Back Box discussion

[markos_7772]

Hello guys! 

My 306 HDI is de-cated. Las weekend, I decided to take out the back box for testing. I opened the flange, take out the back box and tested the car in that situation. The exhaust is 1 meter shorter because of it. It sounds pritty, and at low speed it acelerates much. But I lost final speed (more a less 20Km/k). So, as I can evaluate, a free and shorter exhaust gives more aceleration but less speed. 

What do you think is the best option for a balanced situation? I mean: not loosing so much speed, but improoving aceleration. 

Lets discuss!

[Eeyore]

i was under the impression you just wanted to reduce pressure after the turbo. For reducing pressure and having increased flow people usually use 2.5" exhausts. The standard backbox is restrictive so people often fit a second centre box as a back box. You could fit a full 3" system but it would be a pain to route and would be loud.

[markos_7772]

i was under the impression you just wanted to reduce pressure after the turbo. For reducing pressure and having increased flow people usually use 2.5" exhausts. The standard backbox is restrictive so people often fit a second centre box as a back box. You could fit a full 3" system but it would be a pain to route and would be loud.

I dont get: wich is the difference between 2" stock exhaust, 2.5" and 3"?

[Eeyore]

its the diameter of the pipe. You have a bigger pipe so you can fit more down it. It therefore reduces pressure on the exhaust side of the turbo allowing it to spool up faster and flow more i.e. it removes the restriction which is what you are after.

[Poodle]

As Rowell says, you are just looking to reduce back-pressure. 3" is way too big, 2.5" is good for anything this side of 200bhp. The standard system is 2.25" (more or less). Removing the backbox should not affect your top speed, that will have been down to another factor: weight in the car, weather conditions, fuel quality, etc.

[markos_7772]

As Rowell says, you are just looking to reduce back-pressure. 3" is way too big, 2.5" is good for anything this side of 200bhp. The standard system is 2.25" (more or less). Removing the backbox should not affect your top speed, that will have been down to another factor: weight in the car, weather conditions, fuel quality, etc.

I think I lost speed because the exhaust was 1mt shorter (I didnt plug anything when I toke out the back box) 

I fitted it again now, because of sound.. Maybe in the future I will try a 2.5" exhaust..