MikeH
Member
Registered: 3rd Apr 03
User status: Offline
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Just always wondered.
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AdamF
Premium Member
Registered: 24th Apr 02
Location: Bexhill, East Sussex
User status: Offline
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dont no exactly but i do no it overfuels without it
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Adam_B
Member
Registered: 13th Dec 00
Location: Lancashire
User status: Offline
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if u have no back pressure u will get more bhp at higher revs but fuck all power down at the bottom. i think 
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OzzySRi
Member
Registered: 18th Jun 02
Location: Sydney, Australia Drives: Corsa C 1.8 SRi
User status: Offline
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its all got to do with the combustion chamber. If ur familiar with the 4stroke cycle (1.suck/intake, 2.squeeze/compression, 3.bang/ignition, 4.blow/exhaust) u'll get what i mean.
As the motor goes from the exhaust cycle back to the intake cycle (the top of the piston stroke) there is a thing called 'overlap' caused by the fundamental design of the camshaft.
During this period of 'overlap' the exhaust valves are about to close the intake valves are beginning to open (both intake/exhaust are partially open). Without any backpressure in the exhaust system, the new air/fuel mix will simply pass thru the motor during the overlap... meaning less air/fuel mix in the combustion chamber for the next cycle.
So having backpressure helps keep more of the flamable stuff in so u get a bigger bang.. more power.
Well, thats the technical BS behind it 
[Edited on 17-09-2003 by OzzySRi]
[Edited on 17-09-2003 by OzzySRi]
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Daimo B
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Registered: 20th Mar 00
User status: Offline
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As above.
Also, different size exhaust bores can determin the overall power of the car. I can't remember which way round it it, but its something like, the smaller the exhaust bore, the better lower end torque/performance the car will have, the larger the bore, the more top end performance the car will have.
Also, a turbo'd car works differently. You want to get the exhaust gases away fromt eh turbo as quickly as possible hence most turbo bores are usually bigger.
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OzzySRi
Member
Registered: 18th Jun 02
Location: Sydney, Australia Drives: Corsa C 1.8 SRi
User status: Offline
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yeah theres alot of crap involved with exhausts. Turbos can go large (3") and not be excessively loud coz the turbo itself acts as a muffler.
But there is also considerations about gas velocity. Hot air moves quicker than cold air. By going overly large on an N/A car results in the exhaust gases cooling early in the system. Having the right sized pipe keeps things hot n moving quickly aiding combustion chamber scavenging. U'll also notice that alot of systems purposly put a slight restriction after the cat to create a heat build up which makes the cat work better
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Kris TD
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Registered: 25th Mar 02
Location: Ware, Hertfordshire
User status: Offline
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yeah cos back pressure on a turbo slows the turbo down.
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MikeH
Member
Registered: 3rd Apr 03
User status: Offline
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Wish i had a turbo.... i think they are just fundamentally better in all respects
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Kris TD
Member
Registered: 25th Mar 02
Location: Ware, Hertfordshire
User status: Offline
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quote:
Originally posted by MikeH
Wish i had a turbo.... i think they are just fundamentally better in all respects
yep
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Daimo B
Member
Registered: 20th Mar 00
User status: Offline
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This is true, but, how i think.
Ptissshhhhhh turbo and DV
or
BRAAAAAAAAAAAAAAAAAAAHHHHBBAAA BRRAAAAAAAAHHHHHHHHHH pop pop  or Throttle Bodies.
Unltimatly though, the turbo should always have the outright best performance 
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