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HOW MUCH FOR NEW EXHAUST!!!!


police350z

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I see a lot on the eBay adverts for exhausts that they guarantee anywhere from a 5-15bhp increase, how true is this or is it a typical salesman pitch?

to be serious for a moment, I think you can only get power gains if you decat the car and retune at a place like Abbey Motorsport, but then that's only what I've learnt from the experts here

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I see a lot on the eBay adverts for exhausts that they guarantee anywhere from a 5-15bhp increase, how true is this or is it a typical salesman pitch?

 

Here's my super simplified explanation of exhaust performance:

 

It is genuinely difficult to gain that much power from an exhaust alone on an normally aspirated engine. On a turbocharged car gains can be massive from plain exhaust changes.

 

Exhausts are basically made to silence the sound of combustion gas leaving the engine, channel the exhaust gas away from the cabin, reduce harmful emissions via a catalyst. They are normally designed to minimize the loss of power and torque because of the processes I listed. The basic rule of performance exhausts is to get the waste gas out to atmosphere as quickly as possible which allows the engine to 'breath' or flow better. Back pressure is ALWAYS the enemy - this is normally caused by exhaust pipe restriction causing pressure inside the exhaust.

 

Ok so here's the problem. If you imagine your engine like an outside tap and the exhaust like a hose pipe. If you put a pipe with a much larger diameter on your outside tap, what would happen? It will generally take longer for the water to reach the end of the pipe. If you make the pipe diameter too small masses of pressure will build in the pipe greatly slowing progress. So essentially you go too big with your exhaust and you lose power and torque as the gas meanders its way out of the tail pipe, too small and the pressure also slows the gas and strangles engine power. It's really hard to get this right and established performance parts specialists spend a lot of time optimizing the exhaust to get it right - which they don't always do!

1.0 Saxo's with whacking great 4" exhausts for example will have lost enormous quantities of torque as the tiny engine just isn't a sufficient pump to get that gas out.

 

Will an ASBO exhaust like a Japspeed K1 increase power and torque? Unlikely, more likely to reduce it. Will an exhaust you pay £600 for made their and then compare favourably to an exhaust made by a company that has spent months testing and optimizing their pipes, like Motordyne for example? Well it's unlikely to be as good really is it?

 

The only way to tell for sure is dyno all of them. Listen to what people that run dyno's say as they will know the best as they have probably seen many of the combinations first hand.

 

One thing is for certain on a 350Z, the stock 'Y' pipe is a total piece of @*!#. You can see how restrictive it is just looking at it, if there are gains to be had anywhere it's there.

 

So in reality, bhp gains will be tiny if anything at all, so in the end it comes down to what you can afford and how much noise you want.

 

Anthony.

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I've had my K1 for a while now and there hasnt been any problems with it. One side does sit about 5mm lower then the other though, it sounds alot better then it did when i first fitted it. Best thing was i got it of ebay new for £180 delivered when the guy selling them use to auction them.

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