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Thread: Why Have An Aftermarket Exhaust?

  
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    Why Have An Aftermarket Exhaust?

    It's general knowledge here that if you want your ZLET (Im use with this engine so I'll use it as my example) to produce more power then one of the first things to do is replace the 1st cat with a downpipe and then maybe put a sports cat on and a cat-back system.

    So ... with that in mind and also taking into consideration Courtenays website saying you need a full exhaust to get close to the 240bhp of CS1... I want to know one thing.

    The Z20 LEH is basically a stronger Z20 LET yes? Forged pistons dont give more bhp than normal ones though they can HANDLE more, oil spray bars dont give out more bhp etc

    So ... why can the Astra VXR or even the AstraVan 888 have 240bhp if it has a STANDARD exhaust system? (IE: 1st cat, normal main cat and a normal cat-back system with maybe a sportier backbox) yet if a GSI or Coupe Turbo etc wants 240bhp we need a full exhaust system... ?
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    Ill have 237 bhp when i have my regal phase 1, ill have my standard exhaust system.

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    Maybe the new astra vxr has a bigger bore diameter exhaust hence reducing back pressure. Not sure. Maybe cournteys software is not as aggressive as regals?

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    The Van had a different map to the coupe didn't it?
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    Quote Originally Posted by jimmy_c
    The Van had a different map to the coupe didn't it?
    Yea it has 240bhp but with the standard exhaust (with a milltek backbox) so why is it that if I wanted 240bhp I have to replace my entire exhaust? (or same for those with a GSI/SRI-T/CoupeT)
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    Indeed the MK5 does have a larger bore on the exhaust compared to the MK4 / Coupe. I looked into this a while ago, but I can't remember the exact details.

    That said a decent precat will sort that out.
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    Its because it has a bigger intercooler and a stronger turbo so they could up the boost without cooking the engine...... With our LET's its a tiny intercooler so the exhaust is helping to reduce turbo temps so they can up the boost to get 240ish.....

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    It's all about flow. The quicker the gases can be removed the more air/fuel you can get in. I would imagine that the leh exhaust has a different flow rate to the let.

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    Different intake manifold helps no end to

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    Im not sure if the exhaust does flow that much better...... Maybe a bhp or 2 dunno?!?

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