Race Engine Forum UK

Hi other time Guy,


I'm going to rebuild the engine of my BMW 2002tii and I want to mount a higher bore exhaust system. The original exhaust bore is 45mm.

In the new engine compresion ratio will be about 10-10,5:1, the cams will be a Dr. Schrick 292‚º, with 4-2-1 manifold. I will preserve the original Kugelfischer pump, and probably the original intake manyfold because it's too hard find an Alpina A4 intake manifold.


How can I calculate the best bore (diameter) for my exhaust system? The use will be sportive, but never race.



Best regards,

Alex.

2" ID

GC

Thank's Guy.

I saw a full exhaust system 2" bore but I thought that was too big for a not race use. I will ask for it other time.


Regards,

Alex.

Alex, hi

just to be clear on this: it's the size (perforated pipe bore and absorption volume) of the silencer (muffler) and number of them that control the noise level, not the tailpipe (from collector to silencer). 2" ID will be fine on that engine; it is big enough not to create back-pressure (static pressure) - and not so large that it will upset the gas velocity. This info from me comes from extensive testing and simulations too. The exit pipe to atmosphere from the silencer should be at least as big as the pipe going in. Making it massively bigger might impress some, but it has no influence at all on power.

Of course, if the silencers are too small, whilst the nosie level may be fine, a back-pressure state will exist between the first box and the engine - and this is well-known (or should be by now, I've been on about it for years..!) to rob power and upset fuelling calibration.

GC

Thank's Guy!!!!!!