I'm thinking of going back to the STi one again as I find even the Magnex one quite loud and that's supposed to be quiet......
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