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oversized exhaust? loss of power 

 

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 Post subject: Re: oversized exhaust? loss of power
Posted: Tue Dec 03, 2013 8:10 am 
Getting Side Ways
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Ride: 98 EL Futura

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fiend wrote:
Sure I just said that? Ah well.


Ah yep i had this page just sitting there for a while and hadn't refreshed it

 

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EL Futura: CVE head, Wolf V500, ICE Ignition and Coil, 36lb injectors, Walbro 255lb, Paci comps, 3" exhaust, T5, Harrop Truetrac with 3.9s. Now with 198.9rwkw, (~185rwkw and 13.80 @99.1mph) with more power to come

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 Post subject: Re: oversized exhaust? loss of power
Posted: Tue Dec 03, 2013 11:20 am 
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wrongwaynorris wrote:
WARMACHINE wrote:
The reason why the car feels slow to get going is because it is a ford falcon, it weights near on 2 tonne with people in it...

The exhaust is fine theres nothing wrong with it, myths about exhaust being too big are just that.


Wrong , ever heard of back pressure ? Companies like Caterpillar spend millions of dollars on computer programs to calculate things such as back pressure and dew point . Exhaust size is critical .



your comparing a large capacity low revving high torque diesel engine that needs as much torque as possible at lower rpms to a smaller higher revving efi petrol engine..
look at high performance or race cars, there is next to no back pressure..
so as long as the engine in question has reasonable headers and matching size cat the rest of the system is either or neither imo... having a to small exhaust can hinder the max output of an engine, but within reason a larger than required exhaust isn't going to kill power out put...
I had 2 1/2 and a 3" system on my au i6 and other than the noise difference it made no difference in how the car performed....
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 Post subject: Re: oversized exhaust? loss of power
Posted: Tue Dec 03, 2013 2:11 pm 
Getting Side Ways
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Jmm said they gained 4rwkw on a ba going from their 2.5 to a 3 inch exhaust.that was on an unopened engine.

 

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 Post subject: Re: oversized exhaust? loss of power
Posted: Tue Dec 03, 2013 3:41 pm 
Getting Side Ways
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Back pressure is the most evil word ever. It is a by product, not a target.

A choke can be a benefit in a designed exhaust system, but it is far from the simply being "back pressure"
A choke is normally used in a merge collector to speed up the flow through it, and restrict the back flow.


An example I use is if you have your manifold exit in to a pipe 1m in diameter that has a cap on the end with a very small hole to simulate the 'back pressure' of say a 2" pipe. The results would be very different to actually using a 2" pipe.
What this demonstrates is that there's more to it than just size.
Some exhaust builders actually use something similar to this example, called a wave termination box. this lets the header act they way they planned while still being able to attach to an exhaust system.

With the right header, you can have any size exhaust system you want. (as long as it's not a restriction)

 

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