Catless Downpipes - With and Without Tune

[vinsanem5]

Originally Posted by JrD7

Did you get a check engine light on with the catless downpipes?

you should get a CEL, maybe not right away but you will eventually get one.

[A3ch]

I had catless downpipes on my 335i. My wife hated the constant exhaust smell. I'd love to do downpipes but its not worth it for an extra 30hp. The smell is annoying. I do love burbles and pops tho.

[F10CPROG]

I don't get why people moan about the smell...? Its what petrol engines smell like. I personally prefer the smell of a car with no cats.
Anyway the freer engine and extra sound would be good.
Plus you can get the annoying "cold start" map taken off.
Oh and we all love polluting the world, hence why we drive turbo charged V8s

[MarcF10]

Originally Posted by epiphanyray

1) If you then add downpipes (catless) with no tune and leave it as it, should it make a difference in WHP?

2) If I have a stage two flash (this was when I had OEM downpipes), should tuning company tweak this flash to account for Catless Downpipes now? What I mean is, does a flash tune take into account the fact that the car has Catless DP, and as a result yield even more power?

1. Yes it will make a difference. I don't know how much. The best option is to dyno the car before and after and check the charts for comparison

2. Yes the tuning company should tweak the program accordingly to take into consideration the altered flow and pressure of gasses

Generally speaking downpipes with program (they usually call it stage 2) do add +50 extra horsepower on top of Stage 1 horsepower increase.

(Stage 1 programs do not require downpipes).

What the tuners usually do is, they start with a basic map for your car as a guideline. They tweak some parameters depending on the car sensor reading (think of a real time engine diagnostic) to improve your power and torque output. They take various dyno readings until they are satisfied with results. It's all done with a computer but you also need to understand how each element of the engine works, and what is the + or - contribution of the parts you add or the parts you remove or replace..

Generally speaking, the idea is to push more air+fuel into the cylinder from one side and then remove the burned gasses very fast from the other side.

The cylinder has a standard size that cannot be changed - imagine a bottle of water. But air is the element that can be manipulated. So this is what makes the difference.

Turbo is a fan that accelerates the air speed - incoming and outgoing too -

Ecu is the computer that fundamentaly regulates the air/fuel ratio instead of a carburetor...it takes a lot of information from many sensors in the engine during the 4 stroke cycle to do these calculations and regulate the engine behaviour...this behaviour of the engine at each step of the rev span, is what the map really shows...