Jap Imports

My New Scooby has a Custom made exhaust, Big all the way through but small at the back box.Will this restrict a bit of power. Would it be better to get a New back box like Afterburner one from Scooby world.

scoobyslut

I would presume they have designed it that way to maintain some back pressure in the system to allow the engine to run properly, so by changing the back box you may actually lower the performance of the motor. I wont say "you will", as not seeing the system it is hard to confirm, but sounds as though that is why it has bee fitted,otherwise they would of put a large bore rear box on when they fitted the rest, would they not?

hades

Sorry, but any back pressure downstream of the turbo does not help the car run better.

Probably the reason they have done this is noise. By dropping to a smaller diameter at the backbox, they are reducing the loudness. By the time the gas has reached the backbox, it has cooled off a bit, so is at lower pressure - therefore keeping the diameter big until the last minute arguably gives a good combination of silencing effect without reducing flow too much.

My APS exhaust is 3" all the way to a 2.5" backbox, similar idea -good flowing, but not as loud as many.

Jap Imports

I'll try and get a photo on here. I think it may of had a rally in japan, is there maybe a size restriction on Size, It is well Loud. And i mean Loud, So how loud would it be with a slightly bigger back box.

Jap Imports

Here's a pic, where the exhaust goes under car then it gets bigger.

Jap Imports

So, will this restrict power, or is it better for it too be 1 size al the way through.