csweatherston
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Registered: 16th Jan 06
Location: Devon
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i made a new mid section for my car today as i wanted a flange on there (for easy removal)
but i decided against having a silencer.
Gave it a quick emissions test, and lambda's sat around 1.7 - 1.9.
Theres sod all back pressure, and it keeps sucking back.
so with a rag in the exhaust it passed with a lambda of 1.05.
without adding a silencer is there any way of getting around this??..
richen/lean the mixture off?.
ive heard with the OMP grpN systems you should increase fuel pressure, as it effects running?..
many thanks
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csweatherston
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Registered: 16th Jan 06
Location: Devon
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oh, its a 2" system (so not overly big) lol
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csweatherston
Member
Registered: 16th Jan 06
Location: Devon
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oh, and the damn "quad driver" faults back in the ecu, what exatly does it control?
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Richardhhha
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Registered: 29th Sep 07
Location: Croydon, Greater London
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put a silencer on it.. bloody cars run crap without serten back pressure.
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csweatherston
Member
Registered: 16th Jan 06
Location: Devon
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that means buying more stainless wire..
£15 for a small roll of .8mm :@
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Warren G
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Registered: 14th May 06
Location: Kent
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does it feel like yo uhave lost torque?
i think my exhausts too big, 2.5" bore 
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csweatherston
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Registered: 16th Jan 06
Location: Devon
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lost??..i had bugger all torque to start with lol.
well, mines 2" in some places 2.25" in others with a 3.5" tailpipe
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Superlite Ltd.
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Registered: 9th Jan 07
User status: Offline
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Change the tailpipe 
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Olsrey
Member
Registered: 13th Jan 07
Location: Bradford Drives: LET Vectra B
User status: Offline
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quote:
Originally posted by warren.g
does it feel like yo uhave lost torque?
i think my exhausts too big, 2.5" bore
2.25" would be better suited to an engine like yours.
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matt_aka_smiler
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Registered: 7th Dec 05
Location: Stoke-on-Trent Drives: MK4 Astra GSi Turbo
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2.25" on a 1.6?
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Olsrey
Member
Registered: 13th Jan 07
Location: Bradford Drives: LET Vectra B
User status: Offline
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quote:
Originally posted by matt_aka_smiler
2.25" on a 1.6?
Yes.
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Warren G
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Registered: 14th May 06
Location: Kent
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mines 2.5" - thats turbo bore size!!
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Olsrey
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Registered: 13th Jan 07
Location: Bradford Drives: LET Vectra B
User status: Offline
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quote:
Originally posted by warren.g
mines 2.5" - thats turbo bore size!!
Standard maybe, but 2.0 N/A are best suited to a 2.5" bore system.
[Edited on 07-04-2008 by Olsrey]
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Warren G
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Registered: 14th May 06
Location: Kent
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what about a 1.6 n/a!
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csweatherston
Member
Registered: 16th Jan 06
Location: Devon
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oi!....warren get you own thread!!!...
This ones about my lambaaada being too high now :@
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Warren G
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Registered: 14th May 06
Location: Kent
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sorry my bad
lamba high = oxygen getting to exhaust?
remap to suit?
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csweatherston
Member
Registered: 16th Jan 06
Location: Devon
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oooh..maybe megasquirt?...
im thinking if i turn my cams round a tooth, get rid of ALL overlap just for mot hmmm
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Warren G
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Registered: 14th May 06
Location: Kent
User status: Offline
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Mot
does it realy need a emissions test
mines going to fly past, may cost a few coffee's though 
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csweatherston
Member
Registered: 16th Jan 06
Location: Devon
User status: Offline
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no...but i like being legal.
anti pollution and all that.
think is, co2 is perfect, 14.7 ppm, lovely stochiometric (sp) ratio
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Mobby
Member
Registered: 31st Dec 07
Location: Leicestershire
User status: Offline
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am losing back pressure with a remus center section with no silencer and a peco twin box exhaust
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luke85
Member
Registered: 26th Nov 07
Location: Chesterfield
User status: Offline
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Is the exhaust perfectly air tight? it can be pulling in a bit of air from a leak and making it look mega lean, your measuring an AFR of between 25:1 and 28:1 and im sure the car wouldnt like to tickover that lean.
Then when you shove a rag in it the extra pressure makes the exhaust gas go out the leak instead of drawing air in? might be worth a look
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Vaux Lad
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Registered: 15th Dec 04
Location: Stoke-on-Trent
User status: Offline
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The majority of exhaust backpressure is developed in the primaries anyway, system doesn't usually make a difference(engine forcing a gas down thin tubes=restriction....)
Ive drove mine with no system on at all(just a manifold/downpipe), and it drove fine.
For a lambda reading that high your definently getting a false reading, probably due to a air leak sucking in air which the lambda's then picking up.
[Edited on 08-04-2008 by Vaux Lad]
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Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
User status: Offline
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quote:
Originally posted by Dave A
copy and pasted from another thread I posted on about backpressure:
exhaust design is a lot more complicated than people realise. most off the shelf exhausts are more for the look and sound rather than perfomance really.
what some people term as 'backpressure' does exist but its not strictly backpressure as such. Making an exhaust that is well designed isnt easy, to do it properly everything from inlet design, cylinder pressure, valve overlap values need to be taken into account (sometimes refered to as 'pulse tuning' )
the Idea behind 'backpressure' is this: as exhaust gasses exit the combustion cylinder into the exhaust posrt and into the manifold they are at a high speed. once the exhaust valve closes the gasses create a virtual vaccum behind them, this helps to suck the next load of waste gasses out and so on... if the exhaust bore is too big or too free flowing or the primaries of the manifold are too short or long then the amount of pressure pulling the next lot of waste gasses out of that cylinder is reduced therefore the gasses escape slower and the speed of the engine is reduced and the inlet gasses enter slower and so on....
there is a lot more to exhaust design than you might think......
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